_yamlcache.py: Use a project's junction name if present

This is required because if there are projects with the same name
loaded, that have elements in the same path, with the same contents,
they are considered the same, despite actually belonging to different
Projects.

This fixes buildstream issue #795

buildstream/_yamlcache.py

@@ -68,7 +68,7 @@ class YamlCache():
     #    (bool): Whether the file is cached.
     def is_cached(self, project, filepath):
         cache_path = self._get_filepath(project, filepath)
-        project_name = project.name if project else ""
+        project_name = self._get_project_name(project)
         try:
             project_cache = self._project_caches[project_name]
             if cache_path in project_cache.elements:
@@ -167,7 +167,7 @@ class YamlCache():
     #    value (decorated dict): The data to put into the cache.
     def put_from_key(self, project, filepath, key, value):
         cache_path = self._get_filepath(project, filepath)
-        project_name = project.name if project else ""
+        project_name = self._get_project_name(project)
         try:
             project_cache = self._project_caches[project_name]
         except KeyError:
@@ -237,7 +237,7 @@ class YamlCache():
     #    (decorated dict): The parsed yaml from the cache, or None if the file isn't in the cache.
     def _get(self, project, filepath, key):
         cache_path = self._get_filepath(project, filepath)
-        project_name = project.name if project else ""
+        project_name = self._get_project_name(project)
         try:
             project_cache = self._project_caches[project_name]
             try:
@@ -253,6 +253,30 @@ class YamlCache():
             pass
         return None
 
+    # _get_project_name():
+    #
+    # Gets a name appropriate for Project. Projects must use their junction's
+    # name if present, otherwise elements with the same contents under the
+    # same path with identically-named projects are considered the same yaml
+    # object, despite existing in different Projects.
+    #
+    # Args:
+    #    project (Project): The project this file is in, or None.
+    #
+    # Returns:
+    #    (str): The project's junction's name if present, the project's name,
+    #           or an empty string if there is no project
+    @staticmethod
+    def _get_project_name(project):
+        if project:
+            if project.junction:
+                project_name = project.junction.name
+            else:
+                project_name = project.name
+        else:
+            project_name = ""
+        return project_name
+
 
 CachedProject = namedtuple('CachedProject', ['elements'])
 
@@ -287,7 +311,7 @@ class BstPickler(pickle.Pickler):
         if isinstance(obj, _yaml.ProvenanceFile):
             if obj.project:
                 # ProvenanceFile's project object cannot be stored as it is.
-                project_tag = obj.project.name
+                project_tag = YamlCache._get_project_name(obj.project)
                 # ProvenanceFile's filename must be stored relative to the
                 # project, as the project dir may move.
                 name = os.path.relpath(obj.name, obj.project.directory)
@@ -319,14 +343,17 @@ class BstUnpickler(pickle.Unpickler):
 
             if project_tag is not None:
                 for p in self._context.get_projects():
-                    if project_tag == p.name:
+                    if p.junction and project_tag == p.junction.name:
+                        project = p
+                        break
+                    elif project_tag == p.name:
                         project = p
                         break
 
                 name = os.path.join(project.directory, tagged_name)
 
                 if not project:
-                    projects = [p.name for p in self._context.get_projects()]
+                    projects = [YamlCache._get_project_name(p) for p in self._context.get_projects()]
                     raise pickle.UnpicklingError("No project with name {} found in {}"
                                                  .format(project_tag, projects))
             else: