path: root/src/engine/SCons/Action.py

"""SCons.Action

This encapsulates information about executing any sort of action that
can build one or more target Nodes (typically files) from one or more
source Nodes (also typically files) given a specific Environment.

The base class here is ActionBase.  The base class supplies just a few
OO utility methods and some generic methods for displaying information
about an Action in response to the various commands that control printing.

A second-level base class is _ActionAction.  This extends ActionBase
by providing the methods that can be used to show and perform an
action.  True Action objects will subclass _ActionAction; Action
factory class objects will subclass ActionBase.

The heavy lifting is handled by subclasses for the different types of
actions we might execute:

    CommandAction
    CommandGeneratorAction
    FunctionAction
    ListAction

The subclasses supply the following public interface methods used by
other modules:

    __call__()
        THE public interface, "calling" an Action object executes the
        command or Python function.  This also takes care of printing
        a pre-substitution command for debugging purposes.

    get_contents()
        Fetches the "contents" of an Action for signature calculation.
        This is what the Sig/*.py subsystem uses to decide if a target
        needs to be rebuilt because its action changed.

    genstring()
        Returns a string representation of the Action *without*
        command substitution, but allows a CommandGeneratorAction to
        generate the right action based on the specified target,
        source and env.  This is used by the Signature subsystem
        (through the Executor) to obtain an (imprecise) representation
        of the Action operation for informative purposes.


Subclasses also supply the following methods for internal use within
this module:

    __str__()
        Returns a string approximation of the Action; no variable
        substitution is performed.
        
    execute()
        The internal method that really, truly, actually handles the
        execution of a command or Python function.  This is used so
        that the __call__() methods can take care of displaying any
        pre-substitution representations, and *then* execute an action
        without worrying about the specific Actions involved.

    strfunction()
        Returns a substituted string representation of the Action.
        This is used by the _ActionAction.show() command to display the
        command/function that will be executed to generate the target(s).

There is a related independent ActionCaller class that looks like a
regular Action, and which serves as a wrapper for arbitrary functions
that we want to let the user specify the arguments to now, but actually
execute later (when an out-of-date check determines that it's needed to
be executed, for example).  Objects of this class are returned by an
ActionFactory class that provides a __call__() method as a convenient
way for wrapping up the functions.

"""

#
# __COPYRIGHT__
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
# KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
# WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#

__revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"

import dis
import os
import os.path
import re
import string
import sys

from SCons.Debug import logInstanceCreation
import SCons.Errors
import SCons.Util

class _Null:
    pass

_null = _Null

print_actions = 1
execute_actions = 1
print_actions_presub = 0

default_ENV = None

def rfile(n):
    try:
        return n.rfile()
    except AttributeError:
        return n

def default_exitstatfunc(s):
    return s

try:
    SET_LINENO = dis.SET_LINENO
    HAVE_ARGUMENT = dis.HAVE_ARGUMENT
except AttributeError:
    remove_set_lineno_codes = lambda x: x
else:
    def remove_set_lineno_codes(code):
        result = []
        n = len(code)
        i = 0
        while i < n:
            c = code[i]
            op = ord(c)
            if op >= HAVE_ARGUMENT:
                if op != SET_LINENO:
                    result.append(code[i:i+3])
                i = i+3
            else:
                result.append(c)
                i = i+1
        return string.join(result, '')

def _actionAppend(act1, act2):
    # This function knows how to slap two actions together.
    # Mainly, it handles ListActions by concatenating into
    # a single ListAction.
    a1 = Action(act1)
    a2 = Action(act2)
    if a1 is None or a2 is None:
        raise TypeError, "Cannot append %s to %s" % (type(act1), type(act2))
    if isinstance(a1, ListAction):
        if isinstance(a2, ListAction):
            return ListAction(a1.list + a2.list)
        else:
            return ListAction(a1.list + [ a2 ])
    else:
        if isinstance(a2, ListAction):
            return ListAction([ a1 ] + a2.list)
        else:
            return ListAction([ a1, a2 ])

def _do_create_action(act, *args, **kw):
    """This is the actual "implementation" for the
    Action factory method, below.  This handles the
    fact that passing lists to Action() itself has
    different semantics than passing lists as elements
    of lists.

    The former will create a ListAction, the latter
    will create a CommandAction by converting the inner
    list elements to strings."""

    if isinstance(act, ActionBase):
        return act
    if SCons.Util.is_List(act):
        return apply(CommandAction, (act,)+args, kw)
    if callable(act):
        try:
            gen = kw['generator']
            del kw['generator']
        except KeyError:
            gen = 0
        if gen:
            action_type = CommandGeneratorAction
        else:
            action_type = FunctionAction
        return apply(action_type, (act,)+args, kw)
    if SCons.Util.is_String(act):
        var=SCons.Util.get_environment_var(act)
        if var:
            # This looks like a string that is purely an Environment
            # variable reference, like "$FOO" or "${FOO}".  We do
            # something special here...we lazily evaluate the contents
            # of that Environment variable, so a user could put something
            # like a function or a CommandGenerator in that variable
            # instead of a string.
            return apply(LazyAction, (var,)+args, kw)
        commands = string.split(str(act), '\n')
        if len(commands) == 1:
            return apply(CommandAction, (commands[0],)+args, kw)
        else:
            listCmdActions = map(lambda x, args=args, kw=kw:
                                 apply(CommandAction, (x,)+args, kw),
                                 commands)
            return ListAction(listCmdActions)
    return None

def Action(act, *args, **kw):
    """A factory for action objects."""
    if SCons.Util.is_List(act):
        acts = map(lambda a, args=args, kw=kw:
                          apply(_do_create_action, (a,)+args, kw),
                   act)
        acts = filter(None, acts)
        if len(acts) == 1:
            return acts[0]
        else:
            return ListAction(acts)
    else:
        return apply(_do_create_action, (act,)+args, kw)

class ActionBase:
    """Base class for all types of action objects that can be held by
    other objects (Builders, Executors, etc.)  This provides the
    common methods for manipulating and combining those actions."""
    
    if SCons.Memoize.use_memoizer:
        __metaclass__ = SCons.Memoize.Memoized_Metaclass

    def __cmp__(self, other):
        return cmp(self.__dict__, other)

    def genstring(self, target, source, env):
        return str(self)

    def __add__(self, other):
        return _actionAppend(self, other)

    def __radd__(self, other):
        return _actionAppend(other, self)

    def presub_lines(self, env):
        # CommandGeneratorAction needs a real environment
        # in order to return the proper string here, since
        # it may call LazyAction, which looks up a key
        # in that env.  So we temporarily remember the env here,
        # and CommandGeneratorAction will use this env
        # when it calls its _generate method.
        self.presub_env = env
        lines = string.split(str(self), '\n')
        self.presub_env = None      # don't need this any more
        return lines

    def get_executor(self, env, overrides, tlist, slist, executor_kw):
        """Return the Executor for this Action."""
        return SCons.Executor.Executor(self, env, overrides,
                                       tlist, slist, executor_kw)

if SCons.Memoize.use_old_memoization():
    _Base = ActionBase
    class ActionBase(SCons.Memoize.Memoizer, _Base):
        "Cache-backed version of ActionBase"
        def __init__(self, *args, **kw):
            apply(_Base.__init__, (self,)+args, kw)
            SCons.Memoize.Memoizer.__init__(self)


class _ActionAction(ActionBase):
    """Base class for actions that create output objects."""
    def __init__(self, strfunction=_null, presub=_null, chdir=None, exitstatfunc=None, **kw):
        if not strfunction is _null:
            self.strfunction = strfunction
        if presub is _null:
            presub = print_actions_presub
        self.presub = presub
        self.chdir = chdir
        if not exitstatfunc:
            exitstatfunc = default_exitstatfunc
        self.exitstatfunc = exitstatfunc

    def print_cmd_line(self, s, target, source, env):
        sys.stdout.write(s + "\n")

    def __call__(self, target, source, env,
                               exitstatfunc=_null,
                               presub=_null,
                               show=_null,
                               execute=_null,
                               chdir=_null):
        if not SCons.Util.is_List(target):
            target = [target]
        if not SCons.Util.is_List(source):
            source = [source]
        if exitstatfunc is _null: exitstatfunc = self.exitstatfunc
        if presub is _null:  presub = self.presub
        if show is _null:  show = print_actions
        if execute is _null:  execute = execute_actions
        if chdir is _null: chdir = self.chdir
        save_cwd = None
        if chdir:
            save_cwd = os.getcwd()
            try:
                chdir = str(chdir.abspath)
            except AttributeError:
                if not SCons.Util.is_String(chdir):
                    chdir = str(target[0].dir)
        if presub:
            t = string.join(map(str, target), ' and ')
            l = string.join(self.presub_lines(env), '\n  ')
            out = "Building %s with action:\n  %s\n" % (t, l)
            sys.stdout.write(out)
        s = None
        if show and self.strfunction:
            s = self.strfunction(target, source, env)
            if s:
                if chdir:
                    s = ('os.chdir(%s)\n' % repr(chdir)) + s
                try:
                    get = env.get
                except AttributeError:
                    print_func = self.print_cmd_line
                else:
                    print_func = get('PRINT_CMD_LINE_FUNC')
                    if not print_func:
                        print_func = self.print_cmd_line
                print_func(s, target, source, env)
        stat = 0
        if execute:
            if chdir:
                os.chdir(chdir)
            try:
                stat = self.execute(target, source, env)
                stat = exitstatfunc(stat)
            finally:
                if save_cwd:
                    os.chdir(save_cwd)
        if s and save_cwd:
            print_func('os.chdir(%s)' % repr(save_cwd), target, source, env)
        return stat


def _string_from_cmd_list(cmd_list):
    """Takes a list of command line arguments and returns a pretty
    representation for printing."""
    cl = []
    for arg in map(str, cmd_list):
        if ' ' in arg or '\t' in arg:
            arg = '"' + arg + '"'
        cl.append(arg)
    return string.join(cl)

class CommandAction(_ActionAction):
    """Class for command-execution actions."""
    def __init__(self, cmd, cmdstr=None, *args, **kw):
        # Cmd can actually be a list or a single item; if it's a
        # single item it should be the command string to execute; if a
        # list then it should be the words of the command string to
        # execute.  Only a single command should be executed by this
        # object; lists of commands should be handled by embedding
        # these objects in a ListAction object (which the Action()
        # factory above does).  cmd will be passed to
        # Environment.subst_list() for substituting environment
        # variables.
        if __debug__: logInstanceCreation(self, 'Action.CommandAction')
        apply(_ActionAction.__init__, (self,)+args, kw)
        if SCons.Util.is_List(cmd):
            if filter(SCons.Util.is_List, cmd):
                raise TypeError, "CommandAction should be given only " \
                      "a single command"
        self.cmd_list = cmd
        self.cmdstr = cmdstr

    def __str__(self):
        if SCons.Util.is_List(self.cmd_list):
            return string.join(map(str, self.cmd_list), ' ')
        return str(self.cmd_list)

    def process(self, target, source, env):
        result = env.subst_list(self.cmd_list, 0, target, source)
        silent = None
        ignore = None
        while 1:
            try: c = result[0][0][0]
            except IndexError: c = None
            if c == '@': silent = 1
            elif c == '-': ignore = 1
            else: break
            result[0][0] = result[0][0][1:]
        try:
            if not result[0][0]:
                result[0] = result[0][1:]
        except IndexError:
            pass
        return result, ignore, silent

    def strfunction(self, target, source, env):
        if not self.cmdstr is None:
            c = env.subst(self.cmdstr, 0, target, source)
            if c:
                return c
        cmd_list, ignore, silent = self.process(target, source, env)
        if silent:
            return ''
        return _string_from_cmd_list(cmd_list[0])

    def execute(self, target, source, env):
        """Execute a command action.

        This will handle lists of commands as well as individual commands,
        because construction variable substitution may turn a single
        "command" into a list.  This means that this class can actually
        handle lists of commands, even though that's not how we use it
        externally.
        """
        from SCons.Subst import escape_list
        from SCons.Util import is_String, is_List, flatten

        try:
            shell = env['SHELL']
        except KeyError:
            raise SCons.Errors.UserError('Missing SHELL construction variable.')

        try:
            spawn = env['SPAWN']
        except KeyError:
            raise SCons.Errors.UserError('Missing SPAWN construction variable.')

        escape = env.get('ESCAPE', lambda x: x)

        try:
            ENV = env['ENV']
        except KeyError:
            global default_ENV
            if not default_ENV:
                import SCons.Environment
                default_ENV = SCons.Environment.Environment()['ENV']
            ENV = default_ENV

        # Ensure that the ENV values are all strings:
        for key, value in ENV.items():
            if not is_String(value):
                if is_List(value):
                    # If the value is a list, then we assume it is a
                    # path list, because that's a pretty common list-like
                    # value to stick in an environment variable:
                    value = flatten(value)
                    ENV[key] = string.join(map(str, value), os.pathsep)
                else:
                    # If it isn't a string or a list, then we just coerce
                    # it to a string, which is the proper way to handle
                    # Dir and File instances and will produce something
                    # reasonable for just about everything else:
                    ENV[key] = str(value)

        cmd_list, ignore, silent = self.process(target, map(rfile, source), env)

        # Use len() to filter out any "command" that's zero-length.
        for cmd_line in filter(len, cmd_list):
            # Escape the command line for the interpreter we are using.
            cmd_line = escape_list(cmd_line, escape)
            result = spawn(shell, escape, cmd_line[0], cmd_line, ENV)
            if not ignore and result:
                return result
        return 0

    def get_contents(self, target, source, env):
        """Return the signature contents of this action's command line.

        This strips $(-$) and everything in between the string,
        since those parts don't affect signatures.
        """
        from SCons.Subst import SUBST_SIG
        cmd = self.cmd_list
        if SCons.Util.is_List(cmd):
            cmd = string.join(map(str, cmd))
        else:
            cmd = str(cmd)
        return env.subst_target_source(cmd, SUBST_SIG, target, source)

class CommandGeneratorAction(ActionBase):
    """Class for command-generator actions."""
    def __init__(self, generator, *args, **kw):
        if __debug__: logInstanceCreation(self, 'Action.CommandGeneratorAction')
        self.generator = generator
        self.gen_kw = kw

    def _generate(self, target, source, env, for_signature):
        # ensure that target is a list, to make it easier to write
        # generator functions:
        if not SCons.Util.is_List(target):
            target = [target]

        ret = self.generator(target=target, source=source, env=env, for_signature=for_signature)
        gen_cmd = apply(Action, (ret,), self.gen_kw)
        if not gen_cmd:
            raise SCons.Errors.UserError("Object returned from command generator: %s cannot be used to create an Action." % repr(ret))
        return gen_cmd

    def __str__(self):
        try:
            env = self.presub_env or {}
        except AttributeError:
            env = {}
        act = self._generate([], [], env, 1)
        return str(act)

    def genstring(self, target, source, env):
        return self._generate(target, source, env, 1).genstring(target, source, env)

    def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null):
        act = self._generate(target, source, env, 0)
        return act(target, source, env, exitstatfunc, presub,
                   show, execute, chdir)

    def get_contents(self, target, source, env):
        """Return the signature contents of this action's command line.

        This strips $(-$) and everything in between the string,
        since those parts don't affect signatures.
        """
        return self._generate(target, source, env, 1).get_contents(target, source, env)



# A LazyAction is a kind of hybrid generator and command action for
# strings of the form "$VAR".  These strings normally expand to other
# strings (think "$CCCOM" to "$CC -c -o $TARGET $SOURCE"), but we also
# want to be able to replace them with functions in the construction
# environment.  Consequently, we want lazy evaluation and creation of
# an Action in the case of the function, but that's overkill in the more
# normal case of expansion to other strings.
#
# So we do this with a subclass that's both a generator *and*
# a command action.  The overridden methods all do a quick check
# of the construction variable, and if it's a string we just call
# the corresponding CommandAction method to do the heavy lifting.
# If not, then we call the same-named CommandGeneratorAction method.
# The CommandGeneratorAction methods work by using the overridden
# _generate() method, that is, our own way of handling "generation" of
# an action based on what's in the construction variable.

class LazyAction(CommandGeneratorAction, CommandAction):

    if SCons.Memoize.use_memoizer:
        __metaclass__ = SCons.Memoize.Memoized_Metaclass

    def __init__(self, var, *args, **kw):
        if __debug__: logInstanceCreation(self, 'Action.LazyAction')
        apply(CommandAction.__init__, (self, '$'+var)+args, kw)
        self.var = SCons.Util.to_String(var)
        self.gen_kw = kw

    def get_parent_class(self, env):
        c = env.get(self.var)
        if SCons.Util.is_String(c) and not '\n' in c:
            return CommandAction
        return CommandGeneratorAction

    def _generate_cache(self, env):
        """__cacheable__"""
        c = env.get(self.var, '')
        gen_cmd = apply(Action, (c,), self.gen_kw)
        if not gen_cmd:
            raise SCons.Errors.UserError("$%s value %s cannot be used to create an Action." % (self.var, repr(c)))
        return gen_cmd

    def _generate(self, target, source, env, for_signature):
        return self._generate_cache(env)

    def __call__(self, target, source, env, *args, **kw):
        args = (self, target, source, env) + args
        c = self.get_parent_class(env)
        return apply(c.__call__, args, kw)

    def get_contents(self, target, source, env):
        c = self.get_parent_class(env)
        return c.get_contents(self, target, source, env)

if not SCons.Memoize.has_metaclass:
    _Base = LazyAction
    class LazyAction(SCons.Memoize.Memoizer, _Base):
        def __init__(self, *args, **kw):
            SCons.Memoize.Memoizer.__init__(self)
            apply(_Base.__init__, (self,)+args, kw)



class FunctionAction(_ActionAction):
    """Class for Python function actions."""

    def __init__(self, execfunction, *args, **kw):
        if __debug__: logInstanceCreation(self, 'Action.FunctionAction')
        self.execfunction = execfunction
        apply(_ActionAction.__init__, (self,)+args, kw)
        self.varlist = kw.get('varlist', [])

    def function_name(self):
        try:
            return self.execfunction.__name__
        except AttributeError:
            try:
                return self.execfunction.__class__.__name__
            except AttributeError:
                return "unknown_python_function"

    def strfunction(self, target, source, env):
        def array(a):
            def quote(s):
                return '"' + str(s) + '"'
            return '[' + string.join(map(quote, a), ", ") + ']'
        try:
            strfunc = self.execfunction.strfunction
        except AttributeError:
            pass
        else:
            if strfunc is None:
                return None
            if callable(strfunc):
                return strfunc(target, source, env)
        name = self.function_name()
        tstr = array(target)
        sstr = array(source)
        return "%s(%s, %s)" % (name, tstr, sstr)

    def __str__(self):
        name = self.function_name()
        if name == 'ActionCaller':
            return str(self.execfunction)
        return "%s(target, source, env)" % name

    def execute(self, target, source, env):
        rsources = map(rfile, source)
        try:
            result = self.execfunction(target=target, source=rsources, env=env)
        except EnvironmentError, e:
            # If an IOError/OSError happens, raise a BuildError.
            # Report the name of the file or directory that caused the
            # error, which might be different from the target being built
            # (for example, failure to create the directory in which the
            # target file will appear).
            try: filename = e.filename
            except AttributeError: filename = None
            raise SCons.Errors.BuildError(node=target,
                                          errstr=e.strerror,
                                          filename=filename)
        return result

    def get_contents(self, target, source, env):
        """Return the signature contents of this callable action.

        By providing direct access to the code object of the
        function, Python makes this extremely easy.  Hooray!

        Unfortunately, older versions of Python include line
        number indications in the compiled byte code.  Boo!
        So we remove the line number byte codes to prevent
        recompilations from moving a Python function.
        """
        execfunction = self.execfunction
        try:
            # Test if execfunction is a function.
            code = execfunction.func_code.co_code
        except AttributeError:
            try:
                # Test if execfunction is a method.
                code = execfunction.im_func.func_code.co_code
            except AttributeError:
                try:
                    # Test if execfunction is a callable object.
                    code = execfunction.__call__.im_func.func_code.co_code
                except AttributeError:
                    try:
                        # See if execfunction will do the heavy lifting for us.
                        gc = self.execfunction.get_contents
                    except AttributeError:
                        # This is weird, just do the best we can.
                        contents = str(self.execfunction)
                    else:
                        contents = gc(target, source, env)
                else:
                    contents = str(code)
            else:
                contents = str(code)
        else:
            contents = str(code)
        contents = remove_set_lineno_codes(contents)
        return contents + env.subst(string.join(map(lambda v: '${'+v+'}',
                                                     self.varlist)))

class ListAction(ActionBase):
    """Class for lists of other actions."""
    def __init__(self, list):
        if __debug__: logInstanceCreation(self, 'Action.ListAction')
        def list_of_actions(x):
            if isinstance(x, ActionBase):
                return x
            return Action(x)
        self.list = map(list_of_actions, list)

    def genstring(self, target, source, env):
        return string.join(map(lambda a, t=target, s=source, e=env:
                                  a.genstring(t, s, e),
                               self.list),
                           '\n')

    def __str__(self):
        return string.join(map(str, self.list), '\n')
    
    def presub_lines(self, env):
        return SCons.Util.flatten(map(lambda a, env=env:
                                      a.presub_lines(env),
                                      self.list))

    def get_contents(self, target, source, env):
        """Return the signature contents of this action list.

        Simple concatenation of the signatures of the elements.
        """
        return string.join(map(lambda x, t=target, s=source, e=env:
                                      x.get_contents(t, s, e),
                               self.list),
                           "")

    def __call__(self, target, source, env, exitstatfunc=_null, presub=_null,
                 show=_null, execute=_null, chdir=_null):
        for act in self.list:
            stat = act(target, source, env, exitstatfunc, presub,
                       show, execute, chdir)
            if stat:
                return stat
        return 0

class ActionCaller:
    """A class for delaying calling an Action function with specific
    (positional and keyword) arguments until the Action is actually
    executed.

    This class looks to the rest of the world like a normal Action object,
    but what it's really doing is hanging on to the arguments until we
    have a target, source and env to use for the expansion.
    """
    def __init__(self, parent, args, kw):
        self.parent = parent
        self.args = args
        self.kw = kw
    def get_contents(self, target, source, env):
        actfunc = self.parent.actfunc
        try:
            # "self.actfunc" is a function.
            contents = str(actfunc.func_code.co_code)
        except AttributeError:
            # "self.actfunc" is a callable object.
            try:
                contents = str(actfunc.__call__.im_func.func_code.co_code)
            except AttributeError:
                # No __call__() method, so it might be a builtin
                # or something like that.  Do the best we can.
                contents = str(actfunc)
        contents = remove_set_lineno_codes(contents)
        return contents
    def subst(self, s, target, source, env):
        # Special-case hack:  Let a custom function wrapped in an
        # ActionCaller get at the environment through which the action
        # was called by using this hard-coded value as a special return.
        if s == '$__env__':
            return env
        else:
            return env.subst(s, 0, target, source)
    def subst_args(self, target, source, env):
        return map(lambda x, self=self, t=target, s=source, e=env:
                          self.subst(x, t, s, e),
                   self.args)
    def subst_kw(self, target, source, env):
        kw = {}
        for key in self.kw.keys():
            kw[key] = self.subst(self.kw[key], target, source, env)
        return kw
    def __call__(self, target, source, env):
        args = self.subst_args(target, source, env)
        kw = self.subst_kw(target, source, env)
        return apply(self.parent.actfunc, args, kw)
    def strfunction(self, target, source, env):
        args = self.subst_args(target, source, env)
        kw = self.subst_kw(target, source, env)
        return apply(self.parent.strfunc, args, kw)
    def __str__(self):
        return apply(self.parent.strfunc, self.args, self.kw)

class ActionFactory:
    """A factory class that will wrap up an arbitrary function
    as an SCons-executable Action object.

    The real heavy lifting here is done by the ActionCaller class.
    We just collect the (positional and keyword) arguments that we're
    called with and give them to the ActionCaller object we create,
    so it can hang onto them until it needs them.
    """
    def __init__(self, actfunc, strfunc):
        self.actfunc = actfunc
        self.strfunc = strfunc
    def __call__(self, *args, **kw):
        ac = ActionCaller(self, args, kw)
        action = Action(ac, strfunction=ac.strfunction)
        return action