gopls/internal/golang: check for nil ReceiverNamed

This is a defensive check against a nil result from ReceiverNamed;

I'm unable to reproduce the panic though. It would have to be
hovering over a reference to a method whose receiver is
not a named type (or alias or pointer to named), such as
a slice type, an undeclared type, or somesuch.

Updates golang/go#70969

Change-Id: I1cc2bc3d311a88304a2af525d38c1143f4c513a1
Reviewed-on: https://go-review.googlesource.com/c/tools/+/638597
Auto-Submit: Alan Donovan <[email protected]>
Reviewed-by: Robert Findley <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>

Author: adonovan

gopls/internal/golang/hover.go

@@ -1349,7 +1349,7 @@ func StdSymbolOf(obj types.Object) *stdlib.Symbol {
 	// Handle Method.
 	if fn, _ := obj.(*types.Func); fn != nil {
 		isPtr, named := typesinternal.ReceiverNamed(fn.Signature().Recv())
-		if isPackageLevel(named.Obj()) {
+		if named != nil && isPackageLevel(named.Obj()) {
 			for _, s := range symbols {
 				if s.Kind != stdlib.Method {
 					continue

internal/typesinternal/recv.go

@@ -11,6 +11,8 @@ import (
 // ReceiverNamed returns the named type (if any) associated with the
 // type of recv, which may be of the form N or *N, or aliases thereof.
 // It also reports whether a Pointer was present.
+//
+// The named result may be nil in ill-typed code.
 func ReceiverNamed(recv *types.Var) (isPtr bool, named *types.Named) {
 	t := recv.Type()
 	if ptr, ok := types.Unalias(t).(*types.Pointer); ok {