Make it possible to override more than one package

recipe_engine/package.py

Index: recipe_engine/package.py
diff --git a/recipe_engine/package.py b/recipe_engine/package.py
index 4ada02ac0bd9c7ab3fce47e97ddb0c4d6ae958ef..bc30d4ca0d662a9384f3c8379c705aab1462eaea 100644
--- a/recipe_engine/package.py
+++ b/recipe_engine/package.py
@@ -169,6 +169,12 @@ class RepoSpec(object):
     Requires a good checkout."""
     return ProtoFile(InfraRepoConfig().to_recipes_cfg(self.repo_root(context)))
 
+  def is_consistent_with(self, other):
+    """Returns True iff |other| can be used in place of |self| while keeping
+    the dependency graph consistent. Most often it means being pinned at the
+    same revision, but some specs (like path-based) are always compatible."""
+    return (self == other)

[iannucci, 2017/01/30 17:53:20]

the equality operator overload in this file is a bit surprising :/. it might
make more sense to explicitly define this on GitRepoSpec instead of relying on
it's overload of __eq__ in the base class. Even if you just return self == other
in GitRepoSpec, it's better than going up and down the class hierarchy multiple
times.

(So: make this method raise NotImplementedError in the base class here, and
implement in all subclasses)

[Paweł Hajdan Jr., 2017/01/30 19:20:05]

Done.

+
 
 class GitRepoSpec(RepoSpec):
   def __init__(self, project_id, repo, branch, revision, path, backend):
@@ -324,6 +330,13 @@ class PathRepoSpec(RepoSpec):
       return False
     return self.path == other.path
 
+  def is_consistent_with(self, other):
+    # PathRepoSpec is always compatible, unless it's PathRepoSpec with a
+    # different path.
+    if isinstance(other, type(self)):
+      return self.path == other.path
+    return True
+
 
 class RootRepoSpec(RepoSpec):
   def __init__(self, proto_file):
@@ -654,7 +667,10 @@ class PackageDeps(object):
             'Package %s depends on itself' % project_id)
 
       # Only enforce package consistency within the override boundary.
-      if current.is_override == overriding and repo_spec != current.repo_spec:
+      # It's fine if either spec claims it's consistent with the other.
+      if (current.is_override == overriding and
+          not repo_spec.is_consistent_with(current.repo_spec) and
+          not current.repo_spec.is_consistent_with(repo_spec)):
         raise InconsistentDependencyGraphError(
             project_id, (repo_spec, current.repo_spec))
     self._packages[project_id] = None