Bug 1404067 - [tryselect] Improve error message on parameter mismatch, r=dustin

MozReview-Commit-ID: GMiGuNApoUF

--HG--
extra : rebase_source : 326df920793b54806cd4423ec0bf0e20df6cd42d

taskcluster/docs/mach.rst

@@ -24,19 +24,26 @@ graph-generation process and output the results.
 ``mach taskgraph morphed``
    Get the morhped task graph
 
-Each of these commands takes an optional ``--parameters`` option giving a file
+See :doc:`how-tos` for further practical tips on debugging task-graph mechanics
+locally.
+
+Parameters
+----------
+
+Each of these commands takes an optional ``--parameters`` argument giving a file
 with parameters to guide the graph generation.  The decision task helpfully
 produces such a file on every run, and that is generally the easiest way to get
 a parameter file.  The parameter keys and values are described in
 :doc:`parameters`; using that information, you may modify an existing
 ``parameters.yml`` or create your own.  The ``--parameters`` option can also
-take an argument of the form ``project=<project>`` which will fetch the
-parameters from the latest push on that project; or ``task-id=<task-id>`` which
-will fetch the parameters from the given decision task. It defaults to
-``project=mozilla-central``.
+take the following forms:
 
-See :doc:`how-tos` for further practical tips on debugging task-graph mechanics
-locally.
+``project=<project>``
+   Fetch the parameters from the latest push on that project
+``task-id=<task-id>``
+   Fetch the parameters from the given decision task id
+
+If not specified, parameters will default to ``project=mozilla-central``.
 
 Taskgraph JSON Format
 ---------------------

taskcluster/taskgraph/parameters.py

@@ -10,6 +10,11 @@ import json
 import yaml
 from mozbuild.util import ReadOnlyDict
 
+
+class ParameterMismatch(Exception):
+    """Raised when a parameters.yml has extra or missing parameters."""
+
+
 # Please keep this list sorted and in sync with taskcluster/docs/parameters.rst
 PARAMETER_NAMES = set([
     'base_repository',
@@ -50,7 +55,7 @@ class Parameters(ReadOnlyDict):
             msg.append("extra parameters: " + ", ".join(extra))
 
         if msg:
-            raise Exception("; ".join(msg))
+            raise ParameterMismatch("; ".join(msg))
 
     def __getitem__(self, k):
         if k not in PARAMETER_NAMES:

tools/tryselect/tasks.py

@@ -5,18 +5,34 @@
 from __future__ import absolute_import, print_function, unicode_literals
 
 import os
+import sys
 
 from mozboot.util import get_state_dir
 from mozbuild.base import MozbuildObject
 from mozpack.files import FileFinder
 
 from taskgraph.generator import TaskGraphGenerator
-from taskgraph.parameters import load_parameters_file
+from taskgraph.parameters import (
+    ParameterMismatch,
+    load_parameters_file,
+)
 
 here = os.path.abspath(os.path.dirname(__file__))
 build = MozbuildObject.from_environment(cwd=here)
 
 
+PARAMETER_MISMATCH = """
+ERROR - The parameters being used to generate tasks differ from those defined
+in your working copy:
+
+    {}
+
+To fix this, either rebase onto the latest mozilla-central or pass in
+-p/--parameters. For more information on how to define parameters, see:
+https://firefox-source-docs.mozilla.org/taskcluster/taskcluster/mach.html#parameters
+"""
+
+
 def invalidate(cache):
     if not os.path.isfile(cache):
         return
@@ -45,8 +61,12 @@ def generate_tasks(params=None, full=False):
         os.makedirs(cache_dir)
 
     print("Task configuration changed, generating {}".format(attr.replace('_', ' ')))
-    params = load_parameters_file(params)
-    params.check()
+    try:
+        params = load_parameters_file(params)
+        params.check()
+    except ParameterMismatch as e:
+        print(PARAMETER_MISMATCH.format(e.args[0]))
+        sys.exit(1)
 
     cwd = os.getcwd()
     os.chdir(build.topsrcdir)