Refactor the way that TestApi works so that it is actually useful.

scripts/slave/recipe_util.py

Index: scripts/slave/recipe_util.py
diff --git a/scripts/slave/recipe_util.py b/scripts/slave/recipe_util.py
new file mode 100644
index 0000000000000000000000000000000000000000..76f813d63fe7f2961ba2f95412f88afbb9384497
--- /dev/null
+++ b/scripts/slave/recipe_util.py
@@ -0,0 +1,115 @@
+# Copyright (c) 2013 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.
+import functools
+import os
+
+
+SCRIPT_PATH = os.path.dirname(os.path.abspath(__file__))
+BUILD_ROOT = os.path.dirname(os.path.dirname(SCRIPT_PATH))
+ROOT_PATH = os.path.abspath(os.path.join(
+  SCRIPT_PATH, os.pardir, os.pardir, os.pardir))
+BASE_DIRS = [
+  SCRIPT_PATH,
+  os.path.join(ROOT_PATH, 'build_internal', 'scripts', 'slave'),
+  os.path.join(ROOT_PATH, 'build_internal', 'scripts', 'slave-internal')
+]
+MODULE_DIRS = lambda: [os.path.join(x, 'recipe_modules') for x in BASE_DIRS]
+RECIPE_DIRS = lambda: [os.path.join(x, 'recipes') for x in BASE_DIRS]
+
+class RecipeAbort(Exception):
+  pass
+
+
+class ModuleInjectionSite(object):
+  pass
+
+
+class Placeholder(object):
+  """Base class for json placeholders. Do not use directly."""
+  def __init__(self):
+    self.name_pieces = None
+
+  def render(self, test):  # pragma: no cover
+    """Return [cmd items]*"""
+    raise NotImplementedError
+
+  def result(self, presentation, test):
+    """Called after step completion.
+
+    Args:
+      presentation (StepPresentation) - for the current step.
+      test (PlaceholderTestData) - test data for this placeholder.
+
+    Returns value to add to step result.
+
+    May optionally modify presentation as a side-effect.
+    """
+    pass
+
+  @property
+  def name(self):
+    assert self.name_pieces
+    return "%s.%s" % self.name_pieces
+
+
+def static_wraps(func):
+  wrapped_fn = func
+  if isinstance(func, staticmethod):
+    wrapped_fn = func.__func__
+  return functools.wraps(wrapped_fn)
+
+
+def static_call(obj, func, *args, **kwargs):
+  if isinstance(func, staticmethod):
+    return func.__get__(obj)(*args, **kwargs)
+  else:
+    return func(obj, *args, **kwargs)
+
+
+def static_name(obj, func):
+  if isinstance(func, staticmethod):
+    return func.__get__(obj).__name__
+  else:
+    return func.__name__
+
+
+def returns_placeholder(func):
+  @static_wraps(func)
+  def inner(self, *args, **kwargs):
+    ret = static_call(self, func, *args, **kwargs)
+    assert isinstance(ret, Placeholder)
+    ret.name_pieces = (self.name, static_name(self, func))
+    return ret
+  return inner
+
+
+def wrap_followup(kwargs, pre=False):
+  """
+  Decorator for a new followup_fn.
+
+  Will pop the existing fn out of kwargs (if any), and return a decorator for
+  the new folloup_fn.
+
+  Args:
+    kwargs - dictionary possibly containing folloup_fn
+    pre - If true, the old folloup_fn is called before the wrapped function.
+          Otherwise, the old followup_fn is called after the wrapped function.
+  """
+  null_fn = lambda _: None
+  old_followup = kwargs.pop('followup_fn', null_fn)
+  def decorator(f):
+    @functools.wraps(f)
+    def _inner(step_result):
+      if pre:
+        old_followup(step_result)
+        f(step_result)
+      else:
+        f(step_result)
+        old_followup(step_result)
+    if old_followup is not null_fn:
+      _inner.__name__ += '[%s]' % old_followup.__name__
+    return _inner
+  return decorator
+
+