[context] Split "env" values and prefixes.

recipe_modules/context/api.py

 # Copyright 2017 The LUCI 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.
 
 """The context module provides APIs for manipulating a few pieces of 'ambient'
 data that affect how steps are run:
   cwd - The current working directory.
   env - The environment variables.
   infra_step - Whether or not failures should be treated as infrastructure
     failures vs. normal failures.
@@ skipping 180 matching lines @@
     """Returns the current working directory that steps will run in.
 
     Returns (Path|None) - The current working directory. A value of None is
       equivalent to api.path['start_dir'], though only occurs if no cwd has been
       set (e.g. in the outermost context of RunSteps).
     """
     return self._cwd[-1]
 
   @property
   def env(self):
-    """Returns modifications to the environment.
+    """Returns string modifications to the environment.
 
     By default this is empty; There's no facility to observe the program's
     startup environment. If you want to pass data to the recipe, it should be
     done with properties.
 
+    This will return the string modifications made to the environment. For
+    prefix modifications, use "env_prefixes".
+
     Returns (dict) - The env-key -> value mapping of current environment
       modifications.
     """
     # TODO(iannucci): store env in an immutable way to avoid excessive copies.
     # TODO(iannucci): handle case-insensitive keys on windows
-    def parts(ev):
-      for p in ev.prefixes:
-        yield str(p)
-      if ev.value:
-        yield ev.value
+    return {k: v.value for k, v in self._env[-1].iteritems()}
 
-    ret = {}
-    for k, ev in self._env[-1].iteritems():
-      if ev.value is None:
-        ret[k] = None
-      else:
-        ret[k] = self.m.path.pathsep.join(parts(ev))
+  @property
+  def env_prefixes(self):

[iannucci, 2017/06/09 04:47:45]

I was actually thinking of storing these as separate stacks in context, i.e.
_env_prefixes, and adjusting __call__ appropriately as well.

[dnj, 2017/06/09 04:50:33]

I think that this might be a better API - less things for user to care about. No
user (*) will ever set both via "env=" for the same environment variable, so
keeping the API simple seems advantageous. Are you sold on splitting them?

+    """Returns Path prefix modifications to the environment.
 
-    return ret
+    This will return a mapping of environment key to Path tuple for Path
+    prefixes registered with the environment.
+
+    Returns (dict) - The env-key -> value(Path) mapping of current environment
+      prefix modifications.
+    """
+    return {k: v.prefixes for k, v in self._env[-1].iteritems()
+            if v.prefixes}
 
   @property
   def infra_step(self):
     """Returns the current value of the infra_step setting.
 
     Returns (bool) - True iff steps are currently considered infra steps.
     """
     return self._infra_step[-1]
 
   @property
@@ skipping 21 matching lines @@
     the beginning of an environment variable.
 
     Each path in paths is added, in order, as a prefix to the environment
     variable, delimited by the OS path separator. This can be used for
     easy manipulation of path environment variables such as PATH and PYTHONPATH.
 
     Args:
       paths (...Path): The list of paths to prefix.
     """
     for i, path in enumerate(paths):
-        check_type('path element %d' % (i,), path, Path)
+        check_type('path element %d' % (i,), path, (Path, str))
     return _EnvPathComponent(paths=paths)