cmd/cover: add new "emit meta file" mode for packages without tests

Introduce a new mode of execution for instrumenting packages that have
no test files. Instead of just skipping packages with no test files
(during "go test -cover" runs), the go command will invoke cmd/cover
on the package passing in an option in the config file indicating that
it should emit a coverage meta-data file directly for the package (if
the package has no functions, an empty file is emitted). Note that
this CL doesn't actually wire up this functionality in the Go command,
that will come in a later patch.

Updates #27261.
Updates #58770
Updates #24570.

Cq-Include-Trybots: luci.golang.try:gotip-linux-amd64-longtest,gotip-windows-amd64-longtest
Change-Id: I01e8a3edb62441698c7246596e4bacbd966591c3
Reviewed-on: https://go-review.googlesource.com/c/go/+/495446
Reviewed-by: Bryan Mills <bcmills@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/cover/cfg_test.go

@@ -21,14 +21,15 @@ func writeFile(t *testing.T, path string, contents []byte) {
 	}
 }
 
-func writePkgConfig(t *testing.T, outdir, tag, ppath, pname string, gran string) string {
+func writePkgConfig(t *testing.T, outdir, tag, ppath, pname string, gran string, mpath string) string {
 	incfg := filepath.Join(outdir, tag+"incfg.txt")
 	outcfg := filepath.Join(outdir, "outcfg.txt")
 	p := covcmd.CoverPkgConfig{
-		PkgPath:     ppath,
+		PkgPath:      ppath,
-		PkgName:     pname,
+		PkgName:      pname,
-		Granularity: gran,
+		Granularity:  gran,
-		OutConfig:   outcfg,
+		OutConfig:    outcfg,
+		EmitMetaFile: mpath,
 	}
 	data, err := json.Marshal(p)
 	if err != nil {
@@ -74,10 +75,6 @@ func runPkgCover(t *testing.T, outdir string, tag string, incfg string, mode str
 	}
 }
 
-// Set to true when debugging unit test (to inspect debris, etc).
-// Note that this functionality does not work on windows.
-const debugWorkDir = false
-
 func TestCoverWithCfg(t *testing.T) {
 	testenv.MustHaveGoRun(t)
 
@@ -85,29 +82,7 @@ func TestCoverWithCfg(t *testing.T) {
 
 	// Subdir in testdata that has our input files of interest.
 	tpath := filepath.Join("testdata", "pkgcfg")
-
-	// Helper to collect input paths (go files) for a subdir in 'pkgcfg'
-	pfiles := func(subdir string) []string {
-		de, err := os.ReadDir(filepath.Join(tpath, subdir))
-		if err != nil {
-			t.Fatalf("reading subdir %s: %v", subdir, err)
-		}
-		paths := []string{}
-		for _, e := range de {
-			if !strings.HasSuffix(e.Name(), ".go") || strings.HasSuffix(e.Name(), "_test.go") {
-				continue
-			}
-			paths = append(paths, filepath.Join(tpath, subdir, e.Name()))
-		}
-		return paths
-	}
-
 	dir := tempDir(t)
-	if debugWorkDir {
-		dir = "/tmp/qqq"
-		os.RemoveAll(dir)
-		os.Mkdir(dir, 0777)
-	}
 	instdira := filepath.Join(dir, "insta")
 	if err := os.Mkdir(instdira, 0777); err != nil {
 		t.Fatal(err)
@@ -131,6 +106,7 @@ func TestCoverWithCfg(t *testing.T) {
 	}
 
 	var incfg string
+	apkgfiles := []string{filepath.Join(tpath, "a", "a.go")}
 	for _, scenario := range scenarios {
 		// Instrument package "a", producing a set of instrumented output
 		// files and an 'output config' file to pass on to the compiler.
@@ -139,9 +115,9 @@ func TestCoverWithCfg(t *testing.T) {
 		mode := scenario.mode
 		gran := scenario.gran
 		tag := mode + "_" + gran
-		incfg = writePkgConfig(t, instdira, tag, ppath, pname, gran)
+		incfg = writePkgConfig(t, instdira, tag, ppath, pname, gran, "")
 		ofs, outcfg, _ := runPkgCover(t, instdira, tag, incfg, mode,
-			pfiles("a"), false)
+			apkgfiles, false)
 		t.Logf("outfiles: %+v\n", ofs)
 
 		// Run the compiler on the files to make sure the result is
@@ -161,7 +137,7 @@ func TestCoverWithCfg(t *testing.T) {
 	errExpected := true
 	tag := "errors"
 	_, _, errmsg := runPkgCover(t, instdira, tag, "/not/a/file", mode,
-		pfiles("a"), errExpected)
+		apkgfiles, errExpected)
 	want := "error reading pkgconfig file"
 	if !strings.Contains(errmsg, want) {
 		t.Errorf("'bad config file' test: wanted %s got %s", want, errmsg)
@@ -171,7 +147,7 @@ func TestCoverWithCfg(t *testing.T) {
 	t.Logf("mangling in config")
 	writeFile(t, incfg, []byte("blah=foo\n"))
 	_, _, errmsg = runPkgCover(t, instdira, tag, incfg, mode,
-		pfiles("a"), errExpected)
+		apkgfiles, errExpected)
 	want = "error reading pkgconfig file"
 	if !strings.Contains(errmsg, want) {
 		t.Errorf("'bad config file' test: wanted %s got %s", want, errmsg)
@@ -181,8 +157,115 @@ func TestCoverWithCfg(t *testing.T) {
 	t.Logf("writing empty config")
 	writeFile(t, incfg, []byte("\n"))
 	_, _, errmsg = runPkgCover(t, instdira, tag, incfg, mode,
-		pfiles("a"), errExpected)
+		apkgfiles, errExpected)
 	if !strings.Contains(errmsg, want) {
 		t.Errorf("'bad config file' test: wanted %s got %s", want, errmsg)
 	}
 }
+
+func TestCoverOnPackageWithNoTestFiles(t *testing.T) {
+	testenv.MustHaveGoRun(t)
+
+	// For packages with no test files, the new "go test -cover"
+	// strategy is to run cmd/cover on the package in a special
+	// "EmitMetaFile" mode. When running in this mode, cmd/cover walks
+	// the package doing instrumention, but when finished, instead of
+	// writing out instrumented source files, it directly emits a
+	// meta-data file for the package in question, essentially
+	// simulating the effect that you would get if you added a dummy
+	// "no-op" x_test.go file and then did a build and run of the test.
+
+	t.Run("YesFuncsNoTests", func(t *testing.T) {
+		testCoverNoTestsYesFuncs(t)
+	})
+	t.Run("NoFuncsNoTests", func(t *testing.T) {
+		testCoverNoTestsNoFuncs(t)
+	})
+}
+
+func testCoverNoTestsYesFuncs(t *testing.T) {
+	t.Parallel()
+	dir := tempDir(t)
+
+	// Run the cover command with "emit meta" enabled on a package
+	// with functions but no test files.
+	tpath := filepath.Join("testdata", "pkgcfg")
+	pkg1files := []string{filepath.Join(tpath, "yesFuncsNoTests", "yfnt.go")}
+	ppath := "cfg/yesFuncsNoTests"
+	pname := "yesFuncsNoTests"
+	mode := "count"
+	gran := "perblock"
+	tag := mode + "_" + gran
+	instdir := filepath.Join(dir, "inst")
+	if err := os.Mkdir(instdir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	mdir := filepath.Join(dir, "meta")
+	if err := os.Mkdir(mdir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	mpath := filepath.Join(mdir, "covmeta.xxx")
+	incfg := writePkgConfig(t, instdir, tag, ppath, pname, gran, mpath)
+	_, _, errmsg := runPkgCover(t, instdir, tag, incfg, mode,
+		pkg1files, false)
+	if errmsg != "" {
+		t.Fatalf("runPkgCover err: %q", errmsg)
+	}
+
+	// Check for existence of meta-data file.
+	if inf, err := os.Open(mpath); err != nil {
+		t.Fatalf("meta-data file not created: %v", err)
+	} else {
+		inf.Close()
+	}
+
+	// Make sure it is digestible.
+	cdargs := []string{"tool", "covdata", "percent", "-i", mdir}
+	cmd := testenv.Command(t, testenv.GoToolPath(t), cdargs...)
+	run(cmd, t)
+}
+
+func testCoverNoTestsNoFuncs(t *testing.T) {
+	t.Parallel()
+	dir := tempDir(t)
+
+	// Run the cover command with "emit meta" enabled on a package
+	// with no functions and no test files.
+	tpath := filepath.Join("testdata", "pkgcfg")
+	pkgfiles := []string{filepath.Join(tpath, "noFuncsNoTests", "nfnt.go")}
+	pname := "noFuncsNoTests"
+	mode := "count"
+	gran := "perblock"
+	ppath := "cfg/" + pname
+	tag := mode + "_" + gran
+	instdir := filepath.Join(dir, "inst2")
+	if err := os.Mkdir(instdir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	mdir := filepath.Join(dir, "meta2")
+	if err := os.Mkdir(mdir, 0777); err != nil {
+		t.Fatal(err)
+	}
+	mpath := filepath.Join(mdir, "covmeta.yyy")
+	incfg := writePkgConfig(t, instdir, tag, ppath, pname, gran, mpath)
+	_, _, errmsg := runPkgCover(t, instdir, tag, incfg, mode,
+		pkgfiles, false)
+	if errmsg != "" {
+		t.Fatalf("runPkgCover err: %q", errmsg)
+	}
+
+	// We expect to see an empty meta-data file in this case.
+	if inf, err := os.Open(mpath); err != nil {
+		t.Fatalf("opening meta-data file: error %v", err)
+	} else {
+		defer inf.Close()
+		fi, err := inf.Stat()
+		if err != nil {
+			t.Fatalf("stat meta-data file: %v", err)
+		}
+		if fi.Size() != 0 {
+			t.Fatalf("want zero-sized meta-data file got size %d",
+				fi.Size())
+		}
+	}
+}

src/cmd/cover/cover.go

@@ -64,30 +64,22 @@ func usage() {
 }
 
 var (
-	mode        = flag.String("mode", "", "coverage mode: set, count, atomic")
+	mode             = flag.String("mode", "", "coverage mode: set, count, atomic")
-	varVar      = flag.String("var", "GoCover", "name of coverage variable to generate")
+	varVar           = flag.String("var", "GoCover", "name of coverage variable to generate")
-	output      = flag.String("o", "", "file for output")
+	output           = flag.String("o", "", "file for output")
-	outfilelist = flag.String("outfilelist", "", "file containing list of output files (one per line) if -pkgcfg is in use")
+	outfilelist      = flag.String("outfilelist", "", "file containing list of output files (one per line) if -pkgcfg is in use")
-	htmlOut     = flag.String("html", "", "generate HTML representation of coverage profile")
+	htmlOut          = flag.String("html", "", "generate HTML representation of coverage profile")
-	funcOut     = flag.String("func", "", "output coverage profile information for each function")
+	funcOut          = flag.String("func", "", "output coverage profile information for each function")
-	pkgcfg      = flag.String("pkgcfg", "", "enable full-package instrumentation mode using params from specified config file")
+	pkgcfg           = flag.String("pkgcfg", "", "enable full-package instrumentation mode using params from specified config file")
+	pkgconfig        covcmd.CoverPkgConfig
+	outputfiles      []string // list of *.cover.go instrumented outputs to write, one per input (set when -pkgcfg is in use)
+	profile          string   // The profile to read; the value of -html or -func
+	counterStmt      func(*File, string) string
+	covervarsoutfile string // an additional Go source file into which we'll write definitions of coverage counter variables + meta data variables (set when -pkgcfg is in use).
+	cmode            coverage.CounterMode
+	cgran            coverage.CounterGranularity
 )
 
-var pkgconfig covcmd.CoverPkgConfig
-
-// outputfiles is the list of *.cover.go instrumented outputs to write,
-// one per input (set when -pkgcfg is in use)
-var outputfiles []string
-
-// covervarsoutfile is an additional Go source file into which we'll
-// write definitions of coverage counter variables + meta data variables
-// (set when -pkgcfg is in use).
-var covervarsoutfile string
-
-var profile string // The profile to read; the value of -html or -func
-
-var counterStmt func(*File, string) string
-
 const (
 	atomicPackagePath = "sync/atomic"
 	atomicPackageName = "_cover_atomic_"
@@ -152,12 +144,19 @@ func parseFlags() error {
 		switch *mode {
 		case "set":
 			counterStmt = setCounterStmt
+			cmode = coverage.CtrModeSet
 		case "count":
 			counterStmt = incCounterStmt
+			cmode = coverage.CtrModeCount
 		case "atomic":
 			counterStmt = atomicCounterStmt
-		case "regonly", "testmain":
+			cmode = coverage.CtrModeAtomic
+		case "regonly":
 			counterStmt = nil
+			cmode = coverage.CtrModeRegOnly
+		case "testmain":
+			counterStmt = nil
+			cmode = coverage.CtrModeTestMain
 		default:
 			return fmt.Errorf("unknown -mode %v", *mode)
 		}
@@ -215,7 +214,12 @@ func readPackageConfig(path string) error {
 	if err := json.Unmarshal(data, &pkgconfig); err != nil {
 		return fmt.Errorf("error reading pkgconfig file %q: %v", path, err)
 	}
-	if pkgconfig.Granularity != "perblock" && pkgconfig.Granularity != "perfunc" {
+	switch pkgconfig.Granularity {
+	case "perblock":
+		cgran = coverage.CtrGranularityPerBlock
+	case "perfunc":
+		cgran = coverage.CtrGranularityPerFunc
+	default:
 		return fmt.Errorf(`%s: pkgconfig requires perblock/perfunc value`, path)
 	}
 	return nil
@@ -1088,6 +1092,14 @@ func (p *Package) emitMetaData(w io.Writer) {
 		return
 	}
 
+	// If the "EmitMetaFile" path has been set, invoke a helper
+	// that will write out a pre-cooked meta-data file for this package
+	// to the specified location, in effect simulating the execution
+	// of a test binary that doesn't do any testing to speak of.
+	if pkgconfig.EmitMetaFile != "" {
+		p.emitMetaFile(pkgconfig.EmitMetaFile)
+	}
+
 	// Something went wrong if regonly/testmain mode is in effect and
 	// we have instrumented functions.
 	if counterStmt == nil && len(p.counterLengths) != 0 {
@@ -1158,3 +1170,40 @@ func atomicPackagePrefix() string {
 	}
 	return atomicPackageName + "."
 }
+
+func (p *Package) emitMetaFile(outpath string) {
+	// Open output file.
+	of, err := os.OpenFile(outpath, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0666)
+	if err != nil {
+		log.Fatalf("opening covmeta %s: %v", outpath, err)
+	}
+
+	if len(p.counterLengths) == 0 {
+		// This corresponds to the case where we have no functions
+		// in the package to instrument. Leave the file empty file if
+		// this happens.
+		if err = of.Close(); err != nil {
+			log.Fatalf("closing meta-data file: %v", err)
+		}
+		return
+	}
+
+	// Encode meta-data.
+	var sws slicewriter.WriteSeeker
+	digest, err := p.mdb.Emit(&sws)
+	if err != nil {
+		log.Fatalf("encoding meta-data: %v", err)
+	}
+	payload := sws.BytesWritten()
+	blobs := [][]byte{payload}
+
+	// Write meta-data file directly.
+	mfw := encodemeta.NewCoverageMetaFileWriter(outpath, of)
+	err = mfw.Write(digest, blobs, cmode, cgran)
+	if err != nil {
+		log.Fatalf("writing meta-data file: %v", err)
+	}
+	if err = of.Close(); err != nil {
+		log.Fatalf("closing meta-data file: %v", err)
+	}
+}

src/cmd/cover/testdata/pkgcfg/b/b.go

@@ -1,10 +0,0 @@
-package b
-
-func B(x int) int {
-	if x == 0 {
-		return 22
-	} else if x == 1 {
-		return 33
-	}
-	return 44
-}

src/cmd/cover/testdata/pkgcfg/b/b_test.go

@@ -1,9 +0,0 @@
-package b
-
-import "testing"
-
-func TestB(t *testing.T) {
-	B(0)
-	B(1)
-	B(2)
-}

src/cmd/cover/testdata/pkgcfg/main/main.go

@@ -1,15 +0,0 @@
-package main
-
-import (
-	"cfg/a"
-	"cfg/b"
-)
-
-func main() {
-	a.A(2)
-	a.A(1)
-	a.A(0)
-	b.B(1)
-	b.B(0)
-	println("done")
-}

src/cmd/cover/testdata/pkgcfg/noFuncsNoTests/nfnt.go

@@ -0,0 +1,8 @@
+package noFuncsNoTests
+
+const foo = 1
+
+var G struct {
+	x int
+	y bool
+}

src/cmd/cover/testdata/pkgcfg/yesFuncsNoTests/yfnt.go

@@ -0,0 +1,13 @@
+package yesFuncsNoTests
+
+func F1() {
+	println("hi")
+}
+
+func F2(x int) int {
+	if x < 0 {
+		return 9
+	} else {
+		return 10
+	}
+}

src/internal/coverage/covcmd/cmddefs.go

@@ -32,6 +32,13 @@ type CoverPkgConfig struct {
 	// corresponding field in cmd/go's PackageInternal struct for more
 	// info.
 	Local bool
+
+	// EmitMetaFile if non-empty is the path to which the cover tool should
+	// directly emit a coverage meta-data file for the package, if the
+	// package has any functions in it. The go command will pass in a value
+	// here if we've been asked to run "go test -cover" on a package that
+	// doesn't have any *_test.go files.
+	EmitMetaFile string
 }
 
 // CoverFixupConfig contains annotations/notes generated by the