Add Paths as first-class types in configs.

scripts/slave/recipe_config_types.py

Index: scripts/slave/recipe_config_types.py
diff --git a/scripts/slave/recipe_config_types.py b/scripts/slave/recipe_config_types.py
new file mode 100644
index 0000000000000000000000000000000000000000..06c38cb00ac51c8b907fd1fd4451b702edc5b561
--- /dev/null
+++ b/scripts/slave/recipe_config_types.py
@@ -0,0 +1,90 @@
+import re
+
+def ResetTostringFns():
+  RecipeConfigType._TOSTRING_MAP.clear()  # pylint: disable=W0212
+
+
+def json_fixup(obj):
+  if isinstance(obj, RecipeConfigType):
+    return str(obj)
+  raise TypeError("%r is not JSON serializable" % obj)
+
+
+class RecipeConfigType(object):
+  """Base class for custom Recipe config types, intended to be subclassed.
+
+  RecipeConfigTypes are meant to be PURE data. There should be no dependency on
+  any external systems (i.e. no importing sys, os, etc.).
+
+  The subclasses should override default_tostring_fn. This method should
+  produce a string representation of the object. This string representation
+  should contain all of the data members of the subclass. This representation
+  will be used during the execution of the recipe_config_tests.
+
+  External entities (usually recipe modules), can override the default
+  tostring_fn method by calling <RecipeConfigType
+  subclass>.set_tostring_fn(<new method>). This new method will recieve an
+  instance of the RecipeConfigType subclass as its single argument, and is
+  expected to return a string. There is no restriction on the data that the
+  override tostring_fn may use (for example, the Path class in this module has
+  its tostring_fn overridden by the 'path' recipe_module.  This new tostring_fn
+  uses data from the current recipe run, like the host os, to return platform
+  specific strings using the data in the Path object.)

[agable, 2013/09/27 17:48:17]

nit: your punctuation in/around your parentheses is odd.

[iannucci, 2013/09/27 19:23:37]

Done.

+
+  """
+  _TOSTRING_MAP = {}
+
+  @property
+  def tostring_fn(self):
+    cls = self.__class__
+    return self._TOSTRING_MAP.get(cls.__name__, cls.default_tostring_fn)
+
+  @classmethod
+  def set_tostring_fn(cls, new_tostring_fn):
+    assert cls.__name__ not in cls._TOSTRING_MAP, (
+      'tostring_fn already installed for %s' % cls)
+    cls._TOSTRING_MAP[cls.__name__] = new_tostring_fn
+
+  def default_tostring_fn(self):
+    raise NotImplementedError
+
+  def __str__(self):
+    return self.tostring_fn(self)
+
+
+class Path(RecipeConfigType):
+  """Represents a path which is relative to a semantically-named base.
+
+  Because there's a lot of platform (separator style) and runtime-specific
+  context (working directory) which goes into assembling a final OS-specific
+  absolute path, we only store three attributes in this Path object:
+    * base (str) - The 'name' of a base path, to be filled in at recipe runtime
+        by the 'path' recipe module.
+    * pieces (tuple(str)) - The components of the path relative to base. These
+        pieces must be non-relative (i.e. no '..' or '.' as a piece).
+    * platform_ext (dict(str, str)) - A mapping from platform name (as defined
+        by the 'platform' module), to a suffix for the path.
+  """
+  # Restrict basenames to simple alpha pythonic tokens. This will help catch
+  # errors if someone attempts to provide an actual string path '/some/example'
+  # as the 'base'.
+  BASE_RE = re.compile("[a-z][a-z_]*")
+
+  def __init__(self, base, pieces=(), platform_ext=None):

[agable, 2013/09/27 17:48:17]

I think I would prefer that BASE_RE assert that base is ALLCAPS, and have pieces
still be *pieces. I don't think our test-path-mocking convention is going to
change, so maybe even require Path('[BASE]', 'path', 'to', 'thing').

[iannucci, 2013/09/27 19:23:37]

Done.

+    super(Path, self).__init__()
+    assert not any(x in ('..', '.') for x in pieces)

[agable, 2013/09/27 17:48:17]

Also assert that '/' isn't one of the pieces. IIRC,
os.path.join('foo', 'bar', '/', 'baz', 'boom') == '/baz/boom'

[iannucci, 2013/09/27 19:23:37]

Done.

+    assert self.BASE_RE.match(base)
+
+    self.base = base
+    self.pieces = pieces
+    self.platform_ext = platform_ext or {}
+
+  def __call__(self, *pieces, **kwargs):
+    platform_ext = kwargs.get('platform_ext', self.platform_ext)
+    return Path(self.base, filter(bool, self.pieces + pieces), platform_ext)
+
+  def default_tostring_fn(self):
+    suffix = ''
+    if self.platform_ext:
+      suffix = ', platform_ext=%r' % (self.platform_ext,)
+    return 'Path([%s], %r%s)' % (self.base.upper(), self.pieces, suffix)

[agable, 2013/09/27 17:48:17]

Would still prefer to have this print self.pieces not in a tuple.

[iannucci, 2013/09/27 19:23:37]

Done.