gh-95065: Add Argument Clinic support for deprecating positional use of parameters (#95151)

It is now possible to deprecate passing parameters positionally with
Argument Clinic, using the new '* [from X.Y]' syntax.
(To be read as "keyword-only from Python version X.Y")

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

1 files changed, 154 insertions, 13 deletions

diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
index 47b5f5a..4dfe90b 100755
--- a/Tools/clinic/clinic.py
+++ b/Tools/clinic/clinic.py
@@ -347,6 +347,13 @@ def suffix_all_lines(s: str, suffix: str) -> str:
     return ''.join(final)
 
 
+def pprint_words(items: list[str]) -> str:
+    if len(items) <= 2:
+        return " and ".join(items)
+    else:
+        return ", ".join(items[:-1]) + " and " + items[-1]
+
+
 def version_splitter(s: str) -> tuple[int, ...]:
     """Splits a version string into a tuple of integers.
 
@@ -828,6 +835,22 @@ class CLanguage(Language):
             #define {methoddef_name}
         #endif /* !defined({methoddef_name}) */
     """)
+    DEPRECATED_POSITIONAL_PROTOTYPE: Final[str] = r"""
+        #if PY_VERSION_HEX >= 0x{major:02x}{minor:02x}00C0
+        #  error "{cpp_message}"
+        #elif PY_VERSION_HEX >= 0x{major:02x}{minor:02x}00A0
+        #  ifdef _MSC_VER
+        #    pragma message ("{cpp_message}")
+        #  else
+        #    warning "{cpp_message}"
+        #  endif
+        #endif
+        if ({condition}) {{{{
+            if (PyErr_WarnEx(PyExc_DeprecationWarning, "{depr_message}", 1)) {{{{
+                goto exit;
+            }}}}
+        }}}}
+    """
 
     def __init__(self, filename: str) -> None:
         super().__init__(filename)
@@ -850,6 +873,64 @@ class CLanguage(Language):
                 function = o
         return self.render_function(clinic, function)
 
+    def deprecate_positional_use(
+            self,
+            func: Function,
+            params: dict[int, Parameter],
+    ) -> str:
+        assert len(params) > 0
+        names = [repr(p.name) for p in params.values()]
+        first_pos, first_param = next(iter(params.items()))
+        last_pos, last_param = next(reversed(params.items()))
+
+        # Pretty-print list of names.
+        pstr = pprint_words(names)
+
+        # For now, assume there's only one deprecation level.
+        assert first_param.deprecated_positional == last_param.deprecated_positional
+        thenceforth = first_param.deprecated_positional
+        assert thenceforth is not None
+
+        # Format the preprocessor warning and error messages.
+        assert isinstance(self.cpp.filename, str)
+        source = os.path.basename(self.cpp.filename)
+        major, minor = thenceforth
+        cpp_message = (
+            f"In {source}, update parameter(s) {pstr} in the clinic "
+            f"input of {func.full_name!r} to be keyword-only."
+        )
+        # Format the deprecation message.
+        if first_pos == 0:
+            preamble = "Passing positional arguments to "
+        if len(params) == 1:
+            condition = f"nargs == {first_pos+1}"
+            if first_pos:
+                preamble = f"Passing {first_pos+1} positional arguments to "
+            depr_message = preamble + (
+                f"{func.full_name}() is deprecated. Parameter {pstr} will "
+                f"become a keyword-only parameter in Python {major}.{minor}."
+            )
+        else:
+            condition = f"nargs > {first_pos} && nargs <= {last_pos+1}"
+            if first_pos:
+                preamble = (
+                    f"Passing more than {first_pos} positional "
+                    f"argument{'s' if first_pos != 1 else ''} to "
+                )
+            depr_message = preamble + (
+                f"{func.full_name}() is deprecated. Parameters {pstr} will "
+                f"become keyword-only parameters in Python {major}.{minor}."
+            )
+        # Format and return the code block.
+        code = self.DEPRECATED_POSITIONAL_PROTOTYPE.format(
+            condition=condition,
+            major=major,
+            minor=minor,
+            cpp_message=cpp_message,
+            depr_message=depr_message,
+        )
+        return normalize_snippet(code, indent=4)
+
     def docstring_for_c_string(
             self,
             f: Function
@@ -1199,6 +1280,7 @@ class CLanguage(Language):
                 flags = 'METH_METHOD|' + flags
                 parser_prototype = self.PARSER_PROTOTYPE_DEF_CLASS
 
+            deprecated_positionals: dict[int, Parameter] = {}
             add_label: str | None = None
             for i, p in enumerate(parameters):
                 if isinstance(p.converter, defining_class_converter):
@@ -1213,6 +1295,8 @@ class CLanguage(Language):
                     parser_code.append("%s:" % add_label)
                     add_label = None
                 if not p.is_optional():
+                    if p.deprecated_positional:
+                        deprecated_positionals[i] = p
                     parser_code.append(normalize_snippet(parsearg, indent=4))
                 elif i < pos_only:
                     add_label = 'skip_optional_posonly'
@@ -1242,6 +1326,8 @@ class CLanguage(Language):
                                 goto %s;
                             }}
                             """ % add_label, indent=4))
+                    if p.deprecated_positional:
+                        deprecated_positionals[i] = p
                     if i + 1 == len(parameters):
                         parser_code.append(normalize_snippet(parsearg, indent=4))
                     else:
@@ -1257,6 +1343,12 @@ class CLanguage(Language):
                             }}
                             """ % add_label, indent=4))
 
+            if deprecated_positionals:
+                code = self.deprecate_positional_use(f, deprecated_positionals)
+                assert parser_code is not None
+                # Insert the deprecation code before parameter parsing.
+                parser_code.insert(0, code)
+
             if parser_code is not None:
                 if add_label:
                     parser_code.append("%s:" % add_label)
@@ -2592,6 +2684,9 @@ class Function:
         return f
 
 
+VersionTuple = tuple[int, int]
+
+
 @dc.dataclass(repr=False, slots=True)
 class Parameter:
     """
@@ -2606,6 +2701,8 @@ class Parameter:
     annotation: object = inspect.Parameter.empty
     docstring: str = ''
     group: int = 0
+    # (`None` signifies that there is no deprecation)
+    deprecated_positional: VersionTuple | None = None
     right_bracket_count: int = dc.field(init=False, default=0)
 
     def __repr__(self) -> str:
@@ -4430,6 +4527,7 @@ class DSLParser:
     state: StateKeeper
     keyword_only: bool
     positional_only: bool
+    deprecated_positional: VersionTuple | None
     group: int
     parameter_state: ParamState
     indent: IndentStack
@@ -4437,6 +4535,11 @@ class DSLParser:
     coexist: bool
     parameter_continuation: str
     preserve_output: bool
+    star_from_version_re = create_regex(
+        before="* [from ",
+        after="]",
+        word=False,
+    )
 
     def __init__(self, clinic: Clinic) -> None:
         self.clinic = clinic
@@ -4460,6 +4563,7 @@ class DSLParser:
         self.state = self.state_dsl_start
         self.keyword_only = False
         self.positional_only = False
+        self.deprecated_positional = None
         self.group = 0
         self.parameter_state: ParamState = ParamState.START
         self.indent = IndentStack()
@@ -4622,7 +4726,7 @@ class DSLParser:
                 exc.lineno = line_number
                 raise
 
-        self.do_post_block_processing_cleanup()
+        self.do_post_block_processing_cleanup(line_number)
         block.output.extend(self.clinic.language.render(self.clinic, block.signatures))
 
         if self.preserve_output:
@@ -4908,8 +5012,14 @@ class DSLParser:
             self.parameter_continuation = line[:-1]
             return
 
+        line = line.lstrip()
+        match = self.star_from_version_re.match(line)
+        if match:
+            self.parse_deprecated_positional(match.group(1))
+            return
+
         func = self.function
-        match line.lstrip():
+        match line:
             case '*':
                 self.parse_star(func)
             case '[':
@@ -5182,7 +5292,9 @@ class DSLParser:
                      "after 'self'.")
 
 
-        p = Parameter(parameter_name, kind, function=self.function, converter=converter, default=value, group=self.group)
+        p = Parameter(parameter_name, kind, function=self.function,
+                      converter=converter, default=value, group=self.group,
+                      deprecated_positional=self.deprecated_positional)
 
         names = [k.name for k in self.function.parameters.values()]
         if parameter_name in names[1:]:
@@ -5215,10 +5327,28 @@ class DSLParser:
                     "Annotations must be either a name, a function call, or a string."
                 )
 
+    def parse_deprecated_positional(self, thenceforth: str) -> None:
+        assert isinstance(self.function, Function)
+        fname = self.function.full_name
+
+        if self.keyword_only:
+            fail(f"Function {fname!r}: '* [from ...]' must come before '*'")
+        if self.deprecated_positional:
+            fail(f"Function {fname!r} uses '[from ...]' more than once.")
+        try:
+            major, minor = thenceforth.split(".")
+            self.deprecated_positional = int(major), int(minor)
+        except ValueError:
+            fail(
+                f"Function {fname!r}: expected format '* [from major.minor]' "
+                f"where 'major' and 'minor' are integers; got {thenceforth!r}"
+            )
+
     def parse_star(self, function: Function) -> None:
         """Parse keyword-only parameter marker '*'."""
         if self.keyword_only:
             fail(f"Function {function.name!r} uses '*' more than once.")
+        self.deprecated_positional = None
         self.keyword_only = True
 
     def parse_opening_square_bracket(self, function: Function) -> None:
@@ -5586,23 +5716,34 @@ class DSLParser:
 
         return docstring
 
-    def do_post_block_processing_cleanup(self) -> None:
+    def do_post_block_processing_cleanup(self, lineno: int) -> None:
         """
         Called when processing the block is done.
         """
         if not self.function:
             return
 
-        if self.keyword_only:
-            values = self.function.parameters.values()
-            if not values:
-                no_parameter_after_star = True
+        def check_remaining(
+                symbol: str,
+                condition: Callable[[Parameter], bool]
+        ) -> None:
+            assert isinstance(self.function, Function)
+
+            if values := self.function.parameters.values():
+                last_param = next(reversed(values))
+                no_param_after_symbol = condition(last_param)
             else:
-                last_parameter = next(reversed(list(values)))
-                no_parameter_after_star = last_parameter.kind != inspect.Parameter.KEYWORD_ONLY
-            if no_parameter_after_star:
-                fail(f"Function {self.function.name!r} specifies '*' "
-                     "without any parameters afterwards.")
+                no_param_after_symbol = True
+            if no_param_after_symbol:
+                fname = self.function.full_name
+                fail(f"Function {fname!r} specifies {symbol!r} "
+                     "without any parameters afterwards.", line_number=lineno)
+
+        if self.keyword_only:
+            check_remaining("*", lambda p: p.kind != inspect.Parameter.KEYWORD_ONLY)
+
+        if self.deprecated_positional:
+            check_remaining("* [from ...]", lambda p: not p.deprecated_positional)
 
         self.function.docstring = self.format_docstring()