cmd/go: run vet automatically during go test

This CL adds an automatic, limited "go vet" to "go test".
If the building of a test package fails, vet is not run.
If vet fails, the test is not run.
The goal is that users don't notice vet as part of the "go test"
process at all, until vet speaks up and says something important.
This should help users find real problems in their code faster
(vet can just point to them instead of needing to debug a
test failure) and expands the scope of what kinds of things
vet can help with.

The "go vet" runs in parallel with the linking of the test binary,
so for incremental builds it typically does not slow the overall
"go test" at all: there's spare machine capacity during the link.

all.bash has less spare machine capacity. This CL increases
the time for all.bash on my laptop from 4m41s to 4m48s (+2.5%)

To opt out for a given run, use "go test -vet=off".

The vet checks used during "go test" are a subset of the full set,
restricted to ones that are 100% correct and therefore acceptable
to make mandatory. In this CL, that set is atomic, bool, buildtags,
nilfunc, and printf. Including printf is debatable, but I want to
include it for now and find out what needs to be scaled back.
(It already found one real problem in package os's tests that
previous go vet os had not turned up.)
Now that we can rely on type information it may be that printf
should make its function-name-based heuristic less aggressive
and have a whitelist of known print/printf functions.
Determining the exact set for Go 1.10 is #18085.

Running vet also means that programs now have to type-check
with both cmd/compile and go/types in order to pass "go test".
We don't start vet until cmd/compile has built the test package,
so normally the added go/types check doesn't find anything.
However, there is at least one instance where go/types is more
precise than cmd/compile: declared and not used errors involving
variables captured into closures.

This CL includes a printf fix to os/os_test.go and many declared
and not used fixes in the race detector tests.

Fixes #18084.

Change-Id: I353e00b9d1f9fec540c7557db5653e7501f5e1c9
Reviewed-on: https://go-review.googlesource.com/74356
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Rob Pike <r@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>

misc/cgo/testshared/shared_test.go

@@ -504,7 +504,7 @@ func testABIHashNote(t *testing.T, f *elf.File, note *note) {
 		t.Errorf("%s has incorrect binding %v, want STB_LOCAL", hashbytes.Name, elf.ST_BIND(hashbytes.Info))
 	}
 	if f.Sections[hashbytes.Section] != note.section {
-		t.Errorf("%s has incorrect section %v, want %s", hashbytes.Name, f.Sections[hashbytes.Section].Name, note.section)
+		t.Errorf("%s has incorrect section %v, want %s", hashbytes.Name, f.Sections[hashbytes.Section].Name, note.section.Name)
 	}
 	if hashbytes.Value-note.section.Addr != 16 {
 		t.Errorf("%s has incorrect offset into section %d, want 16", hashbytes.Name, hashbytes.Value-note.section.Addr)

src/cmd/go/alldocs.go

@@ -735,6 +735,13 @@
 // The go tool will ignore a directory named "testdata", making it available
 // to hold ancillary data needed by the tests.
 //
+// As part of building a test binary, go test runs go vet on the package
+// and its test source files to identify significant problems. If go vet
+// finds any problems, go test reports those and does not run the test binary.
+// Only a high-confidence subset of the default go vet checks are used.
+// To disable the running of go vet, use the -vet=off flag.
+//
+//
 // Go test runs in two different modes: local directory mode when invoked with
 // no package arguments (for example, 'go test'), and package list mode when
 // invoked with package arguments (for example 'go test math', 'go test ./...',
@@ -1547,6 +1554,10 @@
 // 	    Verbose output: log all tests as they are run. Also print all
 // 	    text from Log and Logf calls even if the test succeeds.
 //
+// 	-vet mode
+// 	    Configure the invocation of "go vet" during "go test".
+// 	    The default is to run "go vet". If mode is "off", vet is disabled.
+//
 // The following flags are also recognized by 'go test' and can be used to
 // profile the tests during execution:
 //

src/cmd/go/go_test.go

@@ -4748,6 +4748,7 @@ func TestTestCache(t *testing.T) {
 	}
 	tg := testgo(t)
 	defer tg.cleanup()
+	tg.parallel()
 	tg.makeTempdir()
 	tg.setenv("GOPATH", tg.tempdir)
 	tg.setenv("GOCACHE", filepath.Join(tg.tempdir, "cache"))
@@ -4834,3 +4835,37 @@ func TestTestCache(t *testing.T) {
 	tg.grepStderr(`([\\/]link|gccgo).*t4\.test`, "did not relink t4_test")
 	tg.grepStdout(`ok  \tt/t4\t\(cached\)`, "did not cache t/t4")
 }
+
+func TestTestVet(t *testing.T) {
+	tg := testgo(t)
+	defer tg.cleanup()
+	tg.parallel()
+
+	tg.tempFile("p1_test.go", `
+		package p
+		import "testing"
+		func Test(t *testing.T) {
+			t.Logf("%d") // oops
+		}
+	`)
+
+	tg.runFail("test", filepath.Join(tg.tempdir, "p1_test.go"))
+	tg.grepStderr(`Logf format %d`, "did not diagnose bad Logf")
+	tg.run("test", "-vet=off", filepath.Join(tg.tempdir, "p1_test.go"))
+	tg.grepStdout(`^ok`, "did not print test summary")
+
+	tg.tempFile("p1.go", `
+		package p
+		import "fmt"
+		func F() {
+			fmt.Printf("%d") // oops
+		}
+	`)
+	tg.runFail("test", filepath.Join(tg.tempdir, "p1.go"))
+	tg.grepStderr(`Printf format %d`, "did not diagnose bad Printf")
+	tg.run("test", "-x", "-vet=shift", filepath.Join(tg.tempdir, "p1.go"))
+	tg.grepStderr(`[\\/]vet.*-shift`, "did not run vet with -shift")
+	tg.grepStdout(`\[no test files\]`, "did not print test summary")
+	tg.run("test", "-vet=off", filepath.Join(tg.tempdir, "p1.go"))
+	tg.grepStdout(`\[no test files\]`, "did not print test summary")
+}

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

@@ -69,6 +69,12 @@ separate package, and then linked and run with the main test binary.
 The go tool will ignore a directory named "testdata", making it available
 to hold ancillary data needed by the tests.
 
+As part of building a test binary, go test runs go vet on the package
+and its test source files to identify significant problems. If go vet
+finds any problems, go test reports those and does not run the test binary.
+Only a high-confidence subset of the default go vet checks are used.
+To disable the running of go vet, use the -vet=off flag.
+
 Go test runs in two different modes: local directory mode when invoked with
 no package arguments (for example, 'go test'), and package list mode when
 invoked with package arguments (for example 'go test math', 'go test ./...',
@@ -258,6 +264,13 @@ const testFlag2 = `
 	    Verbose output: log all tests as they are run. Also print all
 	    text from Log and Logf calls even if the test succeeds.
 
+	-vet list
+	    Configure the invocation of "go vet" during "go test"
+	    to use the comma-separated list of vet checks.
+	    If list is empty, "go test" runs "go vet" with a curated list of
+	    checks believed to be always worth addressing.
+	    If list is "off", "go test" does not run "go vet" at all.
+
 The following flags are also recognized by 'go test' and can be used to
 profile the tests during execution:
 
@@ -447,6 +460,7 @@ var (
 	testBench      bool
 	testList       bool
 	testShowPass   bool   // show passing output
+	testVetList    string // -vet flag
 	pkgArgs        []string
 	pkgs           []*load.Package
 
@@ -460,6 +474,32 @@ var testMainDeps = []string{
 	"testing/internal/testdeps",
 }
 
+// testVetFlags is the list of flags to pass to vet when invoked automatically during go test.
+var testVetFlags = []string{
+	// TODO(rsc): Decide which tests are enabled by default.
+	// See golang.org/issue/18085.
+	// "-asmdecl",
+	// "-assign",
+	"-atomic",
+	"-bool",
+	"-buildtags",
+	// "-cgocall",
+	// "-composites",
+	// "-copylocks",
+	// "-httpresponse",
+	// "-lostcancel",
+	// "-methods",
+	"-nilfunc",
+	"-printf",
+	// "-rangeloops",
+	// "-shift",
+	// "-structtags",
+	// "-tests",
+	// "-unreachable",
+	// "-unsafeptr",
+	// "-unusedresult",
+}
+
 func runTest(cmd *base.Command, args []string) {
 	pkgArgs, testArgs = testFlags(args)
 
@@ -467,6 +507,8 @@ func runTest(cmd *base.Command, args []string) {
 
 	work.InstrumentInit()
 	work.BuildModeInit()
+	work.VetFlags = testVetFlags
+
 	pkgs = load.PackagesForBuild(pkgArgs)
 	if len(pkgs) == 0 {
 		base.Fatalf("no packages to test")
@@ -668,6 +710,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 	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
 	}
@@ -681,6 +724,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 	var imports, ximports []*load.Package
 	var stk load.ImportStack
 	stk.Push(p.ImportPath + " (test)")
+	rawTestImports := str.StringList(p.TestImports)
 	for i, path := range p.TestImports {
 		p1 := load.LoadImport(path, p.Dir, p, &stk, p.Internal.Build.TestImportPos[path], load.UseVendor)
 		if p1.Error != nil {
@@ -708,6 +752,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 	stk.Pop()
 	stk.Push(p.ImportPath + "_test")
 	pxtestNeedsPtest := false
+	rawXTestImports := str.StringList(p.XTestImports)
 	for i, path := range p.XTestImports {
 		p1 := load.LoadImport(path, p.Dir, p, &stk, p.Internal.Build.XTestImportPos[path], load.UseVendor)
 		if p1.Error != nil {
@@ -753,8 +798,20 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 		ptest.GoFiles = append(ptest.GoFiles, p.GoFiles...)
 		ptest.GoFiles = append(ptest.GoFiles, p.TestGoFiles...)
 		ptest.Target = ""
-		ptest.Imports = str.StringList(p.Imports, p.TestImports)
-		ptest.Internal.Imports = append(append([]*load.Package{}, p.Internal.Imports...), imports...)
+		// Note: The preparation of the vet config requires that common
+		// indexes in ptest.Imports, ptest.Internal.Imports, and ptest.Internal.RawImports
+		// all line up (but RawImports can be shorter than the others).
+		// That is, for 0 ≤ i < len(RawImports),
+		// RawImports[i] is the import string in the program text,
+		// Imports[i] is the expanded import string (vendoring applied or relative path expanded away),
+		// and Internal.Imports[i] is the corresponding *Package.
+		// Any implicitly added imports appear in Imports and Internal.Imports
+		// but not RawImports (because they were not in the source code).
+		// We insert TestImports, imports, and rawTestImports at the start of
+		// these lists to preserve the alignment.
+		ptest.Imports = str.StringList(p.TestImports, p.Imports)
+		ptest.Internal.Imports = append(imports, p.Internal.Imports...)
+		ptest.Internal.RawImports = str.StringList(rawTestImports, p.Internal.RawImports)
 		ptest.Internal.ForceLibrary = true
 		ptest.Internal.Build = new(build.Package)
 		*ptest.Internal.Build = *p.Internal.Build
@@ -795,6 +852,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 					ImportPos: p.Internal.Build.XTestImportPos,
 				},
 				Imports:    ximports,
+				RawImports: rawXTestImports,
 			},
 		}
 		if pxtestNeedsPtest {
@@ -942,6 +1000,7 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 		}
 	}
 	buildAction = a
+	var installAction *work.Action
 
 	if testC || testNeedBinary {
 		// -c or profiling flag: create action to copy binary to ./test.out.
@@ -953,14 +1012,15 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 			}
 		}
 		pmain.Target = target
-		buildAction = &work.Action{
+		installAction = &work.Action{
 			Mode:    "test build",
 			Func:    work.BuildInstallFunc,
 			Deps:    []*work.Action{buildAction},
 			Package: pmain,
 			Target:  target,
 		}
-		runAction = buildAction // make sure runAction != nil even if not running test
+		buildAction = installAction
+		runAction = installAction // make sure runAction != nil even if not running test
 	}
 	if testC {
 		printAction = &work.Action{Mode: "test print (nop)", Package: p, Deps: []*work.Action{runAction}} // nop
@@ -975,6 +1035,12 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 			IgnoreFail: true,
 			TryCache:   c.tryCache,
 		}
+		if len(ptest.GoFiles)+len(ptest.CgoFiles) > 0 {
+			addTestVet(b, ptest, runAction, installAction)
+		}
+		if pxtest != nil {
+			addTestVet(b, pxtest, runAction, installAction)
+		}
 		cleanAction := &work.Action{
 			Mode:    "test clean",
 			Func:    builderCleanTest,
@@ -993,6 +1059,22 @@ func builderTest(b *work.Builder, p *load.Package) (buildAction, runAction, prin
 	return buildAction, runAction, printAction, nil
 }
 
+func addTestVet(b *work.Builder, p *load.Package, runAction, installAction *work.Action) {
+	if testVetList == "off" {
+		return
+	}
+
+	vet := b.VetAction(work.ModeBuild, work.ModeBuild, p)
+	runAction.Deps = append(runAction.Deps, vet)
+	// Install will clean the build directory.
+	// Make sure vet runs first.
+	// The install ordering in b.VetAction does not apply here
+	// because we are using a custom installAction (created above).
+	if installAction != nil {
+		installAction.Deps = append(installAction.Deps, vet)
+	}
+}
+
 func testImportStack(top string, p *load.Package, target string) []string {
 	stk := []string{top, p.ImportPath}
 Search:

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

@@ -33,6 +33,7 @@ var testFlagDefn = []*cmdflag.Defn{
 	{Name: "covermode"},
 	{Name: "coverpkg"},
 	{Name: "exec"},
+	{Name: "vet"},
 
 	// Passed to 6.out, adding a "test." prefix to the name if necessary: -v becomes -test.v.
 	{Name: "bench", PassToTest: true},
@@ -175,6 +176,8 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 				testCover = true
 			case "outputdir":
 				outputDir = value
+			case "vet":
+				testVetList = value
 			}
 		}
 		if extraWord {
@@ -193,6 +196,20 @@ func testFlags(args []string) (packageNames, passToTest []string) {
 		}
 	}
 
+	if testVetList != "" && testVetList != "off" {
+		if strings.Contains(testVetList, "=") {
+			base.Fatalf("-vet argument cannot contain equal signs")
+		}
+		if strings.Contains(testVetList, " ") {
+			base.Fatalf("-vet argument is comma-separated list, cannot contain spaces")
+		}
+		list := strings.Split(testVetList, ",")
+		for i, arg := range list {
+			list[i] = "-" + arg
+		}
+		testVetFlags = list
+	}
+
 	if cfg.BuildRace && testCoverMode != "atomic" {
 		base.Fatalf(`-covermode must be "atomic", not %q, when -race is enabled`, testCoverMode)
 	}

src/cmd/go/testdata/src/testrace/race_test.go

@@ -12,6 +12,7 @@ func TestRace(t *testing.T) {
 		}()
 		x = 3
 		<-c
+		_ = x
 	}
 }
 
@@ -25,5 +26,6 @@ func BenchmarkRace(b *testing.B) {
 		}()
 		x = 3
 		<-c
+		_ = x
 	}
 }

src/cmd/vet/main.go

@@ -425,12 +425,19 @@ func doPackage(names []string, basePkg *Package) *Package {
 	pkg.path = astFiles[0].Name.Name
 	pkg.files = files
 	// Type check the package.
-	err := pkg.check(fs, astFiles)
-	if err != nil {
-		// Note that we only report this error when *verbose.
-		Println(err)
+	errs := pkg.check(fs, astFiles)
+	if errs != nil {
+		if *verbose || mustTypecheck {
+			for _, err := range errs {
+				fmt.Fprintf(os.Stderr, "%v\n", err)
+			}
 			if mustTypecheck {
-			errorf("%v", err)
+				// This message could be silenced, and we could just exit,
+				// but it might be helpful at least at first to make clear that the
+				// above errors are coming from vet and not the compiler
+				// (they often look like compiler errors, such as "declared but not used").
+				errorf("typecheck failures")
+			}
 		}
 	}
 

src/cmd/vet/types.go

@@ -62,7 +62,7 @@ func importType(path, name string) types.Type {
 	return nil
 }
 
-func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) error {
+func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) []error {
 	if stdImporter == nil {
 		if *source {
 			stdImporter = importer.For("source", nil)
@@ -76,13 +76,17 @@ func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) error {
 	pkg.selectors = make(map[*ast.SelectorExpr]*types.Selection)
 	pkg.spans = make(map[types.Object]Span)
 	pkg.types = make(map[ast.Expr]types.TypeAndValue)
+
+	var allErrors []error
 	config := types.Config{
 		// We use the same importer for all imports to ensure that
 		// everybody sees identical packages for the given paths.
 		Importer: stdImporter,
 		// By providing a Config with our own error function, it will continue
-		// past the first error. There is no need for that function to do anything.
-		Error: func(error) {},
+		// past the first error. We collect them all for printing later.
+		Error: func(e error) {
+			allErrors = append(allErrors, e)
+		},
 
 		Sizes: archSizes,
 	}
@@ -93,6 +97,9 @@ func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) error {
 		Uses:       pkg.uses,
 	}
 	typesPkg, err := config.Check(pkg.path, fs, astFiles, info)
+	if len(allErrors) == 0 && err != nil {
+		allErrors = append(allErrors, err)
+	}
 	pkg.typesPkg = typesPkg
 	// update spans
 	for id, obj := range pkg.defs {
@@ -101,7 +108,7 @@ func (pkg *Package) check(fs *token.FileSet, astFiles []*ast.File) error {
 	for id, obj := range pkg.uses {
 		pkg.growSpan(id, obj)
 	}
-	return err
+	return allErrors
 }
 
 // matchArgType reports an error if printf verb t is not appropriate

src/os/os_test.go

@@ -1169,9 +1169,9 @@ func testChtimes(t *testing.T, name string) {
 			// the contents are accessed; also, it is set
 			// whenever mtime is set.
 		case "netbsd":
-			t.Logf("AccessTime didn't go backwards; was=%d, after=%d (Ignoring. See NetBSD issue golang.org/issue/19293)", at, pat)
+			t.Logf("AccessTime didn't go backwards; was=%v, after=%v (Ignoring. See NetBSD issue golang.org/issue/19293)", at, pat)
 		default:
-			t.Errorf("AccessTime didn't go backwards; was=%d, after=%d", at, pat)
+			t.Errorf("AccessTime didn't go backwards; was=%v, after=%v", at, pat)
 		}
 	}
 

src/runtime/race/output_test.go

@@ -185,6 +185,7 @@ import "testing"
 func TestFail(t *testing.T) {
 	done := make(chan bool)
 	x := 0
+	_ = x
 	go func() {
 		x = 42
 		done <- true
@@ -196,7 +197,7 @@ func TestFail(t *testing.T) {
 `, `
 ==================
 --- FAIL: TestFail \(0...s\)
-.*main_test.go:13: true
+.*main_test.go:14: true
 .*testing.go:.*: race detected during execution of test
 FAIL`},
 
@@ -275,6 +276,7 @@ import "testing"
 func TestFail(t *testing.T) {
 	done := make(chan bool)
 	x := 0
+	_ = x
 	go func() {
 		x = 42
 		done <- true

src/runtime/race/testdata/atomic_test.go

@@ -14,6 +14,7 @@ import (
 
 func TestNoRaceAtomicAddInt64(t *testing.T) {
 	var x1, x2 int8
+	_ = x1 + x2
 	var s int64
 	ch := make(chan bool, 2)
 	go func() {
@@ -36,6 +37,7 @@ func TestNoRaceAtomicAddInt64(t *testing.T) {
 
 func TestRaceAtomicAddInt64(t *testing.T) {
 	var x1, x2 int8
+	_ = x1 + x2
 	var s int64
 	ch := make(chan bool, 2)
 	go func() {
@@ -58,6 +60,7 @@ func TestRaceAtomicAddInt64(t *testing.T) {
 
 func TestNoRaceAtomicAddInt32(t *testing.T) {
 	var x1, x2 int8
+	_ = x1 + x2
 	var s int32
 	ch := make(chan bool, 2)
 	go func() {
@@ -80,6 +83,7 @@ func TestNoRaceAtomicAddInt32(t *testing.T) {
 
 func TestNoRaceAtomicLoadAddInt32(t *testing.T) {
 	var x int64
+	_ = x
 	var s int32
 	go func() {
 		x = 2
@@ -93,6 +97,7 @@ func TestNoRaceAtomicLoadAddInt32(t *testing.T) {
 
 func TestNoRaceAtomicLoadStoreInt32(t *testing.T) {
 	var x int64
+	_ = x
 	var s int32
 	go func() {
 		x = 2
@@ -106,6 +111,7 @@ func TestNoRaceAtomicLoadStoreInt32(t *testing.T) {
 
 func TestNoRaceAtomicStoreCASInt32(t *testing.T) {
 	var x int64
+	_ = x
 	var s int32
 	go func() {
 		x = 2
@@ -119,6 +125,7 @@ func TestNoRaceAtomicStoreCASInt32(t *testing.T) {
 
 func TestNoRaceAtomicCASLoadInt32(t *testing.T) {
 	var x int64
+	_ = x
 	var s int32
 	go func() {
 		x = 2
@@ -134,6 +141,7 @@ func TestNoRaceAtomicCASLoadInt32(t *testing.T) {
 
 func TestNoRaceAtomicCASCASInt32(t *testing.T) {
 	var x int64
+	_ = x
 	var s int32
 	go func() {
 		x = 2
@@ -149,6 +157,7 @@ func TestNoRaceAtomicCASCASInt32(t *testing.T) {
 
 func TestNoRaceAtomicCASCASInt32_2(t *testing.T) {
 	var x1, x2 int8
+	_ = x1 + x2
 	var s int32
 	ch := make(chan bool, 2)
 	go func() {
@@ -171,6 +180,7 @@ func TestNoRaceAtomicCASCASInt32_2(t *testing.T) {
 
 func TestNoRaceAtomicLoadInt64(t *testing.T) {
 	var x int32
+	_ = x
 	var s int64
 	go func() {
 		x = 2
@@ -184,6 +194,7 @@ func TestNoRaceAtomicLoadInt64(t *testing.T) {
 
 func TestNoRaceAtomicCASCASUInt64(t *testing.T) {
 	var x int64
+	_ = x
 	var s uint64
 	go func() {
 		x = 2
@@ -199,6 +210,7 @@ func TestNoRaceAtomicCASCASUInt64(t *testing.T) {
 
 func TestNoRaceAtomicLoadStorePointer(t *testing.T) {
 	var x int64
+	_ = x
 	var s unsafe.Pointer
 	var y int = 2
 	var p unsafe.Pointer = unsafe.Pointer(&y)
@@ -214,6 +226,7 @@ func TestNoRaceAtomicLoadStorePointer(t *testing.T) {
 
 func TestNoRaceAtomicStoreCASUint64(t *testing.T) {
 	var x int64
+	_ = x
 	var s uint64
 	go func() {
 		x = 2

src/runtime/race/testdata/chan_test.go

@@ -12,6 +12,7 @@ import (
 
 func TestNoRaceChanSync(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		v = 1
@@ -23,6 +24,7 @@ func TestNoRaceChanSync(t *testing.T) {
 
 func TestNoRaceChanSyncRev(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		c <- 0
@@ -34,6 +36,7 @@ func TestNoRaceChanSyncRev(t *testing.T) {
 
 func TestNoRaceChanAsync(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -45,6 +48,7 @@ func TestNoRaceChanAsync(t *testing.T) {
 
 func TestRaceChanAsyncRev(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		c <- 0
@@ -56,6 +60,7 @@ func TestRaceChanAsyncRev(t *testing.T) {
 
 func TestNoRaceChanAsyncCloseRecv(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -72,6 +77,7 @@ func TestNoRaceChanAsyncCloseRecv(t *testing.T) {
 
 func TestNoRaceChanAsyncCloseRecv2(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -83,6 +89,7 @@ func TestNoRaceChanAsyncCloseRecv2(t *testing.T) {
 
 func TestNoRaceChanAsyncCloseRecv3(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -95,6 +102,7 @@ func TestNoRaceChanAsyncCloseRecv3(t *testing.T) {
 
 func TestNoRaceChanSyncCloseRecv(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		v = 1
@@ -111,6 +119,7 @@ func TestNoRaceChanSyncCloseRecv(t *testing.T) {
 
 func TestNoRaceChanSyncCloseRecv2(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		v = 1
@@ -122,6 +131,7 @@ func TestNoRaceChanSyncCloseRecv2(t *testing.T) {
 
 func TestNoRaceChanSyncCloseRecv3(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		v = 1
@@ -134,6 +144,7 @@ func TestNoRaceChanSyncCloseRecv3(t *testing.T) {
 
 func TestRaceChanSyncCloseSend(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int)
 	go func() {
 		v = 1
@@ -150,6 +161,7 @@ func TestRaceChanSyncCloseSend(t *testing.T) {
 
 func TestRaceChanAsyncCloseSend(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -170,6 +182,7 @@ func TestRaceChanCloseClose(t *testing.T) {
 	compl := make(chan bool, 2)
 	v1 := 0
 	v2 := 0
+	_ = v1 + v2
 	c := make(chan int)
 	go func() {
 		defer func() {
@@ -197,6 +210,7 @@ func TestRaceChanCloseClose(t *testing.T) {
 
 func TestRaceChanSendLen(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	go func() {
 		v = 1
@@ -210,6 +224,7 @@ func TestRaceChanSendLen(t *testing.T) {
 
 func TestRaceChanRecvLen(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	c <- 1
 	go func() {
@@ -226,6 +241,7 @@ func TestRaceChanSendSend(t *testing.T) {
 	compl := make(chan bool, 2)
 	v1 := 0
 	v2 := 0
+	_ = v1 + v2
 	c := make(chan int, 1)
 	go func() {
 		v1 = 1
@@ -264,6 +280,7 @@ func TestNoRaceChanPtr(t *testing.T) {
 func TestRaceChanWrongSend(t *testing.T) {
 	v1 := 0
 	v2 := 0
+	_ = v1 + v2
 	c := make(chan int, 2)
 	go func() {
 		v1 = 1
@@ -284,6 +301,7 @@ func TestRaceChanWrongSend(t *testing.T) {
 func TestRaceChanWrongClose(t *testing.T) {
 	v1 := 0
 	v2 := 0
+	_ = v1 + v2
 	c := make(chan int, 1)
 	done := make(chan bool)
 	go func() {
@@ -561,6 +579,7 @@ func TestRaceChanItselfCap(t *testing.T) {
 
 func TestRaceChanCloseLen(t *testing.T) {
 	v := 0
+	_ = v
 	c := make(chan int, 10)
 	c <- 0
 	go func() {
@@ -587,6 +606,7 @@ func TestNoRaceChanMutex(t *testing.T) {
 	done := make(chan struct{})
 	mtx := make(chan struct{}, 1)
 	data := 0
+	_ = data
 	go func() {
 		mtx <- struct{}{}
 		data = 42
@@ -604,6 +624,7 @@ func TestNoRaceSelectMutex(t *testing.T) {
 	mtx := make(chan struct{}, 1)
 	aux := make(chan bool)
 	data := 0
+	_ = data
 	go func() {
 		select {
 		case mtx <- struct{}{}:
@@ -632,6 +653,7 @@ func TestRaceChanSem(t *testing.T) {
 	done := make(chan struct{})
 	mtx := make(chan bool, 2)
 	data := 0
+	_ = data
 	go func() {
 		mtx <- true
 		data = 42

src/runtime/race/testdata/finalizer_test.go

@@ -53,6 +53,7 @@ func TestNoRaceFinGlobal(t *testing.T) {
 func TestRaceFin(t *testing.T) {
 	c := make(chan bool)
 	y := 0
+	_ = y
 	go func() {
 		x := new(string)
 		runtime.SetFinalizer(x, func(x *string) {

src/runtime/race/testdata/map_test.go

@@ -130,6 +130,7 @@ func TestRaceMapLenDelete(t *testing.T) {
 func TestRaceMapVariable(t *testing.T) {
 	ch := make(chan bool, 1)
 	m := make(map[int]int)
+	_ = m
 	go func() {
 		m = make(map[int]int)
 		ch <- true
@@ -230,6 +231,7 @@ func TestRaceMapAssignMultipleReturn(t *testing.T) {
 	conns[1] = []int{0}
 	ch := make(chan bool, 1)
 	var err error
+	_ = err
 	go func() {
 		conns[1][0], err = connect()
 		ch <- true

src/runtime/race/testdata/mop_test.go

@@ -60,6 +60,7 @@ func TestRaceIntRWGlobalFuncs(t *testing.T) {
 
 func TestRaceIntRWClosures(t *testing.T) {
 	var x, y int
+	_ = y
 	ch := make(chan int, 2)
 
 	go func() {
@@ -76,6 +77,7 @@ func TestRaceIntRWClosures(t *testing.T) {
 
 func TestNoRaceIntRWClosures(t *testing.T) {
 	var x, y int
+	_ = y
 	ch := make(chan int, 1)
 
 	go func() {
@@ -93,6 +95,7 @@ func TestNoRaceIntRWClosures(t *testing.T) {
 
 func TestRaceInt32RWClosures(t *testing.T) {
 	var x, y int32
+	_ = y
 	ch := make(chan bool, 2)
 
 	go func() {
@@ -168,6 +171,7 @@ func TestRaceCaseCondition2(t *testing.T) {
 
 func TestRaceCaseBody(t *testing.T) {
 	var x, y int
+	_ = y
 	ch := make(chan int, 2)
 
 	go func() {
@@ -189,6 +193,7 @@ func TestRaceCaseBody(t *testing.T) {
 
 func TestNoRaceCaseFallthrough(t *testing.T) {
 	var x, y, z int
+	_ = y
 	ch := make(chan int, 2)
 	z = 1
 
@@ -210,6 +215,7 @@ func TestNoRaceCaseFallthrough(t *testing.T) {
 
 func TestRaceCaseFallthrough(t *testing.T) {
 	var x, y, z int
+	_ = y
 	ch := make(chan int, 2)
 	z = 1
 
@@ -323,6 +329,7 @@ func TestRaceRange(t *testing.T) {
 	const N = 2
 	var a [N]int
 	var x, y int
+	_ = x + y
 	done := make(chan bool, N)
 	for i, v := range a {
 		go func(i int) {
@@ -433,6 +440,7 @@ func TestNoRaceForIncr(t *testing.T) {
 
 func TestRacePlus(t *testing.T) {
 	var x, y, z int
+	_ = y
 	ch := make(chan int, 2)
 
 	go func() {
@@ -449,6 +457,7 @@ func TestRacePlus(t *testing.T) {
 
 func TestRacePlus2(t *testing.T) {
 	var x, y, z int
+	_ = y
 	ch := make(chan int, 2)
 
 	go func() {
@@ -465,6 +474,7 @@ func TestRacePlus2(t *testing.T) {
 
 func TestNoRacePlus(t *testing.T) {
 	var x, y, z, f int
+	_ = x + y + f
 	ch := make(chan int, 2)
 
 	go func() {
@@ -481,6 +491,7 @@ func TestNoRacePlus(t *testing.T) {
 
 func TestRaceComplement(t *testing.T) {
 	var x, y, z int
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -497,6 +508,7 @@ func TestRaceComplement(t *testing.T) {
 
 func TestRaceDiv(t *testing.T) {
 	var x, y, z int
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -513,6 +525,7 @@ func TestRaceDiv(t *testing.T) {
 
 func TestRaceDivConst(t *testing.T) {
 	var x, y, z uint32
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -529,6 +542,7 @@ func TestRaceDivConst(t *testing.T) {
 
 func TestRaceMod(t *testing.T) {
 	var x, y, z int
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -545,6 +559,7 @@ func TestRaceMod(t *testing.T) {
 
 func TestRaceModConst(t *testing.T) {
 	var x, y, z int
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -561,6 +576,7 @@ func TestRaceModConst(t *testing.T) {
 
 func TestRaceRotate(t *testing.T) {
 	var x, y, z uint32
+	_ = x
 	ch := make(chan int, 2)
 
 	go func() {
@@ -932,6 +948,7 @@ func TestRaceFuncVariableRW(t *testing.T) {
 
 func TestRaceFuncVariableWW(t *testing.T) {
 	var f func(x int) int
+	_ = f
 	ch := make(chan bool, 1)
 	go func() {
 		f = func(x int) int {
@@ -948,6 +965,7 @@ func TestRaceFuncVariableWW(t *testing.T) {
 // This one should not belong to mop_test
 func TestRacePanic(t *testing.T) {
 	var x int
+	_ = x
 	var zero int = 0
 	ch := make(chan bool, 2)
 	go func() {
@@ -1284,6 +1302,7 @@ func TestNoRaceFuncUnlock(t *testing.T) {
 	ch := make(chan bool, 1)
 	var mu sync.Mutex
 	x := 0
+	_ = x
 	go func() {
 		mu.Lock()
 		x = 42
@@ -1812,6 +1831,7 @@ func TestNoRaceAsFunc4(t *testing.T) {
 	c := make(chan bool, 1)
 	var mu sync.Mutex
 	x := 0
+	_ = x
 	go func() {
 		x = func() int { // Write of x must be under the mutex.
 			mu.Lock()
@@ -2042,6 +2062,7 @@ func TestNoRaceTinyAlloc(t *testing.T) {
 	const P = 4
 	const N = 1e6
 	var tinySink *byte
+	_ = tinySink
 	done := make(chan bool)
 	for p := 0; p < P; p++ {
 		go func() {

src/runtime/race/testdata/mutex_test.go

@@ -13,6 +13,7 @@ import (
 func TestNoRaceMutex(t *testing.T) {
 	var mu sync.Mutex
 	var x int16 = 0
+	_ = x
 	ch := make(chan bool, 2)
 	go func() {
 		mu.Lock()
@@ -33,6 +34,7 @@ func TestNoRaceMutex(t *testing.T) {
 func TestRaceMutex(t *testing.T) {
 	var mu sync.Mutex
 	var x int16 = 0
+	_ = x
 	ch := make(chan bool, 2)
 	go func() {
 		x = 1
@@ -54,6 +56,7 @@ func TestRaceMutex2(t *testing.T) {
 	var mu1 sync.Mutex
 	var mu2 sync.Mutex
 	var x int8 = 0
+	_ = x
 	ch := make(chan bool, 2)
 	go func() {
 		mu1.Lock()
@@ -74,6 +77,7 @@ func TestRaceMutex2(t *testing.T) {
 func TestNoRaceMutexPureHappensBefore(t *testing.T) {
 	var mu sync.Mutex
 	var x int16 = 0
+	_ = x
 	ch := make(chan bool, 2)
 	go func() {
 		x = 1
@@ -96,6 +100,7 @@ func TestNoRaceMutexSemaphore(t *testing.T) {
 	var mu sync.Mutex
 	ch := make(chan bool, 2)
 	x := 0
+	_ = x
 	mu.Lock()
 	go func() {
 		x = 1

src/runtime/race/testdata/rwmutex_test.go

@@ -14,6 +14,7 @@ func TestRaceMutexRWMutex(t *testing.T) {
 	var mu1 sync.Mutex
 	var mu2 sync.RWMutex
 	var x int16 = 0
+	_ = x
 	ch := make(chan bool, 2)
 	go func() {
 		mu1.Lock()
@@ -34,6 +35,7 @@ func TestRaceMutexRWMutex(t *testing.T) {
 func TestNoRaceRWMutex(t *testing.T) {
 	var mu sync.RWMutex
 	var x, y int64 = 0, 1
+	_ = y
 	ch := make(chan bool, 2)
 	go func() {
 		mu.Lock()

src/runtime/race/testdata/select_test.go

@@ -11,6 +11,7 @@ import (
 
 func TestNoRaceSelect1(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool)
 	c := make(chan bool)
 	c1 := make(chan bool)
@@ -36,6 +37,7 @@ func TestNoRaceSelect1(t *testing.T) {
 
 func TestNoRaceSelect2(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool)
 	c := make(chan bool)
 	c1 := make(chan bool)
@@ -55,6 +57,7 @@ func TestNoRaceSelect2(t *testing.T) {
 
 func TestNoRaceSelect3(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool)
 	c := make(chan bool, 10)
 	c1 := make(chan bool)
@@ -112,6 +115,7 @@ func TestNoRaceSelect4(t *testing.T) {
 func TestNoRaceSelect5(t *testing.T) {
 	test := func(sel, needSched bool) {
 		var x int
+		_ = x
 		ch := make(chan bool)
 		c1 := make(chan bool)
 
@@ -158,6 +162,7 @@ func TestNoRaceSelect5(t *testing.T) {
 
 func TestRaceSelect1(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool, 2)
 	c := make(chan bool)
 	c1 := make(chan bool)
@@ -182,6 +187,7 @@ func TestRaceSelect1(t *testing.T) {
 
 func TestRaceSelect2(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool)
 	c := make(chan bool)
 	c1 := make(chan bool)
@@ -200,6 +206,7 @@ func TestRaceSelect2(t *testing.T) {
 
 func TestRaceSelect3(t *testing.T) {
 	var x int
+	_ = x
 	compl := make(chan bool)
 	c := make(chan bool)
 	c1 := make(chan bool)

src/runtime/race/testdata/sync_test.go

@@ -12,6 +12,7 @@ import (
 
 func TestNoRaceCond(t *testing.T) {
 	x := 0
+	_ = x
 	condition := 0
 	var mu sync.Mutex
 	cond := sync.NewCond(&mu)
@@ -35,6 +36,7 @@ func TestRaceCond(t *testing.T) {
 	var mu sync.Mutex
 	cond := sync.NewCond(&mu)
 	x := 0
+	_ = x
 	condition := 0
 	go func() {
 		time.Sleep(10 * time.Millisecond) // Enter cond.Wait loop
@@ -67,6 +69,7 @@ func TestRaceAnnounceThreads(t *testing.T) {
 	allDone := make(chan bool, N)
 
 	var x int
+	_ = x
 
 	var f, g, h func()
 	f = func() {
@@ -133,6 +136,7 @@ func TestNoRaceAfterFunc2(t *testing.T) {
 func TestNoRaceAfterFunc3(t *testing.T) {
 	c := make(chan bool, 1)
 	x := 0
+	_ = x
 	time.AfterFunc(1e7, func() {
 		x = 1
 		c <- true
@@ -143,6 +147,7 @@ func TestNoRaceAfterFunc3(t *testing.T) {
 func TestRaceAfterFunc3(t *testing.T) {
 	c := make(chan bool, 2)
 	x := 0
+	_ = x
 	time.AfterFunc(1e7, func() {
 		x = 1
 		c <- true
@@ -161,6 +166,7 @@ func TestRaceAfterFunc3(t *testing.T) {
 // comprehensible.
 func TestRaceGoroutineCreationStack(t *testing.T) {
 	var x int
+	_ = x
 	var ch = make(chan bool, 1)
 
 	f1 := func() {

src/runtime/race/testdata/waitgroup_test.go

@@ -13,6 +13,7 @@ import (
 
 func TestNoRaceWaitGroup(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	n := 1
 	for i := 0; i < n; i++ {
@@ -28,6 +29,7 @@ func TestNoRaceWaitGroup(t *testing.T) {
 
 func TestRaceWaitGroup(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	n := 2
 	for i := 0; i < n; i++ {
@@ -43,6 +45,7 @@ func TestRaceWaitGroup(t *testing.T) {
 
 func TestNoRaceWaitGroup2(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	wg.Add(1)
 	go func() {
@@ -56,6 +59,7 @@ func TestNoRaceWaitGroup2(t *testing.T) {
 // incrementing counter in Add and locking wg's mutex
 func TestRaceWaitGroupAsMutex(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	c := make(chan bool, 2)
 	go func() {
@@ -82,6 +86,7 @@ func TestRaceWaitGroupAsMutex(t *testing.T) {
 func TestRaceWaitGroupWrongWait(t *testing.T) {
 	c := make(chan bool, 2)
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	go func() {
 		wg.Add(1)
@@ -187,6 +192,7 @@ func TestNoRaceWaitGroupMultipleWait3(t *testing.T) {
 // Correct usage but still a race
 func TestRaceWaitGroup2(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	wg.Add(2)
 	go func() {
@@ -202,6 +208,7 @@ func TestRaceWaitGroup2(t *testing.T) {
 
 func TestNoRaceWaitGroupPanicRecover(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	defer func() {
 		err := recover()
@@ -219,6 +226,7 @@ func TestNoRaceWaitGroupPanicRecover(t *testing.T) {
 // Is it possible to get a race by synchronization via panic?
 func TestNoRaceWaitGroupPanicRecover2(t *testing.T) {
 	var x int
+	_ = x
 	var wg sync.WaitGroup
 	ch := make(chan bool, 1)
 	var f func() = func() {