gistfile1.txt

diff --git a/taskcluster/ci/toolchain/geckodriver.yml b/taskcluster/ci/toolchain/geckodriver.yml
--- a/taskcluster/ci/toolchain/geckodriver.yml
+++ b/taskcluster/ci/toolchain/geckodriver.yml
@@ -7,16 +7,17 @@ job-defaults:
     worker-type: b-linux
     worker:
         max-run-time: 1800
     run-on-projects: ['trunk']
     attributes:
         build_type: opt
         geckodriver: true
         shippable: true
+        rebuild-on-release: true
     run:
         script: build-geckodriver.sh
         toolchain-artifact: public/build/geckodriver.tar.gz
         sparse-profile: null
         resources:
             - 'testing/geckodriver'
             - 'testing/mozbase/rust'
             - 'testing/webdriver'
diff --git a/taskcluster/docs/attributes.rst b/taskcluster/docs/attributes.rst
--- a/taskcluster/docs/attributes.rst
+++ b/taskcluster/docs/attributes.rst
@@ -376,8 +376,14 @@ If set to true, this task will not be ch
 MOZ_AUTOMATION_PACKAGE_TESTS is set correctly based on whether or not the task
 has dependent tests. This should only be used in very unique situations, such
 as Windows AArch64 builds that copy test packages between build tasks.
 
 geckodriver
 ===========
 If non-empty, declares that the (toolchain) task is a `geckodriver`
 task that produces a binary that should be signed.
+
+rebuild-on-release
+==================
+If true, the digest for this task will also depend on if the branch is a
+release branch.  This will cause tasks like toolchains to be rebuilt as they
+move from e.g.  autoland to mozilla-central.
diff --git a/taskcluster/taskgraph/optimize/strategies.py b/taskcluster/taskgraph/optimize/strategies.py
--- a/taskcluster/taskgraph/optimize/strategies.py
+++ b/taskcluster/taskgraph/optimize/strategies.py
@@ -33,21 +33,23 @@ class IndexSearch(OptimizationStrategy):
 
     def should_replace_task(self, task, params, index_paths):
         "Look for a task with one of the given index paths"
         for index_path in index_paths:
             try:
                 task_id = find_task_id(
                     index_path,
                     use_proxy=bool(os.environ.get('TASK_ID')))
+                logger.debug("found task %s for %s: %s", task_id, task.label, index_paths)
                 return task_id
             except KeyError:
                 # 404 will end up here and go on to the next index path
                 pass
 
+        logger.debug("didn't find a cache hit for %s: %s", task.label, index_paths)
         return False
 
 
 @register_strategy("skip-unless-changed")
 class SkipUnlessChanged(OptimizationStrategy):
     def should_remove_task(self, task, params, file_patterns):
         # pushlog_id == -1 - this is the case when run from a cron.yml job
         if params.get('pushlog_id') == -1:
diff --git a/taskcluster/taskgraph/transforms/job/toolchain.py b/taskcluster/taskgraph/transforms/job/toolchain.py
--- a/taskcluster/taskgraph/transforms/job/toolchain.py
+++ b/taskcluster/taskgraph/transforms/job/toolchain.py
@@ -16,16 +16,17 @@ from voluptuous import Optional, Require
 from taskgraph.transforms.job import (
     configure_taskdesc_for_run,
     run_job_using,
 )
 from taskgraph.transforms.job.common import (
     docker_worker_add_artifacts,
 )
 from taskgraph.util.hash import hash_paths
+from taskgraph.util.attributes import RELEASE_PROJECTS
 from taskgraph import GECKO
 import taskgraph
 
 
 CACHE_TYPE = 'toolchains.v3'
 
 toolchain_run_schema = Schema({
     Required('using'): 'toolchain-script',
@@ -95,16 +96,20 @@ def get_digest_data(config, run, taskdes
     image = taskdesc['worker'].get('docker-image', {}).get('in-tree')
     if image:
         data.append(image)
 
     # Likewise script arguments should influence the index.
     args = run.get('arguments')
     if args:
         data.extend(args)
+
+    if taskdesc['attributes'].get('rebuild-on-release'):
+        # Add whether this is a release branch or not
+        data.append(str(config.params['project'] in RELEASE_PROJECTS))
     return data
 
 
 toolchain_defaults = {
     'tooltool-downloads': False,
     'sparse-profile': 'toolchain-build',
 }
 
diff --git a/taskcluster/taskgraph/util/taskcluster.py b/taskcluster/taskgraph/util/taskcluster.py
--- a/taskcluster/taskgraph/util/taskcluster.py
+++ b/taskcluster/taskgraph/util/taskcluster.py
@@ -172,16 +172,17 @@ def get_artifact_path(task, path):
 
 
 def get_index_url(index_path, use_proxy=False, multiple=False):
     index_tmpl = liburls.api(get_root_url(use_proxy), 'index', 'v1', 'task{}/{}')
     return index_tmpl.format('s' if multiple else '', index_path)
 
 
 def find_task_id(index_path, use_proxy=False):
+    logger.debug("looking for %s in the index", index_path)
     try:
         response = _do_request(get_index_url(index_path, use_proxy))
     except requests.exceptions.HTTPError as e:
         if e.response.status_code == 404:
             raise KeyError("index path {} not found".format(index_path))
         raise
     return response.json()['taskId']