cmd/vet: check sync.* types' copying

Embed noLock struct into the following types, so `go vet -copylocks` catches
their copying additionally to types containing sync.Mutex:
  - sync.Cond
  - sync.WaitGroup
  - sync.Pool
  - atomic.Value

Fixes #14582

Change-Id: Icb543ef5ad10524ad239a15eec8a9b334b0e0660
Reviewed-on: https://go-review.googlesource.com/22015
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

7 files changed, 110 insertions, 1 deletions

diff --git a/src/cmd/vet/testdata/copylock.go b/src/cmd/vet/testdata/copylock.go
index cf56802cdb..d49f468627 100644
--- a/src/cmd/vet/testdata/copylock.go
+++ b/src/cmd/vet/testdata/copylock.go
@@ -1,6 +1,9 @@
 package testdata
 
-import "sync"
+import (
+	"sync"
+	"sync/atomic"
+)
 
 func OkFunc() {
 	var x *sync.Mutex
@@ -66,3 +69,72 @@ func BadFunc() {
 	new := func(interface{}) {}
 	new(t) // ERROR "function call copies lock value: testdata.Tlock contains sync.Once contains sync.Mutex"
 }
+
+// SyncTypesCheck checks copying of sync.* types except sync.Mutex
+func SyncTypesCheck() {
+	// sync.RWMutex copying
+	var rwmuX sync.RWMutex
+	var rwmuXX = sync.RWMutex{}
+	rwmuX1 := new(sync.RWMutex)
+	rwmuY := rwmuX     // ERROR "assignment copies lock value to rwmuY: sync.RWMutex"
+	rwmuY = rwmuX      // ERROR "assignment copies lock value to rwmuY: sync.RWMutex"
+	var rwmuYY = rwmuX // ERROR "variable declaration copies lock value to rwmuYY: sync.RWMutex"
+	rwmuP := &rwmuX
+	rwmuZ := &sync.RWMutex{}
+
+	// sync.Cond copying
+	var condX sync.Cond
+	var condXX = sync.Cond{}
+	condX1 := new(sync.Cond)
+	condY := condX     // ERROR "assignment copies lock value to condY: sync.Cond contains sync.noCopy"
+	condY = condX      // ERROR "assignment copies lock value to condY: sync.Cond contains sync.noCopy"
+	var condYY = condX // ERROR "variable declaration copies lock value to condYY: sync.Cond contains sync.noCopy"
+	condP := &condX
+	condZ := &sync.Cond{
+		L: &sync.Mutex{},
+	}
+	condZ = sync.NewCond(&sync.Mutex{})
+
+	// sync.WaitGroup copying
+	var wgX sync.WaitGroup
+	var wgXX = sync.WaitGroup{}
+	wgX1 := new(sync.WaitGroup)
+	wgY := wgX     // ERROR "assignment copies lock value to wgY: sync.WaitGroup contains sync.noCopy"
+	wgY = wgX      // ERROR "assignment copies lock value to wgY: sync.WaitGroup contains sync.noCopy"
+	var wgYY = wgX // ERROR "variable declaration copies lock value to wgYY: sync.WaitGroup contains sync.noCopy"
+	wgP := &wgX
+	wgZ := &sync.WaitGroup{}
+
+	// sync.Pool copying
+	var poolX sync.Pool
+	var poolXX = sync.Pool{}
+	poolX1 := new(sync.Pool)
+	poolY := poolX     // ERROR "assignment copies lock value to poolY: sync.Pool contains sync.noCopy"
+	poolY = poolX      // ERROR "assignment copies lock value to poolY: sync.Pool contains sync.noCopy"
+	var poolYY = poolX // ERROR "variable declaration copies lock value to poolYY: sync.Pool contains sync.noCopy"
+	poolP := &poolX
+	poolZ := &sync.Pool{}
+
+	// sync.Once copying
+	var onceX sync.Once
+	var onceXX = sync.Once{}
+	onceX1 := new(sync.Once)
+	onceY := onceX     // ERROR "assignment copies lock value to onceY: sync.Once contains sync.Mutex"
+	onceY = onceX      // ERROR "assignment copies lock value to onceY: sync.Once contains sync.Mutex"
+	var onceYY = onceX // ERROR "variable declaration copies lock value to onceYY: sync.Once contains sync.Mutex"
+	onceP := &onceX
+	onceZ := &sync.Once{}
+}
+
+// AtomicTypesCheck checks copying of sync/atomic types
+func AtomicTypesCheck() {
+	// atomic.Value copying
+	var vX atomic.Value
+	var vXX = atomic.Value{}
+	vX1 := new(atomic.Value)
+	vY := vX     // ERROR "assignment copies lock value to vY: sync/atomic.Value contains sync/atomic.noCopy"
+	vY = vX      // ERROR "assignment copies lock value to vY: sync/atomic.Value contains sync/atomic.noCopy"
+	var vYY = vX // ERROR "variable declaration copies lock value to vYY: sync/atomic.Value contains sync/atomic.noCopy"
+	vP := &vX
+	vZ := &atomic.Value{}
+}
diff --git a/src/sync/atomic/value.go b/src/sync/atomic/value.go
index ab3aa11285..30abf72634 100644
--- a/src/sync/atomic/value.go
+++ b/src/sync/atomic/value.go
@@ -12,7 +12,11 @@ import (
 // Values can be created as part of other data structures.
 // The zero value for a Value returns nil from Load.
 // Once Store has been called, a Value must not be copied.
+//
+// A Value must not be copied after first use.
 type Value struct {
+	noCopy noCopy
+
 	v interface{}
 }
 
@@ -83,3 +87,13 @@ func (v *Value) Store(x interface{}) {
 // Disable/enable preemption, implemented in runtime.
 func runtime_procPin()
 func runtime_procUnpin()
+
+// noCopy may be embedded into structs which must not be copied
+// after the first use.
+//
+// See https://github.com/golang/go/issues/8005#issuecomment-190753527
+// for details.
+type noCopy struct{}
+
+// Lock is a no-op used by -copylocks checker from `go vet`.
+func (*noCopy) Lock() {}
diff --git a/src/sync/cond.go b/src/sync/cond.go
index f711c39da2..c070d9d84e 100644
--- a/src/sync/cond.go
+++ b/src/sync/cond.go
@@ -20,6 +20,8 @@ import (
 // A Cond can be created as part of other structures.
 // A Cond must not be copied after first use.
 type Cond struct {
+	noCopy noCopy
+
 	// L is held while observing or changing the condition
 	L Locker
 
@@ -84,3 +86,13 @@ func (c *copyChecker) check() {
 		panic("sync.Cond is copied")
 	}
 }
+
+// noCopy may be embedded into structs which must not be copied
+// after the first use.
+//
+// See https://github.com/golang/go/issues/8005#issuecomment-190753527
+// for details.
+type noCopy struct{}
+
+// Lock is a no-op used by -copylocks checker from `go vet`.
+func (*noCopy) Lock() {}
diff --git a/src/sync/mutex.go b/src/sync/mutex.go
index 78b115cf5a..90892793f0 100644
--- a/src/sync/mutex.go
+++ b/src/sync/mutex.go
@@ -19,6 +19,8 @@ import (
 // A Mutex is a mutual exclusion lock.
 // Mutexes can be created as part of other structures;
 // the zero value for a Mutex is an unlocked mutex.
+//
+// A Mutex must not be copied after first use.
 type Mutex struct {
 	state int32
 	sema  uint32
diff --git a/src/sync/pool.go b/src/sync/pool.go
index 2acf505f3c..bf29d88c5c 100644
--- a/src/sync/pool.go
+++ b/src/sync/pool.go
@@ -40,7 +40,10 @@ import (
 // that scenario. It is more efficient to have such objects implement their own
 // free list.
 //
+// A Pool must not be copied after first use.
 type Pool struct {
+	noCopy noCopy
+
 	local     unsafe.Pointer // local fixed-size per-P pool, actual type is [P]poolLocal
 	localSize uintptr        // size of the local array
 
diff --git a/src/sync/rwmutex.go b/src/sync/rwmutex.go
index 9fc6e3bd2c..455d412330 100644
--- a/src/sync/rwmutex.go
+++ b/src/sync/rwmutex.go
@@ -16,6 +16,8 @@ import (
 // RWMutexes can be created as part of other
 // structures; the zero value for a RWMutex is
 // an unlocked mutex.
+//
+// An RWMutex must not be copied after first use.
 type RWMutex struct {
 	w           Mutex  // held if there are pending writers
 	writerSem   uint32 // semaphore for writers to wait for completing readers
diff --git a/src/sync/waitgroup.go b/src/sync/waitgroup.go
index 029e6077cd..b386e1fec2 100644
--- a/src/sync/waitgroup.go
+++ b/src/sync/waitgroup.go
@@ -15,7 +15,11 @@ import (
 // goroutines to wait for. Then each of the goroutines
 // runs and calls Done when finished. At the same time,
 // Wait can be used to block until all goroutines have finished.
+//
+// A WaitGroup must not be copied after first use.
 type WaitGroup struct {
+	noCopy noCopy
+
 	// 64-bit value: high 32 bits are counter, low 32 bits are waiter count.
 	// 64-bit atomic operations require 64-bit alignment, but 32-bit
 	// compilers do not ensure it. So we allocate 12 bytes and then use