pw_presubmit: Only apply coverage to primary change

Bug: b/390206195
Change-Id: I53d696cee91834fe4e752f5dc88752fefb05006a
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/260475
Lint: Lint 🤖 <[email protected]>
Reviewed-by: Ted Pudlik <[email protected]>
Docs-Not-Needed: Rob Mohr <[email protected]>
Presubmit-Verified: CQ Bot Account <[email protected]>
Commit-Queue: Auto-Submit <[email protected]>
Pigweed-Auto-Submit: Rob Mohr <[email protected]>

pw_presubmit/py/pw_presubmit/build.py

@@ -54,6 +54,7 @@
 )
 from pw_presubmit.presubmit_context import (
     LuciContext,
+    LuciTrigger,
     PresubmitContext,
     PresubmitFailure,
 )
@@ -1030,13 +1031,29 @@ def _copy_to_gcs(ctx: PresubmitContext, filepath: Path, gcs_dst: str):
         call(*cmd, tee=outs)
 
 
+class NoPrimaryTriggerError(Exception):
+    pass
+
+
+def _get_primary_change(ctx: PresubmitContext) -> LuciTrigger:
+    assert ctx.luci is not None
+
+    if len(ctx.luci.triggers) == 1:
+        return ctx.luci.triggers[0]
+
+    for trigger in ctx.luci.triggers:
+        if trigger.primary:
+            return trigger
+
+    raise NoPrimaryTriggerError(repr(ctx.luci.triggers))
+
+
 def _write_coverage_metadata(
     ctx: PresubmitContext, options: CoverageOptions
 ) -> Sequence[Path]:
     """Write out Kalypsi coverage metadata file(s) and return their paths."""
     assert ctx.luci is not None
-    assert len(ctx.luci.triggers) == 1
-    change = ctx.luci.triggers[0]
+    change = _get_primary_change(ctx)
 
     metadata = {
         'trace_type': options.common.trace_type,

pw_presubmit/py/pw_presubmit/presubmit_context.py

@@ -141,6 +141,8 @@ class LuciTrigger:
             patch for unsubmitted changes and the hash for submitted changes.
         gerrit_name: The name of the googlesource.com Gerrit host.
         submitted: Whether the change has been submitted or is still pending.
+        primary: Whether this change was the change that triggered a build or
+            if it was imported by that triggering change.
         gerrit_host: The scheme and hostname of the googlesource.com Gerrit
             host.
         gerrit_url: The full URL to this change on the Gerrit host.
@@ -155,6 +157,7 @@ class LuciTrigger:
     ref: str
     gerrit_name: str
     submitted: bool
+    primary: bool
 
     @property
     def gerrit_host(self):
@@ -174,6 +177,7 @@ def gitiles_url(self):
     def create_from_environment(
         env: dict[str, str] | None = None,
     ) -> Sequence['LuciTrigger']:
+        """Create a LuciTrigger from the environment."""
         if not env:
             env = os.environ.copy()
         raw_path = env.get('TRIGGERING_CHANGES_JSON')
@@ -195,6 +199,7 @@ def create_from_environment(
                     'ref',
                     'gerrit_name',
                     'submitted',
+                    'primary',
                 }
                 if keys <= trigger.keys():
                     result.append(LuciTrigger(**{x: trigger[x] for x in keys}))
@@ -203,6 +208,7 @@ def create_from_environment(
 
     @staticmethod
     def create_for_testing(**kwargs):
+        """Create a LuciTrigger for testing."""
         change = {
             'number': 123456,
             'patchset': 1,
@@ -212,6 +218,7 @@ def create_for_testing(**kwargs):
             'ref': 'refs/changes/56/123456/1',
             'gerrit_name': 'pigweed',
             'submitted': True,
+            'primary': True,
         }
         change.update(kwargs)