cmd/dist: always include variant in package names

Our attempt to evenly distribute tests across shards struggles a bit
because certain long-running targets are very difficult to distinguish
in ResultDB, namely racebench and the test directory tests. These are
the only tests where the JSON output from dist omits the variant from
the package, making it impossible to distinguish them in the test result
data. My current suspicion is that this is preventing the load balancing
from being effective for the race builders in particular, though I worry
the longtest builders have a similar situation with the test directory
tests.

For #65814.

Change-Id: I5804c2af092ff9aa4a3f0f6897b4a57c4628f837
Reviewed-on: https://go-review.googlesource.com/c/go/+/681955
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Bypass: Michael Knyszek <mknyszek@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

Author: mknyszek

src/cmd/dist/test.go

@@ -336,6 +336,10 @@ type goTest struct {
 	// omitVariant indicates that variant is used solely for the dist test name and
 	// that the set of test names run by each variant (including empty) of a package
 	// is non-overlapping.
+	//
+	// TODO(mknyszek): Consider removing omitVariant as it is no longer set to true
+	// by any test. It's too valuable to have timing information in ResultDB that
+	// corresponds directly with dist names for tests.
 	omitVariant bool
 
 	// We have both pkg and pkgs as a convenience. Both may be set, in which
@@ -595,8 +599,11 @@ func (t *tester) registerRaceBenchTest(pkg string) {
 		defer timelog("end", dt.name)
 		ranGoBench = true
 		return (&goTest{
-			variant:     "racebench",
-			omitVariant: true,               // The only execution of benchmarks in dist; benchmark names are guaranteed not to overlap with test names.
+			variant: "racebench",
+			// Include the variant even though there's no overlap in test names.
+			// This makes the test targets distinct, allowing our build system to record
+			// elapsed time for each one, which is useful for load-balancing test shards.
+			omitVariant: false,
 			timeout:     1200 * time.Second, // longer timeout for race with benchmarks
 			race:        true,
 			bench:       true,
@@ -983,8 +990,11 @@ func (t *tester) registerTests() {
 			id := fmt.Sprintf("%d_%d", shard, nShards)
 			t.registerTest("../test",
 				&goTest{
-					variant:     id,
-					omitVariant: true, // Shards of the same Go package; tests are guaranteed not to overlap.
+					variant: id,
+					// Include the variant even though there's no overlap in test names.
+					// This makes the test target more clearly distinct in our build
+					// results and is important for load-balancing test shards.
+					omitVariant: false,
 					pkg:         "cmd/internal/testdir",
 					testFlags:   []string{fmt.Sprintf("-shard=%d", shard), fmt.Sprintf("-shards=%d", nShards)},
 					runOnHost:   true,