mesh-delivery-checker: with no cause told apart, a race report is the cause (issue 1901)

An older build module's output for a race after the tests' PASS is now worded
by the race's heading, access and frame, not by go test's PASS or the report's
separator line (1901/AC5).

modules/mesh-delivery-checker/internal/check/judge.go

@@ -583,9 +583,24 @@ func dropSummary(out string) (string, bool) {
 	return strings.TrimSpace(strings.Join(kept, "\n")), passed
 }
 
-// causeIn is the first "panic:", "fatal error:" or "signal:" line of a failure's output, in that order, or "".
+// causeIn is a race the race detector reported, as its heading, its access and the frame that made it ("WARNING: DATA
+// RACE: Write at 0x... by goroutine 9 in pkg.F.func1()"); else the first "panic:", "fatal error:" or "signal:" line of a
+// failure's output, in that order; or "".
 func causeIn(out string) string {
 	lines := strings.Split(out, "\n")
+	for i, l := range lines {
+		if strings.TrimSpace(l) != "WARNING: DATA RACE" {
+			continue
+		}
+		words := "WARNING: DATA RACE"
+		if i+1 < len(lines) && strings.TrimSpace(lines[i+1]) != "" {
+			words += ": " + strings.TrimSuffix(strings.TrimSpace(lines[i+1]), ":")
+			if i+2 < len(lines) && strings.HasPrefix(lines[i+2], "  ") {
+				words += " in " + strings.TrimSpace(lines[i+2])
+			}
+		}
+		return words
+	}
 	for _, prefix := range []string{"panic: ", "fatal error: ", "signal: "} {
 		for _, l := range lines {
 			if l = strings.TrimSpace(l); strings.HasPrefix(l, prefix) {

modules/mesh-delivery-checker/internal/check/package_cause_test.go

@@ -8,13 +8,15 @@ import (
 // What the build module before this fix sent for two packages that failed after their tests passed (issue 1901, its third
 // meeting: a try of mesh-controller kept "PASS" as its failure's words). Each is that build module's Output for the real
 // `go test -json` of a throwaway package (mesh-catalog modules/mesh-build-go testdata/captured/go-test-json-pkg-*.jsonl):
-// TestMain panicking in a goroutine after m.Run, and TestMain exiting 2 after m.Run.
+// TestMain panicking in a goroutine after m.Run, TestMain exiting 2 after m.Run, and TestMain racing after m.Run.
 const (
 	oldPassThenPanic = "PASS\npanic: the bus closed after the tests: nats: connection closed\ngoroutine 20 [running]:\n" +
 		"example.com/passthenfail.TestMain.func1()\n\t/tmp/fix-1901b/passthenfail/p_test.go:13 +0x25\n" +
 		"created by example.com/passthenfail.TestMain in goroutine 1\n\t/tmp/fix-1901b/passthenfail/p_test.go:13 +0x25\n" +
 		"FAIL\texample.com/passthenfail\t0.005s"
 	oldPassThenExit = "PASS\nFAIL\texample.com/mainexit\t0.004s"
+	// TestMain racing after m.Run passed, under go test -race (go-test-json-pkg-racemain.jsonl).
+	oldPassThenRace = "PASS\n==================\nWARNING: DATA RACE\nWrite at 0x000000836428 by goroutine 9:\n  example.com/racemain.TestMain.func1()\n      /tmp/fix-1901b/racemain/p_test.go:15 +0x24\nPrevious write at 0x000000836428 by main goroutine:\n  example.com/racemain.TestMain()\n      /tmp/fix-1901b/racemain/p_test.go:16 +0x44\n  main.main()\n      _testmain.go:48 +0x171\nGoroutine 9 (running) created at:\n  example.com/racemain.TestMain()\n      /tmp/fix-1901b/racemain/p_test.go:15 +0x37\n  main.main()\n      _testmain.go:48 +0x171\n==================\nFound 1 data race(s)\nFAIL\texample.com/racemain\t1.031s"
 )
 
 // A failure with no cause told apart never has "PASS" or "ok" as its words: the checker takes the panic line from the
@@ -25,6 +27,7 @@ func TestAPackageFailureIsNeverWordedPass(t *testing.T) { // 1901/AC5
 	}{
 		{"panic after the tests", oldPassThenPanic, "panic: the bus closed after the tests: nats: connection closed"},
 		{"exit after the tests", oldPassThenExit, "the tests passed, then the test program exited with a failure"},
+		{"race after the tests", oldPassThenRace, "WARNING: DATA RACE: Write at 0x000000836428 by goroutine 9 in example.com/racemain.TestMain.func1()"},
 		{"a panic deep in a long output", "PASS\npanic: the seat row vanished\n" + strings.Repeat("goroutine 7 [chan receive]:\n\tsome/frame.go:1 +0x1\n", 300) + "FAIL\tp\t2.0s", "panic: the seat row vanished"},
 	}
 	for _, c := range cases {