oracle: handle implicit selections in callees

The types only optimization for callees looked at the type of the
receiver to figure out if it was a dynamic call. If the selection
involves any implicit selections, we cannot be sure that this type
is the one that will actually receive the call.

Fix by working backwards from function signature to find the true
receiver

Change-Id: If79e3de7af33480e37bcf1081abe44bb04914da4
Reviewed-on: https://go-review.googlesource.com/18563
Reviewed-by: Alan Donovan <adonovan@google.com>

oracle/callees.go

@@ -92,12 +92,17 @@ func callees(q *Query) error {
 				return nil
 			}
 		} else if sel.Kind() == types.MethodVal {
-			recvtype := sel.Recv()
+			// Inspect the receiver type of the selected method.
+			// If it is concrete, the call is statically dispatched.
+			// (Due to implicit field selections, it is not enough to look
+			// at sel.Recv(), the type of the actual receiver expression.)
+			method := sel.Obj().(*types.Func)
+			recvtype := method.Type().(*types.Signature).Recv().Type()
 			if !types.IsInterface(recvtype) {
 				// static method call
 				q.result = &calleesTypesResult{
 					site:   e,
-					callee: sel.Obj().(*types.Func),
+					callee: method,
 				}
 				return nil
 			}

oracle/callees14.go

@@ -92,12 +92,17 @@ func callees(q *Query) error {
 				return nil
 			}
 		} else if sel.Kind() == types.MethodVal {
-			recvtype := sel.Recv()
+			// Inspect the receiver type of the selected method.
+			// If it is concrete, the call is statically dispatched.
+			// (Due to implicit field selections, it is not enough to look
+			// at sel.Recv(), the type of the actual receiver expression.)
+			method := sel.Obj().(*types.Func)
+			recvtype := method.Type().(*types.Signature).Recv().Type()
 			if !types.IsInterface(recvtype) {
 				// static method call
 				q.result = &calleesTypesResult{
 					site:   e,
-					callee: sel.Obj().(*types.Func),
+					callee: method,
 				}
 				return nil
 			}

oracle/testdata/src/calls/main.go

@@ -83,6 +83,9 @@ func main() {
 	fmt.Println() // @callees callees-qualified-call "Println"
 	m := new(method)
 	m.f() // @callees callees-static-method-call "f"
+	g := new(embeddedIface)
+	g.iface = m
+	g.f() // @callees callees-implicit-selection-method-call "f"
 }
 
 type myint int
@@ -96,6 +99,14 @@ type method int
 func (method) f() {
 }
 
+type embeddedIface struct {
+	iface
+}
+
+type iface interface {
+	f()
+}
+
 var dynamic = func() {}
 
 func deadcode() {

oracle/testdata/src/calls/main.golden

@@ -96,6 +96,10 @@ this static function call dispatches to:
 this static function call dispatches to:
 	(main.method).f
 
+-------- @callees callees-implicit-selection-method-call --------
+this dynamic method call dispatches to:
+	(main.method).f
+
 -------- @callers callers-not-a-wrapper --------
 (main.myint).f is called from these 1 sites:
 	dynamic method call from main.main