1 files changed, 72 insertions, 0 deletions
diff --git a/taskcluster/taskgraph/parameters.py b/taskcluster/taskgraph/parameters.py
new file mode 100644
index 0000000000..51b9e77c7e
--- /dev/null
+++ b/taskcluster/taskgraph/parameters.py
@@ -0,0 +1,72 @@
+# -*- coding: utf-8 -*-
+
+# 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/.
+
+from __future__ import absolute_import, print_function, unicode_literals
+
+import json
+import yaml
+from mozbuild.util import ReadOnlyDict
+
+# Please keep this list sorted and in sync with taskcluster/docs/parameters.rst
+PARAMETER_NAMES = set([
+    'base_repository',
+    'build_date',
+    'head_ref',
+    'head_repository',
+    'head_rev',
+    'level',
+    'message',
+    'moz_build_date',
+    'optimize_target_tasks',
+    'owner',
+    'project',
+    'pushdate',
+    'pushlog_id',
+    'target_tasks_method',
+    'triggered_by',
+])
+
+
+class Parameters(ReadOnlyDict):
+    """An immutable dictionary with nicer KeyError messages on failure"""
+    def check(self):
+        names = set(self)
+        msg = []
+
+        missing = PARAMETER_NAMES - names
+        if missing:
+            msg.append("missing parameters: " + ", ".join(missing))
+
+        extra = names - PARAMETER_NAMES
+        if extra:
+            msg.append("extra parameters: " + ", ".join(extra))
+
+        if msg:
+            raise Exception("; ".join(msg))
+
+    def __getitem__(self, k):
+        if k not in PARAMETER_NAMES:
+            raise KeyError("no such parameter {!r}".format(k))
+        try:
+            return super(Parameters, self).__getitem__(k)
+        except KeyError:
+            raise KeyError("taskgraph parameter {!r} not found".format(k))
+
+
+def load_parameters_file(options):
+    """
+    Load parameters from the --parameters option
+    """
+    filename = options['parameters']
+    if not filename:
+        return Parameters()
+    with open(filename) as f:
+        if filename.endswith('.yml'):
+            return Parameters(**yaml.safe_load(f))
+        elif filename.endswith('.json'):
+            return Parameters(**json.load(f))
+        else:
+            raise TypeError("Parameters file `{}` is not JSON or YAML".format(filename))