Do not cache "file:///" resources (#1697)

Fixes #1695

We generally cache to save the network latency, not because our
transformations of the data were so expensive.

We expect that "file:///" protocol resources can be read fast enough for our
purposes and want to ensure that changes of such local files are available
immediately, e.g. without restart Sublime Text or clearing the cache as a
whole (`clear_cache`).

Note that we only refuse to read from the cache (`get_cache`) and thus imitate
a fresh install.  We still write to the cache in case that is observable by
other parts of our source code.

Author: kaste

package_control/package_manager.py

@@ -493,7 +493,10 @@ def list_repositories(self):
 
             # Caches various info from channels for performance
             cache_key = channel + '.repositories'
-            channel_repositories = get_cache(cache_key)
+            if channel[:8].lower() == "file:///":
+                channel_repositories = None
+            else:
+                channel_repositories = get_cache(cache_key)
 
             merge_cache_under_settings(self, 'renamed_packages', channel)
             merge_cache_under_settings(self, 'unavailable_packages', channel, list_=True)
@@ -512,7 +515,8 @@ def list_repositories(self):
 
                 try:
                     channel_repositories = provider.get_repositories()
-                    set_cache(cache_key, channel_repositories, cache_ttl)
+                    if channel[:8].lower() != "file:///":
+                        set_cache(cache_key, channel_repositories, cache_ttl)
 
                     unavailable_packages = []
                     unavailable_libraries = []
@@ -636,17 +640,19 @@ def download_repo(url):
                 console_write('Removed malicious repository %s' % repo)
                 continue
 
-            cache_key = repo + '.packages'
-            repository_packages = get_cache(cache_key)
-
-            if repository_packages:
-                packages.update(repository_packages)
-
-            cache_key = repo + '.libraries'
-            repository_libraries = get_cache(cache_key)
+            if repo[:8].lower() == "file:///":
+                repository_packages = None
+                repository_libraries = None
+            else:
+                cache_key = repo + '.packages'
+                repository_packages = get_cache(cache_key)
+                if repository_packages:
+                    packages.update(repository_packages)
 
-            if repository_libraries:
-                libraries.update(repository_libraries)
+                cache_key = repo + '.libraries'
+                repository_libraries = get_cache(cache_key)
+                if repository_libraries:
+                    libraries.update(repository_libraries)
 
             if repository_packages is None and repository_libraries is None:
                 if executor is None:
@@ -692,12 +698,13 @@ def download_repo(url):
             for _, exception in provider.get_broken_libraries():
                 console_write(exception)
 
-            cache_key = provider.repo_url + '.packages'
-            set_cache(cache_key, repository_packages, cache_ttl)
-            packages.update(repository_packages)
+            if provider.repo_url[:8].lower() != "file:///":
+                cache_key = provider.repo_url + '.packages'
+                set_cache(cache_key, repository_packages, cache_ttl)
+                cache_key = provider.repo_url + '.libraries'
+                set_cache(cache_key, repository_libraries, cache_ttl)
 
-            cache_key = provider.repo_url + '.libraries'
-            set_cache(cache_key, repository_libraries, cache_ttl)
+            packages.update(repository_packages)
             libraries.update(repository_libraries)
 
             renamed_packages = provider.get_renamed_packages()