Bug 1670240 - [tryselect] Use the 'TestManifestLoader' when resolving test paths r=jmaher

This walks the file system to read moz.build files, rather than following the DIRS
traversal. The latter is problematic because many moz.build files that happen to
define manifests could be excluded by the local build config.

Differential Revision: https://phabricator.services.mozilla.com/D94197

tools/tryselect/tasks.py

@@ -13,7 +13,7 @@ from collections import defaultdict
 from mozboot.util import get_state_dir
 from mozbuild.base import MozbuildObject
 from mozpack.files import FileFinder
-from moztest.resolve import TestResolver, get_suite_definition
+from moztest.resolve import TestResolver, TestManifestLoader, get_suite_definition
 
 import taskgraph
 from taskgraph.generator import TaskGraphGenerator
@@ -116,7 +116,7 @@ def generate_tasks(params=None, full=False, disable_target_task_filter=False):
 
 
 def filter_tasks_by_paths(tasks, paths):
-    resolver = TestResolver.from_environment(cwd=here)
+    resolver = TestResolver.from_environment(cwd=here, loader_cls=TestManifestLoader)
     run_suites, run_tests = resolver.resolve_metadata(paths)
     flavors = set([(t['flavor'], t.get('subsuite')) for t in run_tests])
 
@@ -137,7 +137,7 @@ def filter_tasks_by_paths(tasks, paths):
 
 
 def resolve_tests_by_suite(paths):
-    resolver = TestResolver.from_environment(cwd=here)
+    resolver = TestResolver.from_environment(cwd=here, loader_cls=TestManifestLoader)
     _, run_tests = resolver.resolve_metadata(paths)
 
     suite_to_tests = defaultdict(list)