layout.conf: allow a repository to state the cache is authorative

By authorative, this means "the cache is accurate; skip validation".  While
a useful hint for a slight speedup in validation, the true gain is for
repositories that are distributed in a fashion that doesn't preserve mtime;
git primarily.  Setting authorative-cache = true results in portage
skipping mtime validation checks for the bundled cache, allowing
for git vcs based repos to distribute a cache.

BUG=chromium-os:21049
TEST=dump a cache into metadata/cache, touch it to now, set layout.conf
     to authorative-cache=true, verify it doesn't generate cache entries
     for that repo.

Change-Id: I92423e679bc171d2411a18d6d3ac22e8ef457753

3 files changed, 13 insertions, 7 deletions

diff --git a/pym/portage/cache/template.py b/pym/portage/cache/template.py
index f84d8f4b9..4cb27bff9 100644
--- a/pym/portage/cache/template.py
+++ b/pym/portage/cache/template.py
@@ -30,6 +30,7 @@ class database(object):
 		self.readonly = readonly
 		self.sync_rate = 0
 		self.updates = 0
+		self.is_authorative = False
 	
 	def __getitem__(self, cpv):
 		"""set a cpv to values
diff --git a/pym/portage/dbapi/porttree.py b/pym/portage/dbapi/porttree.py
index e679f000c..ab3824727 100644
--- a/pym/portage/dbapi/porttree.py
+++ b/pym/portage/dbapi/porttree.py
@@ -215,10 +215,12 @@ class portdbapi(dbapi):
 				if x in self._pregen_auxdb:
 					continue
 				if os.path.isdir(os.path.join(x, "metadata", "cache")):
-					self._pregen_auxdb[x] = self.metadbmodule(
+					conf = self.repositories.get_repo_for_location(x)
+					cache = self._pregen_auxdb[x] = self.metadbmodule(
 						x, "metadata/cache", filtered_auxdbkeys, readonly=True)
+					cache.is_authorative = conf.cache_is_authorative
 					try:
-						self._pregen_auxdb[x].ec = self._repo_info[x].eclass_db
+						cache.ec = self._repo_info[x].eclass_db
 					except AttributeError:
 						pass
 		# Selectively cache metadata in order to optimize dep matching.
@@ -441,10 +443,11 @@ class portdbapi(dbapi):
 				eapi = metadata.get('EAPI', '').strip()
 				if not eapi:
 					eapi = '0'
-				if not (eapi[:1] == '-' and eapi_is_supported(eapi[1:])) and \
-					emtime == metadata['_mtime_'] and \
-					eclass_db.is_eclass_data_valid(metadata['_eclasses_']):
-					doregen = False
+				if not (eapi[:1] == '-' and eapi_is_supported(eapi[1:])):
+					if auxdb.is_authorative or ( \
+						emtime == metadata['_mtime_'] and \
+						eclass_db.is_eclass_data_valid(metadata['_eclasses_'])):
+						doregen = False
 
 			if not doregen:
 				break
diff --git a/pym/portage/repository/config.py b/pym/portage/repository/config.py
index 3cb550152..692445013 100644
--- a/pym/portage/repository/config.py
+++ b/pym/portage/repository/config.py
@@ -43,7 +43,7 @@ class RepoConfig(object):
 
 	__slots__ = ['aliases', 'eclass_overrides', 'eclass_locations', 'location', 'user_location', 'masters', 'main_repo',
 		'missing_repo_name', 'name', 'priority', 'sync', 'format', 'sign_manifest', 'thin_manifest',
-		'allow_missing_manifest', 'create_manifest', 'disable_manifest']
+		'allow_missing_manifest', 'create_manifest', 'disable_manifest', 'cache_is_authorative']
 
 	def __init__(self, name, repo_opts):
 		"""Build a RepoConfig with options in repo_opts
@@ -117,6 +117,7 @@ class RepoConfig(object):
 		self.allow_missing_manifest = False
 		self.create_manifest = True
 		self.disable_manifest = False
+		self.cache_is_authorative = False
 
 	def load_manifest(self, *args, **kwds):
 		kwds['thin'] = self.thin_manifest
@@ -357,6 +358,7 @@ class RepoConfigLoader(object):
 			repo.allow_missing_manifest = manifest_policy != 'strict'
 			repo.create_manifest = manifest_policy != 'false'
 			repo.disable_manifest = manifest_policy == 'false'
+			repo.cache_is_authorative = layout_data.get('authorative-cache', 'false').lower() == 'true'
 
 		#Take aliases into account.
 		new_prepos = {}