Add a presubmit check to guard changes with an active outages config.

Change-Id: Ic04dbb979d49437347ccb46e31f134b826165dcd
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2432860Reviewed-by: Stephen Martinis <martiniss@chromium.org>
Commit-Queue: Garrett Beaty <gbeaty@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812900}

infra/config/PRESUBMIT.py

@@ -49,3 +49,93 @@ def CheckLucicfgGenOutputDev(input_api, output_api):
 def CheckChangedLUCIConfigs(input_api, output_api):
   return input_api.canned_checks.CheckChangedLUCIConfigs(
       input_api, output_api)
+
+
+# Footer indicating a CL that is trying to address an outage by some mechanism
+# other than those in infra/config/outages
+_OUTAGE_ACTION_FOOTER = 'Infra-Config-Outage-Action'
+# Footer acknowledging that an outages configuration is in effect when making an
+# unrelated change
+_IGNORE_OUTAGE_FOOTER = 'Infra-Config-Ignore-Outage'
+
+def CheckOutagesConfigOnCommit(input_api, output_api):
+  outages_pyl = input_api.os_path.join(
+      input_api.PresubmitLocalPath(), 'generated/outages.pyl')
+  with open(outages_pyl) as f:
+    outages_config = input_api.ast.literal_eval(f.read())
+
+  if not outages_config:
+    footers = input_api.change.GitFootersFromDescription()
+    return [
+        output_api.PresubmitError(
+            'There is no outages configuration in effect, '
+            'please remove the {} footer from your CL description.'
+            .format(footer))
+        for footer in (_OUTAGE_ACTION_FOOTER, _IGNORE_OUTAGE_FOOTER)
+        if footer in footers
+    ]
+
+  # Any of the config files under infra/config/outages
+  outages_config_files = set()
+  # Any of the config files under infra/config/generated
+  generated_config_files = set()
+  # Any config files that are not under infra/config/outages or
+  # infra/config/generated
+  config_files = set()
+  for p in input_api.LocalPaths():
+    if p in ('README.md', 'OWNERS'):
+      continue
+    if p.startswith('infra/config/outages/'):
+      outages_config_files.add(p)
+      continue
+    if p.startswith('infra/config/generated/'):
+      generated_config_files.add(p)
+      continue
+    config_files.add(p)
+
+  # If the only changes to non-generated config fies were the outages files,
+  # assume the change was addressing an outage and that no additional mechanism
+  # needs to be added
+  if outages_config_files and not config_files:
+    # REVIEWER: Should we prevent the footers from being here in this case?
+    return []
+
+  # If any non-generated, non-outages files were modified or if the generated
+  # config files were modified without any config files being modified (lucicfg
+  # change, etc.) then make sure the user knows that when the outages
+  # configuration is disabled, the generated configuration may change
+  if config_files or generated_config_files:
+    footers = input_api.change.GitFootersFromDescription()
+
+    has_action_footer = _OUTAGE_ACTION_FOOTER in footers
+    has_ignore_footer = _IGNORE_OUTAGE_FOOTER in footers
+
+    if has_action_footer and has_ignore_footer:
+      return [
+          output_api.PresubmitError(
+              'Only one of {} or {} should be present in your CL description'
+              .format(_OUTAGE_ACTION_FOOTER, _IGNORE_OUTAGE_FOOTER)),
+      ]
+
+    if not has_action_footer and not has_ignore_footer:
+      outages_config_lines = ['{}: {}'.format(k, v)
+                              for k, v in sorted(outages_config.items())]
+      return [
+          output_api.PresubmitError('\n'.join([
+              'The following outages configuration is in effect:\n  {}'
+              .format('\n  '.join(outages_config_lines)),
+              ('The effect of your change may not be visible '
+               'in the generated configuration.'),
+              ('If your change is addressing the outage, '
+               'please add the footer {} with a link for the outage.')
+              .format(_OUTAGE_ACTION_FOOTER),
+              ('If your change is not addressing the outage '
+               'but you still wish to land it, please add the footer '
+               '{} with a reason.')
+              .format(_IGNORE_OUTAGE_FOOTER),
+              ('For more information on outages configuration, '
+               'see https://chromium.googlesource.com/chromium/src/+/refs/heads/master/infra/config/outages'),
+          ])),
+      ]
+
+  return []

infra/config/generated/outages.pyl

+# This is a non-LUCI generated file
+# This details the current configuration modifications for outages settings
+{}

infra/config/main.star

@@ -32,6 +32,7 @@ lucicfg.config(
         "luci-notify.cfg",
         "luci-notify/email-templates/*.template",
         "luci-scheduler.cfg",
+        "outages.pyl",
         "project.cfg",
         "project.pyl",
         "realms.cfg",

infra/config/outages/README.md

@@ -29,3 +29,27 @@ available parameters are:
   other workarounds to improve the CQ experience for developers rather than
   tracking down which experimental tryjobs would be using the capacity that is
   needed for the particular outage.
+
+# Making changes during an outage
+
+If you attempt to make a configuration change while an outages configuration is
+enabled then the actual effect of your change may not be apparent if the outages
+configuration impacts the portion of the configuration that you are modifying.
+To prevent someone from unknowingly making such a change, a presubmit check will
+prevent changes from being landed if there is an outages configuration in effect
+unless all of the following are true:
+
+* 1 or more LUCI configuration files within //infra/config/outages are modified.
+* 0 or more LUCI configuration files within //infra/config/generated are
+  modified.
+* 0 other LUCI configuration files within //infra/config are modified.
+
+If an outages configuration is in effect and you need to make a change that
+doesn't meet these conditions to try and address the outage, add the footer
+`Infra-Config-Outage-Action`. The value for the footer should be some link that
+provides context on the outage being addressed.
+
+If an outages configuration is in effect and you need to make an unrelated
+change that cannot wait until the outage has been addressed, add the footer
+`Infra-Config-Ignore-Outage`. The value for the footer should explain why it is
+necessary to make such a change.

infra/config/outages/config.star

@@ -7,6 +7,10 @@ def _outages_config(*, disable_cq_experiments = False):
         disable_cq_experiments = disable_cq_experiments,
     )
 
+# The default value that is used by a generator to compare against the current
+# config to output the effective outages configuration
+DEFAULT_CONFIG = _outages_config()
+
 # See README.md for documentation on allowable configuration values
 config = _outages_config(
 )

infra/config/outages/outages.star

@@ -2,9 +2,24 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-load("./config.star", "config")
+load("./config.star", "DEFAULT_CONFIG", "config")
 load("@stdlib//internal/luci/proto.star", "cq_pb")
 
+def _generate_outages_file(ctx):
+    config_to_write = {}
+    for a in dir(config):
+        value = getattr(config, a)
+        if value != getattr(DEFAULT_CONFIG, a):
+            config_to_write[a] = value
+    ctx.output["outages.pyl"] = "\n".join([
+        "# This is a non-LUCI generated file",
+        "# This details the current configuration modifications for outages settings",
+        repr(config_to_write),
+        "",
+    ])
+
+lucicfg.generator(_generate_outages_file)
+
 def _disable_cq_experiments(ctx):
     if not config.disable_cq_experiments:
         return
@@ -12,8 +27,7 @@ def _disable_cq_experiments(ctx):
     for c in ctx.output["commit-queue.cfg"].config_groups:
         if c.verifiers.tryjob == cq_pb.Verifiers.Tryjob():
             # Accessing the tryjob field where it wasn't set causes it to be set
-            # to an empty message and added to the output, setting to None
-            # prevents the change to the output
+            # to an empty message and added to the output
             c.verifiers.tryjob = None
             continue
         for b in c.verifiers.tryjob.builders: