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>

11 files changed, 90 insertions, 1 deletions

diff --git a/src/runtime/race/output_test.go b/src/runtime/race/output_test.go
index ee6bf6b035..45c9afae23 100644
--- a/src/runtime/race/output_test.go
+++ b/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
diff --git a/src/runtime/race/testdata/atomic_test.go b/src/runtime/race/testdata/atomic_test.go
index 232744b3dd..769c8d7398 100644
--- a/src/runtime/race/testdata/atomic_test.go
+++ b/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
diff --git a/src/runtime/race/testdata/chan_test.go b/src/runtime/race/testdata/chan_test.go
index 449191639e..7f349c42ed 100644
--- a/src/runtime/race/testdata/chan_test.go
+++ b/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
diff --git a/src/runtime/race/testdata/finalizer_test.go b/src/runtime/race/testdata/finalizer_test.go
index 222cbf67a8..3ac33d2b59 100644
--- a/src/runtime/race/testdata/finalizer_test.go
+++ b/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) {
diff --git a/src/runtime/race/testdata/map_test.go b/src/runtime/race/testdata/map_test.go
index a8d8148d0e..88e735ecd3 100644
--- a/src/runtime/race/testdata/map_test.go
+++ b/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
diff --git a/src/runtime/race/testdata/mop_test.go b/src/runtime/race/testdata/mop_test.go
index c96acb9021..5d25ed4bb6 100644
--- a/src/runtime/race/testdata/mop_test.go
+++ b/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() {
diff --git a/src/runtime/race/testdata/mutex_test.go b/src/runtime/race/testdata/mutex_test.go
index 3cf03ae6b8..cbed2d370c 100644
--- a/src/runtime/race/testdata/mutex_test.go
+++ b/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
diff --git a/src/runtime/race/testdata/rwmutex_test.go b/src/runtime/race/testdata/rwmutex_test.go
index 7ac829d759..39219e58ae 100644
--- a/src/runtime/race/testdata/rwmutex_test.go
+++ b/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()
diff --git a/src/runtime/race/testdata/select_test.go b/src/runtime/race/testdata/select_test.go
index 9969f47e8e..3827867687 100644
--- a/src/runtime/race/testdata/select_test.go
+++ b/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)
diff --git a/src/runtime/race/testdata/sync_test.go b/src/runtime/race/testdata/sync_test.go
index d48680d5e6..2b2d95d76b 100644
--- a/src/runtime/race/testdata/sync_test.go
+++ b/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() {
diff --git a/src/runtime/race/testdata/waitgroup_test.go b/src/runtime/race/testdata/waitgroup_test.go
index ff152b0abe..169337315b 100644
--- a/src/runtime/race/testdata/waitgroup_test.go
+++ b/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() {