Fix background layout updates in zuul-web

Change Ia0a524053a110e8e48f709d219651e2ad9c8513d updated the scheduler
to more aggressively use the file cache, but did not make the corresponding
updates to zuul-web.  This means that configuration changes are not being
reflected in the web UI until the service restarts.

This corrects that and adds a test.

Change-Id: Iebdf485105bd02e57fa0d3db5ba162308b640ca0

tests/fixtures/config/empty-config/git/common-config/README

@@ -0,0 +1 @@
+test

tests/fixtures/config/empty-config/git/common-config/new-zuul.yaml

@@ -0,0 +1,52 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+        - event: comment-added
+          comment: '^(Patch Set [0-9]+:\n\n)?(?i:recheck)$'
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- pipeline:
+    name: gate
+    manager: dependent
+    success-message: Build succeeded (gate).
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - Approved: 1
+    success:
+      gerrit:
+        Verified: 2
+        submit: true
+    failure:
+      gerrit:
+        Verified: -2
+    start:
+      gerrit:
+        Verified: 0
+    precedence: high
+
+- job:
+    name: base
+    parent: null
+
+- job:
+    name: test
+    run: playbooks/run.yaml
+    
+- project:
+    name: common-config
+    check:
+      jobs:
+        - test
+    gate:
+      jobs:
+        - test

tests/fixtures/config/empty-config/git/common-config/playbooks/run.yaml

@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []

tests/fixtures/config/empty-config/git/org_project/README

@@ -0,0 +1 @@
+test

tests/fixtures/config/empty-config/main.yaml

@@ -0,0 +1,8 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project

tests/unit/test_web.py

@@ -1265,6 +1265,23 @@ class TestWebMultiTenant(BaseTestWeb):
                          sorted(["tenant-one", "tenant-two", "tenant-four"]))
 
 
+class TestEmptyConfig(BaseTestWeb):
+    tenant_config_file = 'config/empty-config/main.yaml'
+
+    def test_empty_config_startup(self):
+        # Test that we can bootstrap a tenant with an empty config
+
+        resp = self.get_url("api/tenant/tenant-one/jobs").json()
+        self.assertEqual(len(resp), 1)
+        self.commitConfigUpdate(
+            'common-config',
+            'config/empty-config/git/common-config/new-zuul.yaml')
+        self.scheds.execute(lambda app: app.sched.reconfigure(app.config))
+        self.waitUntilSettled()
+        resp = self.get_url("api/tenant/tenant-one/jobs").json()
+        self.assertEqual(len(resp), 3)
+
+
 class TestWebSecrets(BaseTestWeb):
     tenant_config_file = 'config/secrets/main.yaml'
 

zuul/web/__init__.py

@@ -2084,7 +2084,6 @@ class ZuulWeb(object):
         tenant_names = set(self.abide.tenants)
         tenant_names.update(self.unparsed_abide.tenants.keys())
 
-        min_ltimes = defaultdict(lambda: defaultdict(lambda: -1))
         for tenant_name in tenant_names:
             # Reload the tenant if the layout changed.
             if (self.local_layout_state.get(tenant_name)
@@ -2096,11 +2095,15 @@ class ZuulWeb(object):
                 layout_uuid = layout_state and layout_state.uuid
 
                 if layout_state:
+                    min_ltimes = self.tenant_layout_state.getMinLtimes(
+                        layout_state)
                     branch_cache_min_ltimes = (
                         layout_state.branch_cache_min_ltimes)
                 else:
                     # Consider all project branch caches valid if
                     # we don't have a layout state.
+                    min_ltimes = defaultdict(
+                        lambda: defaultdict(lambda: -1))
                     branch_cache_min_ltimes = defaultdict(lambda: -1)
 
                 # The tenant will be stored in self.abide.tenants after