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

"""SCons.SConf

Autoconf-like configuration support.

In other words, SConf allows to run tests on the build machine to detect
capabilities of system and do some things based on result: generate config
files, header files for C/C++, update variables in environment.

Tests on the build system can detect if compiler sees header files, if
libraries are installed, if some command line options are supported etc.

"""

#
# __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.
#
from __future__ import print_function

__revision__ = "__FILE__ __REVISION__ __DATE__ __DEVELOPER__"

import SCons.compat

import io
import os
import re
import sys
import traceback

import SCons.Action
import SCons.Builder
import SCons.Errors
import SCons.Job
import SCons.Node.FS
import SCons.Taskmaster
import SCons.Util
import SCons.Warnings
import SCons.Conftest

from SCons.Debug import Trace

# Turn off the Conftest error logging
SCons.Conftest.LogInputFiles = 0
SCons.Conftest.LogErrorMessages = 0

# Set
build_type = None
build_types = ['clean', 'help']

def SetBuildType(type):
    global build_type
    build_type = type

# to be set, if we are in dry-run mode
dryrun = 0

AUTO=0  # use SCons dependency scanning for up-to-date checks
FORCE=1 # force all tests to be rebuilt
CACHE=2 # force all tests to be taken from cache (raise an error, if necessary)
cache_mode = AUTO

def SetCacheMode(mode):
    """Set the Configure cache mode. mode must be one of "auto", "force",
    or "cache"."""
    global cache_mode
    if mode == "auto":
        cache_mode = AUTO
    elif mode == "force":
        cache_mode = FORCE
    elif mode == "cache":
        cache_mode = CACHE
    else:
        raise ValueError("SCons.SConf.SetCacheMode: Unknown mode " + mode)

progress_display = SCons.Util.display # will be overwritten by SCons.Script
def SetProgressDisplay(display):
    """Set the progress display to use (called from SCons.Script)"""
    global progress_display
    progress_display = display

SConfFS = None

_ac_build_counter = 0 # incremented, whenever TryBuild is called
_ac_config_logs = {}  # all config.log files created in this build
_ac_config_hs   = {}  # all config.h files created in this build
sconf_global = None   # current sconf object

def _createConfigH(target, source, env):
    t = open(str(target[0]), "w")
    defname = re.sub('[^A-Za-z0-9_]', '_', str(target[0]).upper())
    t.write("""#ifndef %(DEFNAME)s_SEEN
#define %(DEFNAME)s_SEEN

""" % {'DEFNAME' : defname})
    t.write(source[0].get_contents())
    t.write("""
#endif /* %(DEFNAME)s_SEEN */
""" % {'DEFNAME' : defname})
    t.close()

def _stringConfigH(target, source, env):
    return "scons: Configure: creating " + str(target[0])


def NeedConfigHBuilder():
    if len(_ac_config_hs) == 0:
       return False
    else:
       return True

def CreateConfigHBuilder(env):
    """Called if necessary just before the building targets phase begins."""
    action = SCons.Action.Action(_createConfigH,
                                 _stringConfigH)
    sconfigHBld = SCons.Builder.Builder(action=action)
    env.Append( BUILDERS={'SConfigHBuilder':sconfigHBld} )
    for k in list(_ac_config_hs.keys()):
        env.SConfigHBuilder(k, env.Value(_ac_config_hs[k]))


class SConfWarning(SCons.Warnings.Warning):
    pass
SCons.Warnings.enableWarningClass(SConfWarning)

# some error definitions
class SConfError(SCons.Errors.UserError):
    def __init__(self,msg):
        SCons.Errors.UserError.__init__(self,msg)

class ConfigureDryRunError(SConfError):
    """Raised when a file or directory needs to be updated during a Configure
    process, but the user requested a dry-run"""
    def __init__(self,target):
        if not isinstance(target, SCons.Node.FS.File):
            msg = 'Cannot create configure directory "%s" within a dry-run.' % str(target)
        else:
            msg = 'Cannot update configure test "%s" within a dry-run.' % str(target)
        SConfError.__init__(self,msg)

class ConfigureCacheError(SConfError):
    """Raised when a use explicitely requested the cache feature, but the test
    is run the first time."""
    def __init__(self,target):
        SConfError.__init__(self, '"%s" is not yet built and cache is forced.' % str(target))

# define actions for building text files
def _createSource( target, source, env ):
    fd = open(str(target[0]), "w")
    fd.write(source[0].get_contents())
    fd.close()
def _stringSource( target, source, env ):
    return (str(target[0]) + ' <-\n  |' +
            source[0].get_contents().replace( '\n', "\n  |" ) )

class SConfBuildInfo(SCons.Node.FS.FileBuildInfo):
    """
    Special build info for targets of configure tests. Additional members
    are result (did the builder succeed last time?) and string, which
    contains messages of the original build phase.
    """
    __slots__ = ('result', 'string')

    def __init__(self):
        self.result = None # -> 0/None -> no error, != 0 error
        self.string = None # the stdout / stderr output when building the target

    def set_build_result(self, result, string):
        self.result = result
        self.string = string


class Streamer(object):
    """
    'Sniffer' for a file-like writable object. Similar to the unix tool tee.
    """
    def __init__(self, orig):
        self.orig = orig
        self.s = io.StringIO()

    def write(self, str):
        if self.orig:
            self.orig.write(str)
        try:
            self.s.write(str)
        except TypeError as e:
            # "unicode argument expected" bug in IOStream (python 2.x)
            self.s.write(str.decode())

    def writelines(self, lines):
        for l in lines:
            self.write(l + '\n')

    def getvalue(self):
        """
        Return everything written to orig since the Streamer was created.
        """
        return self.s.getvalue()

    def flush(self):
        if self.orig:
            self.orig.flush()
        self.s.flush()


class SConfBuildTask(SCons.Taskmaster.AlwaysTask):
    """
    This is almost the same as SCons.Script.BuildTask. Handles SConfErrors
    correctly and knows about the current cache_mode.
    """
    def display(self, message):
        if sconf_global.logstream:
            sconf_global.logstream.write("scons: Configure: " + message + "\n")

    def display_cached_string(self, bi):
        """
        Logs the original builder messages, given the SConfBuildInfo instance
        bi.
        """
        if not isinstance(bi, SConfBuildInfo):
            SCons.Warnings.warn(SConfWarning,
              "The stored build information has an unexpected class: %s" % bi.__class__)
        else:
            self.display("The original builder output was:\n" +
                         ("  |" + str(bi.string)).replace("\n", "\n  |"))

    def failed(self):
        # check, if the reason was a ConfigureDryRunError or a
        # ConfigureCacheError and if yes, reraise the exception
        exc_type = self.exc_info()[0]
        if issubclass(exc_type, SConfError):
            raise
        elif issubclass(exc_type, SCons.Errors.BuildError):
            # we ignore Build Errors (occurs, when a test doesn't pass)
            # Clear the exception to prevent the contained traceback
            # to build a reference cycle.
            self.exc_clear()
        else:
            self.display('Caught exception while building "%s":\n' %
                         self.targets[0])
            sys.excepthook(*self.exc_info())
        return SCons.Taskmaster.Task.failed(self)

    def collect_node_states(self):
        # returns (is_up_to_date, cached_error, cachable)
        # where is_up_to_date is 1, if the node(s) are up_to_date
        #       cached_error  is 1, if the node(s) are up_to_date, but the
        #                           build will fail
        #       cachable      is 0, if some nodes are not in our cache
        T = 0
        changed = False
        cached_error = False
        cachable = True
        for t in self.targets:
            if T: Trace('%s' % (t))
            bi = t.get_stored_info().binfo
            if isinstance(bi, SConfBuildInfo):
                if T: Trace(': SConfBuildInfo')
                if cache_mode == CACHE:
                    t.set_state(SCons.Node.up_to_date)
                    if T: Trace(': set_state(up_to-date)')
                else:
                    if T: Trace(': get_state() %s' % t.get_state())
                    if T: Trace(': changed() %s' % t.changed())
                    if (t.get_state() != SCons.Node.up_to_date and t.changed()):
                        changed = True
                    if T: Trace(': changed %s' % changed)
                cached_error = cached_error or bi.result
            else:
                if T: Trace(': else')
                # the node hasn't been built in a SConf context or doesn't
                # exist
                cachable = False
                changed = ( t.get_state() != SCons.Node.up_to_date )
                if T: Trace(': changed %s' % changed)
        if T: Trace('\n')
        return (not changed, cached_error, cachable)

    def execute(self):
        if not self.targets[0].has_builder():
            return

        sconf = sconf_global

        is_up_to_date, cached_error, cachable = self.collect_node_states()

        if cache_mode == CACHE and not cachable:
            raise ConfigureCacheError(self.targets[0])
        elif cache_mode == FORCE:
            is_up_to_date = 0

        if cached_error and is_up_to_date:
            self.display("Building \"%s\" failed in a previous run and all "
                         "its sources are up to date." % str(self.targets[0]))
            binfo = self.targets[0].get_stored_info().binfo
            self.display_cached_string(binfo)
            raise SCons.Errors.BuildError # will be 'caught' in self.failed
        elif is_up_to_date:
            self.display("\"%s\" is up to date." % str(self.targets[0]))
            binfo = self.targets[0].get_stored_info().binfo
            self.display_cached_string(binfo)
        elif dryrun:
            raise ConfigureDryRunError(self.targets[0])
        else:
            # note stdout and stderr are the same here
            s = sys.stdout = sys.stderr = Streamer(sys.stdout)
            try:
                env = self.targets[0].get_build_env()
                if cache_mode == FORCE:
                    # Set up the Decider() to force rebuilds by saying
                    # that every source has changed.  Note that we still
                    # call the environment's underlying source decider so
                    # that the correct .sconsign info will get calculated
                    # and keep the build state consistent.
                    def force_build(dependency, target, prev_ni,
                                    env_decider=env.decide_source):
                        env_decider(dependency, target, prev_ni)
                        return True
                    if env.decide_source.__code__ is not force_build.__code__:
                        env.Decider(force_build)
                env['PSTDOUT'] = env['PSTDERR'] = s
                try:
                    sconf.cached = 0
                    self.targets[0].build()
                finally:
                    sys.stdout = sys.stderr = env['PSTDOUT'] = \
                                 env['PSTDERR'] = sconf.logstream
            except KeyboardInterrupt:
                raise
            except SystemExit:
                exc_value = sys.exc_info()[1]
                raise SCons.Errors.ExplicitExit(self.targets[0],exc_value.code)
            except Exception as e:
                for t in self.targets:
                    binfo = SConfBuildInfo()
                    binfo.merge(t.get_binfo())
                    binfo.set_build_result(1, s.getvalue())
                    sconsign_entry = SCons.SConsign.SConsignEntry()
                    sconsign_entry.binfo = binfo
                    #sconsign_entry.ninfo = self.get_ninfo()
                    # We'd like to do this as follows:
                    #    t.store_info(binfo)
                    # However, we need to store it as an SConfBuildInfo
                    # object, and store_info() will turn it into a
                    # regular FileNodeInfo if the target is itself a
                    # regular File.
                    sconsign = t.dir.sconsign()
                    sconsign.set_entry(t.name, sconsign_entry)
                    sconsign.merge()
                raise e
            else:
                for t in self.targets:
                    binfo = SConfBuildInfo()
                    binfo.merge(t.get_binfo())
                    binfo.set_build_result(0, s.getvalue())
                    sconsign_entry = SCons.SConsign.SConsignEntry()
                    sconsign_entry.binfo = binfo
                    #sconsign_entry.ninfo = self.get_ninfo()
                    # We'd like to do this as follows:
                    #    t.store_info(binfo)
                    # However, we need to store it as an SConfBuildInfo
                    # object, and store_info() will turn it into a
                    # regular FileNodeInfo if the target is itself a
                    # regular File.
                    sconsign = t.dir.sconsign()
                    sconsign.set_entry(t.name, sconsign_entry)
                    sconsign.merge()

class SConfBase(object):
    """This is simply a class to represent a configure context. After
    creating a SConf object, you can call any tests. After finished with your
    tests, be sure to call the Finish() method, which returns the modified
    environment.
    Some words about caching: In most cases, it is not necessary to cache
    Test results explicitly. Instead, we use the scons dependency checking
    mechanism. For example, if one wants to compile a test program
    (SConf.TryLink), the compiler is only called, if the program dependencies
    have changed. However, if the program could not be compiled in a former
    SConf run, we need to explicitly cache this error.
    """

    def __init__(self, env, custom_tests = {}, conf_dir='$CONFIGUREDIR',
                 log_file='$CONFIGURELOG', config_h = None, _depth = 0):
        """Constructor. Pass additional tests in the custom_tests-dictionary,
        e.g. custom_tests={'CheckPrivate':MyPrivateTest}, where MyPrivateTest
        defines a custom test.
        Note also the conf_dir and log_file arguments (you may want to
        build tests in the VariantDir, not in the SourceDir)
        """
        global SConfFS
        if not SConfFS:
            SConfFS = SCons.Node.FS.default_fs or \
                      SCons.Node.FS.FS(env.fs.pathTop)
        if sconf_global is not None:
            raise SCons.Errors.UserError
        self.env = env
        if log_file is not None:
            log_file = SConfFS.File(env.subst(log_file))
        self.logfile = log_file
        self.logstream = None
        self.lastTarget = None
        self.depth = _depth
        self.cached = 0 # will be set, if all test results are cached

        # add default tests
        default_tests = {
                 'CheckCC'            : CheckCC,
                 'CheckCXX'           : CheckCXX,
                 'CheckSHCC'          : CheckSHCC,
                 'CheckSHCXX'         : CheckSHCXX,
                 'CheckFunc'          : CheckFunc,
                 'CheckType'          : CheckType,
                 'CheckTypeSize'      : CheckTypeSize,
                 'CheckDeclaration'   : CheckDeclaration,
                 'CheckHeader'        : CheckHeader,
                 'CheckCHeader'       : CheckCHeader,
                 'CheckCXXHeader'     : CheckCXXHeader,
                 'CheckLib'           : CheckLib,
                 'CheckLibWithHeader' : CheckLibWithHeader,
                 'CheckProg'          : CheckProg,
               }
        self.AddTests(default_tests)
        self.AddTests(custom_tests)
        self.confdir = SConfFS.Dir(env.subst(conf_dir))
        if config_h is not None:
            config_h = SConfFS.File(config_h)
        self.config_h = config_h
        self._startup()

    def Finish(self):
        """Call this method after finished with your tests:
                env = sconf.Finish()
        """
        self._shutdown()
        return self.env

    def Define(self, name, value = None, comment = None):
        """
        Define a pre processor symbol name, with the optional given value in the
        current config header.

        If value is None (default), then #define name is written. If value is not
        none, then #define name value is written.

        comment is a string which will be put as a C comment in the
        header, to explain the meaning of the value (appropriate C comments /* and
        */ will be put automatically."""
        lines = []
        if comment:
            comment_str = "/* %s */" % comment
            lines.append(comment_str)

        if value is not None:
            define_str = "#define %s %s" % (name, value)
        else:
            define_str = "#define %s" % name
        lines.append(define_str)
        lines.append('')

        self.config_h_text = self.config_h_text + '\n'.join(lines)

    def BuildNodes(self, nodes):
        """
        Tries to build the given nodes immediately. Returns 1 on success,
        0 on error.
        """
        if self.logstream is not None:
            # override stdout / stderr to write in log file
            oldStdout = sys.stdout
            sys.stdout = self.logstream
            oldStderr = sys.stderr
            sys.stderr = self.logstream

        # the engine assumes the current path is the SConstruct directory ...
        old_fs_dir = SConfFS.getcwd()
        old_os_dir = os.getcwd()
        SConfFS.chdir(SConfFS.Top, change_os_dir=1)

        # Because we take responsibility here for writing out our
        # own .sconsign info (see SConfBuildTask.execute(), above),
        # we override the store_info() method with a null place-holder
        # so we really control how it gets written.
        for n in nodes:
            n.store_info = 0
            if not hasattr(n, 'attributes'):
                n.attributes = SCons.Node.Node.Attrs()
            n.attributes.keep_targetinfo = 1

        ret = 1

        try:
            # ToDo: use user options for calc
            save_max_drift = SConfFS.get_max_drift()
            SConfFS.set_max_drift(0)
            tm = SCons.Taskmaster.Taskmaster(nodes, SConfBuildTask)
            # we don't want to build tests in parallel
            jobs = SCons.Job.Jobs(1, tm )
            jobs.run()
            for n in nodes:
                state = n.get_state()
                if (state != SCons.Node.executed and
                    state != SCons.Node.up_to_date):
                    # the node could not be built. we return 0 in this case
                    ret = 0
        finally:
            SConfFS.set_max_drift(save_max_drift)
            os.chdir(old_os_dir)
            SConfFS.chdir(old_fs_dir, change_os_dir=0)
            if self.logstream is not None:
                # restore stdout / stderr
                sys.stdout = oldStdout
                sys.stderr = oldStderr
        return ret

    def pspawn_wrapper(self, sh, escape, cmd, args, env):
        """Wrapper function for handling piped spawns.

        This looks to the calling interface (in Action.py) like a "normal"
        spawn, but associates the call with the PSPAWN variable from
        the construction environment and with the streams to which we
        want the output logged.  This gets slid into the construction
        environment as the SPAWN variable so Action.py doesn't have to
        know or care whether it's spawning a piped command or not.
        """
        return self.pspawn(sh, escape, cmd, args, env, self.logstream, self.logstream)


    def TryBuild(self, builder, text = None, extension = ""):
        """Low level TryBuild implementation. Normally you don't need to
        call that - you can use TryCompile / TryLink / TryRun instead
        """
        global _ac_build_counter

        # Make sure we have a PSPAWN value, and save the current
        # SPAWN value.
        try:
            self.pspawn = self.env['PSPAWN']
        except KeyError:
            raise SCons.Errors.UserError('Missing PSPAWN construction variable.')
        try:
            save_spawn = self.env['SPAWN']
        except KeyError:
            raise SCons.Errors.UserError('Missing SPAWN construction variable.')

        nodesToBeBuilt = []

        f = "conftest_" + str(_ac_build_counter)
        pref = self.env.subst( builder.builder.prefix )
        suff = self.env.subst( builder.builder.suffix )
        target = self.confdir.File(pref + f + suff)

        try:
            # Slide our wrapper into the construction environment as
            # the SPAWN function.
            self.env['SPAWN'] = self.pspawn_wrapper
            sourcetext = self.env.Value(text)

            if text is not None:
                textFile = self.confdir.File(f + extension)
                textFileNode = self.env.SConfSourceBuilder(target=textFile,
                                                           source=sourcetext)
                nodesToBeBuilt.extend(textFileNode)
                source = textFileNode
            else:
                source = None

            nodes = builder(target = target, source = source)
            if not SCons.Util.is_List(nodes):
                nodes = [nodes]
            nodesToBeBuilt.extend(nodes)
            result = self.BuildNodes(nodesToBeBuilt)

        finally:
            self.env['SPAWN'] = save_spawn

        _ac_build_counter = _ac_build_counter + 1
        if result:
            self.lastTarget = nodes[0]
        else:
            self.lastTarget = None

        return result

    def TryAction(self, action, text = None, extension = ""):
        """Tries to execute the given action with optional source file
        contents <text> and optional source file extension <extension>,
        Returns the status (0 : failed, 1 : ok) and the contents of the
        output file.
        """
        builder = SCons.Builder.Builder(action=action)
        self.env.Append( BUILDERS = {'SConfActionBuilder' : builder} )
        ok = self.TryBuild(self.env.SConfActionBuilder, text, extension)
        del self.env['BUILDERS']['SConfActionBuilder']
        if ok:
            outputStr = self.lastTarget.get_contents()
            return (1, outputStr)
        return (0, "")

    def TryCompile( self, text, extension):
        """Compiles the program given in text to an env.Object, using extension
        as file extension (e.g. '.c'). Returns 1, if compilation was
        successful, 0 otherwise. The target is saved in self.lastTarget (for
        further processing).
        """
        return self.TryBuild(self.env.Object, text, extension)

    def TryLink( self, text, extension ):
        """Compiles the program given in text to an executable env.Program,
        using extension as file extension (e.g. '.c'). Returns 1, if
        compilation was successful, 0 otherwise. The target is saved in
        self.lastTarget (for further processing).
        """
        return self.TryBuild(self.env.Program, text, extension )

    def TryRun(self, text, extension ):
        """Compiles and runs the program given in text, using extension
        as file extension (e.g. '.c'). Returns (1, outputStr) on success,
        (0, '') otherwise. The target (a file containing the program's stdout)
        is saved in self.lastTarget (for further processing).
        """
        ok = self.TryLink(text, extension)
        if( ok ):
            prog = self.lastTarget
            pname = prog.get_internal_path()
            output = self.confdir.File(os.path.basename(pname)+'.out')
            node = self.env.Command(output, prog, [ [ pname, ">", "${TARGET}"] ])
            ok = self.BuildNodes(node)
            if ok:
                outputStr = SCons.Util.to_str(output.get_contents())
                return( 1, outputStr)
        return (0, "")

    class TestWrapper(object):
        """A wrapper around Tests (to ensure sanity)"""
        def __init__(self, test, sconf):
            self.test = test
            self.sconf = sconf
        def __call__(self, *args, **kw):
            if not self.sconf.active:
                raise SCons.Errors.UserError
            context = CheckContext(self.sconf)
            ret = self.test(context, *args, **kw)
            if self.sconf.config_h is not None:
                self.sconf.config_h_text = self.sconf.config_h_text + context.config_h
            context.Result("error: no result")
            return ret

    def AddTest(self, test_name, test_instance):
        """Adds test_class to this SConf instance. It can be called with
        self.test_name(...)"""
        setattr(self, test_name, SConfBase.TestWrapper(test_instance, self))

    def AddTests(self, tests):
        """Adds all the tests given in the tests dictionary to this SConf
        instance
        """
        for name in list(tests.keys()):
            self.AddTest(name, tests[name])

    def _createDir( self, node ):
        dirName = str(node)
        if dryrun:
            if not os.path.isdir( dirName ):
                raise ConfigureDryRunError(dirName)
        else:
            if not os.path.isdir( dirName ):
                os.makedirs( dirName )

    def _startup(self):
        """Private method. Set up logstream, and set the environment
        variables necessary for a piped build
        """
        global _ac_config_logs
        global sconf_global
        global SConfFS

        self.lastEnvFs = self.env.fs
        self.env.fs = SConfFS
        self._createDir(self.confdir)
        self.confdir.up().add_ignore( [self.confdir] )

        if self.logfile is not None and not dryrun:
            # truncate logfile, if SConf.Configure is called for the first time
            # in a build
            if self.logfile in _ac_config_logs:
                log_mode = "a"
            else:
                _ac_config_logs[self.logfile] = None
                log_mode = "w"
            fp = open(str(self.logfile), log_mode)
            self.logstream = SCons.Util.Unbuffered(fp)
            # logfile may stay in a build directory, so we tell
            # the build system not to override it with a eventually
            # existing file with the same name in the source directory
            self.logfile.dir.add_ignore( [self.logfile] )

            tb = traceback.extract_stack()[-3-self.depth]
            old_fs_dir = SConfFS.getcwd()
            SConfFS.chdir(SConfFS.Top, change_os_dir=0)
            self.logstream.write('file %s,line %d:\n\tConfigure(confdir = %s)\n' %
                                 (tb[0], tb[1], str(self.confdir)) )
            SConfFS.chdir(old_fs_dir)
        else:
            self.logstream = None
        # we use a special builder to create source files from TEXT
        action = SCons.Action.Action(_createSource,
                                     _stringSource)
        sconfSrcBld = SCons.Builder.Builder(action=action)
        self.env.Append( BUILDERS={'SConfSourceBuilder':sconfSrcBld} )
        self.config_h_text = _ac_config_hs.get(self.config_h, "")
        self.active = 1
        # only one SConf instance should be active at a time ...
        sconf_global = self

    def _shutdown(self):
        """Private method. Reset to non-piped spawn"""
        global sconf_global, _ac_config_hs

        if not self.active:
            raise SCons.Errors.UserError("Finish may be called only once!")
        if self.logstream is not None and not dryrun:
            self.logstream.write("\n")
            self.logstream.close()
            self.logstream = None
        # remove the SConfSourceBuilder from the environment
        blds = self.env['BUILDERS']
        del blds['SConfSourceBuilder']
        self.env.Replace( BUILDERS=blds )
        self.active = 0
        sconf_global = None
        if not self.config_h is None:
            _ac_config_hs[self.config_h] = self.config_h_text
        self.env.fs = self.lastEnvFs

class CheckContext(object):
    """Provides a context for configure tests. Defines how a test writes to the
    screen and log file.

    A typical test is just a callable with an instance of CheckContext as
    first argument:

        def CheckCustom(context, ...):
            context.Message('Checking my weird test ... ')
            ret = myWeirdTestFunction(...)
            context.Result(ret)

    Often, myWeirdTestFunction will be one of
    context.TryCompile/context.TryLink/context.TryRun. The results of
    those are cached, for they are only rebuild, if the dependencies have
    changed.
    """

    def __init__(self, sconf):
        """Constructor. Pass the corresponding SConf instance."""
        self.sconf = sconf
        self.did_show_result = 0

        # for Conftest.py:
        self.vardict = {}
        self.havedict = {}
        self.headerfilename = None
        self.config_h = "" # config_h text will be stored here
        # we don't regenerate the config.h file after each test. That means,
        # that tests won't be able to include the config.h file, and so
        # they can't do an #ifdef HAVE_XXX_H. This shouldn't be a major
        # issue, though. If it turns out, that we need to include config.h
        # in tests, we must ensure, that the dependencies are worked out
        # correctly. Note that we can't use Conftest.py's support for config.h,
        # cause we will need to specify a builder for the config.h file ...

    def Message(self, text):
        """Inform about what we are doing right now, e.g.
        'Checking for SOMETHING ... '
        """
        self.Display(text)
        self.sconf.cached = 1
        self.did_show_result = 0

    def Result(self, res):
        """Inform about the result of the test. If res is not a string, displays
        'yes' or 'no' depending on whether res is evaluated as true or false.
        The result is only displayed when self.did_show_result is not set.
        """
        if isinstance(res, str):
            text = res
        elif res:
            text = "yes"
        else:
            text = "no"

        if self.did_show_result == 0:
            # Didn't show result yet, do it now.
            self.Display(text + "\n")
            self.did_show_result = 1

    def TryBuild(self, *args, **kw):
        return self.sconf.TryBuild(*args, **kw)

    def TryAction(self, *args, **kw):
        return self.sconf.TryAction(*args, **kw)

    def TryCompile(self, *args, **kw):
        return self.sconf.TryCompile(*args, **kw)

    def TryLink(self, *args, **kw):
        return self.sconf.TryLink(*args, **kw)

    def TryRun(self, *args, **kw):
        return self.sconf.TryRun(*args, **kw)

    def __getattr__( self, attr ):
        if( attr == 'env' ):
            return self.sconf.env
        elif( attr == 'lastTarget' ):
            return self.sconf.lastTarget
        else:
            raise AttributeError("CheckContext instance has no attribute '%s'" % attr)

    #### Stuff used by Conftest.py (look there for explanations).

    def BuildProg(self, text, ext):
        self.sconf.cached = 1
        # TODO: should use self.vardict for $CC, $CPPFLAGS, etc.
        return not self.TryBuild(self.env.Program, text, ext)

    def CompileProg(self, text, ext):
        self.sconf.cached = 1
        # TODO: should use self.vardict for $CC, $CPPFLAGS, etc.
        return not self.TryBuild(self.env.Object, text, ext)

    def CompileSharedObject(self, text, ext):
        self.sconf.cached = 1
        # TODO: should use self.vardict for $SHCC, $CPPFLAGS, etc.
        return not self.TryBuild(self.env.SharedObject, text, ext)

    def RunProg(self, text, ext):
        self.sconf.cached = 1
        # TODO: should use self.vardict for $CC, $CPPFLAGS, etc.
        st, out = self.TryRun(text, ext)
        return not st, out

    def AppendLIBS(self, lib_name_list):
        oldLIBS = self.env.get( 'LIBS', [] )
        self.env.Append(LIBS = lib_name_list)
        return oldLIBS

    def PrependLIBS(self, lib_name_list):
        oldLIBS = self.env.get( 'LIBS', [] )
        self.env.Prepend(LIBS = lib_name_list)
        return oldLIBS

    def SetLIBS(self, val):
        oldLIBS = self.env.get( 'LIBS', [] )
        self.env.Replace(LIBS = val)
        return oldLIBS

    def Display(self, msg):
        if self.sconf.cached:
            # We assume that Display is called twice for each test here
            # once for the Checking for ... message and once for the result.
            # The self.sconf.cached flag can only be set between those calls
            msg = "(cached) " + msg
            self.sconf.cached = 0
        progress_display(msg, append_newline=0)
        self.Log("scons: Configure: " + msg + "\n")

    def Log(self, msg):
        if self.sconf.logstream is not None:
            self.sconf.logstream.write(msg)

    #### End of stuff used by Conftest.py.


def SConf(*args, **kw):
    if kw.get(build_type, True):
        kw['_depth'] = kw.get('_depth', 0) + 1
        for bt in build_types:
            try:
                del kw[bt]
            except KeyError:
                pass
        return SConfBase(*args, **kw)
    else:
        return SCons.Util.Null()


def CheckFunc(context, function_name, header = None, language = None):
    res = SCons.Conftest.CheckFunc(context, function_name, header = header, language = language)
    context.did_show_result = 1
    return not res

def CheckType(context, type_name, includes = "", language = None):
    res = SCons.Conftest.CheckType(context, type_name,
                                   header = includes, language = language)
    context.did_show_result = 1
    return not res

def CheckTypeSize(context, type_name, includes = "", language = None, expect = None):
    res = SCons.Conftest.CheckTypeSize(context, type_name,
                                       header = includes, language = language,
                                       expect = expect)
    context.did_show_result = 1
    return res

def CheckDeclaration(context, declaration, includes = "", language = None):
    res = SCons.Conftest.CheckDeclaration(context, declaration,
                                          includes = includes,
                                          language = language)
    context.did_show_result = 1
    return not res

def createIncludesFromHeaders(headers, leaveLast, include_quotes = '""'):
    # used by CheckHeader and CheckLibWithHeader to produce C - #include
    # statements from the specified header (list)
    if not SCons.Util.is_List(headers):
        headers = [headers]
    l = []
    if leaveLast:
        lastHeader = headers[-1]
        headers = headers[:-1]
    else:
        lastHeader = None
    for s in headers:
        l.append("#include %s%s%s\n"
                 % (include_quotes[0], s, include_quotes[1]))
    return ''.join(l), lastHeader

def CheckHeader(context, header, include_quotes = '<>', language = None):
    """
    A test for a C or C++ header file.
    """
    prog_prefix, hdr_to_check = \
                 createIncludesFromHeaders(header, 1, include_quotes)
    res = SCons.Conftest.CheckHeader(context, hdr_to_check, prog_prefix,
                                     language = language,
                                     include_quotes = include_quotes)
    context.did_show_result = 1
    return not res

def CheckCC(context):
    res = SCons.Conftest.CheckCC(context)
    context.did_show_result = 1
    return not res

def CheckCXX(context):
    res = SCons.Conftest.CheckCXX(context)
    context.did_show_result = 1
    return not res

def CheckSHCC(context):
    res = SCons.Conftest.CheckSHCC(context)
    context.did_show_result = 1
    return not res

def CheckSHCXX(context):
    res = SCons.Conftest.CheckSHCXX(context)
    context.did_show_result = 1
    return not res

# Bram: Make this function obsolete?  CheckHeader() is more generic.

def CheckCHeader(context, header, include_quotes = '""'):
    """
    A test for a C header file.
    """
    return CheckHeader(context, header, include_quotes, language = "C")


# Bram: Make this function obsolete?  CheckHeader() is more generic.

def CheckCXXHeader(context, header, include_quotes = '""'):
    """
    A test for a C++ header file.
    """
    return CheckHeader(context, header, include_quotes, language = "C++")


def CheckLib(context, library = None, symbol = "main",
             header = None, language = None, autoadd = 1):
    """
    A test for a library. See also CheckLibWithHeader.
    Note that library may also be None to test whether the given symbol
    compiles without flags.
    """

    if library == []:
        library = [None]

    if not SCons.Util.is_List(library):
        library = [library]

    # ToDo: accept path for the library
    res = SCons.Conftest.CheckLib(context, library, symbol, header = header,
                                        language = language, autoadd = autoadd)
    context.did_show_result = 1
    return not res

# XXX
# Bram: Can only include one header and can't use #ifdef HAVE_HEADER_H.

def CheckLibWithHeader(context, libs, header, language,
                       call = None, autoadd = 1):
    # ToDo: accept path for library. Support system header files.
    """
    Another (more sophisticated) test for a library.
    Checks, if library and header is available for language (may be 'C'
    or 'CXX'). Call maybe be a valid expression _with_ a trailing ';'.
    As in CheckLib, we support library=None, to test if the call compiles
    without extra link flags.
    """
    prog_prefix, dummy = \
                 createIncludesFromHeaders(header, 0)
    if libs == []:
        libs = [None]

    if not SCons.Util.is_List(libs):
        libs = [libs]

    res = SCons.Conftest.CheckLib(context, libs, None, prog_prefix,
            call = call, language = language, autoadd = autoadd)
    context.did_show_result = 1
    return not res

def CheckProg(context, prog_name):
    """Simple check if a program exists in the path.  Returns the path
    for the application, or None if not found.
    """
    res = SCons.Conftest.CheckProg(context, prog_name)
    context.did_show_result = 1
    return res

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