complain when trying to put T into an interface

if T has pointer methods.  this is just a heuristic
but it catches the problem robert ran into and
lets me put the larger interface issues aside for
now.  found one bug in pretty.

R=ken
OCL=26141
CL=26141

src/cmd/gc/subr.c

@@ -2805,12 +2805,23 @@ ifacelookdot(Sym *s, Type *t)
 // check whether non-interface type t
 // satisifes inteface type iface.
 int
-ifaceokT2I(Type *t, Type *iface, Type **m)
+ifaceokT2I(Type *t0, Type *iface, Type **m)
 {
-	Type *im, *tm;
+	Type *t, *im, *tm;
 	int imhash;
 
-	t = methtype(t);
+	t = methtype(t0);
+
+	// stopgap: check for
+	// non-pointer type in T2I, methods want pointers.
+	// supposed to do something better eventually
+	// but this will catch errors while we decide the
+	// details of the "better" solution.
+	if(t == t0 && t->methptr == 2) {
+		yyerror("probably wanted *%T not %T", t, t);
+		*m = iface->type;
+		return 0;
+	}
 
 	// if this is too slow,
 	// could sort these first

test/golden.out

@@ -64,10 +64,6 @@ Faulting address: 0x0
 pc: xxx
 
 
-=========== ./interface6.go
-failure in f4 i
-BUG interface6
-
 =========== ./peano.go
 0! = 1
 1! = 1

test/interface4.go

@@ -35,11 +35,11 @@ func ptrs() {
 	var smallptr SmallPtr = SmallPtr{ 12345 };
 	var intptr IntPtr = 12345;
 
-	test("bigptr", bigptr);
+//	test("bigptr", bigptr);
 	test("&bigptr", &bigptr);
-	test("smallptr", smallptr);
+//	test("smallptr", smallptr);
 	test("&smallptr", &smallptr);
-	test("intptr", intptr);
+//	test("intptr", intptr);
 	test("&intptr", &intptr);
 }
 

test/interface6.go

@@ -49,13 +49,13 @@ type S2 struct { i int }
 func (p *S2) Get() int { return p.i }
 func (p *S2) Put(i int) { p.i = i }
 
-func f4() {
-  s := S2{1};
-  var i I1 = s;
-  i.Put(2);
-  check(i.Get() == 2, "f4 i");
-  check(s.i == 1, "f4 s");
-}
+// func f4() {
+//   s := S2{1};
+//   var i I1 = s;
+//   i.Put(2);
+//   check(i.Get() == 2, "f4 i");
+//   check(s.i == 1, "f4 s");
+// }
 
 func f5() {
   s := S2{1};
@@ -107,13 +107,13 @@ type S4 struct { i, j, k, l int64 }
 func (p *S4) Get() int64 { return p.l }
 func (p *S4) Put(i int64) { p.l = i }
 
-func f10() {
-  s := S4{1, 2, 3, 4};
-  var i I2 = s;
-  i.Put(5);
-  check(i.Get() == 5, "f10 i");
-  check(s.l == 4, "f10 s");
-}
+// func f10() {
+//   s := S4{1, 2, 3, 4};
+//   var i I2 = s;
+//   i.Put(5);
+//   check(i.Get() == 5, "f10 i");
+//   check(s.l == 4, "f10 s");
+// }
 
 func f11() {
   s := S4{1, 2, 3, 4};
@@ -135,13 +135,13 @@ func main() {
   f1();
   f2();
   f3();
-  f4();
+//  f4();
   f5();
   f6();
   f7();
   f8();
   f9();
-  f10();
+//  f10();
   f11();
   f12();
   if fail > 0 {

usr/gri/pretty/parser.go

@@ -642,7 +642,7 @@ func (P *Parser) parseStructType() ast.Expr {
 		}
 	}
 
-	return ast.StructType{loc, fields, end};
+	return &ast.StructType{loc, fields, end};
 }