Don't run most builders on infra/config changes.

Change-Id: Ib91c6c6d7876b2200d09f6e79a35d8a257375d4d
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2314164
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Auto-Submit: Garrett Beaty <gbeaty@chromium.org>
Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791297}

infra/config/generated/cq-builders.md

@@ -5,13 +5,17 @@
 
 [TOC]
 
+Changes that only modify files in //infra/config, which do not change any build
+outputs, only require the chromium_presubmit builder to pass before landing.
+
 Each builder name links to that builder on Milo. The "matching builders" links
 point to the file used to determine which configurations a builder should copy
 when running. These links might 404 or error; they are hard-coded right now,
 using common assumptions about how builders are configured.
 
 ## Required builders
-These builders must pass before a CL may land.
+These builders must pass before a CL may land that affects files outside of
+//infra/config.
 
 * [android-binary-size](https://ci.chromium.org/p/chromium/builders/try/android-binary-size) ([definition](https://cs.chromium.org/search?q=package:%5Echromium$+file:/cq.star$+-file:/beta/+-file:/stable/+android-binary-size)) ([matching builders](https://cs.chromium.org/search?q=+file:trybots.py+android-binary-size))
 

infra/config/generators/cq-builders-md.star

@@ -2,6 +2,9 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
+load('//lib/try.star', 'INFRA_CONFIG_LOCATION_REGEXP')
+
+
 _MD_HEADER = """\
 <!-- Auto-generated by lucicfg (via cq-builders-md.star). -->
 <!-- Do not modify manually. -->
@@ -10,6 +13,9 @@ _MD_HEADER = """\
 
 [TOC]
 
+Changes that only modify files in //infra/config, which do not change any build
+outputs, only require the chromium_presubmit builder to pass before landing.
+
 Each builder name links to that builder on Milo. The "matching builders" links
 point to the file used to determine which configurations a builder should copy
 when running. These links might 404 or error; they are hard-coded right now,
@@ -17,7 +23,8 @@ using common assumptions about how builders are configured.
 """
 
 _REQUIRED_HEADER = """\
-These builders must pass before a CL may land.
+These builders must pass before a CL may land that affects files outside of
+//infra/config.
 """
 
 _OPTIONAL_HEADER = """\
@@ -62,12 +69,27 @@ def _get_main_config_group_builders(ctx):
   fail('Could not find the main CQ group')
 
 
+def _normalize_builder(builder):
+  location_regexp_exclude = [r for r in builder.location_regexp_exclude
+                             if r != INFRA_CONFIG_LOCATION_REGEXP]
+  location_regexp = builder.location_regexp
+  if list(location_regexp) == ['.*'] and not location_regexp_exclude:
+    location_regexp = None
+  return struct(
+      name = builder.name,
+      experiment_percentage = builder.experiment_percentage,
+      includable_only = builder.includable_only,
+      location_regexp = location_regexp,
+      location_regexp_exclude = location_regexp_exclude,
+  )
+
 def _group_builders_by_section(builders):
   required = []
   experimental = []
   optional = []
 
   for builder in builders:
+    builder = _normalize_builder(builder)
     if builder.experiment_percentage:
       experimental.append(builder)
     elif builder.location_regexp or builder.location_regexp_exclude:

infra/config/lib/try.star

@@ -23,6 +23,9 @@ load('./builders.star', 'builders')
 load('./args.star', 'args')
 
 
+INFRA_CONFIG_LOCATION_REGEXP = 'infra/config/.+'
+
+
 defaults = args.defaults(
     extends=builders.defaults,
     add_to_list_view = False,
@@ -165,17 +168,23 @@ def tryjob(
     experiment_percentage=None,
     location_regexp=None,
     location_regexp_exclude=None,
-    cancel_stale=None):
+    cancel_stale=None,
+    run_on_infra_config_changes=False):
   """Specifies the details of a tryjob verifier.
 
   See https://chromium.googlesource.com/infra/luci/luci-go/+/refs/heads/master/lucicfg/doc/README.md#luci.cq_tryjob_verifier
-  for details on the arguments. The cq_group parameter supports a module-level
-  default that defaults to None.
+  for details on the most of the arguments.
+
+  Arguments:
+    run_on_infra_changes - A bool indicating whether the try job should be run
+      for changes against //infra/config.
 
   Returns:
     A struct that can be passed to the `tryjob` argument of `try_.builder` to
     enable the builder for CQ.
   """
+  if not run_on_infra_config_changes:
+    location_regexp_exclude = [INFRA_CONFIG_LOCATION_REGEXP] + (location_regexp_exclude or [])
   return struct(
       disable_reuse = disable_reuse,
       experiment_percentage = experiment_percentage,

infra/config/subprojects/chromium/try.star

@@ -343,6 +343,7 @@ try_.chromium_linux_builder(
     },
     tryjob = try_.job(
         disable_reuse = True,
+        run_on_infra_config_changes = True,
     ),
 )
 

infra/config/subprojects/chromium/versioned/m84/buckets/try.star

@@ -311,6 +311,7 @@ try_.chromium_linux_builder(
     },
     tryjob = try_.job(
         disable_reuse = True,
+        run_on_infra_config_changes = True,
     ),
 )
 

infra/config/subprojects/chromium/versioned/m85/buckets/try.star

@@ -315,6 +315,7 @@ try_.chromium_linux_builder(
     },
     tryjob = try_.job(
         disable_reuse = True,
+        run_on_infra_config_changes = True,
     ),
 )