go/*: use go/types.Func.Signature and go/ast.Preorder

In the few obvious candidates that I found after a bit of grepping.

Change-Id: I36af79c46d29e4422bce1f43bbbac9db7de2001a
Reviewed-on: https://go-review.googlesource.com/c/go/+/650656
Reviewed-by: Alan Donovan <adonovan@google.com>
Auto-Submit: Alan Donovan <adonovan@google.com>
Commit-Queue: Alan Donovan <adonovan@google.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

src/cmd/api/main_test.go

@@ -1058,7 +1058,7 @@ func (w *Walker) emitIfaceType(name string, typ *types.Interface) {
 		if w.isDeprecated(m) {
 			w.emitf("%s //deprecated", m.Name())
 		}
-		w.emitf("%s%s", m.Name(), w.signatureString(m.Type().(*types.Signature)))
+		w.emitf("%s%s", m.Name(), w.signatureString(m.Signature()))
 	}
 
 	if !complete {
@@ -1088,7 +1088,7 @@ func (w *Walker) emitIfaceType(name string, typ *types.Interface) {
 }
 
 func (w *Walker) emitFunc(f *types.Func) {
-	sig := f.Type().(*types.Signature)
+	sig := f.Signature()
 	if sig.Recv() != nil {
 		panic("method considered a regular function: " + f.String())
 	}

src/go/doc/example.go

@@ -491,17 +491,14 @@ func findDeclsAndUnresolved(body ast.Node, topDecls map[*ast.Object]ast.Decl, ty
 }
 
 func hasIota(s ast.Spec) bool {
-	has := false
+	for n := range ast.Preorder(s) {
-	ast.Inspect(s, func(n ast.Node) bool {
 		// Check that this is the special built-in "iota" identifier, not
 		// a user-defined shadow.
 		if id, ok := n.(*ast.Ident); ok && id.Name == "iota" && id.Obj == nil {
-			has = true
-			return false
-		}
 			return true
-	})
+		}
-	return has
+	}
+	return false
 }
 
 // findImportGroupStarts finds the start positions of each sequence of import

src/go/internal/gcimporter/gcimporter_test.go

@@ -472,7 +472,7 @@ func verifyInterfaceMethodRecvs(t *testing.T, named *types.Named, level int) {
 	// check explicitly declared methods
 	for i := 0; i < iface.NumExplicitMethods(); i++ {
 		m := iface.ExplicitMethod(i)
-		recv := m.Type().(*types.Signature).Recv()
+		recv := m.Signature().Recv()
 		if recv == nil {
 			t.Errorf("%s: missing receiver type", m)
 			continue

src/go/internal/gcimporter/ureader.go

@@ -525,7 +525,7 @@ func (pr *pkgReader) objIdx(idx pkgbits.Index) (*types.Package, string) {
 				methods := make([]*types.Func, iface.NumExplicitMethods())
 				for i := range methods {
 					fn := iface.ExplicitMethod(i)
-					sig := fn.Type().(*types.Signature)
+					sig := fn.Signature()
 
 					recv := types.NewVar(fn.Pos(), fn.Pkg(), "", named)
 					methods[i] = types.NewFunc(fn.Pos(), fn.Pkg(), fn.Name(), types.NewSignature(recv, sig.Params(), sig.Results(), sig.Variadic()))

src/go/internal/srcimporter/srcimporter_test.go

@@ -157,7 +157,7 @@ func verifyInterfaceMethodRecvs(t *testing.T, named *types.Named, level int) {
 	// check explicitly declared methods
 	for i := 0; i < iface.NumExplicitMethods(); i++ {
 		m := iface.ExplicitMethod(i)
-		recv := m.Type().(*types.Signature).Recv()
+		recv := m.Signature().Recv()
 		if recv == nil {
 			t.Errorf("%s: missing receiver type", m)
 			continue