[misc] Split output events into lines and key build events by full path

Build output events may carry several lines in one payload; buffering
them as one entry undercounted the caps and skipped the indentation of
continuation lines. Each payload is split into lines first.

A package compiled for several test binaries reports build events under
"pkg [a.test]" and "pkg [b.test]". Cutting the suffix off merged their
buffers, and the first build-fail printed and deleted both. The full
import path is now the key and the suffix is only dropped for display.

tools/gotestsummary/main.go

@@ -48,8 +48,9 @@ type event struct {
 	Test    string  `json:"Test"`
 	Output  string  `json:"Output"`
 	Elapsed float64 `json:"Elapsed"`
-	// ImportPath is set instead of Package on build events; it carries a
-	// " [pkg.test]" suffix for a test binary.
+	// ImportPath is set instead of Package on build events. It carries a
+	// " [pkg.test]" suffix naming the test binary the package was compiled
+	// for, and the same package can be built for several binaries at once.
 	ImportPath string `json:"ImportPath"`
 }
 
@@ -150,8 +151,10 @@ func (s *summarizer) consume(r io.Reader) error {
 }
 
 func (s *summarizer) handle(ev event) {
-	if ev.Package == "" && ev.ImportPath != "" {
-		ev.Package, _, _ = strings.Cut(ev.ImportPath, " [")
+	if ev.Package == "" {
+		// Keep the full path as the key so concurrent builds of one package for
+		// different test binaries do not share, and delete, each other's state.
+		ev.Package = ev.ImportPath
 	}
 	key := testKey{pkg: ev.Package, name: ev.Test}
 	switch ev.Action {
@@ -164,7 +167,10 @@ func (s *summarizer) handle(ev event) {
 			}
 		}
 	case "output", "build-output":
-		s.handleOutput(key, strings.TrimRight(ev.Output, "\n"))
+		// Test output arrives one line per event; build output may carry several.
+		for _, line := range strings.Split(strings.TrimRight(ev.Output, "\n"), "\n") {
+			s.handleOutput(key, line)
+		}
 	case "build-fail":
 		s.handlePackageResult(ev)
 	case "pass", "fail", "skip":
@@ -384,5 +390,6 @@ func (s *summarizer) printSlowest(title string, limit int, keep func(testResult)
 }
 
 func shortPkg(pkg string) string {
+	pkg, _, _ = strings.Cut(pkg, " [")
 	return strings.TrimPrefix(pkg, modulePrefix)
 }

tools/gotestsummary/main_test.go

@@ -84,15 +84,14 @@ func TestStoreSetupTimeIsAttributedToTheTest(t *testing.T) {
 
 func TestBuildFailureShowsCompilerOutput(t *testing.T) {
 	events := `
-{"Action":"build-output","ImportPath":"a [a.test]","Output":"# a [a.test]\n"}
-{"Action":"build-output","ImportPath":"a [a.test]","Output":"a_test.go:7:2: undefined: nope\n"}
+{"Action":"build-output","ImportPath":"a [a.test]","Output":"# a [a.test]\na_test.go:7:2: undefined: nope\na_test.go:9:2: undefined: nope2\n"}
 {"Action":"build-fail","ImportPath":"a [a.test]"}
 `
 	got := feed(t, events)
 	for _, want := range []string{
 		"FAIL a 0s",
 		"==== output of a outside tests ====",
-		"    a_test.go:7:2: undefined: nope",
+		"    a_test.go:7:2: undefined: nope\n    a_test.go:9:2: undefined: nope2",
 	} {
 		if !strings.Contains(got, want) {
 			t.Errorf("output lacks %q:\n%s", want, got)
@@ -100,6 +99,24 @@ func TestBuildFailureShowsCompilerOutput(t *testing.T) {
 	}
 }
 
+func TestBuildVariantsOfOnePackageKeepSeparateOutput(t *testing.T) {
+	events := `
+{"Action":"build-output","ImportPath":"a [a.test]","Output":"a.go:1:1: broken for a.test\n"}
+{"Action":"build-output","ImportPath":"a [b.test]","Output":"a.go:1:1: broken for b.test\n"}
+{"Action":"build-fail","ImportPath":"a [a.test]"}
+{"Action":"build-fail","ImportPath":"a [b.test]"}
+`
+	got := feed(t, events)
+	if strings.Count(got, "==== output of a outside tests ====") != 2 {
+		t.Errorf("expected one output block per build variant:\n%s", got)
+	}
+	for _, want := range []string{"broken for a.test", "broken for b.test"} {
+		if strings.Count(got, want) != 1 {
+			t.Errorf("expected %q exactly once:\n%s", want, got)
+		}
+	}
+}
+
 func TestPassingPackageOutputIsNotPrinted(t *testing.T) {
 	events := `
 {"Action":"output","Package":"a","Output":"level=info msg=\"noise between tests\"\n"}