go/callgraph/rta: audit for types.Alias safety

Updates golang/go#65294

Change-Id: I90fe0cc3ab5a6171e112e2eb0e452efb172d9980
Reviewed-on: https://go-review.googlesource.com/c/tools/+/559937
Reviewed-by: Zvonimir Pavlinovic <zpavlinovic@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

go/callgraph/rta/rta.go

@@ -45,6 +45,7 @@ import (
 	"golang.org/x/tools/go/callgraph"
 	"golang.org/x/tools/go/ssa"
 	"golang.org/x/tools/go/types/typeutil"
+	"golang.org/x/tools/internal/aliases"
 	"golang.org/x/tools/internal/compat"
 )
 
@@ -416,6 +417,9 @@ func (r *rta) implementations(I *types.Interface) []types.Type {
 // dynamic type of some interface or reflect.Value.
 // Adapted from needMethods in go/ssa/builder.go
 func (r *rta) addRuntimeType(T types.Type, skip bool) {
+	// Never record aliases.
+	T = aliases.Unalias(T)
+
 	if prev, ok := r.result.RuntimeTypes.At(T).(bool); ok {
 		if skip && !prev {
 			r.result.RuntimeTypes.Set(T, skip)
@@ -457,7 +461,7 @@ func (r *rta) addRuntimeType(T types.Type, skip bool) {
 	case *types.Named:
 		n = T
 	case *types.Pointer:
-		n, _ = T.Elem().(*types.Named)
+		n, _ = aliases.Unalias(T.Elem()).(*types.Named)
 	}
 	if n != nil {
 		owner := n.Obj().Pkg()
@@ -476,6 +480,9 @@ func (r *rta) addRuntimeType(T types.Type, skip bool) {
 	}
 
 	switch t := T.(type) {
+	case *aliases.Alias:
+		panic("unreachable")
+
 	case *types.Basic:
 		// nop
 

go/callgraph/rta/rta_test.go

@@ -23,6 +23,7 @@ import (
 	"golang.org/x/tools/go/loader"
 	"golang.org/x/tools/go/ssa"
 	"golang.org/x/tools/go/ssa/ssautil"
+	"golang.org/x/tools/internal/aliases"
 )
 
 // TestRTA runs RTA on each testdata/*.go file and compares the
@@ -200,7 +201,7 @@ func check(t *testing.T, f *ast.File, pkg *ssa.Package, res *rta.Result) {
 		got := make(stringset)
 		res.RuntimeTypes.Iterate(func(key types.Type, value interface{}) {
 			if !value.(bool) { // accessible to reflection
-				typ := types.TypeString(key, types.RelativeTo(pkg.Pkg))
+				typ := types.TypeString(aliases.Unalias(key), types.RelativeTo(pkg.Pkg))
 				got[typ] = true
 			}
 		})