config/check_spidermonkey_style.py
author Petru Lingurar <petru.lingurar@softvision.ro>
Fri, 21 Dec 2018 08:56:47 +0000
changeset 501492 65621d0fe1262af0643cec37c23b2d9ec42588ad
parent 490083 7a34cfe5e1962171bf56bdb9dd162e538dfefc95
child 507730 02386132c1e9bfa3ef88b9ae7d967f90b6e1045e
permissions -rw-r--r--
Bug 1513938 - Enforce a Bundle size limit and drop `privateSession` if exceeds it. r=JanH, a=jcristau The `privateSession` key would normally allow persisting the Private Browsing session across OOMs in Activity's Bundle. We need to do that to avoid storing private, sensible data on disk like we do with the normal browsing session. In some cases `privateSession` would contain a lot of data which, along with other possible concurrent transactions could overflow Binder's buffer which has a limited fixed size, currently 1Mb. To avoid this, we will drop `privateSession` from the Bundle if the resulting size is greater than a _speculative_ size of 300KBs which would mean that in the case of an OOM all Private Browsing state would be lost. Bug 1515592 is filed to investigate for a better solution. Differential Revision: https://phabricator.services.mozilla.com/D15067

# vim: set ts=8 sts=4 et sw=4 tw=99:
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

# ----------------------------------------------------------------------------
# This script checks various aspects of SpiderMonkey code style.  The current checks are as
# follows.
#
# We check the following things in headers.
#
# - No cyclic dependencies.
#
# - No normal header should #include a inlines.h/-inl.h file.
#
# - #ifndef wrappers should have the right form. (XXX: not yet implemented)
#   - Every header file should have one.
#   - The guard name used should be appropriate for the filename.
#
# We check the following things in all files.
#
# - #includes should have full paths, e.g. "jit/Ion.h", not "Ion.h".
#
# - #includes should use the appropriate form for system headers (<...>) and
#   local headers ("...").
#
# - #includes should be ordered correctly.
#   - Each one should be in the correct section.
#   - Alphabetical order should be used within sections.
#   - Sections should be in the right order.
#   Note that the presence of #if/#endif blocks complicates things, to the
#   point that it's not always clear where a conditionally-compiled #include
#   statement should go, even to a human.  Therefore, we check the #include
#   statements within each #if/#endif block (including nested ones) in
#   isolation, but don't try to do any order checking between such blocks.
# ----------------------------------------------------------------------------

from __future__ import print_function

import difflib
import os
import re
import sys

# We don't bother checking files in these directories, because they're (a) auxiliary or (b)
# imported code that doesn't follow our coding style.
ignored_js_src_dirs = [
    'js/src/config/',            # auxiliary stuff
    'js/src/ctypes/libffi/',     # imported code
    'js/src/devtools/',          # auxiliary stuff
    'js/src/editline/',          # imported code
    'js/src/gdb/',               # auxiliary stuff
    'js/src/vtune/'              # imported code
]

# We ignore #includes of these files, because they don't follow the usual rules.
included_inclnames_to_ignore = set([
    'ffi.h',                    # generated in ctypes/libffi/
    'devtools/sharkctl.h',      # we ignore devtools/ in general
    'devtools/Instruments.h',   # we ignore devtools/ in general
    'double-conversion/double-conversion.h',  # strange MFBT case
    'javascript-trace.h',       # generated in $OBJDIR if HAVE_DTRACE is defined
    'frontend/ReservedWordsGenerated.h',  # generated in $OBJDIR
    'gc/StatsPhasesGenerated.h',         # generated in $OBJDIR
    'gc/StatsPhasesGenerated.cpp',       # generated in $OBJDIR
    'jit/LOpcodes.h',           # generated in $OBJDIR
    'jit/MOpcodes.h',           # generated in $OBJDIR
    'jscustomallocator.h',      # provided by embedders;  allowed to be missing
    'js-config.h',              # generated in $OBJDIR
    'fdlibm.h',                 # fdlibm
    'FuzzerDefs.h',             # included without a path
    'FuzzingInterface.h',       # included without a path
    'mozmemory.h',              # included without a path
    'pratom.h',                 # NSPR
    'prcvar.h',                 # NSPR
    'prerror.h',                # NSPR
    'prinit.h',                 # NSPR
    'prio.h',                   # NSPR
    'private/pprio.h',          # NSPR
    'prlink.h',                 # NSPR
    'prlock.h',                 # NSPR
    'prprf.h',                  # NSPR
    'prthread.h',               # NSPR
    'prtypes.h',                # NSPR
    'selfhosted.out.h',         # generated in $OBJDIR
    'shellmoduleloader.out.h',  # generated in $OBJDIR
    'unicode/basictz.h',        # ICU
    'unicode/locid.h',          # ICU
    'unicode/plurrule.h',       # ICU
    'unicode/timezone.h',       # ICU
    'unicode/ucal.h',           # ICU
    'unicode/uchar.h',          # ICU
    'unicode/uclean.h',         # ICU
    'unicode/ucol.h',           # ICU
    'unicode/udat.h',           # ICU
    'unicode/udatpg.h',         # ICU
    'unicode/udisplaycontext.h',  # ICU
    'unicode/uenum.h',          # ICU
    'unicode/uloc.h',           # ICU
    'unicode/unistr.h',         # ICU
    'unicode/unorm2.h',         # ICU
    'unicode/unum.h',           # ICU
    'unicode/unumsys.h',        # ICU
    'unicode/upluralrules.h',   # ICU
    'unicode/ureldatefmt.h',    # ICU
    'unicode/ustring.h',        # ICU
    'unicode/utypes.h',         # ICU
    'unicode/uversion.h',       # ICU
    'vtune/VTuneWrapper.h'      # VTune
])

# These files have additional constraints on where they are #included, so we
# ignore #includes of them when checking #include ordering.
oddly_ordered_inclnames = set([
    'ctypes/typedefs.h',        # Included multiple times in the body of ctypes/CTypes.h
    'frontend/BinSource-auto.h',  # Included in the body of frontend/BinSource.h
    # Included in the body of frontend/TokenStream.h
    'frontend/ReservedWordsGenerated.h',
    'gc/StatsPhasesGenerated.h',         # Included in the body of gc/Statistics.h
    'gc/StatsPhasesGenerated.cpp',       # Included in the body of gc/Statistics.cpp
    'psapi.h',                  # Must be included after "util/Windows.h" on Windows
    'machine/endian.h',         # Must be included after <sys/types.h> on BSD
    'winbase.h',                # Must precede other system headers(?)
    'windef.h'                  # Must precede other system headers(?)
])

# The files in tests/style/ contain code that fails this checking in various
# ways.  Here is the output we expect.  If the actual output differs from
# this, one of the following must have happened.
# - New SpiderMonkey code violates one of the checked rules.
# - The tests/style/ files have changed without expected_output being changed
#   accordingly.
# - This script has been broken somehow.
#
expected_output = '''\
js/src/tests/style/BadIncludes.h:3: error:
    the file includes itself

js/src/tests/style/BadIncludes.h:6: error:
    "BadIncludes2.h" is included using the wrong path;
    did you forget a prefix, or is the file not yet committed?

js/src/tests/style/BadIncludes.h:8: error:
    <tests/style/BadIncludes2.h> should be included using
    the #include "..." form

js/src/tests/style/BadIncludes.h:10: error:
    "stdio.h" is included using the wrong path;
    did you forget a prefix, or is the file not yet committed?

js/src/tests/style/BadIncludes2.h:1: error:
    vanilla header includes an inline-header file "tests/style/BadIncludes2-inl.h"

js/src/tests/style/BadIncludesOrder-inl.h:5:6: error:
    "vm/JSScript-inl.h" should be included after "vm/Interpreter-inl.h"

js/src/tests/style/BadIncludesOrder-inl.h:6:7: error:
    "vm/Interpreter-inl.h" should be included after "js/Value.h"

js/src/tests/style/BadIncludesOrder-inl.h:7:8: error:
    "js/Value.h" should be included after "ds/LifoAlloc.h"

js/src/tests/style/BadIncludesOrder-inl.h:8:9: error:
    "ds/LifoAlloc.h" should be included after "jsapi.h"

js/src/tests/style/BadIncludesOrder-inl.h:9:10: error:
    "jsapi.h" should be included after <stdio.h>

js/src/tests/style/BadIncludesOrder-inl.h:10:11: error:
    <stdio.h> should be included after "mozilla/HashFunctions.h"

js/src/tests/style/BadIncludesOrder-inl.h:28:29: error:
    "vm/JSScript.h" should be included after "vm/JSFunction.h"

(multiple files): error:
    header files form one or more cycles

   tests/style/HeaderCycleA1.h
   -> tests/style/HeaderCycleA2.h
      -> tests/style/HeaderCycleA3.h
         -> tests/style/HeaderCycleA1.h

   tests/style/HeaderCycleB1-inl.h
   -> tests/style/HeaderCycleB2-inl.h
      -> tests/style/HeaderCycleB3-inl.h
         -> tests/style/HeaderCycleB4-inl.h
            -> tests/style/HeaderCycleB1-inl.h
            -> tests/style/jsheadercycleB5inlines.h
               -> tests/style/HeaderCycleB1-inl.h
      -> tests/style/HeaderCycleB4-inl.h

'''.splitlines(True)

actual_output = []


def out(*lines):
    for line in lines:
        actual_output.append(line + '\n')


def error(filename, linenum, *lines):
    location = filename
    if linenum is not None:
        location += ':' + str(linenum)
    out(location + ': error:')
    for line in (lines):
        out('    ' + line)
    out('')


class FileKind(object):
    C = 1
    CPP = 2
    INL_H = 3
    H = 4
    TBL = 5
    MSG = 6

    @staticmethod
    def get(filename):
        if filename.endswith('.c'):
            return FileKind.C

        if filename.endswith('.cpp'):
            return FileKind.CPP

        if filename.endswith(('inlines.h', '-inl.h')):
            return FileKind.INL_H

        if filename.endswith('.h'):
            return FileKind.H

        if filename.endswith('.tbl'):
            return FileKind.TBL

        if filename.endswith('.msg'):
            return FileKind.MSG

        error(filename, None, 'unknown file kind')


def check_style(enable_fixup):
    # We deal with two kinds of name.
    # - A "filename" is a full path to a file from the repository root.
    # - An "inclname" is how a file is referred to in a #include statement.
    #
    # Examples (filename -> inclname)
    # - "mfbt/Attributes.h"         -> "mozilla/Attributes.h"
    # - "mfbt/decimal/Decimal.h     -> "mozilla/Decimal.h"
    # - "mozglue/misc/TimeStamp.h   -> "mozilla/TimeStamp.h"
    # - "memory/mozalloc/mozalloc.h -> "mozilla/mozalloc.h"
    # - "js/public/Vector.h"        -> "js/Vector.h"
    # - "js/src/vm/String.h"        -> "vm/String.h"

    non_js_dirnames = ('mfbt/',
                       'memory/mozalloc/',
                       'mozglue/')  # type: tuple(str)
    non_js_inclnames = set()        # type: set(inclname)
    js_names = dict()               # type: dict(filename, inclname)

    # Process files in js/src.
    js_src_root = os.path.join('js', 'src')
    for dirpath, dirnames, filenames in os.walk(js_src_root):
        if dirpath == js_src_root:
            # Skip any subdirectories that contain a config.status file
            # (likely objdirs).
            builddirs = []
            for dirname in dirnames:
                path = os.path.join(dirpath, dirname, 'config.status')
                if os.path.isfile(path):
                    builddirs.append(dirname)
            for dirname in builddirs:
                dirnames.remove(dirname)
        for filename in filenames:
            filepath = os.path.join(dirpath, filename).replace('\\', '/')
            if not filepath.startswith(tuple(ignored_js_src_dirs)) and \
               filepath.endswith(('.c', '.cpp', '.h', '.tbl', '.msg')):
                inclname = filepath[len('js/src/'):]
                js_names[filepath] = inclname

    # Look for header files in directories in non_js_dirnames.
    for non_js_dir in non_js_dirnames:
        for dirpath, dirnames, filenames in os.walk(non_js_dir):
            for filename in filenames:
                if filename.endswith('.h'):
                    inclname = 'mozilla/' + filename
                    non_js_inclnames.add(inclname)

    # Look for header files in js/public.
    js_public_root = os.path.join('js', 'public')
    for dirpath, dirnames, filenames in os.walk(js_public_root):
        for filename in filenames:
            if filename.endswith('.h'):
                filepath = os.path.join(dirpath, filename).replace('\\', '/')
                inclname = 'js/' + filepath[len('js/public/'):]
                js_names[filepath] = inclname

    all_inclnames = non_js_inclnames | set(js_names.values())

    edges = dict()      # type: dict(inclname, set(inclname))

    # We don't care what's inside the MFBT and MOZALLOC files, but because they
    # are #included from JS files we have to add them to the inclusion graph.
    for inclname in non_js_inclnames:
        edges[inclname] = set()

    # Process all the JS files.
    for filename in sorted(js_names.keys()):
        inclname = js_names[filename]
        file_kind = FileKind.get(filename)
        if file_kind == FileKind.C or file_kind == FileKind.CPP or \
           file_kind == FileKind.H or file_kind == FileKind.INL_H:
            included_h_inclnames = set()    # type: set(inclname)

            with open(filename) as f:
                code = read_file(f)

            if enable_fixup:
                code = code.sorted(inclname)
                with open(filename, 'w') as f:
                    f.write(code.to_source())

            check_file(filename, inclname, file_kind, code,
                       all_inclnames, included_h_inclnames)

        edges[inclname] = included_h_inclnames

    find_cycles(all_inclnames, edges)

    # Compare expected and actual output.
    difflines = difflib.unified_diff(expected_output, actual_output,
                                     fromfile='check_spidermonkey_style.py expected output',
                                     tofile='check_spidermonkey_style.py actual output')
    ok = True
    for diffline in difflines:
        ok = False
        print(diffline, end='')

    return ok


def module_name(name):
    '''Strip the trailing .cpp, .h, inlines.h or -inl.h from a filename.'''

    return name.replace('inlines.h', '').replace('-inl.h', '').replace('.h', '').replace('.cpp', '')  # NOQA: E501


def is_module_header(enclosing_inclname, header_inclname):
    '''Determine if an included name is the "module header", i.e. should be
    first in the file.'''

    module = module_name(enclosing_inclname)

    # Normal case, e.g. module == "foo/Bar", header_inclname == "foo/Bar.h".
    if module == module_name(header_inclname):
        return True

    # A public header, e.g. module == "foo/Bar", header_inclname == "js/Bar.h".
    m = re.match(r'js\/(.*)\.h', header_inclname)
    if m is not None and module.endswith('/' + m.group(1)):
        return True

    return False


class Include(object):
    '''Important information for a single #include statement.'''

    def __init__(self, include_prefix, inclname, line_suffix, linenum, is_system):
        self.include_prefix = include_prefix
        self.line_suffix = line_suffix
        self.inclname = inclname
        self.linenum = linenum
        self.is_system = is_system

    def is_style_relevant(self):
        # Includes are style-relevant; that is, they're checked by the pairwise
        # style-checking algorithm in check_file.
        return True

    def section(self, enclosing_inclname):
        '''Identify which section inclname belongs to.

        The section numbers are as follows.
          0. Module header (e.g. jsfoo.h or jsfooinlines.h within jsfoo.cpp)
          1. mozilla/Foo.h
          2. <foo.h> or <foo>
          3. jsfoo.h, prmjtime.h, etc
          4. foo/Bar.h
          5. jsfooinlines.h
          6. foo/Bar-inl.h
          7. non-.h, e.g. *.tbl, *.msg
        '''

        if self.is_system:
            return 2

        if not self.inclname.endswith('.h'):
            return 7

        # A couple of modules have the .h file in js/ and the .cpp file elsewhere and so need
        # special handling.
        if is_module_header(enclosing_inclname, self.inclname):
            return 0

        if '/' in self.inclname:
            if self.inclname.startswith('mozilla/'):
                return 1

            if self.inclname.endswith('-inl.h'):
                return 6

            return 4

        if self.inclname.endswith('inlines.h'):
            return 5

        return 3

    def quote(self):
        if self.is_system:
            return '<' + self.inclname + '>'
        else:
            return '"' + self.inclname + '"'

    def sort_key(self, enclosing_inclname):
        return (self.section(enclosing_inclname), self.inclname.lower())

    def to_source(self):
        return self.include_prefix + self.quote() + self.line_suffix + '\n'


class CppBlock(object):
    '''C preprocessor block: a whole file or a single #if/#elif/#else block.

    A #if/#endif block is the contents of a #if/#endif (or similar) section.
    The top-level block, which is not within a #if/#endif pair, is also
    considered a block.

    Each kid is either an Include (representing a #include), OrdinaryCode, or
    a nested CppBlock.'''

    def __init__(self, start_line=""):
        self.start = start_line
        self.end = ''
        self.kids = []

    def is_style_relevant(self):
        return True

    def append_ordinary_line(self, line):
        if len(self.kids) == 0 or not isinstance(self.kids[-1], OrdinaryCode):
            self.kids.append(OrdinaryCode())
        self.kids[-1].lines.append(line)

    def style_relevant_kids(self):
        """ Return a list of kids in this block that are style-relevant. """
        return [kid for kid in self.kids if kid.is_style_relevant()]

    def sorted(self, enclosing_inclname):
        """Return a hopefully-sorted copy of this block. Implements --fixup.

        When in doubt, this leaves the code unchanged.
        """

        def pretty_sorted_includes(includes):
            """ Return a new list containing the given includes, in order,
            with blank lines separating sections. """
            keys = [inc.sort_key(enclosing_inclname) for inc in includes]
            if sorted(keys) == keys:
                return includes  # if nothing is out of order, don't touch anything

            output = []
            current_section = None
            for (section, _), inc in sorted(zip(keys, includes)):
                if current_section is not None and section != current_section:
                    output.append(OrdinaryCode(["\n"]))  # blank line
                output.append(inc)
                current_section = section
            return output

        def should_try_to_sort(includes):
            if 'tests/style/BadIncludes' in enclosing_inclname:
                return False  # don't straighten the counterexample
            if any(inc.inclname in oddly_ordered_inclnames for inc in includes):
                return False  # don't sort batches containing odd includes
            if includes == sorted(includes, key=lambda inc: inc.sort_key(enclosing_inclname)):
                return False  # it's already sorted, avoid whitespace-only fixups
            return True

        # The content of the eventual output of this method.
        output = []

        # The current batch of includes to sort. This list only ever contains Include objects
        # and whitespace OrdinaryCode objects.
        batch = []

        def flush_batch():
            """Sort the contents of `batch` and move it to `output`."""

            assert all(isinstance(item, Include)
                       or (isinstance(item, OrdinaryCode) and "".join(item.lines).isspace())
                       for item in batch)

            # Here we throw away the blank lines.
            # `pretty_sorted_includes` puts them back.
            includes = []
            last_include_index = -1
            for i, item in enumerate(batch):
                if isinstance(item, Include):
                    includes.append(item)
                    last_include_index = i
            cutoff = last_include_index + 1

            if should_try_to_sort(includes):
                output.extend(pretty_sorted_includes(
                    includes) + batch[cutoff:])
            else:
                output.extend(batch)
            del batch[:]

        for kid in self.kids:
            if isinstance(kid, CppBlock):
                flush_batch()
                output.append(kid.sorted(enclosing_inclname))
            elif isinstance(kid, Include):
                batch.append(kid)
            else:
                assert isinstance(kid, OrdinaryCode)
                if kid.to_source().isspace():
                    batch.append(kid)
                else:
                    flush_batch()
                    output.append(kid)
        flush_batch()

        result = CppBlock()
        result.start = self.start
        result.end = self.end
        result.kids = output
        return result

    def to_source(self):
        return self.start + ''.join(kid.to_source() for kid in self.kids) + self.end


class OrdinaryCode(object):
    ''' A list of lines of code that aren't #include/#if/#else/#endif lines. '''

    def __init__(self, lines=None):
        self.lines = lines if lines is not None else []

    def is_style_relevant(self):
        return False

    def to_source(self):
        return ''.join(self.lines)


# A "snippet" is one of:
#
# *   Include - representing an #include line
# *   CppBlock - a whole file or #if/#elif/#else block; contains a list of snippets
# *   OrdinaryCode - representing lines of non-#include-relevant code

def read_file(f):
    block_stack = [CppBlock()]

    # Extract the #include statements as a tree of snippets.
    for linenum, line in enumerate(f, start=1):
        if line.lstrip().startswith('#'):
            # Look for a |#include "..."| line.
            m = re.match(r'(\s*#\s*include\s+)"([^"]*)"(.*)', line)
            if m is not None:
                prefix, inclname, suffix = m.groups()
                block_stack[-1].kids.append(Include(prefix,
                                                    inclname, suffix, linenum, is_system=False))
                continue

            # Look for a |#include <...>| line.
            m = re.match(r'(\s*#\s*include\s+)<([^>]*)>(.*)', line)
            if m is not None:
                prefix, inclname, suffix = m.groups()
                block_stack[-1].kids.append(Include(prefix,
                                                    inclname, suffix, linenum, is_system=True))
                continue

            # Look for a |#{if,ifdef,ifndef}| line.
            m = re.match(r'\s*#\s*(if|ifdef|ifndef)\b', line)
            if m is not None:
                # Open a new block.
                new_block = CppBlock(line)
                block_stack[-1].kids.append(new_block)
                block_stack.append(new_block)
                continue

            # Look for a |#{elif,else}| line.
            m = re.match(r'\s*#\s*(elif|else)\b', line)
            if m is not None:
                # Close the current block, and open an adjacent one.
                block_stack.pop()
                new_block = CppBlock(line)
                block_stack[-1].kids.append(new_block)
                block_stack.append(new_block)
                continue

            # Look for a |#endif| line.
            m = re.match(r'\s*#\s*endif\b', line)
            if m is not None:
                # Close the current block.
                block_stack.pop().end = line
                if len(block_stack) == 0:
                    raise ValueError(
                        "#endif without #if at line " + str(linenum))
                continue

        # Otherwise, we have an ordinary line.
        block_stack[-1].append_ordinary_line(line)

    if len(block_stack) > 1:
        raise ValueError("unmatched #if")
    return block_stack[-1]


def check_file(filename, inclname, file_kind, code, all_inclnames, included_h_inclnames):

    def check_include_statement(include):
        '''Check the style of a single #include statement.'''

        if include.is_system:
            # Check it is not a known local file (in which case it's probably a system header).
            if include.inclname in included_inclnames_to_ignore or \
               include.inclname in all_inclnames:
                error(filename, include.linenum,
                      include.quote() + ' should be included using',
                      'the #include "..." form')

        else:
            if include.inclname not in included_inclnames_to_ignore:
                included_kind = FileKind.get(include.inclname)

                # Check the #include path has the correct form.
                if include.inclname not in all_inclnames:
                    error(filename, include.linenum,
                          include.quote() + ' is included using the wrong path;',
                          'did you forget a prefix, or is the file not yet committed?')

                # Record inclusions of .h files for cycle detection later.
                # (Exclude .tbl and .msg files.)
                elif included_kind == FileKind.H or included_kind == FileKind.INL_H:
                    included_h_inclnames.add(include.inclname)

                # Check a H file doesn't #include an INL_H file.
                if file_kind == FileKind.H and included_kind == FileKind.INL_H:
                    error(filename, include.linenum,
                          'vanilla header includes an inline-header file ' + include.quote())

                # Check a file doesn't #include itself.  (We do this here because the cycle
                # detection below doesn't detect this case.)
                if inclname == include.inclname:
                    error(filename, include.linenum,
                          'the file includes itself')

    def check_includes_order(include1, include2):
        '''Check the ordering of two #include statements.'''

        if include1.inclname in oddly_ordered_inclnames or \
           include2.inclname in oddly_ordered_inclnames:
            return

        section1 = include1.section(inclname)
        section2 = include2.section(inclname)
        if (section1 > section2) or \
           ((section1 == section2) and (include1.inclname.lower() > include2.inclname.lower())):
            error(filename, str(include1.linenum) + ':' + str(include2.linenum),
                  include1.quote() + ' should be included after ' + include2.quote())

    # Check the extracted #include statements, both individually, and the ordering of
    # adjacent pairs that live in the same block.
    def pair_traverse(prev, this):
        if isinstance(this, Include):
            check_include_statement(this)
            if isinstance(prev, Include):
                check_includes_order(prev, this)
        else:
            kids = this.style_relevant_kids()
            for prev2, this2 in zip([None] + kids[0:-1], kids):
                pair_traverse(prev2, this2)

    pair_traverse(None, code)


def find_cycles(all_inclnames, edges):
    '''Find and draw any cycles.'''

    SCCs = tarjan(all_inclnames, edges)

    # The various sorted() calls below ensure the output is deterministic.

    def draw_SCC(c):
        cset = set(c)
        drawn = set()

        def draw(v, indent):
            out('   ' * indent + ('-> ' if indent else '   ') + v)
            if v in drawn:
                return
            drawn.add(v)
            for succ in sorted(edges[v]):
                if succ in cset:
                    draw(succ, indent + 1)
        draw(sorted(c)[0], 0)
        out('')

    have_drawn_an_SCC = False
    for scc in sorted(SCCs):
        if len(scc) != 1:
            if not have_drawn_an_SCC:
                error('(multiple files)', None,
                      'header files form one or more cycles')
                have_drawn_an_SCC = True

            draw_SCC(scc)


# Tarjan's algorithm for finding the strongly connected components (SCCs) of a graph.
# https://en.wikipedia.org/wiki/Tarjan%27s_strongly_connected_components_algorithm
def tarjan(V, E):
    vertex_index = {}
    vertex_lowlink = {}
    index = 0
    S = []
    all_SCCs = []

    def strongconnect(v, index):
        # Set the depth index for v to the smallest unused index
        vertex_index[v] = index
        vertex_lowlink[v] = index
        index += 1
        S.append(v)

        # Consider successors of v
        for w in E[v]:
            if w not in vertex_index:
                # Successor w has not yet been visited; recurse on it
                index = strongconnect(w, index)
                vertex_lowlink[v] = min(vertex_lowlink[v], vertex_lowlink[w])
            elif w in S:
                # Successor w is in stack S and hence in the current SCC
                vertex_lowlink[v] = min(vertex_lowlink[v], vertex_index[w])

        # If v is a root node, pop the stack and generate an SCC
        if vertex_lowlink[v] == vertex_index[v]:
            i = S.index(v)
            scc = S[i:]
            del S[i:]
            all_SCCs.append(scc)

        return index

    for v in V:
        if v not in vertex_index:
            index = strongconnect(v, index)

    return all_SCCs


def main():
    if sys.argv[1:] == ["--fixup"]:
        # Sort #include directives in-place.  Fixup mode doesn't solve
        # all possible silliness that the script checks for; it's just a
        # hack for the common case where renaming a header causes style
        # errors.
        fixup = True
    elif sys.argv[1:] == []:
        fixup = False
    else:
        print("TEST-UNEXPECTED-FAIL | check_spidermonkey_style.py | unexpected command "
              "line options: " + repr(sys.argv[1:]))
        sys.exit(1)

    ok = check_style(fixup)

    if ok:
        print('TEST-PASS | check_spidermonkey_style.py | ok')
    else:
        print('TEST-UNEXPECTED-FAIL | check_spidermonkey_style.py | ' +
              'actual output does not match expected output;  diff is above.')
        print('TEST-UNEXPECTED-FAIL | check_spidermonkey_style.py | ' +
              'Hint: If the problem is that you renamed a header, and many #includes ' +
              'are no longer in alphabetical order, commit your work and then try ' +
              '`check_spidermonkey_style.py --fixup`. ' +
              'You need to commit first because --fixup modifies your files in place.')

    sys.exit(0 if ok else 1)


if __name__ == '__main__':
    main()