Implement ability to specify temporarily-allowed dependencies in DEPS

tools/checkdeps/rules.py

Index: tools/checkdeps/rules.py
diff --git a/tools/checkdeps/rules.py b/tools/checkdeps/rules.py
new file mode 100644
index 0000000000000000000000000000000000000000..08dd13ec0e497b83b04a110a2d3a72499fc9d1c4
--- /dev/null
+++ b/tools/checkdeps/rules.py
@@ -0,0 +1,89 @@
+# Copyright (c) 2012 The Chromium Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style license that can be
+# found in the LICENSE file.
+
+"""Base classes to represent dependency rules, used by checkdeps.py"""
+
+
+class Rule(object):
+  """Specifies a single rule for an include, which can be one of
+  ALLOW, DISALLOW and TEMP_ALLOW.
+  """
+
+  # These are the prefixes used to indicate each type of rule. These
+  # are also used as values for self.allow to indicate which type of
+  # rule this is.
+  ALLOW = "+"
+  DISALLOW = "-"
+  TEMP_ALLOW = "!"
+
+  def __init__(self, allow, directory, source):
+    self.allow = allow
+    self._dir = directory
+    self._source = source
+
+  def __str__(self):
+    return '"%s%s" from %s.' % (self.allow, self._dir, self._source)
+
+  def ParentOrMatch(self, other):
+    """Returns true if the input string is an exact match or is a parent
+    of the current rule. For example, the input "foo" would match "foo/bar"."""
+    return self._dir == other or self._dir.startswith(other + "/")
+
+  def ChildOrMatch(self, other):
+    """Returns true if the input string would be covered by this rule. For
+    example, the input "foo/bar" would match the rule "foo"."""
+    return self._dir == other or other.startswith(self._dir + "/")
+
+
+def ParseRuleString(rule_string, source):
+  """Returns a tuple of a boolean indicating whether the directory is an allow
+  rule, and a string holding the directory name.
+  """
+  if not rule_string:
+    raise Exception('The rule string "%s" is empty\nin %s' %
+                    (rule_string, source))
+
+  if not rule_string[0] in [Rule.ALLOW, Rule.DISALLOW, Rule.TEMP_ALLOW]:
+    raise Exception(
+      'The rule string "%s" does not begin with a "+", "-" or "!".' %
+      rule_string)
+
+  return (rule_string[0], rule_string[1:])
+
+
+class Rules(object):
+  def __init__(self):
+    """Initializes the current rules with an empty rule list."""
+    self._rules = []
+
+  def __str__(self):
+    return 'Rules = [\n%s]' % '\n'.join(' %s' % x for x in self._rules)
+
+  def AddRule(self, rule_string, source):
+    """Adds a rule for the given rule string.
+
+    Args:
+      rule_string: The include_rule string read from the DEPS file to apply.
+      source: A string representing the location of that string (filename, etc.)
+              so that we can give meaningful errors.
+    """
+    (add_rule, rule_dir) = ParseRuleString(rule_string, source)
+    # Remove any existing rules or sub-rules that apply. For example, if we're
+    # passed "foo", we should remove "foo", "foo/bar", but not "foobar".
+    self._rules = [x for x in self._rules if not x.ParentOrMatch(rule_dir)]
+    self._rules.insert(0, Rule(add_rule, rule_dir, source))
+
+  def DirAllowed(self, allowed_dir):
+    """Returns a tuple (success, message), where success indicates if the given
+    directory is allowed given the current set of rules, and the message tells
+    why if the comparison failed."""
+    for rule in self._rules:
+      if rule.ChildOrMatch(allowed_dir):
+        # This rule applies.
+        why_failed = ""
+        if rule.allow != Rule.ALLOW:
+          why_failed = str(rule)
+        return (rule.allow, why_failed)
+    # No rules apply, fail.
+    return (Rule.DISALLOW, "no rule applying")