more interface checks:

	- pointer to interface cannot have methods
	- record type names for better runtime error

R=r,ken
DELTA=85  (80 added, 0 deleted, 5 changed)
OCL=16658
CL=16722

3 files changed, 19 insertions, 6 deletions

diff --git a/src/cmd/6g/obj.c b/src/cmd/6g/obj.c
index 28eb6b1c51..b4f44bbc3f 100644
--- a/src/cmd/6g/obj.c
+++ b/src/cmd/6g/obj.c
@@ -466,6 +466,7 @@ dumpsignatures(void)
 	Addr at, ao, ac, ad;
 	Prog *p;
 	char *sp;
+	char buf[NSYMB];
 
 	// copy externdcl list to signatlist
 	for(d=externdcl; d!=D; d=d->forw) {
@@ -583,7 +584,7 @@ dumpsignatures(void)
 			sp = strchr(s1->name, '_');
 			if(sp != nil)
 				a->name = sp+1;
-			
+
 			a->hash = PRIME8*stringhash(a->name) + PRIME9*typehash(f->type, 0);
 			a->perm = o;
 			snprint(namebuf, sizeof(namebuf), "%s_%s",
@@ -608,7 +609,9 @@ dumpsignatures(void)
 		p->to.offset = stringo;
 		ot += widthptr;
 
-		datastring("", 1);
+		// save type name for runtime error message
+		snprint(buf, sizeof buf, "%T", t);
+		datastring(buf, strlen(buf)+1);
 
 		if(et == TINTER) {
 			// first field of an interface signature
@@ -733,6 +736,7 @@ dumpsignatures(void)
 				ot += widthptr;
 			}
 			datastring(b->name, strlen(b->name)+1);
+
 		}
 
 		// nil field name at end
diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index c15039e36f..ddce14e6f3 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -1406,6 +1406,10 @@ ismethod(Type *t)
 	if(t == T)
 		return T;
 
+	// no interfaces
+	if(t->etype == TINTER || (t->etype == tptr && t->type->etype == TINTER))
+		return T;
+
 	a = algtype(t);
 
 	// direct receiver
diff --git a/src/runtime/iface.c b/src/runtime/iface.c
index e8c4cd6939..089975b923 100644
--- a/src/runtime/iface.c
+++ b/src/runtime/iface.c
@@ -40,7 +40,7 @@ static	Map*	hash[1009];
 static void
 printsigi(Sigi *si)
 {
-	int32 i, n;
+	int32 i;
 	byte *name;
 
 	sys·printpointer(si);
@@ -125,7 +125,7 @@ hashmap(Sigi *si, Sigt *st)
 	m->sigi = si;
 	m->sigt = st;
 
-	nt = 0;
+	nt = 1;
 	for(ni=1; (iname=si[ni].name) != nil; ni++) {	// ni=1: skip first word
 		// pick up next name from
 		// interface signature
@@ -136,9 +136,14 @@ hashmap(Sigi *si, Sigt *st)
 			// from structure signature
 			sname = st[nt].name;
 			if(sname == nil) {
+				prints("cannot convert type ");
+				prints((int8*)st[0].name);
+				prints(" to interface ");
+				prints((int8*)si[0].name);
+				prints(": missing method ");
 				prints((int8*)iname);
-				prints(": ");
-				throw("hashmap: failed to find method");
+				prints("\n");
+				throw("interface conversion");
 				m->bad = 1;
 				m->link = hash[h];
 				hash[h] = m;