1 files changed, 65 insertions, 0 deletions
diff --git a/taskcluster/taskgraph/files_changed.py b/taskcluster/taskgraph/files_changed.py
new file mode 100644
index 0000000000..973a62bb84
--- /dev/null
+++ b/taskcluster/taskgraph/files_changed.py
@@ -0,0 +1,65 @@
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+"""
+Support for optimizing tasks based on the set of files that have changed.
+"""
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+import logging
+import requests
+from redo import retry
+from mozpack.path import match as mozpackmatch
+
+logger = logging.getLogger(__name__)
+_cache = {}
+
+
+def get_changed_files(repository, revision):
+    """
+    Get the set of files changed in the push headed by the given revision.
+    Responses are cached, so multiple calls with the same arguments are OK.
+    """
+    key = repository, revision
+    if key not in _cache:
+        url = '%s/json-automationrelevance/%s' % (repository.rstrip('/'), revision)
+        logger.debug("Querying version control for metadata: %s", url)
+
+        def get_automationrelevance():
+            response = requests.get(url, timeout=5)
+            return response.json()
+        contents = retry(get_automationrelevance, attempts=2, sleeptime=10)
+
+        logger.debug('{} commits influencing task scheduling:'
+                     .format(len(contents['changesets'])))
+        changed_files = set()
+        for c in contents['changesets']:
+            logger.debug(" {cset} {desc}".format(
+                cset=c['node'][0:12],
+                desc=c['desc'].splitlines()[0].encode('ascii', 'ignore')))
+            changed_files |= set(c['files'])
+
+        _cache[key] = changed_files
+    return _cache[key]
+
+
+def check(params, file_patterns):
+    """Determine whether any of the files changed in the indicated push to
+    https://hg.mozilla.org match any of the given file patterns."""
+    repository = params.get('head_repository')
+    revision = params.get('head_rev')
+    if not repository or not revision:
+        logger.warning("Missing `head_repository` or `head_rev` parameters; "
+                       "assuming all files have changed")
+        return True
+
+    changed_files = get_changed_files(repository, revision)
+
+    for pattern in file_patterns:
+        for path in changed_files:
+            if mozpackmatch(path, pattern):
+                return True
+
+    return False