cmd/vet: teach vet about ast.AliasSpec

Fixes #17755

Change-Id: I1ad1edc382b1312d992963054eb82648cb5112d2
Reviewed-on: https://go-review.googlesource.com/32588
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/vet/copylock.go

@@ -61,7 +61,10 @@ func checkCopyLocksGenDecl(f *File, gd *ast.GenDecl) {
 		return
 	}
 	for _, spec := range gd.Specs {
-		valueSpec := spec.(*ast.ValueSpec)
+		valueSpec, ok := spec.(*ast.ValueSpec)
+		if !ok {
+			continue
+		}
 		for i, x := range valueSpec.Values {
 			if path := lockPathRhs(f, x); path != nil {
 				f.Badf(x.Pos(), "variable declaration copies lock value to %v: %v", valueSpec.Names[i].Name, path)

src/cmd/vet/shadow.go

@@ -188,8 +188,7 @@ func checkShadowDecl(f *File, d *ast.GenDecl) {
 	for _, spec := range d.Specs {
 		valueSpec, ok := spec.(*ast.ValueSpec)
 		if !ok {
-			f.Badf(spec.Pos(), "invalid AST: var GenDecl not ValueSpec")
-			return
+			continue
 		}
 		// Don't complain about deliberate redeclarations of the form
 		//	var i = i

src/cmd/vet/testdata/copylock.go

 package testdata
 
 import (
+	"runtime"
 	"sync"
 	"sync/atomic"
 )
@@ -156,3 +157,11 @@ func AtomicTypesCheck() {
 	vP := &vX
 	vZ := &atomic.Value{}
 }
+
+// ensure we don't crash when we encounter aliases; issue 17755
+
+var _ => runtime.MemProfileRate
+
+const _ => runtime.Compiler
+
+type _ => sync.Mutex