Issue #16612: Add "Argument Clinic", a compile-time preprocessor

for C files to generate argument parsing code.  (See PEP 436.)

2 files changed, 3176 insertions, 0 deletions

diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
new file mode 100755
index 0000000..836b030
--- /dev/null
+++ b/Tools/clinic/clinic.py
@@ -0,0 +1,2477 @@
+#!/usr/bin/env python3
+#
+# Argument Clinic
+# Copyright 2012-2013 by Larry Hastings.
+# Licensed to the PSF under a contributor agreement.
+#
+
+import abc
+import ast
+import atexit
+import clinic
+import collections
+import contextlib
+import functools
+import hashlib
+import inspect
+import io
+import itertools
+import os
+import re
+import shlex
+import sys
+import tempfile
+import textwrap
+
+
+# TODO:
+# converters for
+#
+#       es
+#       es#
+#       et
+#       et#
+#       s#
+#       u#
+#       y#
+#       z#
+#       Z#
+#
+# soon:
+#
+# * allow mixing any two of {positional-only, positional-or-keyword,
+#   keyword-only}
+#       * dict constructor uses positional-only and keyword-only
+#       * max and min use positional only with an optional group
+#         and keyword-only
+#
+# * Generate forward slash for docstring first line
+#   (if I get positional-only syntax pep accepted)
+#
+# * Add "version" directive, so we can complain if the file
+#   is too new for us.
+#
+
+_empty = inspect._empty
+_void = inspect._void
+
+
+class Unspecified:
+    def __repr__(self):
+        return '<Unspecified>'
+
+unspecified = Unspecified()
+
+
+class Null:
+    def __repr__(self):
+        return '<Null>'
+
+NULL = Null()
+
+
+def _text_accumulator():
+    text = []
+    def output():
+        s = ''.join(text)
+        text.clear()
+        return s
+    return text, text.append, output
+
+
+def text_accumulator():
+    """
+    Creates a simple text accumulator / joiner.
+
+    Returns a pair of callables:
+        append, output
+    "append" appends a string to the accumulator.
+    "output" returns the contents of the accumulator
+       joined together (''.join(accumulator)) and
+       empties the accumulator.
+    """
+    text, append, output = _text_accumulator()
+    return append, output
+
+
+def fail(*args, filename=None, line_number=None):
+    joined = " ".join([str(a) for a in args])
+    add, output = text_accumulator()
+    add("Error")
+    if clinic:
+        if filename is None:
+            filename = clinic.filename
+        if clinic.block_parser and (line_number is None):
+            line_number = clinic.block_parser.line_number
+    if filename is not None:
+        add(' in file "' + filename + '"')
+    if line_number is not None:
+        add(" on line " + str(line_number))
+    add(':\n')
+    add(joined)
+    print(output())
+    sys.exit(-1)
+
+
+
+def quoted_for_c_string(s):
+    for old, new in (
+        ('"', '\\"'),
+        ("'", "\\'"),
+        ):
+        s = s.replace(old, new)
+    return s
+
+# added "self", "cls", and "null" just to be safe
+# (clinic will generate variables with these names)
+c_keywords = set("""
+asm auto break case char cls const continue default do double
+else enum extern float for goto if inline int long null register
+return self short signed sizeof static struct switch typedef
+typeof union unsigned void volatile while
+""".strip().split())
+
+def legal_c_identifier(s):
+    # if we picked a C keyword, pick something else
+    if s in c_keywords:
+        return s + "_value"
+    return s
+
+def rstrip_lines(s):
+    text, add, output = _text_accumulator()
+    for line in s.split('\n'):
+        add(line.rstrip())
+        add('\n')
+    text.pop()
+    return output()
+
+def linear_format(s, **kwargs):
+    """
+    Perform str.format-like substitution, except:
+      * The strings substituted must be on lines by
+        themselves.  (This line is the "source line".)
+      * If the substitution text is empty, the source line
+        is removed in the output.
+      * If the substitution text is not empty:
+          * Each line of the substituted text is indented
+            by the indent of the source line.
+          * A newline will be added to the end.
+    """
+
+    add, output = text_accumulator()
+    for line in s.split('\n'):
+        indent, curly, trailing = line.partition('{')
+        if not curly:
+            add(line)
+            add('\n')
+            continue
+
+        name, curl, trailing = trailing.partition('}')
+        if not curly or name not in kwargs:
+            add(line)
+            add('\n')
+            continue
+
+        if trailing:
+            fail("Text found after {" + name + "} block marker!  It must be on a line by itself.")
+        if indent.strip():
+            fail("Non-whitespace characters found before {" + name + "} block marker!  It must be on a line by itself.")
+
+        value = kwargs[name]
+        if not value:
+            continue
+
+        value = textwrap.indent(rstrip_lines(value), indent)
+        add(value)
+        add('\n')
+
+    return output()[:-1]
+
+
+class CRenderData:
+    def __init__(self):
+
+        # The C statements to declare variables.
+        # Should be full lines with \n eol characters.
+        self.declarations = []
+
+        # The C statements required to initialize the variables before the parse call.
+        # Should be full lines with \n eol characters.
+        self.initializers = []
+
+        # The entries for the "keywords" array for PyArg_ParseTuple.
+        # Should be individual strings representing the names.
+        self.keywords = []
+
+        # The "format units" for PyArg_ParseTuple.
+        # Should be individual strings that will get
+        self.format_units = []
+
+        # The varargs arguments for PyArg_ParseTuple.
+        self.parse_arguments = []
+
+        # The parameter declarations for the impl function.
+        self.impl_parameters = []
+
+        # The arguments to the impl function at the time it's called.
+        self.impl_arguments = []
+
+        # For return converters: the name of the variable that
+        # should receive the value returned by the impl.
+        self.return_value = "return_value"
+
+        # For return converters: the code to convert the return
+        # value from the parse function.  This is also where
+        # you should check the _return_value for errors, and
+        # "goto exit" if there are any.
+        self.return_conversion = []
+
+        # The C statements required to clean up after the impl call.
+        self.cleanup = []
+
+
+class Language(metaclass=abc.ABCMeta):
+
+    start_line = ""
+    body_prefix = ""
+    stop_line = ""
+    checksum_line = ""
+
+    @abc.abstractmethod
+    def render(self, block):
+        pass
+
+    def validate(self):
+        def assert_only_one(field, token='dsl_name'):
+            line = getattr(self, field)
+            token = '{' + token + '}'
+            if len(line.split(token)) != 2:
+                fail(self.__class__.__name__ + " " + field + " must contain " + token + " exactly once!")
+        assert_only_one('start_line')
+        assert_only_one('stop_line')
+        assert_only_one('checksum_line')
+        assert_only_one('checksum_line', 'checksum')
+
+        if len(self.body_prefix.split('{dsl_name}')) >= 3:
+            fail(self.__class__.__name__ + " body_prefix may contain " + token + " once at most!")
+
+
+
+class PythonLanguage(Language):
+
+    language      = 'Python'
+    start_line    = "#/*[{dsl_name}]"
+    body_prefix   = "#"
+    stop_line     = "#[{dsl_name}]*/"
+    checksum_line = "#/*[{dsl_name} checksum: {checksum}]*/"
+
+
+def permute_left_option_groups(l):
+    """
+    Given [1, 2, 3], should yield:
+       ()
+       (3,)
+       (2, 3)
+       (1, 2, 3)
+    """
+    yield tuple()
+    accumulator = []
+    for group in reversed(l):
+        accumulator = list(group) + accumulator
+        yield tuple(accumulator)
+
+
+def permute_right_option_groups(l):
+    """
+    Given [1, 2, 3], should yield:
+      ()
+      (1,)
+      (1, 2)
+      (1, 2, 3)
+    """
+    yield tuple()
+    accumulator = []
+    for group in l:
+        accumulator.extend(group)
+        yield tuple(accumulator)
+
+
+def permute_optional_groups(left, required, right):
+    """
+    Generator function that computes the set of acceptable
+    argument lists for the provided iterables of
+    argument groups.  (Actually it generates a tuple of tuples.)
+
+    Algorithm: prefer left options over right options.
+
+    If required is empty, left must also be empty.
+    """
+    required = tuple(required)
+    result = []
+
+    if not required:
+        assert not left
+
+    accumulator = []
+    counts = set()
+    for r in permute_right_option_groups(right):
+        for l in permute_left_option_groups(left):
+            t = l + required + r
+            if len(t) in counts:
+                continue
+            counts.add(len(t))
+            accumulator.append(t)
+
+    accumulator.sort(key=len)
+    return tuple(accumulator)
+
+
+class CLanguage(Language):
+
+    language      = 'C'
+    start_line    = "/*[{dsl_name}]"
+    body_prefix   = ""
+    stop_line     = "[{dsl_name}]*/"
+    checksum_line = "/*[{dsl_name} checksum: {checksum}]*/"
+
+    def render(self, signatures):
+        function = None
+        for o in signatures:
+            if isinstance(o, Function):
+                if function:
+                    fail("You may specify at most one function per block.\nFound a block containing at least two:\n\t" + repr(function) + " and " + repr(o))
+                function = o
+        return self.render_function(function)
+
+    def docstring_for_c_string(self, f):
+        text, add, output = _text_accumulator()
+        # turn docstring into a properly quoted C string
+        for line in f.docstring.split('\n'):
+            add('"')
+            add(quoted_for_c_string(line))
+            add('\\n"\n')
+
+        text.pop()
+        add('"')
+        return ''.join(text)
+
+    impl_prototype_template = "{c_basename}_impl({impl_parameters})"
+
+    @staticmethod
+    def template_base(*args):
+        flags = '|'.join(f for f in args if f)
+        return """
+PyDoc_STRVAR({c_basename}__doc__,
+{docstring});
+
+#define {methoddef_name}    \\
+    {{"{name}", (PyCFunction){c_basename}, {meth_flags}, {c_basename}__doc__}},
+""".replace('{meth_flags}', flags)
+
+    def meth_noargs_pyobject_template(self, meth_flags=""):
+        return self.template_base("METH_NOARGS", meth_flags) + """
+static PyObject *
+{c_basename}(PyObject *{self_name})
+"""
+
+    def meth_noargs_template(self, meth_flags=""):
+        return self.template_base("METH_NOARGS", meth_flags) + """
+static {impl_return_type}
+{impl_prototype};
+
+static PyObject *
+{c_basename}(PyObject *{self_name})
+{{
+    PyObject *return_value = NULL;
+    {declarations}
+    {initializers}
+
+    {return_value} = {c_basename}_impl({impl_arguments});
+    {return_conversion}
+
+{exit_label}
+    {cleanup}
+    return return_value;
+}}
+
+static {impl_return_type}
+{impl_prototype}
+"""
+
+    def meth_o_template(self, meth_flags=""):
+        return self.template_base("METH_O", meth_flags) + """
+static PyObject *
+{c_basename}({impl_parameters})
+"""
+
+    def meth_o_return_converter_template(self, meth_flags=""):
+        return self.template_base("METH_O", meth_flags) + """
+static {impl_return_type}
+{impl_prototype};
+
+static PyObject *
+{c_basename}({impl_parameters})
+{{
+    PyObject *return_value = NULL;
+    {declarations}
+    {initializers}
+    _return_value = {c_basename}_impl({impl_arguments});
+    {return_conversion}
+
+{exit_label}
+    {cleanup}
+    return return_value;
+}}
+
+static {impl_return_type}
+{impl_prototype}
+"""
+
+    def option_group_template(self, meth_flags=""):
+        return self.template_base("METH_VARARGS", meth_flags) + """
+static {impl_return_type}
+{impl_prototype};
+
+static PyObject *
+{c_basename}(PyObject *{self_name}, PyObject *args)
+{{
+    PyObject *return_value = NULL;
+    {declarations}
+    {initializers}
+
+    {option_group_parsing}
+    {return_value} = {c_basename}_impl({impl_arguments});
+    {return_conversion}
+
+{exit_label}
+    {cleanup}
+    return return_value;
+}}
+
+static {impl_return_type}
+{impl_prototype}
+"""
+
+    def keywords_template(self, meth_flags=""):
+        return self.template_base("METH_VARARGS|METH_KEYWORDS", meth_flags) + """
+static {impl_return_type}
+{impl_prototype};
+
+static PyObject *
+{c_basename}(PyObject *{self_name}, PyObject *args, PyObject *kwargs)
+{{
+    PyObject *return_value = NULL;
+    static char *_keywords[] = {{{keywords}, NULL}};
+    {declarations}
+    {initializers}
+
+    if (!PyArg_ParseTupleAndKeywords(args, kwargs,
+        "{format_units}:{name}", _keywords,
+        {parse_arguments}))
+        goto exit;
+    {return_value} = {c_basename}_impl({impl_arguments});
+    {return_conversion}
+
+{exit_label}
+    {cleanup}
+    return return_value;
+}}
+
+static {impl_return_type}
+{impl_prototype}
+"""
+
+    def positional_only_template(self, meth_flags=""):
+        return self.template_base("METH_VARARGS", meth_flags) + """
+static {impl_return_type}
+{impl_prototype};
+
+static PyObject *
+{c_basename}(PyObject *{self_name}, PyObject *args)
+{{
+    PyObject *return_value = NULL;
+    {declarations}
+    {initializers}
+
+    if (!PyArg_ParseTuple(args,
+        "{format_units}:{name}",
+        {parse_arguments}))
+        goto exit;
+    {return_value} = {c_basename}_impl({impl_arguments});
+    {return_conversion}
+
+{exit_label}
+    {cleanup}
+    return return_value;
+}}
+
+static {impl_return_type}
+{impl_prototype}
+"""
+
+    @staticmethod
+    def group_to_variable_name(group):
+        adjective = "left_" if group < 0 else "right_"
+        return "group_" + adjective + str(abs(group))
+
+    def render_option_group_parsing(self, f, template_dict):
+        # positional only, grouped, optional arguments!
+        # can be optional on the left or right.
+        # here's an example:
+        #
+        # [ [ [ A1 A2 ] B1 B2 B3 ] C1 C2 ] D1 D2 D3 [ E1 E2 E3 [ F1 F2 F3 ] ]
+        #
+        # Here group D are required, and all other groups are optional.
+        # (Group D's "group" is actually None.)
+        # We can figure out which sets of arguments we have based on
+        # how many arguments are in the tuple.
+        #
+        # Note that you need to count up on both sides.  For example,
+        # you could have groups C+D, or C+D+E, or C+D+E+F.
+        #
+        # What if the number of arguments leads us to an ambiguous result?
+        # Clinic prefers groups on the left.  So in the above example,
+        # five arguments would map to B+C, not C+D.
+
+        add, output = text_accumulator()
+        parameters = list(f.parameters.values())
+
+        groups = []
+        group = None
+        left = []
+        right = []
+        required = []
+        last = unspecified
+
+        for p in parameters:
+            group_id = p.group
+            if group_id != last:
+                last = group_id
+                group = []
+                if group_id < 0:
+                    left.append(group)
+                elif group_id == 0:
+                    group = required
+                else:
+                    right.append(group)
+            group.append(p)
+
+        count_min = sys.maxsize
+        count_max = -1
+
+        add("switch (PyTuple_Size(args)) {{\n")
+        for subset in permute_optional_groups(left, required, right):
+            count = len(subset)
+            count_min = min(count_min, count)
+            count_max = max(count_max, count)
+
+            group_ids = {p.group for p in subset}  # eliminate duplicates
+            d = {}
+            d['count'] = count
+            d['name'] = f.name
+            d['groups'] = sorted(group_ids)
+            d['format_units'] = "".join(p.converter.format_unit for p in subset)
+
+            parse_arguments = []
+            for p in subset:
+                p.converter.parse_argument(parse_arguments)
+            d['parse_arguments'] = ", ".join(parse_arguments)
+
+            group_ids.discard(0)
+            lines = [self.group_to_variable_name(g) + " = 1;" for g in group_ids]
+            lines = "\n".join(lines)
+
+            s = """
+    case {count}:
+        if (!PyArg_ParseTuple(args, "{format_units}:{name}", {parse_arguments}))
+            return NULL;
+        {group_booleans}
+        break;
+"""[1:]
+            s = linear_format(s, group_booleans=lines)
+            s = s.format_map(d)
+            add(s)
+
+        add("    default:\n")
+        s = '        PyErr_SetString(PyExc_TypeError, "{} requires {} to {} arguments");\n'
+        add(s.format(f.full_name, count_min, count_max))
+        add('        return NULL;\n')
+        add("}}")
+        template_dict['option_group_parsing'] = output()
+
+    def render_function(self, f):
+        if not f:
+            return ""
+
+        add, output = text_accumulator()
+        data = CRenderData()
+
+        if f.kind == STATIC_METHOD:
+            meth_flags = 'METH_STATIC'
+            self_name = "null"
+        else:
+            if f.kind == CALLABLE:
+                meth_flags = ''
+                self_name = "self"
+            elif f.kind == CLASS_METHOD:
+                meth_flags = 'METH_CLASS'
+                self_name = "cls"
+            else:
+                fail("Unrecognized 'kind' " + repr(f.kind) + " for function " + f.name)
+
+            data.impl_parameters.append("PyObject *" + self_name)
+            data.impl_arguments.append(self_name)
+
+        if f.coexist:
+            if meth_flags:
+                meth_flags += '|'
+            meth_flags += 'METH_COEXIST'
+
+        parameters = list(f.parameters.values())
+        converters = [p.converter for p in parameters]
+
+        template_dict = {}
+
+        full_name = f.full_name
+        template_dict['full_name'] = full_name
+
+        name = full_name.rpartition('.')[2]
+        template_dict['name'] = name
+
+        c_basename = f.c_basename or full_name.replace(".", "_")
+        template_dict['c_basename'] = c_basename
+
+        methoddef_name = "{}_METHODDEF".format(c_basename.upper())
+        template_dict['methoddef_name'] = methoddef_name
+
+        template_dict['docstring'] = self.docstring_for_c_string(f)
+
+        template_dict['self_name'] = self_name
+
+        positional = has_option_groups =  False
+
+        if parameters:
+            last_group = 0
+
+            for p in parameters:
+                c = p.converter
+
+                # insert group variable
+                group = p.group
+                if last_group != group:
+                    last_group = group
+                    if group:
+                        group_name = self.group_to_variable_name(group)
+                        data.impl_arguments.append(group_name)
+                        data.declarations.append("int " + group_name + " = 0;")
+                        data.impl_parameters.append("int " + group_name)
+                        has_option_groups = True
+                c.render(p, data)
+
+            positional = parameters[-1].kind == inspect.Parameter.POSITIONAL_ONLY
+            if has_option_groups:
+                assert positional
+
+        f.return_converter.render(f, data)
+        template_dict['impl_return_type'] = f.return_converter.type
+
+        template_dict['declarations'] = "\n".join(data.declarations)
+        template_dict['initializers'] = "\n\n".join(data.initializers)
+        template_dict['keywords'] = '"' + '", "'.join(data.keywords) + '"'
+        template_dict['format_units'] = ''.join(data.format_units)
+        template_dict['parse_arguments'] = ', '.join(data.parse_arguments)
+        template_dict['impl_parameters'] = ", ".join(data.impl_parameters)
+        template_dict['impl_arguments'] = ", ".join(data.impl_arguments)
+        template_dict['return_conversion'] = "".join(data.return_conversion).rstrip()
+        template_dict['cleanup'] = "".join(data.cleanup)
+        template_dict['return_value'] = data.return_value
+
+        template_dict['impl_prototype'] = self.impl_prototype_template.format_map(template_dict)
+
+        default_return_converter = (not f.return_converter or
+            f.return_converter.type == 'PyObject *')
+
+        if not parameters:
+            if default_return_converter:
+                template = self.meth_noargs_pyobject_template(meth_flags)
+            else:
+                template = self.meth_noargs_template(meth_flags)
+        elif (len(parameters) == 1 and
+              parameters[0].kind == inspect.Parameter.POSITIONAL_ONLY and
+              not converters[0].is_optional() and
+              isinstance(converters[0], object_converter) and
+              converters[0].format_unit == 'O'):
+            if default_return_converter:
+                template = self.meth_o_template(meth_flags)
+            else:
+                # HACK
+                # we're using "impl_parameters" for the
+                # non-impl function, because that works
+                # better for METH_O.  but that means we
+                # must surpress actually declaring the
+                # impl's parameters as variables in the
+                # non-impl.  but since it's METH_O, we
+                # only have one anyway, and it's the first one.
+                declarations_copy = list(data.declarations)
+                before, pyobject, after = declarations_copy[0].partition('PyObject *')
+                assert not before, "hack failed, see comment"
+                assert pyobject, "hack failed, see comment"
+                assert after and after[0].isalpha(), "hack failed, see comment"
+                del declarations_copy[0]
+                template_dict['declarations'] = "\n".join(declarations_copy)
+                template = self.meth_o_return_converter_template(meth_flags)
+        elif has_option_groups:
+            self.render_option_group_parsing(f, template_dict)
+            template = self.option_group_template(meth_flags)
+            template = linear_format(template,
+                option_group_parsing=template_dict['option_group_parsing'])
+        elif positional:
+            template = self.positional_only_template(meth_flags)
+        else:
+            template = self.keywords_template(meth_flags)
+
+        template = linear_format(template,
+            declarations=template_dict['declarations'],
+            return_conversion=template_dict['return_conversion'],
+            initializers=template_dict['initializers'],
+            cleanup=template_dict['cleanup'],
+            )
+
+        # Only generate the "exit:" label
+        # if we have any gotos
+        need_exit_label = "goto exit;" in template
+        template = linear_format(template,
+            exit_label="exit:" if need_exit_label else ''
+            )
+
+        return template.format_map(template_dict)
+
+
+@contextlib.contextmanager
+def OverrideStdioWith(stdout):
+    saved_stdout = sys.stdout
+    sys.stdout = stdout
+    try:
+        yield
+    finally:
+        assert sys.stdout is stdout
+        sys.stdout = saved_stdout
+
+
+def create_regex(before, after):
+    """Create an re object for matching marker lines."""
+    pattern = r'^{}(\w+){}$'
+    return re.compile(pattern.format(re.escape(before), re.escape(after)))
+
+
+class Block:
+    r"""
+    Represents a single block of text embedded in
+    another file.  If dsl_name is None, the block represents
+    verbatim text, raw original text from the file, in
+    which case "input" will be the only non-false member.
+    If dsl_name is not None, the block represents a Clinic
+    block.
+
+    input is always str, with embedded \n characters.
+    input represents the original text from the file;
+    if it's a Clinic block, it is the original text with
+    the body_prefix and redundant leading whitespace removed.
+
+    dsl_name is either str or None.  If str, it's the text
+    found on the start line of the block between the square
+    brackets.
+
+    signatures is either list or None.  If it's a list,
+    it may only contain clinic.Module, clinic.Class, and
+    clinic.Function objects.  At the moment it should
+    contain at most one of each.
+
+    output is either str or None.  If str, it's the output
+    from this block, with embedded '\n' characters.
+
+    indent is either str or None.  It's the leading whitespace
+    that was found on every line of input.  (If body_prefix is
+    not empty, this is the indent *after* removing the
+    body_prefix.)
+
+    preindent is either str or None.  It's the whitespace that
+    was found in front of every line of input *before* the
+    "body_prefix" (see the Language object).  If body_prefix
+    is empty, preindent must always be empty too.
+
+    To illustrate indent and preindent: Assume that '_'
+    represents whitespace.  If the block processed was in a
+    Python file, and looked like this:
+      ____#/*[python]
+      ____#__for a in range(20):
+      ____#____print(a)
+      ____#[python]*/
+    "preindent" would be "____" and "indent" would be "__".
+
+    """
+    def __init__(self, input, dsl_name=None, signatures=None, output=None, indent='', preindent=''):
+        assert isinstance(input, str)
+        self.input = input
+        self.dsl_name = dsl_name
+        self.signatures = signatures or []
+        self.output = output
+        self.indent = indent
+        self.preindent = preindent
+
+
+class BlockParser:
+    """
+    Block-oriented parser for Argument Clinic.
+    Iterator, yields Block objects.
+    """
+
+    def __init__(self, input, language, *, verify=True):
+        """
+        "input" should be a str object
+        with embedded \n characters.
+
+        "language" should be a Language object.
+        """
+        language.validate()
+
+        self.input = collections.deque(reversed(input.splitlines(keepends=True)))
+        self.block_start_line_number = self.line_number = 0
+
+        self.language = language
+        before, _, after = language.start_line.partition('{dsl_name}')
+        assert _ == '{dsl_name}'
+        self.start_re = create_regex(before, after)
+        self.verify = verify
+        self.last_checksum_re = None
+        self.last_dsl_name = None
+        self.dsl_name = None
+
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        if not self.input:
+            raise StopIteration
+
+        if self.dsl_name:
+            return_value = self.parse_clinic_block(self.dsl_name)
+            self.dsl_name = None
+            return return_value
+        return self.parse_verbatim_block()
+
+    def is_start_line(self, line):
+        match = self.start_re.match(line.lstrip())
+        return match.group(1) if match else None
+
+    def _line(self):
+        self.line_number += 1
+        return self.input.pop()
+
+    def parse_verbatim_block(self):
+        add, output = text_accumulator()
+        self.block_start_line_number = self.line_number
+
+        while self.input:
+            line = self._line()
+            dsl_name = self.is_start_line(line)
+            if dsl_name:
+                self.dsl_name = dsl_name
+                break
+            add(line)
+
+        return Block(output())
+
+    def parse_clinic_block(self, dsl_name):
+        input_add, input_output = text_accumulator()
+        self.block_start_line_number = self.line_number + 1
+        stop_line = self.language.stop_line.format(dsl_name=dsl_name) + '\n'
+        body_prefix = self.language.body_prefix.format(dsl_name=dsl_name)
+
+        # consume body of program
+        while self.input:
+            line = self._line()
+            if line == stop_line or self.is_start_line(line):
+                break
+            if body_prefix:
+                line = line.lstrip()
+                assert line.startswith(body_prefix)
+                line = line[len(body_prefix):]
+            input_add(line)
+
+        # consume output and checksum line, if present.
+        if self.last_dsl_name == dsl_name:
+            checksum_re = self.last_checksum_re
+        else:
+            before, _, after = self.language.checksum_line.format(dsl_name=dsl_name, checksum='{checksum}').partition('{checksum}')
+            assert _ == '{checksum}'
+            checksum_re = create_regex(before, after)
+            self.last_dsl_name = dsl_name
+            self.last_checksum_re = checksum_re
+
+        # scan forward for checksum line
+        output_add, output_output = text_accumulator()
+        checksum = None
+        while self.input:
+            line = self._line()
+            match = checksum_re.match(line.lstrip())
+            checksum = match.group(1) if match else None
+            if checksum:
+                break
+            output_add(line)
+            if self.is_start_line(line):
+                break
+
+        if checksum:
+            output = output_output()
+            if self.verify:
+                computed = compute_checksum(output)
+                if checksum != computed:
+                    fail("Checksum mismatch!\nExpected: {}\nComputed: {}".format(checksum, computed))
+        else:
+            # put back output
+            self.input.extend(reversed(output.splitlines(keepends=True)))
+            self.line_number -= len(output)
+            output = None
+
+        return Block(input_output(), dsl_name, output=output)
+
+
+class BlockPrinter:
+
+    def __init__(self, language, f=None):
+        self.language = language
+        self.f = f or io.StringIO()
+
+    def print_block(self, block):
+        input = block.input
+        output = block.output
+        dsl_name = block.dsl_name
+        write = self.f.write
+
+        assert (not input) or (input.endswith('\n'))
+        assert not ((dsl_name == None) ^ (output == None)), "you must specify dsl_name and output together, dsl_name " + repr(dsl_name)
+
+        if not dsl_name:
+            write(input)
+            return
+
+        write(self.language.start_line.format(dsl_name=dsl_name))
+        write("\n")
+
+        body_prefix = self.language.body_prefix.format(dsl_name=dsl_name)
+        if not body_prefix:
+            write(input)
+        else:
+            for line in input.split('\n'):
+                write(body_prefix)
+                write(line)
+                write("\n")
+
+        write(self.language.stop_line.format(dsl_name=dsl_name))
+        write("\n")
+
+        output = block.output
+        if output:
+            write(output)
+            if not output.endswith('\n'):
+                write('\n')
+
+        write(self.language.checksum_line.format(dsl_name=dsl_name, checksum=compute_checksum(output)))
+        write("\n")
+
+
+# maps strings to Language objects.
+# "languages" maps the name of the language ("C", "Python").
+# "extensions" maps the file extension ("c", "py").
+languages = { 'C': CLanguage, 'Python': PythonLanguage }
+extensions = { 'c': CLanguage, 'h': CLanguage, 'py': PythonLanguage }
+
+
+# maps strings to callables.
+# these callables must be of the form:
+#   def foo(name, default, *, ...)
+# The callable may have any number of keyword-only parameters.
+# The callable must return a CConverter object.
+# The callable should not call builtins.print.
+converters = {}
+
+# maps strings to callables.
+# these callables follow the same rules as those for "converters" above.
+# note however that they will never be called with keyword-only parameters.
+legacy_converters = {}
+
+
+# maps strings to callables.
+# these callables must be of the form:
+#   def foo(*, ...)
+# The callable may have any number of keyword-only parameters.
+# The callable must return a CConverter object.
+# The callable should not call builtins.print.
+return_converters = {}
+
+class Clinic:
+    def __init__(self, language, printer=None, *, verify=True, filename=None):
+        # maps strings to Parser objects.
+        # (instantiated from the "parsers" global.)
+        self.parsers = {}
+        self.language = language
+        self.printer = printer or BlockPrinter(language)
+        self.verify = verify
+        self.filename = filename
+        self.modules = collections.OrderedDict()
+
+        global clinic
+        clinic = self
+
+    def parse(self, input):
+        printer = self.printer
+        self.block_parser = BlockParser(input, self.language, verify=self.verify)
+        for block in self.block_parser:
+            dsl_name = block.dsl_name
+            if dsl_name:
+                if dsl_name not in self.parsers:
+                    assert dsl_name in parsers, "No parser to handle {!r} block.".format(dsl_name)
+                    self.parsers[dsl_name] = parsers[dsl_name](self)
+                parser = self.parsers[dsl_name]
+                parser.parse(block)
+            printer.print_block(block)
+        return printer.f.getvalue()
+
+    def _module_and_class(self, fields):
+        """
+        fields should be an iterable of field names.
+        returns a tuple of (module, class).
+        the module object could actually be self (a clinic object).
+        this function is only ever used to find the parent of where
+        a new class/module should go.
+        """
+        in_classes = False
+        parent = module = self
+        cls = None
+        so_far = []
+
+        for field in fields:
+            so_far.append(field)
+            if not in_classes:
+                child = parent.modules.get(field)
+                if child:
+                    module = child
+                    continue
+                in_classes = True
+            if not hasattr(parent, 'classes'):
+                return module, cls
+            child = parent.classes.get(field)
+            if not child:
+                fail('Parent class or module ' + '.'.join(so_far) + " does not exist.")
+            cls = parent = child
+
+        return module, cls
+
+
+def parse_file(filename, *, verify=True, output=None, encoding='utf-8'):
+    extension = os.path.splitext(filename)[1][1:]
+    if not extension:
+        fail("Can't extract file type for file " + repr(filename))
+
+    try:
+        language = extensions[extension]()
+    except KeyError:
+        fail("Can't identify file type for file " + repr(filename))
+
+    clinic = Clinic(language, verify=verify, filename=filename)
+
+    with open(filename, 'r', encoding=encoding) as f:
+        text = clinic.parse(f.read())
+
+    directory = os.path.dirname(filename) or '.'
+
+    with tempfile.TemporaryDirectory(prefix="clinic", dir=directory) as tmpdir:
+        bytes = text.encode(encoding)
+        tmpfilename = os.path.join(tmpdir, os.path.basename(filename))
+        with open(tmpfilename, "wb") as f:
+            f.write(bytes)
+        os.replace(tmpfilename, output or filename)
+
+
+def compute_checksum(input):
+    input = input or ''
+    return hashlib.sha1(input.encode('utf-8')).hexdigest()
+
+
+
+
+class PythonParser:
+    def __init__(self, clinic):
+        pass
+
+    def parse(self, block):
+        s = io.StringIO()
+        with OverrideStdioWith(s):
+            exec(block.input)
+        block.output = s.getvalue()
+
+
+class Module:
+    def __init__(self, name, module=None):
+        self.name = name
+        self.module = self.parent = module
+
+        self.modules = collections.OrderedDict()
+        self.classes = collections.OrderedDict()
+        self.functions = []
+
+class Class:
+    def __init__(self, name, module=None, cls=None):
+        self.name = name
+        self.module = module
+        self.cls = cls
+        self.parent = cls or module
+
+        self.classes = collections.OrderedDict()
+        self.functions = []
+
+DATA, CALLABLE, METHOD, STATIC_METHOD, CLASS_METHOD = range(5)
+
+class Function:
+    """
+    Mutable duck type for inspect.Function.
+
+    docstring - a str containing
+        * embedded line breaks
+        * text outdented to the left margin
+        * no trailing whitespace.
+        It will always be true that
+            (not docstring) or ((not docstring[0].isspace()) and (docstring.rstrip() == docstring))
+    """
+
+    def __init__(self, parameters=None, *, name,
+                 module, cls=None, c_basename=None,
+                 full_name=None,
+                 return_converter, return_annotation=_empty,
+                 docstring=None, kind=CALLABLE, coexist=False):
+        self.parameters = parameters or collections.OrderedDict()
+        self.return_annotation = return_annotation
+        self.name = name
+        self.full_name = full_name
+        self.module = module
+        self.cls = cls
+        self.parent = cls or module
+        self.c_basename = c_basename
+        self.return_converter = return_converter
+        self.docstring = docstring or ''
+        self.kind = kind
+        self.coexist = coexist
+
+    def __repr__(self):
+        return '<clinic.Function ' + self.name + '>'
+
+
+class Parameter:
+    """
+    Mutable duck type of inspect.Parameter.
+    """
+
+    def __init__(self, name, kind, *, default=_empty,
+                 function, converter, annotation=_empty,
+                 docstring=None, group=0):
+        self.name = name
+        self.kind = kind
+        self.default = default
+        self.function = function
+        self.converter = converter
+        self.annotation = annotation
+        self.docstring = docstring or ''
+        self.group = group
+
+    def __repr__(self):
+        return '<clinic.Parameter ' + self.name + '>'
+
+    def is_keyword_only(self):
+        return self.kind == inspect.Parameter.KEYWORD_ONLY
+
+py_special_values = {
+    NULL: "None",
+}
+
+def py_repr(o):
+    special = py_special_values.get(o)
+    if special:
+        return special
+    return repr(o)
+
+
+c_special_values = {
+    NULL: "NULL",
+    None: "Py_None",
+}
+
+def c_repr(o):
+    special = c_special_values.get(o)
+    if special:
+        return special
+    if isinstance(o, str):
+        return '"' + quoted_for_c_string(o) + '"'
+    return repr(o)
+
+def add_c_converter(f, name=None):
+    if not name:
+        name = f.__name__
+        if not name.endswith('_converter'):
+            return f
+        name = name[:-len('_converter')]
+    converters[name] = f
+    return f
+
+def add_default_legacy_c_converter(cls):
+    # automatically add converter for default format unit
+    # (but without stomping on the existing one if it's already
+    # set, in case you subclass)
+    if ((cls.format_unit != 'O&') and
+        (cls.format_unit not in legacy_converters)):
+        legacy_converters[cls.format_unit] = cls
+    return cls
+
+def add_legacy_c_converter(format_unit, **kwargs):
+    """
+    Adds a legacy converter.
+    """
+    def closure(f):
+        if not kwargs:
+            added_f = f
+        else:
+            added_f = functools.partial(f, **kwargs)
+        legacy_converters[format_unit] = added_f
+        return f
+    return closure
+
+class CConverterAutoRegister(type):
+    def __init__(cls, name, bases, classdict):
+        add_c_converter(cls)
+        add_default_legacy_c_converter(cls)
+
+class CConverter(metaclass=CConverterAutoRegister):
+    """
+    For the init function, self, name, function, and default
+    must be keyword-or-positional parameters.  All other
+    parameters (including "required" and "doc_default")
+    must be keyword-only.
+    """
+
+    type = None
+    format_unit = 'O&'
+
+    # The Python default value for this parameter, as a Python value.
+    # Or "unspecified" if there is no default.
+    default = unspecified
+
+    # "default" converted into a str for rendering into Python code.
+    py_default = None
+
+    # "default" as it should appear in the documentation, as a string.
+    # Or None if there is no default.
+    doc_default = None
+
+    # "default" converted into a C value, as a string.
+    # Or None if there is no default.
+    c_default = None
+
+    # The C converter *function* to be used, if any.
+    # (If this is not None, format_unit must be 'O&'.)
+    converter = None
+    encoding = None
+    impl_by_reference = False
+    parse_by_reference = True
+    length = False
+
+    def __init__(self, name, function, default=unspecified, *, doc_default=None, required=False, annotation=unspecified, **kwargs):
+        self.function = function
+        self.name = name
+
+        if default is not unspecified:
+            self.default = default
+            self.py_default = py_repr(default)
+            self.doc_default = doc_default if doc_default is not None else self.py_default
+            self.c_default = c_repr(default)
+        elif doc_default is not None:
+            fail(function.fullname + " argument " + name + " specified a 'doc_default' without having a 'default'")
+        if annotation != unspecified:
+            fail("The 'annotation' parameter is not currently permitted.")
+        self.required = required
+        self.converter_init(**kwargs)
+
+    def converter_init(self):
+        pass
+
+    def is_optional(self):
+        return (self.default is not unspecified) and (not self.required)
+
+    def render(self, parameter, data):
+        """
+        parameter is a clinic.Parameter instance.
+        data is a CRenderData instance.
+        """
+        name = legal_c_identifier(self.name)
+
+        # declarations
+        d = self.declaration()
+        data.declarations.append(d)
+
+        # initializers
+        initializers = self.initialize()
+        if initializers:
+            data.initializers.append('/* initializers for ' + name + ' */\n' + initializers.rstrip())
+
+        # impl_arguments
+        s = ("&" if self.impl_by_reference else "") + name
+        data.impl_arguments.append(s)
+
+        # keywords
+        data.keywords.append(name)
+
+        # format_units
+        if self.is_optional() and '|' not in data.format_units:
+            data.format_units.append('|')
+        if parameter.is_keyword_only() and '$' not in data.format_units:
+            data.format_units.append('$')
+        data.format_units.append(self.format_unit)
+
+        # parse_arguments
+        self.parse_argument(data.parse_arguments)
+
+        # impl_parameters
+        data.impl_parameters.append(self.simple_declaration(by_reference=self.impl_by_reference))
+
+        # cleanup
+        cleanup = self.cleanup()
+        if cleanup:
+            data.cleanup.append('/* Cleanup for ' + name + ' */\n' + cleanup.rstrip() + "\n")
+
+    # Why is this one broken out separately?
+    # For "positional-only" function parsing,
+    # which generates a bunch of PyArg_ParseTuple calls.
+    def parse_argument(self, list):
+        assert not (self.converter and self.encoding)
+        if self.format_unit == 'O&':
+            assert self.converter
+            list.append(self.converter)
+
+        if self.encoding:
+            list.append(self.encoding)
+
+        s = ("&" if self.parse_by_reference else "") + legal_c_identifier(self.name)
+        list.append(s)
+
+    #
+    # All the functions after here are intended as extension points.
+    #
+
+    def simple_declaration(self, by_reference=False):
+        """
+        Computes the basic declaration of the variable.
+        Used in computing the prototype declaration and the
+        variable declaration.
+        """
+        prototype = [self.type]
+        if by_reference or not self.type.endswith('*'):
+            prototype.append(" ")
+        if by_reference:
+            prototype.append('*')
+        prototype.append(legal_c_identifier(self.name))
+        return "".join(prototype)
+
+    def declaration(self):
+        """
+        The C statement to declare this variable.
+        """
+        declaration = [self.simple_declaration()]
+        if self.c_default:
+            declaration.append(" = ")
+            declaration.append(self.c_default)
+        declaration.append(";")
+        return "".join(declaration)
+
+    def initialize(self):
+        """
+        The C statements required to set up this variable before parsing.
+        Returns a string containing this code indented at column 0.
+        If no initialization is necessary, returns an empty string.
+        """
+        return ""
+
+    def cleanup(self):
+        """
+        The C statements required to clean up after this variable.
+        Returns a string containing this code indented at column 0.
+        If no cleanup is necessary, returns an empty string.
+        """
+        return ""
+
+
+class bool_converter(CConverter):
+    type = 'int'
+    format_unit = 'p'
+
+    def converter_init(self):
+        self.default = bool(self.default)
+        self.c_default = str(int(self.default))
+
+class char_converter(CConverter):
+    type = 'char'
+    format_unit = 'c'
+
+@add_legacy_c_converter('B', bitwise=True)
+class byte_converter(CConverter):
+    type = 'byte'
+    format_unit = 'b'
+
+    def converter_init(self, *, bitwise=False):
+        if bitwise:
+            format_unit = 'B'
+
+class short_converter(CConverter):
+    type = 'short'
+    format_unit = 'h'
+
+class unsigned_short_converter(CConverter):
+    type = 'unsigned short'
+    format_unit = 'H'
+
+    def converter_init(self, *, bitwise=False):
+        if not bitwise:
+            fail("Unsigned shorts must be bitwise (for now).")
+
+@add_legacy_c_converter('C', from_str=True)
+class int_converter(CConverter):
+    type = 'int'
+    format_unit = 'i'
+
+    def converter_init(self, *, from_str=False):
+        if from_str:
+            format_unit = 'C'
+
+class unsigned_int_converter(CConverter):
+    type = 'unsigned int'
+    format_unit = 'I'
+
+    def converter_init(self, *, bitwise=False):
+        if not bitwise:
+            fail("Unsigned ints must be bitwise (for now).")
+
+class long_converter(CConverter):
+    type = 'long'
+    format_unit = 'l'
+
+class unsigned_long_converter(CConverter):
+    type = 'unsigned long'
+    format_unit = 'k'
+
+    def converter_init(self, *, bitwise=False):
+        if not bitwise:
+            fail("Unsigned longs must be bitwise (for now).")
+
+class PY_LONG_LONG_converter(CConverter):
+    type = 'PY_LONG_LONG'
+    format_unit = 'L'
+
+class unsigned_PY_LONG_LONG_converter(CConverter):
+    type = 'unsigned PY_LONG_LONG'
+    format_unit = 'K'
+
+    def converter_init(self, *, bitwise=False):
+        if not bitwise:
+            fail("Unsigned PY_LONG_LONGs must be bitwise (for now).")
+
+class Py_ssize_t_converter(CConverter):
+    type = 'Py_ssize_t'
+    format_unit = 'n'
+
+
+class float_converter(CConverter):
+    type = 'float'
+    format_unit = 'f'
+
+class double_converter(CConverter):
+    type = 'double'
+    format_unit = 'd'
+
+
+class Py_complex_converter(CConverter):
+    type = 'Py_complex'
+    format_unit = 'D'
+
+
+class object_converter(CConverter):
+    type = 'PyObject *'
+    format_unit = 'O'
+
+    def converter_init(self, *, type=None):
+        if type:
+            assert isinstance(type, str)
+            assert type.isidentifier()
+            try:
+                type = eval(type)
+                # need more of these!
+                type = {
+                    str: '&PyUnicode_Type',
+                    }[type]
+            except NameError:
+                type = type
+            self.format_unit = 'O!'
+            self.encoding = type
+
+
+@add_legacy_c_converter('y', from_bytes=True)
+@add_legacy_c_converter('z', nullable=True)
+class str_converter(CConverter):
+    type = 'const char *'
+    format_unit = 's'
+
+    def converter_init(self, *, nullable=False, from_bytes=False):
+        if from_bytes:
+            assert not nullable
+            format_unit = 'y'
+        if nullable:
+            format_unit = 'z'
+
+
+class PyBytesObject_converter(CConverter):
+    type = 'PyBytesObject *'
+    format_unit = 'S'
+
+class PyByteArrayObject_converter(CConverter):
+    type = 'PyByteArrayObject *'
+    format_unit = 'Y'
+
+class unicode_converter(CConverter):
+    type = 'PyObject *'
+    format_unit = 'U'
+
+@add_legacy_c_converter('Z', nullable=True)
+class Py_UNICODE_converter(CConverter):
+    type = 'Py_UNICODE *'
+    format_unit = 'u'
+
+    def converter_init(self, *, nullable=False):
+        if nullable:
+            format_unit = 'Z'
+
+@add_legacy_c_converter('s*', zeroes=True)
+@add_legacy_c_converter('w*', read_write=True)
+@add_legacy_c_converter('z*', zeroes=True, nullable=True)
+class Py_buffer_converter(CConverter):
+    type = 'Py_buffer'
+    format_unit = 'y*'
+    impl_by_reference = True
+
+    def converter_init(self, *, str=False, zeroes=False, nullable=False, read_write=False):
+        if not str:
+            assert not (zeroes or nullable or read_write)
+        elif read_write:
+            assert not (zeroes or nullable)
+            self.format_unit = 'w*'
+        else:
+            assert zeroes
+            self.format_unit = 'z*' if nullable else 's*'
+
+    def cleanup(self):
+        return "PyBuffer_Release(&" + legal_c_identifier(self.name) + ");\n"
+
+
+def add_c_return_converter(f, name=None):
+    if not name:
+        name = f.__name__
+        if not name.endswith('_return_converter'):
+            return f
+        name = name[:-len('_return_converter')]
+    return_converters[name] = f
+    return f
+
+
+class CReturnConverterAutoRegister(type):
+    def __init__(cls, name, bases, classdict):
+        add_c_return_converter(cls)
+
+class CReturnConverter(metaclass=CReturnConverterAutoRegister):
+
+    type = 'PyObject *'
+    default = None
+
+    def __init__(self, *, doc_default=None, **kwargs):
+        self.doc_default = doc_default
+        try:
+            self.return_converter_init(**kwargs)
+        except TypeError as e:
+            s = ', '.join(name + '=' + repr(value) for name, value in kwargs.items())
+            sys.exit(self.__class__.__name__ + '(' + s + ')\n' + str(e))
+
+    def return_converter_init(self):
+        pass
+
+    def declare(self, data, name="_return_value"):
+        line = []
+        add = line.append
+        add(self.type)
+        if not self.type.endswith('*'):
+            add(' ')
+        add(name + ';')
+        data.declarations.append(''.join(line))
+        data.return_value = name
+
+    def err_occurred_if(self, expr, data):
+        data.return_conversion.append('if (({}) && PyErr_Occurred())\n    goto exit;\n'.format(expr))
+
+    def err_occurred_if_null_pointer(self, variable, data):
+        data.return_conversion.append('if ({} == NULL)\n    goto exit;\n'.format(variable))
+
+    def render(self, function, data):
+        """
+        function is a clinic.Function instance.
+        data is a CRenderData instance.
+        """
+        pass
+
+add_c_return_converter(CReturnConverter, 'object')
+
+class int_return_converter(CReturnConverter):
+    type = 'int'
+
+    def render(self, function, data):
+        self.declare(data)
+        self.err_occurred_if("_return_value == -1", data)
+        data.return_conversion.append(
+            'return_value = PyLong_FromLong((long)_return_value);\n')
+
+
+class long_return_converter(CReturnConverter):
+    type = 'long'
+
+    def render(self, function, data):
+        self.declare(data)
+        self.err_occurred_if("_return_value == -1", data)
+        data.return_conversion.append(
+            'return_value = PyLong_FromLong(_return_value);\n')
+
+
+class Py_ssize_t_return_converter(CReturnConverter):
+    type = 'Py_ssize_t'
+
+    def render(self, function, data):
+        self.declare(data)
+        self.err_occurred_if("_return_value == -1", data)
+        data.return_conversion.append(
+            'return_value = PyLong_FromSsize_t(_return_value);\n')
+
+
+class DecodeFSDefault_return_converter(CReturnConverter):
+    type = 'char *'
+
+    def render(self, function, data):
+        self.declare(data)
+        self.err_occurred_if_null_pointer("_return_value", data)
+        data.return_conversion.append(
+            'return_value = PyUnicode_DecodeFSDefault(_return_value);\n')
+
+
+class IndentStack:
+    def __init__(self):
+        self.indents = []
+        self.margin = None
+
+    def _ensure(self):
+        if not self.indents:
+            fail('IndentStack expected indents, but none are defined.')
+
+    def measure(self, line):
+        """
+        Returns the length of the line's margin.
+        """
+        if '\t' in line:
+            fail('Tab characters are illegal in the Clinic DSL.')
+        stripped = line.lstrip()
+        if not len(stripped):
+            # we can't tell anything from an empty line
+            # so just pretend it's indented like our current indent
+            self._ensure()
+            return self.indents[-1]
+        return len(line) - len(stripped)
+
+    def infer(self, line):
+        """
+        Infer what is now the current margin based on this line.
+        Returns:
+            1 if we have indented (or this is the first margin)
+            0 if the margin has not changed
+           -N if we have dedented N times
+        """
+        indent = self.measure(line)
+        margin = ' ' * indent
+        if not self.indents:
+            self.indents.append(indent)
+            self.margin = margin
+            return 1
+        current = self.indents[-1]
+        if indent == current:
+            return 0
+        if indent > current:
+            self.indents.append(indent)
+            self.margin = margin
+            return 1
+        # indent < current
+        if indent not in self.indents:
+            fail("Illegal outdent.")
+        outdent_count = 0
+        while indent != current:
+            self.indents.pop()
+            current = self.indents[-1]
+            outdent_count -= 1
+        self.margin = margin
+        return outdent_count
+
+    @property
+    def depth(self):
+        """
+        Returns how many margins are currently defined.
+        """
+        return len(self.indents)
+
+    def indent(self, line):
+        """
+        Indents a line by the currently defined margin.
+        """
+        return self.margin + line
+
+    def dedent(self, line):
+        """
+        Dedents a line by the currently defined margin.
+        (The inverse of 'indent'.)
+        """
+        margin = self.margin
+        indent = self.indents[-1]
+        if not line.startswith(margin):
+            fail('Cannot dedent, line does not start with the previous margin:')
+        return line[indent:]
+
+
+class DSLParser:
+    def __init__(self, clinic):
+        self.clinic = clinic
+
+        self.directives = {}
+        for name in dir(self):
+            # functions that start with directive_ are added to directives
+            _, s, key = name.partition("directive_")
+            if s:
+                self.directives[key] = getattr(self, name)
+
+            # functions that start with at_ are too, with an @ in front
+            _, s, key = name.partition("at_")
+            if s:
+                self.directives['@' + key] = getattr(self, name)
+
+        self.reset()
+
+    def reset(self):
+        self.function = None
+        self.state = self.state_dsl_start
+        self.parameter_indent = None
+        self.keyword_only = False
+        self.group = 0
+        self.parameter_state = self.ps_start
+        self.indent = IndentStack()
+        self.kind = CALLABLE
+        self.coexist = False
+
+    def directive_module(self, name):
+        fields = name.split('.')
+        new = fields.pop()
+        module, cls = self.clinic._module_and_class(fields)
+        if cls:
+            fail("Can't nest a module inside a class!")
+        m = Module(name, module)
+        module.modules[name] = m
+        self.block.signatures.append(m)
+
+    def directive_class(self, name):
+        fields = name.split('.')
+        in_classes = False
+        parent = self
+        name = fields.pop()
+        so_far = []
+        module, cls = self.clinic._module_and_class(fields)
+
+        if not module:
+            fail("You must explicitly specify the module for the class.")
+
+        c = Class(name, module, cls)
+        module.classes[name] = c
+        if cls:
+            cls.classes[name] = c
+        self.block.signatures.append(c)
+
+    def at_classmethod(self):
+        assert self.kind is CALLABLE
+        self.kind = CLASS_METHOD
+
+    def at_staticmethod(self):
+        assert self.kind is CALLABLE
+        self.kind = STATIC_METHOD
+
+    def at_coexist(self):
+        assert self.coexist == False
+        self.coexist = True
+
+    def parse(self, block):
+        self.reset()
+        self.block = block
+        block_start = self.clinic.block_parser.line_number
+        lines = block.input.split('\n')
+        for line_number, line in enumerate(lines, self.clinic.block_parser.block_start_line_number):
+            if '\t' in line:
+                fail('Tab characters are illegal in the Clinic DSL.\n\t' + repr(line), line_number=block_start)
+            self.state(line)
+
+        self.next(self.state_terminal)
+        self.state(None)
+
+        block.output = self.clinic.language.render(block.signatures)
+
+    @staticmethod
+    def ignore_line(line):
+        # ignore comment-only lines
+        if line.lstrip().startswith('#'):
+            return True
+
+        # Ignore empty lines too
+        # (but not in docstring sections!)
+        if not line.strip():
+            return True
+
+        return False
+
+    @staticmethod
+    def calculate_indent(line):
+        return len(line) - len(line.strip())
+
+    def next(self, state, line=None):
+        # real_print(self.state.__name__, "->", state.__name__, ", line=", line)
+        self.state = state
+        if line is not None:
+            self.state(line)
+
+    def state_dsl_start(self, line):
+        # self.block = self.ClinicOutputBlock(self)
+        if self.ignore_line(line):
+            return
+        self.next(self.state_modulename_name, line)
+
+    def state_modulename_name(self, line):
+        # looking for declaration, which establishes the leftmost column
+        # line should be
+        #     modulename.fnname [as c_basename] [-> return annotation]
+        # square brackets denote optional syntax.
+        #
+        # (but we might find a directive first!)
+        #
+        # this line is permitted to start with whitespace.
+        # we'll call this number of spaces F (for "function").
+
+        if not line.strip():
+            return
+
+        self.indent.infer(line)
+
+        # is it a directive?
+        fields = shlex.split(line)
+        directive_name = fields[0]
+        directive = self.directives.get(directive_name, None)
+        if directive:
+            directive(*fields[1:])
+            return
+
+        line, _, returns = line.partition('->')
+
+        full_name, _, c_basename = line.partition(' as ')
+        full_name = full_name.strip()
+        c_basename = c_basename.strip() or None
+
+        if not returns:
+            return_converter = CReturnConverter()
+        else:
+            ast_input = "def x() -> {}: pass".format(returns)
+            module = None
+            try:
+                module = ast.parse(ast_input)
+            except SyntaxError:
+                pass
+            if not module:
+                fail("Badly-formed annotation for " + full_name + ": " + returns)
+            try:
+                name, legacy, kwargs = self.parse_converter(module.body[0].returns)
+                assert not legacy
+                if name not in return_converters:
+                    fail("Error: No available return converter called " + repr(name))
+                return_converter = return_converters[name](**kwargs)
+            except ValueError:
+                fail("Badly-formed annotation for " + full_name + ": " + returns)
+
+        fields = [x.strip() for x in full_name.split('.')]
+        function_name = fields.pop()
+        module, cls = self.clinic._module_and_class(fields)
+
+        if not module:
+            fail("Undefined module used in declaration of " + repr(full_name.strip()) + ".")
+        self.function = Function(name=function_name, full_name=full_name, module=module, cls=cls, c_basename=c_basename,
+                                 return_converter=return_converter, kind=self.kind, coexist=self.coexist)
+        self.block.signatures.append(self.function)
+        self.next(self.state_parameters_start)
+
+    # Now entering the parameters section.  The rules, formally stated:
+    #
+    #   * All lines must be indented with spaces only.
+    #   * The first line must be a parameter declaration.
+    #   * The first line must be indented.
+    #       * This first line establishes the indent for parameters.
+    #       * We'll call this number of spaces P (for "parameter").
+    #   * Thenceforth:
+    #       * Lines indented with P spaces specify a parameter.
+    #       * Lines indented with > P spaces are docstrings for the previous
+    #         parameter.
+    #           * We'll call this number of spaces D (for "docstring").
+    #           * All subsequent lines indented with >= D spaces are stored as
+    #             part of the per-parameter docstring.
+    #           * All lines will have the first D spaces of the indent stripped
+    #             before they are stored.
+    #           * It's illegal to have a line starting with a number of spaces X
+    #             such that P < X < D.
+    #       * A line with < P spaces is the first line of the function
+    #         docstring, which ends processing for parameters and per-parameter
+    #         docstrings.
+    #           * The first line of the function docstring must be at the same
+    #             indent as the function declaration.
+    #       * It's illegal to have any line in the parameters section starting
+    #         with X spaces such that F < X < P.  (As before, F is the indent
+    #         of the function declaration.)
+    #
+    ##############
+    #
+    # Also, currently Argument Clinic places the following restrictions on groups:
+    #   * Each group must contain at least one parameter.
+    #   * Each group may contain at most one group, which must be the furthest
+    #     thing in the group from the required parameters.  (The nested group
+    #     must be the first in the group when it's before the required
+    #     parameters, and the last thing in the group when after the required
+    #     parameters.)
+    #   * There may be at most one (top-level) group to the left or right of
+    #     the required parameters.
+    #   * You must specify a slash, and it must be after all parameters.
+    #     (In other words: either all parameters are positional-only,
+    #      or none are.)
+    #
+    #  Said another way:
+    #   * Each group must contain at least one parameter.
+    #   * All left square brackets before the required parameters must be
+    #     consecutive.  (You can't have a left square bracket followed
+    #     by a parameter, then another left square bracket.  You can't
+    #     have a left square bracket, a parameter, a right square bracket,
+    #     and then a left square bracket.)
+    #   * All right square brackets after the required parameters must be
+    #     consecutive.
+    #
+    # These rules are enforced with a single state variable:
+    # "parameter_state".  (Previously the code was a miasma of ifs and
+    # separate boolean state variables.)  The states are:
+    #
+    #  [ [ a, b, ] c, ] d, e, f, [ g, h, [ i ] ] /   <- line
+    # 01   2          3          4           5   6   <- state transitions
+    #
+    # 0: ps_start.  before we've seen anything.  legal transitions are to 1 or 3.
+    # 1: ps_left_square_before.  left square brackets before required parameters.
+    # 2: ps_group_before.  in a group, before required parameters.
+    # 3: ps_required.  required parameters.  (renumber left groups!)
+    # 4: ps_group_after.  in a group, after required parameters.
+    # 5: ps_right_square_after.  right square brackets after required parameters.
+    # 6: ps_seen_slash.  seen slash.
+    ps_start, ps_left_square_before, ps_group_before, ps_required, \
+    ps_group_after, ps_right_square_after, ps_seen_slash = range(7)
+
+    def state_parameters_start(self, line):
+        if self.ignore_line(line):
+            return
+
+        # if this line is not indented, we have no parameters
+        if not self.indent.infer(line):
+            return self.next(self.state_function_docstring, line)
+
+        return self.next(self.state_parameter, line)
+
+
+    def to_required(self):
+        """
+        Transition to the "required" parameter state.
+        """
+        if self.parameter_state != self.ps_required:
+            self.parameter_state = self.ps_required
+            for p in self.function.parameters.values():
+                p.group = -p.group
+
+    def state_parameter(self, line):
+        if self.ignore_line(line):
+            return
+
+        assert self.indent.depth == 2
+        indent = self.indent.infer(line)
+        if indent == -1:
+            # we outdented, must be to definition column
+            return self.next(self.state_function_docstring, line)
+
+        if indent == 1:
+            # we indented, must be to new parameter docstring column
+            return self.next(self.state_parameter_docstring_start, line)
+
+        line = line.lstrip()
+
+        if line in ('*', '/', '[', ']'):
+            self.parse_special_symbol(line)
+            return
+
+        if self.parameter_state in (self.ps_start, self.ps_required):
+            self.to_required()
+        elif self.parameter_state == self.ps_left_square_before:
+            self.parameter_state = self.ps_group_before
+        elif self.parameter_state == self.ps_group_before:
+            if not self.group:
+                self.to_required()
+        elif self.parameter_state == self.ps_group_after:
+            pass
+        else:
+            fail("Function " + self.function.name + " has an unsupported group configuration. (Unexpected state " + str(self.parameter_state) + ")")
+
+        ast_input = "def x({}): pass".format(line)
+        module = None
+        try:
+            module = ast.parse(ast_input)
+        except SyntaxError:
+            pass
+        if not module:
+            fail("Function " + clinic.name + " has an invalid parameter declaration:\n\t" + line)
+
+        function_args = module.body[0].args
+        parameter = function_args.args[0]
+
+        if function_args.defaults:
+            expr = function_args.defaults[0]
+            # mild hack: explicitly support NULL as a default value
+            if isinstance(expr, ast.Name) and expr.id == 'NULL':
+                value = NULL
+            else:
+                value = ast.literal_eval(expr)
+        else:
+            value = unspecified
+
+        parameter_name = parameter.arg
+        name, legacy, kwargs = self.parse_converter(parameter.annotation)
+        dict = legacy_converters if legacy else converters
+        legacy_str = "legacy " if legacy else ""
+        if name not in dict:
+            fail('{} is not a valid {}converter'.format(name, legacy_str))
+        converter = dict[name](parameter_name, self.function, value, **kwargs)
+
+        kind = inspect.Parameter.KEYWORD_ONLY if self.keyword_only else inspect.Parameter.POSITIONAL_OR_KEYWORD
+        p = Parameter(parameter_name, kind, function=self.function, converter=converter, default=value, group=self.group)
+        self.function.parameters[parameter_name] = p
+
+    def parse_converter(self, annotation):
+        if isinstance(annotation, ast.Str):
+            return annotation.s, True, {}
+
+        if isinstance(annotation, ast.Name):
+            return annotation.id, False, {}
+
+        assert isinstance(annotation, ast.Call)
+
+        name = annotation.func.id
+        kwargs = {node.arg: ast.literal_eval(node.value) for node in annotation.keywords}
+        return name, False, kwargs
+
+    def parse_special_symbol(self, symbol):
+        if self.parameter_state == self.ps_seen_slash:
+            fail("Function " + self.function.name + " specifies " + symbol + " after /, which is unsupported.")
+
+        if symbol == '*':
+            if self.keyword_only:
+                fail("Function " + self.function.name + " uses '*' more than once.")
+            self.keyword_only = True
+        elif symbol == '[':
+            if self.parameter_state in (self.ps_start, self.ps_left_square_before):
+                self.parameter_state = self.ps_left_square_before
+            elif self.parameter_state in (self.ps_required, self.ps_group_after):
+                self.parameter_state = self.ps_group_after
+            else:
+                fail("Function " + self.function.name + " has an unsupported group configuration. (Unexpected state " + str(self.parameter_state) + ")")
+            self.group += 1
+        elif symbol == ']':
+            if not self.group:
+                fail("Function " + self.function.name + " has a ] without a matching [.")
+            if not any(p.group == self.group for p in self.function.parameters.values()):
+                fail("Function " + self.function.name + " has an empty group.\nAll groups must contain at least one parameter.")
+            self.group -= 1
+            if self.parameter_state in (self.ps_left_square_before, self.ps_group_before):
+                self.parameter_state = self.ps_group_before
+            elif self.parameter_state in (self.ps_group_after, self.ps_right_square_after):
+                self.parameter_state = self.ps_right_square_after
+            else:
+                fail("Function " + self.function.name + " has an unsupported group configuration. (Unexpected state " + str(self.parameter_state) + ")")
+        elif symbol == '/':
+            # ps_required is allowed here, that allows positional-only without option groups
+            # to work (and have default values!)
+            if (self.parameter_state not in (self.ps_required, self.ps_right_square_after, self.ps_group_before)) or self.group:
+                fail("Function " + self.function.name + " has an unsupported group configuration. (Unexpected state " + str(self.parameter_state) + ")")
+            if self.keyword_only:
+                fail("Function " + self.function.name + " mixes keyword-only and positional-only parameters, which is unsupported.")
+            self.parameter_state = self.ps_seen_slash
+            # fixup preceeding parameters
+            for p in self.function.parameters.values():
+                if p.kind != inspect.Parameter.POSITIONAL_OR_KEYWORD:
+                    fail("Function " + self.function.name + " mixes keyword-only and positional-only parameters, which is unsupported.")
+                p.kind = inspect.Parameter.POSITIONAL_ONLY
+
+    def state_parameter_docstring_start(self, line):
+        self.parameter_docstring_indent = len(self.indent.margin)
+        assert self.indent.depth == 3
+        return self.next(self.state_parameter_docstring, line)
+
+    # every line of the docstring must start with at least F spaces,
+    # where F > P.
+    # these F spaces will be stripped.
+    def state_parameter_docstring(self, line):
+        stripped = line.strip()
+        if stripped.startswith('#'):
+            return
+
+        indent = self.indent.measure(line)
+        if indent < self.parameter_docstring_indent:
+            self.indent.infer(line)
+            assert self.indent.depth < 3
+            if self.indent.depth == 2:
+                # back to a parameter
+                return self.next(self.state_parameter, line)
+            assert self.indent.depth == 1
+            return self.next(self.state_function_docstring, line)
+
+        assert self.function.parameters
+        last_parameter = next(reversed(list(self.function.parameters.values())))
+
+        new_docstring = last_parameter.docstring
+
+        if new_docstring:
+            new_docstring += '\n'
+        if stripped:
+            new_docstring += self.indent.dedent(line)
+
+        last_parameter.docstring = new_docstring
+
+    # the final stanza of the DSL is the docstring.
+    def state_function_docstring(self, line):
+        if self.group:
+            fail("Function " + self.function.name + " has a ] without a matching [.")
+
+        stripped = line.strip()
+        if stripped.startswith('#'):
+            return
+
+        new_docstring = self.function.docstring
+        if new_docstring:
+            new_docstring += "\n"
+        if stripped:
+            line = self.indent.dedent(line).rstrip()
+        else:
+            line = ''
+        new_docstring += line
+        self.function.docstring = new_docstring
+
+    def format_docstring(self):
+        f = self.function
+
+        add, output = text_accumulator()
+        parameters = list(f.parameters.values())
+
+        ##
+        ## docstring first line
+        ##
+
+        add(f.full_name)
+        add('(')
+
+        # populate "right_bracket_count" field for every parameter
+        if parameters:
+            # for now, the only way Clinic supports positional-only parameters
+            # is if all of them are positional-only.
+            positional_only_parameters = [p.kind == inspect.Parameter.POSITIONAL_ONLY for p in parameters]
+            if parameters[0].kind == inspect.Parameter.POSITIONAL_ONLY:
+                assert all(positional_only_parameters)
+                for p in parameters:
+                    p.right_bracket_count = abs(p.group)
+            else:
+                # don't put any right brackets around non-positional-only parameters, ever.
+                for p in parameters:
+                    p.right_bracket_count = 0
+
+        right_bracket_count = 0
+
+        def fix_right_bracket_count(desired):
+            nonlocal right_bracket_count
+            s = ''
+            while right_bracket_count < desired:
+                s += '['
+                right_bracket_count += 1
+            while right_bracket_count > desired:
+                s += ']'
+                right_bracket_count -= 1
+            return s
+
+        added_star = False
+        add_comma = False
+
+        for p in parameters:
+            assert p.name
+
+            if p.is_keyword_only() and not added_star:
+                added_star = True
+                if add_comma:
+                    add(', ')
+                add('*')
+
+            a = [p.name]
+            if p.converter.is_optional():
+                a.append('=')
+                value = p.converter.default
+                a.append(p.converter.doc_default)
+            s = fix_right_bracket_count(p.right_bracket_count)
+            s += "".join(a)
+            if add_comma:
+                add(', ')
+            add(s)
+            add_comma = True
+
+        add(fix_right_bracket_count(0))
+        add(')')
+
+        if f.return_converter.doc_default:
+            add(' -> ')
+            add(f.return_converter.doc_default)
+
+        docstring_first_line = output()
+
+        # now fix up the places where the brackets look wrong
+        docstring_first_line = docstring_first_line.replace(', ]', ',] ')
+
+        # okay.  now we're officially building the
+        # "prototype" section.
+        add(docstring_first_line)
+
+        # create substitution text for {parameters}
+        for p in parameters:
+            if not p.docstring.strip():
+                continue
+            add('\n')
+            add("  ")
+            add(p.name)
+            add('\n')
+            add(textwrap.indent(rstrip_lines(p.docstring.rstrip()), "    "))
+        prototype = output()
+
+        ##
+        ## docstring body
+        ##
+
+        docstring = f.docstring.rstrip()
+        lines = [line.rstrip() for line in docstring.split('\n')]
+
+        # Enforce the summary line!
+        # The first line of a docstring should be a summary of the function.
+        # It should fit on one line (80 columns? 79 maybe?) and be a paragraph
+        # by itself.
+        #
+        # Argument Clinic enforces the following rule:
+        #  * either the docstring is empty,
+        #  * or it must have a summary line.
+        #
+        # Guido said Clinic should enforce this:
+        # http://mail.python.org/pipermail/python-dev/2013-June/127110.html
+
+        if len(lines) >= 2:
+            if lines[1]:
+                fail("Docstring for " + f.full_name + " does not have a summary line!\n" +
+                    "Every non-blank function docstring must start with\n" +
+                    "a single line summary followed by an empty line.")
+        elif len(lines) == 1:
+            # the docstring is only one line right now--the summary line.
+            # add an empty line after the summary line so we have space
+            # between it and the {prototype} we're about to add.
+            lines.append('')
+
+        prototype_marker_count = len(docstring.split('{prototype}')) - 1
+        if prototype_marker_count:
+            fail('You may not specify {prototype} in a docstring!')
+        # insert *after* the summary line
+        lines.insert(2, '{prototype}\n')
+
+        docstring = "\n".join(lines)
+
+        add(docstring)
+        docstring = output()
+
+        docstring = linear_format(docstring, prototype=prototype)
+        docstring = docstring.rstrip()
+
+        return docstring
+
+    def state_terminal(self, line):
+        """
+        Called when processing the block is done.
+        """
+        assert not line
+
+        if not self.function:
+            return
+
+        if self.keyword_only:
+            values = self.function.parameters.values()
+            if not values:
+                no_parameter_after_star = True
+            else:
+                last_parameter = next(reversed(list(values)))
+                no_parameter_after_star = last_parameter.kind != inspect.Parameter.KEYWORD_ONLY
+            if no_parameter_after_star:
+                fail("Function " + self.function.name + " specifies '*' without any parameters afterwards.")
+
+        # remove trailing whitespace from all parameter docstrings
+        for name, value in self.function.parameters.items():
+            if not value:
+                continue
+            value.docstring = value.docstring.rstrip()
+
+        self.function.docstring = self.format_docstring()
+
+
+# maps strings to callables.
+# the callable should return an object
+# that implements the clinic parser
+# interface (__init__ and parse).
+#
+# example parsers:
+#   "clinic", handles the Clinic DSL
+#   "python", handles running Python code
+#
+parsers = {'clinic' : DSLParser, 'python': PythonParser}
+
+
+clinic = None
+
+
+def main(argv):
+    import sys
+
+    if sys.version_info.major < 3 or sys.version_info.minor < 3:
+        sys.exit("Error: clinic.py requires Python 3.3 or greater.")
+
+    import argparse
+    cmdline = argparse.ArgumentParser()
+    cmdline.add_argument("-f", "--force", action='store_true')
+    cmdline.add_argument("-o", "--output", type=str)
+    cmdline.add_argument("--converters", action='store_true')
+    cmdline.add_argument("filename", type=str, nargs="*")
+    ns = cmdline.parse_args(argv)
+
+    if ns.converters:
+        if ns.filename:
+            print("Usage error: can't specify --converters and a filename at the same time.")
+            print()
+            cmdline.print_usage()
+            sys.exit(-1)
+        converters = []
+        return_converters = []
+        ignored = set("""
+            add_c_converter
+            add_c_return_converter
+            add_default_legacy_c_converter
+            add_legacy_c_converter
+            """.strip().split())
+        module = globals()
+        for name in module:
+            for suffix, ids in (
+                ("_return_converter", return_converters),
+                ("_converter", converters),
+            ):
+                if name in ignored:
+                    continue
+                if name.endswith(suffix):
+                    ids.append((name, name[:-len(suffix)]))
+                    break
+        print()
+
+        print("Legacy converters:")
+        legacy = sorted(legacy_converters)
+        print('    ' + ' '.join(c for c in legacy if c[0].isupper()))
+        print('    ' + ' '.join(c for c in legacy if c[0].islower()))
+        print()
+
+        for title, attribute, ids in (
+            ("Converters", 'converter_init', converters),
+            ("Return converters", 'return_converter_init', return_converters),
+        ):
+            print(title + ":")
+            longest = -1
+            for name, short_name in ids:
+                longest = max(longest, len(short_name))
+            for name, short_name in sorted(ids, key=lambda x: x[1].lower()):
+                cls = module[name]
+                callable = getattr(cls, attribute, None)
+                if not callable:
+                    continue
+                signature = inspect.signature(callable)
+                parameters = []
+                for parameter_name, parameter in signature.parameters.items():
+                    if parameter.kind == inspect.Parameter.KEYWORD_ONLY:
+                        if parameter.default != inspect.Parameter.empty:
+                            s = '{}={!r}'.format(parameter_name, parameter.default)
+                        else:
+                            s = parameter_name
+                        parameters.append(s)
+                print('    {}({})'.format(short_name, ', '.join(parameters)))
+                # add_comma = False
+                # for parameter_name, parameter in signature.parameters.items():
+                #     if parameter.kind == inspect.Parameter.KEYWORD_ONLY:
+                #         if add_comma:
+                #             parameters.append(', ')
+                #         else:
+                #             add_comma = True
+                #         s = parameter_name
+                #         if parameter.default != inspect.Parameter.empty:
+                #             s += '=' + repr(parameter.default)
+                #         parameters.append(s)
+                # parameters.append(')')
+
+                # print("   ", short_name + "".join(parameters))
+            print()
+        print("All converters also accept (doc_default=None, required=False).")
+        print("All return converters also accept (doc_default=None).")
+        sys.exit(0)
+
+    if not ns.filename:
+        cmdline.print_usage()
+        sys.exit(-1)
+
+    if ns.output and len(ns.filename) > 1:
+        print("Usage error: can't use -o with multiple filenames.")
+        print()
+        cmdline.print_usage()
+        sys.exit(-1)
+
+    for filename in ns.filename:
+        parse_file(filename, output=ns.output, verify=not ns.force)
+
+
+if __name__ == "__main__":
+    sys.exit(main(sys.argv[1:]))
diff --git a/Tools/clinic/clinic_test.py b/Tools/clinic/clinic_test.py
new file mode 100644
index 0000000..81a0050
--- /dev/null
+++ b/Tools/clinic/clinic_test.py
@@ -0,0 +1,699 @@
+#!/usr/bin/env python3
+#
+# Argument Clinic
+# Copyright 2012-2013 by Larry Hastings.
+# Licensed to the PSF under a contributor agreement.
+#
+
+import builtins
+import clinic
+from clinic import DSLParser
+import collections
+import inspect
+from test import support
+import unittest
+from unittest import TestCase
+
+class FakeConverter:
+    def __init__(self, name, args):
+        self.name = name
+        self.args = args
+
+
+class FakeConverterFactory:
+    def __init__(self, name):
+        self.name = name
+
+    def __call__(self, name, default, **kwargs):
+        return FakeConverter(self.name, kwargs)
+
+
+class FakeConvertersDict:
+    def __init__(self):
+        self.used_converters = {}
+
+    def get(self, name, default):
+        return self.used_converters.setdefault(name, FakeConverterFactory(name))
+
+class FakeClinic:
+    def __init__(self):
+        self.converters = FakeConvertersDict()
+        self.legacy_converters = FakeConvertersDict()
+        self.language = clinic.CLanguage()
+        self.filename = None
+        self.block_parser = clinic.BlockParser('', self.language)
+        self.modules = collections.OrderedDict()
+        clinic.clinic = self
+        self.name = "FakeClinic"
+
+    def is_directive(self, name):
+        return name == "module"
+
+    def directive(self, name, args):
+        self.called_directives[name] = args
+
+    _module_and_class = clinic.Clinic._module_and_class
+
+
+
+class ClinicGroupPermuterTest(TestCase):
+    def _test(self, l, m, r, output):
+        computed = clinic.permute_optional_groups(l, m, r)
+        self.assertEqual(output, computed)
+
+    def test_range(self):
+        self._test([['start']], ['stop'], [['step']],
+          (
+            ('stop',),
+            ('start', 'stop',),
+            ('start', 'stop', 'step',),
+          ))
+
+    def test_add_window(self):
+        self._test([['x', 'y']], ['ch'], [['attr']],
+          (
+            ('ch',),
+            ('ch', 'attr'),
+            ('x', 'y', 'ch',),
+            ('x', 'y', 'ch', 'attr'),
+          ))
+
+    def test_ludicrous(self):
+        self._test([['a1', 'a2', 'a3'], ['b1', 'b2']], ['c1'], [['d1', 'd2'], ['e1', 'e2', 'e3']],
+          (
+          ('c1',),
+          ('b1', 'b2', 'c1'),
+          ('b1', 'b2', 'c1', 'd1', 'd2'),
+          ('a1', 'a2', 'a3', 'b1', 'b2', 'c1'),
+          ('a1', 'a2', 'a3', 'b1', 'b2', 'c1', 'd1', 'd2'),
+          ('a1', 'a2', 'a3', 'b1', 'b2', 'c1', 'd1', 'd2', 'e1', 'e2', 'e3'),
+          ))
+
+    def test_right_only(self):
+        self._test([], [], [['a'],['b'],['c']],
+          (
+          (),
+          ('a',),
+          ('a', 'b'),
+          ('a', 'b', 'c')
+          ))
+
+    def test_have_left_options_but_required_is_empty(self):
+        def fn():
+            clinic.permute_optional_groups(['a'], [], [])
+        self.assertRaises(AssertionError, fn)
+
+
+class ClinicLinearFormatTest(TestCase):
+    def _test(self, input, output, **kwargs):
+        computed = clinic.linear_format(input, **kwargs)
+        self.assertEqual(output, computed)
+
+    def test_empty_strings(self):
+        self._test('', '')
+
+    def test_solo_newline(self):
+        self._test('\n', '\n')
+
+    def test_no_substitution(self):
+        self._test("""
+          abc
+          """, """
+          abc
+          """)
+
+    def test_empty_substitution(self):
+        self._test("""
+          abc
+          {name}
+          def
+          """, """
+          abc
+          def
+          """, name='')
+
+    def test_single_line_substitution(self):
+        self._test("""
+          abc
+          {name}
+          def
+          """, """
+          abc
+          GARGLE
+          def
+          """, name='GARGLE')
+
+    def test_multiline_substitution(self):
+        self._test("""
+          abc
+          {name}
+          def
+          """, """
+          abc
+          bingle
+          bungle
+
+          def
+          """, name='bingle\nbungle\n')
+
+class InertParser:
+    def __init__(self, clinic):
+        pass
+
+    def parse(self, block):
+        pass
+
+class CopyParser:
+    def __init__(self, clinic):
+        pass
+
+    def parse(self, block):
+        block.output = block.input
+
+
+class ClinicBlockParserTest(TestCase):
+    def _test(self, input, output):
+        language = clinic.CLanguage()
+
+        blocks = list(clinic.BlockParser(input, language))
+        writer = clinic.BlockPrinter(language)
+        for block in blocks:
+            writer.print_block(block)
+        output = writer.f.getvalue()
+        assert output == input, "output != input!\n\noutput " + repr(output) + "\n\n input " + repr(input)
+
+    def round_trip(self, input):
+        return self._test(input, input)
+
+    def test_round_trip_1(self):
+        self.round_trip("""
+    verbatim text here
+    lah dee dah
+""")
+    def test_round_trip_2(self):
+        self.round_trip("""
+    verbatim text here
+    lah dee dah
+/*[inert]
+abc
+[inert]*/
+def
+/*[inert checksum: 7b18d017f89f61cf17d47f92749ea6930a3f1deb]*/
+xyz
+""")
+
+    def _test_clinic(self, input, output):
+        language = clinic.CLanguage()
+        c = clinic.Clinic(language)
+        c.parsers['inert'] = InertParser(c)
+        c.parsers['copy'] = CopyParser(c)
+        computed = c.parse(input)
+        self.assertEqual(output, computed)
+
+    def test_clinic_1(self):
+        self._test_clinic("""
+    verbatim text here
+    lah dee dah
+/*[copy]
+def
+[copy]*/
+abc
+/*[copy checksum: 03cfd743661f07975fa2f1220c5194cbaff48451]*/
+xyz
+""", """
+    verbatim text here
+    lah dee dah
+/*[copy]
+def
+[copy]*/
+def
+/*[copy checksum: 7b18d017f89f61cf17d47f92749ea6930a3f1deb]*/
+xyz
+""")
+
+
+class ClinicParserTest(TestCase):
+    def test_trivial(self):
+        parser = DSLParser(FakeClinic())
+        block = clinic.Block("module os\nos.access")
+        parser.parse(block)
+        module, function = block.signatures
+        self.assertEqual("access", function.name)
+        self.assertEqual("os", module.name)
+
+    def test_ignore_line(self):
+        block = self.parse("#\nmodule os\nos.access")
+        module, function = block.signatures
+        self.assertEqual("access", function.name)
+        self.assertEqual("os", module.name)
+
+    def test_param(self):
+        function = self.parse_function("module os\nos.access\n   path: int")
+        self.assertEqual("access", function.name)
+        self.assertEqual(1, len(function.parameters))
+        p = function.parameters['path']
+        self.assertEqual('path', p.name)
+        self.assertIsInstance(p.converter, clinic.int_converter)
+
+    def test_param_default(self):
+        function = self.parse_function("module os\nos.access\n    follow_symlinks: bool = True")
+        p = function.parameters['follow_symlinks']
+        self.assertEqual(True, p.default)
+
+    def test_param_no_docstring(self):
+        function = self.parse_function("""
+module os
+os.access
+    follow_symlinks: bool = True
+    something_else: str""")
+        p = function.parameters['follow_symlinks']
+        self.assertEqual(2, len(function.parameters))
+        self.assertIsInstance(function.parameters['something_else'].converter, clinic.str_converter)
+
+    def disabled_test_converter_arguments(self):
+        function = self.parse_function("module os\nos.access\n    path: path_t(allow_fd=1)")
+        p = function.parameters['path']
+        self.assertEqual(1, p.converter.args['allow_fd'])
+
+    def test_param_docstring(self):
+        function = self.parse_function("""
+module os
+os.stat as os_stat_fn -> object(doc_default='stat_result')
+
+   path: str
+       Path to be examined""")
+        p = function.parameters['path']
+        self.assertEqual("Path to be examined", p.docstring)
+        self.assertEqual(function.return_converter.doc_default, 'stat_result')
+
+    def test_function_docstring(self):
+        function = self.parse_function("""
+module os
+os.stat as os_stat_fn
+
+   path: str
+       Path to be examined
+
+Perform a stat system call on the given path.""")
+        self.assertEqual("""
+Perform a stat system call on the given path.
+
+os.stat(path)
+  path
+    Path to be examined
+""".strip(), function.docstring)
+
+    def test_explicit_parameters_in_docstring(self):
+        function = self.parse_function("""
+module foo
+foo.bar
+  x: int
+     Documentation for x.
+  y: int
+
+This is the documentation for foo.
+
+Okay, we're done here.
+""")
+        self.assertEqual("""
+This is the documentation for foo.
+
+foo.bar(x, y)
+  x
+    Documentation for x.
+
+Okay, we're done here.
+""".strip(), function.docstring)
+
+    def test_parser_regression_special_character_in_parameter_column_of_docstring_first_line(self):
+        function = self.parse_function("""
+module os
+os.stat
+    path: str
+This/used to break Clinic!
+""")
+        self.assertEqual("os.stat(path)\n\nThis/used to break Clinic!", function.docstring)
+
+    def test_c_name(self):
+        function = self.parse_function("module os\nos.stat as os_stat_fn")
+        self.assertEqual("os_stat_fn", function.c_basename)
+
+    def test_return_converter(self):
+        function = self.parse_function("module os\nos.stat -> int")
+        self.assertIsInstance(function.return_converter, clinic.int_return_converter)
+
+    def test_star(self):
+        function = self.parse_function("module os\nos.access\n    *\n    follow_symlinks: bool = True")
+        p = function.parameters['follow_symlinks']
+        self.assertEqual(inspect.Parameter.KEYWORD_ONLY, p.kind)
+        self.assertEqual(0, p.group)
+
+    def test_group(self):
+        function = self.parse_function("module window\nwindow.border\n [\n ls : int\n ]\n /\n")
+        p = function.parameters['ls']
+        self.assertEqual(1, p.group)
+
+    def test_left_group(self):
+        function = self.parse_function("""
+module curses
+curses.window.addch
+   [
+   y: int
+     Y-coordinate.
+   x: int
+     X-coordinate.
+   ]
+   ch: char
+     Character to add.
+   [
+   attr: long
+     Attributes for the character.
+   ]
+   /
+""")
+        for name, group in (
+            ('y', -1), ('x', -1),
+            ('ch', 0),
+            ('attr', 1),
+            ):
+            p = function.parameters[name]
+            self.assertEqual(p.group, group)
+            self.assertEqual(p.kind, inspect.Parameter.POSITIONAL_ONLY)
+        self.assertEqual(function.docstring.strip(), """
+curses.window.addch([y, x,] ch, [attr])
+  y
+    Y-coordinate.
+  x
+    X-coordinate.
+  ch
+    Character to add.
+  attr
+    Attributes for the character.
+            """.strip())
+
+    def test_nested_groups(self):
+        function = self.parse_function("""
+module curses
+curses.window.imaginary
+   [
+   [
+   y1: int
+     Y-coordinate.
+   y2: int
+     Y-coordinate.
+   ]
+   x1: int
+     X-coordinate.
+   x2: int
+     X-coordinate.
+   ]
+   ch: char
+     Character to add.
+   [
+   attr1: long
+     Attributes for the character.
+   attr2: long
+     Attributes for the character.
+   attr3: long
+     Attributes for the character.
+   [
+   attr4: long
+     Attributes for the character.
+   attr5: long
+     Attributes for the character.
+   attr6: long
+     Attributes for the character.
+   ]
+   ]
+   /
+""")
+        for name, group in (
+            ('y1', -2), ('y2', -2),
+            ('x1', -1), ('x2', -1),
+            ('ch', 0),
+            ('attr1', 1), ('attr2', 1), ('attr3', 1),
+            ('attr4', 2), ('attr5', 2), ('attr6', 2),
+            ):
+            p = function.parameters[name]
+            self.assertEqual(p.group, group)
+            self.assertEqual(p.kind, inspect.Parameter.POSITIONAL_ONLY)
+
+        self.assertEqual(function.docstring.strip(), """
+curses.window.imaginary([[y1, y2,] x1, x2,] ch, [attr1, attr2, attr3, [attr4, attr5, attr6]])
+  y1
+    Y-coordinate.
+  y2
+    Y-coordinate.
+  x1
+    X-coordinate.
+  x2
+    X-coordinate.
+  ch
+    Character to add.
+  attr1
+    Attributes for the character.
+  attr2
+    Attributes for the character.
+  attr3
+    Attributes for the character.
+  attr4
+    Attributes for the character.
+  attr5
+    Attributes for the character.
+  attr6
+    Attributes for the character.
+                """.strip())
+
+    def parse_function_should_fail(self, s):
+        with support.captured_stdout() as stdout:
+            with self.assertRaises(SystemExit):
+                self.parse_function(s)
+        return stdout.getvalue()
+
+    def test_disallowed_grouping__two_top_groups_on_left(self):
+        s = self.parse_function_should_fail("""
+module foo
+foo.two_top_groups_on_left
+    [
+    group1 : int
+    ]
+    [
+    group2 : int
+    ]
+    param: int
+            """)
+        self.assertEqual(s,
+            ('Error on line 0:\n'
+            'Function two_top_groups_on_left has an unsupported group configuration. (Unexpected state 2)\n'))
+
+    def test_disallowed_grouping__two_top_groups_on_right(self):
+        self.parse_function_should_fail("""
+module foo
+foo.two_top_groups_on_right
+    param: int
+    [
+    group1 : int
+    ]
+    [
+    group2 : int
+    ]
+            """)
+
+    def test_disallowed_grouping__parameter_after_group_on_right(self):
+        self.parse_function_should_fail("""
+module foo
+foo.parameter_after_group_on_right
+    param: int
+    [
+    [
+    group1 : int
+    ]
+    group2 : int
+    ]
+            """)
+
+    def test_disallowed_grouping__group_after_parameter_on_left(self):
+        self.parse_function_should_fail("""
+module foo
+foo.group_after_parameter_on_left
+    [
+    group2 : int
+    [
+    group1 : int
+    ]
+    ]
+    param: int
+            """)
+
+    def test_disallowed_grouping__empty_group_on_left(self):
+        self.parse_function_should_fail("""
+module foo
+foo.empty_group
+    [
+    [
+    ]
+    group2 : int
+    ]
+    param: int
+            """)
+
+    def test_disallowed_grouping__empty_group_on_right(self):
+        self.parse_function_should_fail("""
+module foo
+foo.empty_group
+    param: int
+    [
+    [
+    ]
+    group2 : int
+    ]
+            """)
+
+    def test_no_parameters(self):
+        function = self.parse_function("""
+module foo
+foo.bar
+
+Docstring
+
+""")
+        self.assertEqual("Docstring\n\nfoo.bar()", function.docstring)
+        self.assertEqual(0, len(function.parameters))
+
+    def test_single_star(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    *
+    *
+""")
+
+    def test_parameters_required_after_star_without_initial_parameters_or_docstring(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    *
+""")
+
+    def test_parameters_required_after_star_without_initial_parameters_with_docstring(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    *
+Docstring here.
+""")
+
+    def test_parameters_required_after_star_with_initial_parameters_without_docstring(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    this: int
+    *
+""")
+
+    def test_parameters_required_after_star_with_initial_parameters_and_docstring(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    this: int
+    *
+Docstring.
+""")
+
+    def test_single_slash(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    /
+    /
+""")
+
+    def test_mix_star_and_slash(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+   x: int
+   y: int
+   *
+   z: int
+   /
+""")
+
+    def test_parameters_not_permitted_after_slash_for_now(self):
+        self.parse_function_should_fail("""
+module foo
+foo.bar
+    /
+    x: int
+""")
+
+    def test_function_not_at_column_0(self):
+        function = self.parse_function("""
+  module foo
+  foo.bar
+    x: int
+      Nested docstring here, goeth.
+    *
+    y: str
+  Not at column 0!
+""")
+        self.assertEqual("""
+Not at column 0!
+
+foo.bar(x, *, y)
+  x
+    Nested docstring here, goeth.
+""".strip(), function.docstring)
+
+    def test_parser_regression_special_character_in_parameter_column_of_docstring_first_line(self):
+        function = self.parse_function("""
+module os
+os.stat
+    path: str
+This/used to break Clinic!
+""")
+        self.assertEqual("This/used to break Clinic!\n\nos.stat(path)", function.docstring)
+
+    def test_directive(self):
+        c = FakeClinic()
+        parser = DSLParser(c)
+        parser.flag = False
+        parser.directives['setflag'] = lambda : setattr(parser, 'flag', True)
+        block = clinic.Block("setflag")
+        parser.parse(block)
+        self.assertTrue(parser.flag)
+
+    def test_legacy_converters(self):
+        block = self.parse('module os\nos.access\n   path: "s"')
+        module, function = block.signatures
+        self.assertIsInstance((function.parameters['path']).converter, clinic.str_converter)
+
+    def parse(self, text):
+        c = FakeClinic()
+        parser = DSLParser(c)
+        block = clinic.Block(text)
+        parser.parse(block)
+        return block
+
+    def parse_function(self, text):
+        block = self.parse(text)
+        s = block.signatures
+        assert len(s) == 2
+        assert isinstance(s[0], clinic.Module)
+        assert isinstance(s[1], clinic.Function)
+        return s[1]
+
+    def test_scaffolding(self):
+        # test repr on special values
+        self.assertEqual(repr(clinic.unspecified), '<Unspecified>')
+        self.assertEqual(repr(clinic.NULL), '<Null>')
+
+        # test that fail fails
+        with support.captured_stdout() as stdout:
+            with self.assertRaises(SystemExit):
+                clinic.fail('The igloos are melting!', filename='clown.txt', line_number=69)
+        self.assertEqual(stdout.getvalue(), 'Error in file "clown.txt" on line 69:\nThe igloos are melting!\n')
+
+
+if __name__ == "__main__":
+    unittest.main()