cmd/compile: adjust annotation of implicit operations.

Limit probe to ODOT/OIND/ODOTPTR for now; that works.

Fixes #11790

Change-Id: I411271e702c5fe6ceb880ca47c7dacc37ffcbb6a
Reviewed-on: https://go-review.googlesource.com/12532Reviewed-by: Russ Cox <rsc@golang.org>

src/cmd/compile/internal/gc/subr.go

@@ -2145,10 +2145,8 @@ func adddot(n *Node) *Node {
 
 			// rebuild elided dots
 			for c := d - 1; c >= 0; c-- {
-				if n.Left.Type != nil && Isptr[n.Left.Type.Etype] {
-					n.Left.Implicit = true
-				}
 				n.Left = Nod(ODOT, n.Left, newname(dotlist[c].field.Sym))
+				n.Left.Implicit = true
 			}
 
 			return n

src/cmd/compile/internal/gc/typecheck.go

@@ -2582,18 +2582,18 @@ func lookdot(n *Node, t *Type, dostrcmp int) *Type {
 			}
 		}
 
+		pll := n
 		ll := n.Left
-		for ll.Left != nil {
+		for ll.Left != nil && (ll.Op == ODOT || ll.Op == ODOTPTR || ll.Op == OIND) {
+			pll = ll
 			ll = ll.Left
 		}
-		if ll.Implicit {
-			if Isptr[ll.Type.Etype] && ll.Type.Sym != nil && ll.Type.Sym.Def != nil && ll.Type.Sym.Def.Op == OTYPE {
+		if pll.Implicit && Isptr[ll.Type.Etype] && ll.Type.Sym != nil && ll.Type.Sym.Def != nil && ll.Type.Sym.Def.Op == OTYPE {
 			// It is invalid to automatically dereference a named pointer type when selecting a method.
 			// Make n->left == ll to clarify error message.
 			n.Left = ll
 			return nil
 		}
-		}
 
 		n.Right = methodname(n.Right, n.Left.Type)
 		n.Xoffset = f2.Width

test/fixedbugs/issue11790.go

+// compile
+
+// Copyright 2015 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Issue 11790: Incorrect error following named pointer dereference on field
+
+package main
+
+import "fmt"
+
+type T0 struct {
+	x int
+}
+
+func (*T0) M0() {
+	fmt.Println("M0")
+}
+
+type T2 struct {
+	*T0
+}
+
+type Q *T2
+
+func main() {
+	// If run, expected output is
+	// 42
+	// M0
+	t0 := T0{42}
+	t2 := T2{&t0}
+	var q Q = &t2
+	fmt.Println(q.x) // Comment out either this line or the next line and the program works
+	(*q).T0.M0()
+}