cmd/go: revert "output coverage report even if there are no test files"

Original CL description:

    When using test -cover or -coverprofile the output for "no test files"
    is the same format as for "no tests to run".

Reverting because this CL changed cmd/go to build test binaries for
packages that have no tests, leading to extra work and confusion.

Updates #24570
Fixes #25789
Fixes #26157
Fixes #26242

Change-Id: Ibab1307d39dfaec0de9359d6d96706e3910c8efd
Reviewed-on: https://go-review.googlesource.com/122518
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/go/go_test.go

@@ -3262,43 +3262,6 @@ func TestGoTestBuildsAnXtestContainingOnlyNonRunnableExamples(t *testing.T) {
 	tg.grepStdout("File with non-runnable example was built.", "file with non-runnable example was not built")
 }
 
-// issue 24570
-func TestGoTestCoverMultiPackage(t *testing.T) {
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.run("test", "-cover", "./testdata/testcover/...")
-	tg.grepStdout(`\?.*testdata/testcover/pkg1.*(\d\.\d\d\ds|cached).*coverage:.*0\.0% of statements \[no test files\]`, "expected [no test files] for pkg1")
-	tg.grepStdout(`ok.*testdata/testcover/pkg2.*(\d\.\d\d\ds|cached).*coverage:.*0\.0% of statements \[no tests to run\]`, "expected [no tests to run] for pkg2")
-	tg.grepStdout(`ok.*testdata/testcover/pkg3.*(\d\.\d\d\ds|cached).*coverage:.*100\.0% of statements`, "expected 100% coverage for pkg3")
-}
-
-// issue 24570
-func TestGoTestCoverprofileMultiPackage(t *testing.T) {
-	tg := testgo(t)
-	defer tg.cleanup()
-	tg.creatingTemp("testdata/cover.out")
-	tg.run("test", "-coverprofile=testdata/cover.out", "./testdata/testcover/...")
-	tg.grepStdout(`\?.*testdata/testcover/pkg1.*(\d\.\d\d\ds|cached).*coverage:.*0\.0% of statements \[no test files\]`, "expected [no test files] for pkg1")
-	tg.grepStdout(`ok.*testdata/testcover/pkg2.*(\d\.\d\d\ds|cached).*coverage:.*0\.0% of statements \[no tests to run\]`, "expected [no tests to run] for pkg2")
-	tg.grepStdout(`ok.*testdata/testcover/pkg3.*(\d\.\d\d\ds|cached).*coverage:.*100\.0% of statements`, "expected 100% coverage for pkg3")
-	if out, err := ioutil.ReadFile("testdata/cover.out"); err != nil {
-		t.Error(err)
-	} else {
-		if !bytes.Contains(out, []byte("mode: set")) {
-			t.Errorf(`missing "mode: set" in %s`, out)
-		}
-		if !bytes.Contains(out, []byte(`pkg1/a.go:5.10,7.2 1 0`)) && !bytes.Contains(out, []byte(`pkg1\a.go:5.10,7.2 1 0`)) {
-			t.Errorf(`missing "pkg1/a.go:5.10,7.2 1 0" in %s`, out)
-		}
-		if !bytes.Contains(out, []byte(`pkg2/a.go:5.10,7.2 1 0`)) && !bytes.Contains(out, []byte(`pkg2\a.go:5.10,7.2 1 0`)) {
-			t.Errorf(`missing "pkg2/a.go:5.10,7.2 1 0" in %s`, out)
-		}
-		if !bytes.Contains(out, []byte(`pkg3/a.go:5.10,7.2 1 1`)) && !bytes.Contains(out, []byte(`pkg3\a.go:5.10,7.2 1 1`)) {
-			t.Errorf(`missing "pkg3/a.go:5.10,7.2 1 1" in %s`, out)
-		}
-	}
-}
-
 func TestGoGenerateHandlesSimpleCommand(t *testing.T) {
 	if runtime.GOOS == "windows" {
 		t.Skip("skipping because windows has no echo command")

src/cmd/go/internal/load/test.go

@@ -49,6 +49,9 @@ type TestCover struct {
 // (for example, if there are no "package p" test files and
 // package p need not be instrumented for coverage or any other reason),
 // then the returned ptest == p.
+//
+// The caller is expected to have checked that len(p.TestGoFiles)+len(p.XTestGoFiles) > 0,
+// or else there's no point in any of this.
 func TestPackagesFor(p *Package, cover *TestCover) (pmain, ptest, pxtest *Package, err error) {
 	var imports, ximports []*Package
 	var stk ImportStack

src/cmd/go/internal/test/test.go

@@ -781,6 +781,14 @@ var windowsBadWords = []string{
 }
 
 func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, printAction *work.Action, err error) {
+	if len(p.TestGoFiles)+len(p.XTestGoFiles) == 0 {
+		build := b.CompileAction(work.ModeBuild, work.ModeBuild, p)
+		run := &work.Action{Mode: "test run", Package: p, Deps: []*work.Action{build}}
+		addTestVet(b, p, run, nil)
+		print := &work.Action{Mode: "test print", Func: builderNoTest, Package: p, Deps: []*work.Action{run}}
+		return build, run, print, nil
+	}
+
 	// Build Package structs describing:
 	//	pmain - pkg.test binary
 	//	ptest - package + test files
@@ -1168,17 +1176,13 @@ func (c *runCache) builderRunTest(b *work.Builder, a *work.Action) error {
 
 	if err == nil {
 		norun := ""
-		res := "ok"
 		if !testShowPass && !testJSON {
 			buf.Reset()
 		}
-		if len(a.Package.TestGoFiles)+len(a.Package.XTestGoFiles) == 0 {
-			res = "? "
-			norun = " [no test files]"
-		} else if bytes.HasPrefix(out, noTestsToRun[1:]) || bytes.Contains(out, noTestsToRun) {
+		if bytes.HasPrefix(out, noTestsToRun[1:]) || bytes.Contains(out, noTestsToRun) {
 			norun = " [no tests to run]"
 		}
-		fmt.Fprintf(cmd.Stdout, "%s  \t%s\t%s%s%s\n", res, a.Package.ImportPath, t, coveragePercentage(out), norun)
+		fmt.Fprintf(cmd.Stdout, "ok  \t%s\t%s%s%s\n", a.Package.ImportPath, t, coveragePercentage(out), norun)
 		c.saveOutput(a)
 	} else {
 		base.SetExitStatus(1)
@@ -1592,3 +1596,15 @@ func builderPrintTest(b *work.Builder, a *work.Action) error {
 	}
 	return nil
 }
+
+// builderNoTest is the action for testing a package with no test files.
+func builderNoTest(b *work.Builder, a *work.Action) error {
+	var stdout io.Writer = os.Stdout
+	if testJSON {
+		json := test2json.NewConverter(lockedStdout{}, a.Package.ImportPath, test2json.Timestamp)
+		defer json.Close()
+		stdout = json
+	}
+	fmt.Fprintf(stdout, "?   \t%s\t[no test files]\n", a.Package.ImportPath)
+	return nil
+}

src/cmd/go/testdata/testcover/pkg1/a.go

@@ -1,7 +0,0 @@
-package pkg1
-
-import "fmt"
-
-func F() {
-	fmt.Println("pkg1")
-}

src/cmd/go/testdata/testcover/pkg2/a.go

@@ -1,7 +0,0 @@
-package pkg2
-
-import "fmt"
-
-func F() {
-	fmt.Println("pkg2")
-}

src/cmd/go/testdata/testcover/pkg2/a_test.go

@@ -1 +0,0 @@
-package pkg2

src/cmd/go/testdata/testcover/pkg3/a.go

@@ -1,7 +0,0 @@
-package pkg3
-
-import "fmt"
-
-func F() {
-	fmt.Println("pkg3")
-}

src/cmd/go/testdata/testcover/pkg3/a_test.go

@@ -1,7 +0,0 @@
-package pkg3
-
-import "testing"
-
-func TestF(t *testing.T) {
-	F()
-}

src/cmd/internal/test2json/test2json.go

@@ -147,7 +147,7 @@ var (
 	fourSpace = []byte("    ")
 
 	skipLinePrefix = []byte("?   \t")
-	skipLineSuffix = []byte(" [no test files]\n")
+	skipLineSuffix = []byte("\t[no test files]\n")
 )
 
 // handleInputLine handles a single whole test output line.
@@ -166,7 +166,7 @@ func (c *converter) handleInputLine(line []byte) {
 		return
 	}
 
-	// Special case for entirely skipped test binary: "?   \tpkgname\t0.001s [no test files]\n" is only line.
+	// Special case for entirely skipped test binary: "?   \tpkgname\t[no test files]\n" is only line.
 	// Report it as plain output but remember to say skip in the final summary.
 	if bytes.HasPrefix(line, skipLinePrefix) && bytes.HasSuffix(line, skipLineSuffix) && len(c.report) == 0 {
 		c.result = "skip"