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>

1 files changed, 14 insertions, 0 deletions

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() {}