isolate_format.py

# Copyright 2014 The Swarming Authors. All rights reserved.
# Use of this source code is governed under the Apache License, Version 2.0 that
# can be found in the LICENSE file.

"""Contains logic to parse .isolate files.

This module doesn't touch the file system. It's the job of the client code to do
I/O on behalf of this module.

See more information at
  https://code.google.com/p/swarming/wiki/IsolateDesign
  https://code.google.com/p/swarming/wiki/IsolateUserGuide
"""

import ast
import itertools
import logging
import os
import posixpath
import re
import sys

from utils import short_expression_finder

# Files that should be 0-length when mapped.
KEY_TOUCHED = 'isolate_dependency_touched'
# Files that should be tracked by the build tool.
KEY_TRACKED = 'isolate_dependency_tracked'
# Files that should not be tracked by the build tool.
KEY_UNTRACKED = 'isolate_dependency_untracked'

# Valid variable name.
VALID_VARIABLE = '[A-Za-z_][A-Za-z_0-9]*'


class IsolateError(ValueError):
  """Generic failure to load a .isolate file."""
  pass


def determine_root_dir(relative_root, infiles):
  """For a list of infiles, determines the deepest root directory that is
  referenced indirectly.

  All arguments must be using os.path.sep.
  """
  # The trick used to determine the root directory is to look at "how far" back
  # up it is looking up.
  deepest_root = relative_root
  for i in infiles:
    x = relative_root
    while i.startswith('..' + os.path.sep):
      i = i[3:]
      assert not i.startswith(os.path.sep)
      x = os.path.dirname(x)
    if deepest_root.startswith(x):
      deepest_root = x
  logging.info(
      'determine_root_dir(%s, %d files) -> %s',
      relative_root, len(infiles), deepest_root)
  return deepest_root


def replace_variable(part, variables):
  m = re.match(r'<\((' + VALID_VARIABLE + ')\)', part)
  if m:
    if m.group(1) not in variables:
      raise IsolateError(
        'Variable "%s" was not found in %s.\nDid you forget to specify '
        '--path-variable?' % (m.group(1), variables))
    return str(variables[m.group(1)])
  return part


def eval_variables(item, variables):
  """Replaces the .isolate variables in a string item.

  Note that the .isolate format is a subset of the .gyp dialect.
  """
  return ''.join(
      replace_variable(p, variables)
      for p in re.split(r'(<\(' + VALID_VARIABLE + '\))', item))


def split_touched(files):
  """Splits files that are touched vs files that are read."""
  tracked = []
  touched = []
  for f in files:
    if f.size:
      tracked.append(f)
    else:
      touched.append(f)
  return tracked, touched


def pretty_print(variables, stdout):
  """Outputs a .isolate file from the decoded variables.

  The .isolate format is GYP compatible.

  Similar to pprint.print() but with NIH syndrome.
  """
  # Order the dictionary keys by these keys in priority.
  ORDER = (
      'variables', 'condition', 'command', 'read_only',
      KEY_TRACKED, KEY_UNTRACKED)

  def sorting_key(x):
    """Gives priority to 'most important' keys before the others."""
    if x in ORDER:
      return str(ORDER.index(x))
    return x

  def loop_list(indent, items):
    for item in items:
      if isinstance(item, basestring):
        stdout.write('%s\'%s\',\n' % (indent, item))
      elif isinstance(item, dict):
        stdout.write('%s{\n' % indent)
        loop_dict(indent + '  ', item)
        stdout.write('%s},\n' % indent)
      elif isinstance(item, list):
        # A list inside a list will write the first item embedded.
        stdout.write('%s[' % indent)
        for index, i in enumerate(item):
          if isinstance(i, basestring):
            stdout.write(
                '\'%s\', ' % i.replace('\\', '\\\\').replace('\'', '\\\''))
          elif isinstance(i, dict):
            stdout.write('{\n')
            loop_dict(indent + '  ', i)
            if index != len(item) - 1:
              x = ', '
            else:
              x = ''
            stdout.write('%s}%s' % (indent, x))
          else:
            assert False
        stdout.write('],\n')
      else:
        assert False

  def loop_dict(indent, items):
    for key in sorted(items, key=sorting_key):
      item = items[key]
      stdout.write("%s'%s': " % (indent, key))
      if isinstance(item, dict):
        stdout.write('{\n')
        loop_dict(indent + '  ', item)
        stdout.write(indent + '},\n')
      elif isinstance(item, list):
        stdout.write('[\n')
        loop_list(indent + '  ', item)
        stdout.write(indent + '],\n')
      elif isinstance(item, basestring):
        stdout.write(
            '\'%s\',\n' % item.replace('\\', '\\\\').replace('\'', '\\\''))
      elif isinstance(item, (int, bool)) or item is None:
        stdout.write('%s,\n' % item)
      else:
        assert False, item

  stdout.write('{\n')
  loop_dict('  ', variables)
  stdout.write('}\n')


def print_all(comment, data, stream):
  """Prints a complete .isolate file and its top-level file comment into a
  stream.
  """
  if comment:
    stream.write(comment)
  pretty_print(data, stream)


def extract_comment(content):
  """Extracts file level comment."""
  out = []
  for line in content.splitlines(True):
    if line.startswith('#'):
      out.append(line)
    else:
      break
  return ''.join(out)


def eval_content(content):
  """Evaluates a python file and return the value defined in it.

  Used in practice for .isolate files.
  """
  globs = {'__builtins__': None}
  locs = {}
  try:
    value = eval(content, globs, locs)
  except TypeError as e:
    e.args = list(e.args) + [content]
    raise
  assert locs == {}, locs
  assert globs == {'__builtins__': None}, globs
  return value


def match_configs(expr, config_variables, all_configs):
  """Returns the list of values from |values| that match the condition |expr|.

  Arguments:
    expr: string that is evaluatable with eval(). It is a GYP condition.
    config_variables: list of the name of the variables.
    all_configs: list of the list of possible values.

  If a variable is not referenced at all, it is marked as unbounded (free) with
  a value set to None.
  """
  # It is more than just eval'ing the variable, it needs to be double checked to
  # see if the variable is referenced at all. If not, the variable is free
  # (unbounded).
  # TODO(maruel): Use the intelligent way by inspecting expr instead of doing
  # trial and error to figure out which variable is bound.
  combinations = []
  for bound_variables in itertools.product(
      (True, False), repeat=len(config_variables)):
    # Add the combination of variables bound.
    combinations.append(
        (
          [c for c, b in zip(config_variables, bound_variables) if b],
          set(
            tuple(v if b else None for v, b in zip(line, bound_variables))
            for line in all_configs)
        ))

  out = []
  for variables, configs in combinations:
    # Strip variables and see if expr can still be evaluated.
    for values in configs:
      globs = {'__builtins__': None}
      globs.update(zip(variables, (v for v in values if v is not None)))
      try:
        assertion = eval(expr, globs, {})
      except NameError:
        continue
      if not isinstance(assertion, bool):
        raise IsolateError('Invalid condition')
      if assertion:
        out.append(values)
  return out


def verify_variables(variables):
  """Verifies the |variables| dictionary is in the expected format."""
  VALID_VARIABLES = [
    KEY_TOUCHED,
    KEY_TRACKED,
    KEY_UNTRACKED,
    'command',
    'read_only',
  ]
  assert isinstance(variables, dict), variables
  assert set(VALID_VARIABLES).issuperset(set(variables)), variables.keys()
  for name, value in variables.iteritems():
    if name == 'read_only':
      assert value in (0, 1, 2, None), value
    else:
      assert isinstance(value, list), value
      assert all(isinstance(i, basestring) for i in value), value


def verify_ast(expr, variables_and_values):
  """Verifies that |expr| is of the form
  expr ::= expr ( "or" | "and" ) expr
         | identifier "==" ( string | int )
  Also collects the variable identifiers and string/int values in the dict
  |variables_and_values|, in the form {'var': set([val1, val2, ...]), ...}.
  """
  assert isinstance(expr, (ast.BoolOp, ast.Compare))
  if isinstance(expr, ast.BoolOp):
    assert isinstance(expr.op, (ast.And, ast.Or))
    for subexpr in expr.values:
      verify_ast(subexpr, variables_and_values)
  else:
    assert isinstance(expr.left.ctx, ast.Load)
    assert len(expr.ops) == 1
    assert isinstance(expr.ops[0], ast.Eq)
    var_values = variables_and_values.setdefault(expr.left.id, set())
    rhs = expr.comparators[0]
    assert isinstance(rhs, (ast.Str, ast.Num))
    var_values.add(rhs.n if isinstance(rhs, ast.Num) else rhs.s)


def verify_condition(condition, variables_and_values):
  """Verifies the |condition| dictionary is in the expected format.
  See verify_ast() for the meaning of |variables_and_values|.
  """
  VALID_INSIDE_CONDITION = ['variables']
  assert isinstance(condition, list), condition
  assert len(condition) == 2, condition
  expr, then = condition

  test_ast = compile(expr, '<condition>', 'eval', ast.PyCF_ONLY_AST)
  verify_ast(test_ast.body, variables_and_values)

  assert isinstance(then, dict), then
  assert set(VALID_INSIDE_CONDITION).issuperset(set(then)), then.keys()
  if not 'variables' in then:
    raise IsolateError('Missing \'variables\' in condition %s' % condition)
  verify_variables(then['variables'])


def verify_root(value, variables_and_values):
  """Verifies that |value| is the parsed form of a valid .isolate file.

  See verify_ast() for the meaning of |variables_and_values|.
  """
  VALID_ROOTS = ['includes', 'conditions', 'variables']
  assert isinstance(value, dict), value
  assert set(VALID_ROOTS).issuperset(set(value)), value.keys()

  includes = value.get('includes', [])
  assert isinstance(includes, list), includes
  for include in includes:
    assert isinstance(include, basestring), include

  conditions = value.get('conditions', [])
  assert isinstance(conditions, list), conditions
  for condition in conditions:
    verify_condition(condition, variables_and_values)

  variables = value.get('variables', {})
  verify_variables(variables)


def remove_weak_dependencies(values, key, item, item_configs):
  """Removes any configs from this key if the item is already under a
  strong key.
  """
  if key == KEY_TOUCHED:
    item_configs = set(item_configs)
    for stronger_key in (KEY_TRACKED, KEY_UNTRACKED):
      try:
        item_configs -= values[stronger_key][item]
      except KeyError:
        pass

  return item_configs


def remove_repeated_dependencies(folders, key, item, item_configs):
  """Removes any configs from this key if the item is in a folder that is
  already included."""

  if key in (KEY_UNTRACKED, KEY_TRACKED, KEY_TOUCHED):
    item_configs = set(item_configs)
    for (folder, configs) in folders.iteritems():
      if folder != item and item.startswith(folder):
        item_configs -= configs

  return item_configs


def get_folders(values_dict):
  """Returns a dict of all the folders in the given value_dict."""
  return dict(
    (item, configs) for (item, configs) in values_dict.iteritems()
    if item.endswith('/')
  )


def invert_map(variables):
  """Converts {config: {deptype: list(depvals)}} to
  {deptype: {depval: set(configs)}}.
  """
  KEYS = (
    KEY_TOUCHED,
    KEY_TRACKED,
    KEY_UNTRACKED,
    'command',
    'read_only',
  )
  out = dict((key, {}) for key in KEYS)
  for config, values in variables.iteritems():
    for key in KEYS:
      if key == 'command':
        items = [tuple(values[key])] if key in values else []
      elif key == 'read_only':
        items = [values[key]] if key in values else []
      else:
        assert key in (KEY_TOUCHED, KEY_TRACKED, KEY_UNTRACKED)
        items = values.get(key, [])
      for item in items:
        out[key].setdefault(item, set()).add(config)
  return out


def reduce_inputs(values):
  """Reduces the output of invert_map() to the strictest minimum list.

  Looks at each individual file and directory, maps where they are used and
  reconstructs the inverse dictionary.

  Returns the minimized dictionary.
  """
  KEYS = (
    KEY_TOUCHED,
    KEY_TRACKED,
    KEY_UNTRACKED,
    'command',
    'read_only',
  )

  # Folders can only live in KEY_UNTRACKED.
  folders = get_folders(values.get(KEY_UNTRACKED, {}))

  out = dict((key, {}) for key in KEYS)
  for key in KEYS:
    for item, item_configs in values.get(key, {}).iteritems():
      item_configs = remove_weak_dependencies(values, key, item, item_configs)
      item_configs = remove_repeated_dependencies(
          folders, key, item, item_configs)
      if item_configs:
        out[key][item] = item_configs
  return out


def convert_map_to_isolate_dict(values, config_variables):
  """Regenerates back a .isolate configuration dict from files and dirs
  mappings generated from reduce_inputs().
  """
  # Gather a list of configurations for set inversion later.
  all_mentioned_configs = set()
  for configs_by_item in values.itervalues():
    for configs in configs_by_item.itervalues():
      all_mentioned_configs.update(configs)

  # Invert the mapping to make it dict first.
  conditions = {}
  for key in values:
    for item, configs in values[key].iteritems():
      then = conditions.setdefault(frozenset(configs), {})
      variables = then.setdefault('variables', {})

      if key == 'read_only':
        if not isinstance(item, int):
          raise IsolateError(
              'Unexpected entry type %r for key %s' % (item, key))
        variables[key] = item
      elif key == 'command':
        if not isinstance(item, tuple):
          raise IsolateError(
              'Unexpected entry type %r for key %s' % (item, key))
        if key in variables:
          raise IsolateError('Unexpected duplicate key %s' % key)
        if not item:
          raise IsolateError('Expected non empty entry in %s' % key)
        variables[key] = list(item)
      elif key in (KEY_TOUCHED, KEY_TRACKED, KEY_UNTRACKED):
        if not isinstance(item, basestring):
          raise IsolateError('Unexpected entry type %r' % item)
        if not item:
          raise IsolateError('Expected non empty entry in %s' % key)
        # The list of items (files or dirs). Append the new item and keep
        # the list sorted.
        l = variables.setdefault(key, [])
        l.append(item)
        l.sort()
      else:
        raise IsolateError('Unexpected key %s' % key)

  if all_mentioned_configs:
    # Change [(1, 2), (3, 4)] to [set(1, 3), set(2, 4)]
    config_values = map(set, zip(*all_mentioned_configs))
    for i in config_values:
      i.discard(None)
    sef = short_expression_finder.ShortExpressionFinder(
        zip(config_variables, config_values))
    conditions = sorted([sef.get_expr(c), v] for c, v in conditions.iteritems())
  else:
    conditions = []
  out = {'conditions': conditions}
  for c in conditions:
    if c[0] == '':
      # Extract the global.
      out.update(c[1])
      conditions.remove(c)
      break
  return out


class ConfigSettings(object):
  """Represents the dependency variables for a single build configuration.

  The structure is immutable.

  .touch, .tracked and .untracked are the list of dependencies. The items in
      these lists use '/' as a path separator.
  .command and .isolate_dir describe how to run the command. .isolate_dir uses
      the OS' native path separator. It must be an absolute path, it's the path
      where to start the command from.
  .read_only describe how to map the files.
  """
  def __init__(self, values, isolate_dir):
    verify_variables(values)
    if isolate_dir is None:
      # It must be an empty object if isolate_dir is None.
      assert values == {}, values
    else:
      # Otherwise, the path must be absolute.
      assert os.path.isabs(isolate_dir), isolate_dir
    self.touched = sorted(values.get(KEY_TOUCHED, []))
    self.tracked = sorted(values.get(KEY_TRACKED, []))
    self.untracked = sorted(values.get(KEY_UNTRACKED, []))
    self.command = values.get('command', [])[:]
    self.isolate_dir = isolate_dir
    self.read_only = values.get('read_only')

  def union(self, rhs):
    """Merges two config settings together into a new instance.

    A new instance is not created and self or rhs is returned if the other
    object is the empty object.

    self has priority over rhs for .command. Use the same .isolate_dir as the
    one having a .command.

    Dependencies listed in rhs are patch adjusted ONLY if they don't start with
    a path variable, e.g. the characters '<('.
    """
    # When an object has .isolate_dir == None, it means it is the empty object.
    if rhs.isolate_dir is None:
      return self
    if self.isolate_dir is None:
      return rhs

    if sys.platform == 'win32':
      assert self.isolate_dir[0].lower() == rhs.isolate_dir[0].lower()

    # Takes the difference between the two isolate_dir. Note that while
    # isolate_dir is in native path case, all other references are in posix.
    l_rel_cwd, r_rel_cwd = self.isolate_dir, rhs.isolate_dir
    if self.command or rhs.command:
      use_rhs = bool(not self.command and rhs.command)
    else:
      # If self doesn't define any file, use rhs.
      use_rhs = not bool(self.touched or self.tracked or self.untracked)
    if use_rhs:
      # Rebase files in rhs.
      l_rel_cwd, r_rel_cwd = r_rel_cwd, l_rel_cwd

    rebase_path = os.path.relpath(r_rel_cwd, l_rel_cwd).replace(
        os.path.sep, '/')
    def rebase_item(f):
      if f.startswith('<(') or rebase_path == '.':
        return f
      return posixpath.join(rebase_path, f)

    def map_both(l, r):
      """Rebase items in either lhs or rhs, as needed."""
      if use_rhs:
        l, r = r, l
      return sorted(l + map(rebase_item, r))

    var = {
      KEY_TOUCHED: map_both(self.touched, rhs.touched),
      KEY_TRACKED: map_both(self.tracked, rhs.tracked),
      KEY_UNTRACKED: map_both(self.untracked, rhs.untracked),
      'command': self.command or rhs.command,
      'read_only': rhs.read_only if self.read_only is None else self.read_only,
    }
    return ConfigSettings(var, l_rel_cwd)

  def flatten(self):
    """Converts the object into a dict."""
    out = {}
    if self.command:
      out['command'] = self.command
    if self.touched:
      out[KEY_TOUCHED] = self.touched
    if self.tracked:
      out[KEY_TRACKED] = self.tracked
    if self.untracked:
      out[KEY_UNTRACKED] = self.untracked
    if self.read_only is not None:
      out['read_only'] = self.read_only
    # TODO(maruel): Probably better to not output it if command is None?
    if self.isolate_dir is not None:
      out['isolate_dir'] = self.isolate_dir
    return out

  def __str__(self):
    """Returns a short representation useful for debugging."""
    files = ''.join(
        '\n    ' + f for f in (self.touched + self.tracked + self.untracked))
    return 'ConfigSettings(%s, %s, %s, %s)' % (
        self.command,
        self.isolate_dir,
        self.read_only,
        files or '[]')


def _safe_index(l, k):
  try:
    return l.index(k)
  except ValueError:
    return None


def _get_map_keys(dest_keys, in_keys):
  """Returns a tuple of the indexes of each item in in_keys found in dest_keys.

  For example, if in_keys is ('A', 'C') and dest_keys is ('A', 'B', 'C'), the
  return value will be (0, None, 1).
  """
  return tuple(_safe_index(in_keys, k) for k in dest_keys)


def _map_keys(mapping, items):
  """Returns a tuple with items placed at mapping index.

  For example, if mapping is (1, None, 0) and items is ('a', 'b'), it will
  return ('b', None, 'c').
  """
  return tuple(items[i] if i != None else None for i in mapping)


class Configs(object):
  """Represents a processed .isolate file.

  Stores the file in a processed way, split by configuration.

  At this point, we don't know all the possibilities. So mount a partial view
  that we have.

  This class doesn't hold isolate_dir, since it is dependent on the final
  configuration selected. It is implicitly dependent on which .isolate defines
  the 'command' that will take effect.
  """
  def __init__(self, file_comment, config_variables):
    self.file_comment = file_comment
    # Contains the names of the config variables seen while processing
    # .isolate file(s). The order is important since the same order is used for
    # keys in self._by_config.
    assert isinstance(config_variables, tuple)
    assert all(isinstance(c, basestring) for c in config_variables), (
        config_variables)
    config_variables = tuple(config_variables)
    assert tuple(sorted(config_variables)) == config_variables, config_variables
    self._config_variables = config_variables
    # The keys of _by_config are tuples of values for each of the items in
    # self._config_variables. A None item in the list of the key means the value
    # is unbounded.
    self._by_config = {}

  @property
  def config_variables(self):
    return self._config_variables

  def get_config(self, config):
    """Returns all configs that matches this config as a single ConfigSettings.

    Returns an empty ConfigSettings if none apply.
    """
    # TODO(maruel): Fix ordering based on the bounded values. The keys are not
    # necessarily sorted in the way that makes sense, they are alphabetically
    # sorted. It is important because the left-most takes predescence.
    out = ConfigSettings({}, None)
    for k, v in sorted(self._by_config.iteritems()):
      if all(i == j or j is None for i, j in zip(config, k)):
        out = out.union(v)
    return out

  def set_config(self, key, value):
    """Sets the ConfigSettings for this key.

    The key is a tuple of bounded or unbounded variables. The global variable
    is the key where all values are unbounded, e.g.:
      (None,) * len(self._config_variables)
    """
    assert key not in self._by_config, (key, self._by_config.keys())
    assert isinstance(key, tuple)
    assert len(key) == len(self._config_variables), (
        key, self._config_variables)
    assert isinstance(value, ConfigSettings)
    self._by_config[key] = value

  def union(self, rhs):
    """Returns a new Configs instance, the union of variables from self and rhs.

    Uses self.file_comment if available, otherwise rhs.file_comment.
    It keeps config_variables sorted in the output.
    """
    # Merge the keys of config_variables for each Configs instances. All the new
    # variables will become unbounded. This requires realigning the keys.
    config_variables = tuple(sorted(
        set(self.config_variables) | set(rhs.config_variables)))
    out = Configs(self.file_comment or rhs.file_comment, config_variables)
    mapping_lhs = _get_map_keys(out.config_variables, self.config_variables)
    mapping_rhs = _get_map_keys(out.config_variables, rhs.config_variables)
    lhs_config = dict(
        (_map_keys(mapping_lhs, k), v) for k, v in self._by_config.iteritems())
    # pylint: disable=W0212
    rhs_config = dict(
        (_map_keys(mapping_rhs, k), v) for k, v in rhs._by_config.iteritems())

    for key in set(lhs_config) | set(rhs_config):
      l = lhs_config.get(key)
      r = rhs_config.get(key)
      out.set_config(key, l.union(r) if (l and r) else (l or r))
    return out

  def flatten(self):
    """Returns a flat dictionary representation of the configuration.
    """
    return dict((k, v.flatten()) for k, v in self._by_config.iteritems())

  def make_isolate_file(self):
    """Returns a dictionary suitable for writing to a .isolate file.
    """
    dependencies_by_config = self.flatten()
    configs_by_dependency = reduce_inputs(invert_map(dependencies_by_config))
    return convert_map_to_isolate_dict(configs_by_dependency,
                                       self.config_variables)

  def __str__(self):
    return 'Configs(%s,%s)' % (
      self._config_variables,
      ''.join('\n  %s' % str(f) for f in self._by_config))


def load_isolate_as_config(isolate_dir, value, file_comment):
  """Parses one .isolate file and returns a Configs() instance.

  Arguments:
    isolate_dir: only used to load relative includes so it doesn't depend on
                 cwd.
    value: is the loaded dictionary that was defined in the gyp file.
    file_comment: comments found at the top of the file so it can be preserved.

  The expected format is strict, anything diverting from the format below will
  throw an assert:
  {
    'includes': [
      'foo.isolate',
    ],
    'conditions': [
      ['OS=="vms" and foo=42', {
        'variables': {
          'command': [
            ...
          ],
          'isolate_dependency_tracked': [
            ...
          ],
          'isolate_dependency_untracked': [
            ...
          ],
          'read_only': 0,
        },
      }],
      ...
    ],
    'variables': {
      ...
    },
  }
  """
  assert os.path.isabs(isolate_dir), isolate_dir
  if any(len(cond) == 3 for cond in value.get('conditions', [])):
    raise IsolateError('Using \'else\' is not supported anymore.')
  variables_and_values = {}
  verify_root(value, variables_and_values)
  if variables_and_values:
    config_variables, config_values = zip(
        *sorted(variables_and_values.iteritems()))
    all_configs = list(itertools.product(*config_values))
  else:
    config_variables = ()
    all_configs = []

  isolate = Configs(file_comment, config_variables)

  # Add global variables. The global variables are on the empty tuple key.
  isolate.set_config(
      (None,) * len(config_variables),
      ConfigSettings(value.get('variables', {}), isolate_dir))

  # Add configuration-specific variables.
  for expr, then in value.get('conditions', []):
    configs = match_configs(expr, config_variables, all_configs)
    new = Configs(None, config_variables)
    for config in configs:
      new.set_config(config, ConfigSettings(then['variables'], isolate_dir))
    isolate = isolate.union(new)

  # Load the includes. Process them in reverse so the last one take precedence.
  for include in reversed(value.get('includes', [])):
    if os.path.isabs(include):
      raise IsolateError(
          'Failed to load configuration; absolute include path \'%s\'' %
          include)
    included_isolate = os.path.normpath(os.path.join(isolate_dir, include))
    if sys.platform == 'win32':
      if included_isolate[0].lower() != isolate_dir[0].lower():
        raise IsolateError(
            'Can\'t reference a .isolate file from another drive')
    with open(included_isolate, 'r') as f:
      included_isolate = load_isolate_as_config(
          os.path.dirname(included_isolate),
          eval_content(f.read()),
          None)
    isolate = isolate.union(included_isolate)

  return isolate


def load_isolate_for_config(isolate_dir, content, config_variables):
  """Loads the .isolate file and returns the information unprocessed but
  filtered for the specific OS.

  Returns:
    tuple of command, dependencies, touched, read_only flag, isolate_dir.
    The dependencies are fixed to use os.path.sep.
  """
  # Load the .isolate file, process its conditions, retrieve the command and
  # dependencies.
  isolate = load_isolate_as_config(isolate_dir, eval_content(content), None)
  try:
    config_name = tuple(
        config_variables[var] for var in isolate.config_variables)
  except KeyError:
    raise IsolateError(
        'These configuration variables were missing from the command line: %s' %
        ', '.join(
            sorted(set(isolate.config_variables) - set(config_variables))))

  # A configuration is to be created with all the combinations of free
  # variables.
  config = isolate.get_config(config_name)
  # Merge tracked and untracked variables, isolate.py doesn't care about the
  # trackability of the variables, only the build tool does.
  dependencies = sorted(
    f.replace('/', os.path.sep) for f in config.tracked + config.untracked
  )
  touched = sorted(f.replace('/', os.path.sep) for f in config.touched)
  return (
      config.command, dependencies, touched, config.read_only,
      config.isolate_dir)