Bug 1919640 - Avoid expensive check for changed files when bootstrapping. r=taskgraph-reviewers,jcristau

Loading the tasks for the toolchain kind doesn't trigger the
optimization passes that use files_changed, so we can just override the
parameter to avoid the defaults expensively trying to determine what
they are.

We also change the default parameters in gecko_taskgraph to apply the
same change as taskcluster/taskgraph#624.

Differential Revision: https://phabricator.services.mozilla.com/D234628

Author: glandium

python/mozbuild/mozbuild/toolchains.py

@@ -14,7 +14,7 @@ def toolchain_task_definitions():
 
     # Don't import globally to allow this module being imported without
     # the taskgraph module being available (e.g. standalone js)
-    params = {"level": os.environ.get("MOZ_SCM_LEVEL", "3")}
+    params = {"level": os.environ.get("MOZ_SCM_LEVEL", "3"), "files_changed": []}
     root_dir = os.path.join(os.path.dirname(__file__), "..", "..", "..", "taskcluster")
     toolchains = load_tasks_for_kind(params, "toolchain", root_dir=root_dir)
     aliased = {}

taskcluster/gecko_taskgraph/parameters.py

@@ -116,7 +116,7 @@ def get_defaults(repo_root=None):
         "base_repository": "https://hg.mozilla.org/mozilla-unified",
         "build_number": 1,
         "enable_always_target": ["docker-image"],
-        "files_changed": sorted(get_locally_changed_files(repo_root)),
+        "files_changed": lambda: sorted(get_locally_changed_files(repo_root)),
         "head_repository": "https://hg.mozilla.org/mozilla-central",
         "hg_branch": "default",
         "message": "",