go/callgraph/vta: use core type for struct fields

Fixes golang/go#63146

Change-Id: Iafcd171b727ecf8bab04fdd2dbc06823574050df
Reviewed-on: https://go-review.googlesource.com/c/tools/+/536035
LUCI-TryBot-Result: Go LUCI <[email protected]>
Run-TryBot: Tim King <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Reviewed-by: Zvonimir Pavlinovic <[email protected]>

Author: timothy-king

go/callgraph/vta/graph.go

@@ -106,12 +106,12 @@ type field struct {
 }
 
 func (f field) Type() types.Type {
-	s := f.StructType.Underlying().(*types.Struct)
+	s := typeparams.CoreType(f.StructType).(*types.Struct)
 	return s.Field(f.index).Type()
 }
 
 func (f field) String() string {
-	s := f.StructType.Underlying().(*types.Struct)
+	s := typeparams.CoreType(f.StructType).(*types.Struct)
 	return fmt.Sprintf("Field(%v:%s)", f.StructType, s.Field(f.index).Name())
 }
 
@@ -434,7 +434,7 @@ func (b *builder) field(f *ssa.Field) {
 }
 
 func (b *builder) fieldAddr(f *ssa.FieldAddr) {
-	t := f.X.Type().Underlying().(*types.Pointer).Elem()
+	t := typeparams.CoreType(f.X.Type()).(*types.Pointer).Elem()
 
 	// Since we are getting pointer to a field, make a bidirectional edge.
 	fnode := field{StructType: t, index: f.Field}

go/callgraph/vta/testdata/src/issue63146.go

@@ -0,0 +1,26 @@
+package test
+
+type embedded struct{}
+
+type S struct{ embedded }
+
+func (_ S) M() {}
+
+type C interface {
+	M()
+	S
+}
+
+func G[T C]() {
+	t := T{embedded{}}
+	t.M()
+}
+
+func F() {
+	G[S]()
+}
+
+// WANT:
+// F: G[testdata.S]() -> G[testdata.S]
+// G[testdata.S]: (S).M(t2) -> S.M
+// S.M: (testdata.S).M(t1) -> S.M

go/callgraph/vta/vta_test.go

@@ -127,6 +127,7 @@ func TestVTACallGraphGenerics(t *testing.T) {
 	files := []string{
 		"testdata/src/arrays_generics.go",
 		"testdata/src/callgraph_generics.go",
+		"testdata/src/issue63146.go",
 	}
 	for _, file := range files {
 		t.Run(file, func(t *testing.T) {