cmd/coordinator: use corresponding Go for x repo release branch with suffix

When a golang.org/x repo release branch is being tested, the intention
is to test it with the same Go version where it will be used, rather
than the latest Go version in development plus prior releases of Go.

The previous equality check was very strict and did not work for
golang.org/x release branches with a dash-separated suffix. We have
a need for such release branches occasionally and want them to work.

Fixes golang/go#42127.

Change-Id: I934b540f83a2b8c616e3d3a5477fb3c471aa595b
Reviewed-on: https://go-review.googlesource.com/c/build/+/264203
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Trust: Dmitri Shuralyov <[email protected]>
Reviewed-by: Alexander Rakoczy <[email protected]>

Author: dmitshur

cmd/coordinator/coordinator.go

@@ -1216,8 +1216,11 @@ func newTrySet(work *apipb.GerritTryWorkItem) *trySet {
 		// By default, use the first GoCommit, which represents Go tip (master branch).
 		goRev = work.GoCommit[0]
 	}
-	for i, branch := range work.GoBranch {
-		if branch == work.Branch {
+	for i, goBranch := range work.GoBranch {
+		// There are two cases where we want to change goRev to work.GoCommit[i]:
+		// 1. CL branch is like "master" or "release-branch.go1.15" and matches the Go branch exactly.
+		// 2. CL branch is like "release-branch.go1.15-suffix" and its prefix matches.
+		if work.Branch == goBranch || strings.HasPrefix(work.Branch, goBranch+"-") {
 			goRev = work.GoCommit[i]
 		}
 	}

cmd/coordinator/coordinator_test.go

@@ -180,6 +180,33 @@ func TestIssue28891(t *testing.T) {
 	}
 }
 
+// Test that trybot on release-branch.go1.N-{suffix} branch of a golang.org/x repo
+// uses the Go revision from Go repository's release-branch.go1.N branch.
+// See golang.org/issue/42127.
+func TestIssue42127(t *testing.T) {
+	testingKnobSkipBuilds = true
+
+	work := &apipb.GerritTryWorkItem{ // Roughly based on https://go-review.googlesource.com/c/net/+/264058/1.
+		Project:   "net",
+		Branch:    "release-branch.go1.15-bundle",
+		ChangeId:  "I546597cedf3715e6617babcb3b62140bf1857a27",
+		Commit:    "286322bb8662ddff3686e42a01c33a1d47d25153",
+		GoCommit:  []string{"b2a8317b31d652b3ee293a313269b8290bcdf96c", "3b1f07fff774f86f13316f7bec6552566568fc10", "768b64711ae4292bd9a02c9cc8d44282f5fac66b"},
+		GoBranch:  []string{"master", "release-branch.go1.15", "release-branch.go1.14"},
+		GoVersion: []*apipb.MajorMinor{{1, 16}, {1, 15}, {1, 14}},
+	}
+	ts := newTrySet(work)
+	if len(ts.builds) == 0 {
+		t.Fatal("no builders in try set, want at least 1")
+	}
+	for i, bs := range ts.builds {
+		const go115Revision = "3b1f07fff774f86f13316f7bec6552566568fc10"
+		if bs.BuilderRev.Rev != go115Revision {
+			t.Errorf("build[%d]: %s: x/net on release-branch.go1.15-bundle branch should be tested with Go 1.15, but isn't", i, bs.NameAndBranch())
+		}
+	}
+}
+
 // tests that we don't test Go 1.10 for the build repo
 func TestNewTrySetBuildRepoGo110(t *testing.T) {
 	testingKnobSkipBuilds = true