gc: recursive interface embedding

Fixes #287.

R=ken2
CC=golang-dev
https://golang.org/cl/215048

src/cmd/gc/dcl.c

@@ -809,6 +809,15 @@ stotype(NodeList *l, int et, Type **t)
 		if(n->op != ODCLFIELD)
 			fatal("stotype: oops %N\n", n);
 		if(n->right != N) {
+			if(et == TINTER && n->left != N) {
+				// queue resolution of method type for later.
+				// right now all we need is the name list.
+				// avoids cycles for recursive interface types.
+				n->type = typ(TINTERMETH);
+				n->type->nod = n->right;
+				n->right = N;
+				queuemethod(n);
+			} else {
 				typecheck(&n->right, Etype);
 				n->type = n->right->type;
 				if(n->type == T) {
@@ -828,6 +837,7 @@ stotype(NodeList *l, int et, Type **t)
 						t1->embedlineno = lineno;
 				}
 			}
+		}
 
 		if(n->type == T) {
 			// assume error already printed

src/cmd/gc/go.h

@@ -462,6 +462,7 @@ enum
 	// pseudo-type for frame layout
 	TFUNCARGS,
 	TCHANARGS,
+	TINTERMETH,
 
 	NTYPE,
 };
@@ -1088,6 +1089,7 @@ Node*	typecheckconv(Node*, Node*, Type*, int, char*);
 int	checkconv(Type*, Type*, int, int*, int*, char*);
 Node*	typecheck(Node**, int);
 int	islvalue(Node*);
+void	queuemethod(Node*);
 
 /*
  *	const.c

src/cmd/gc/typecheck.c

@@ -51,7 +51,7 @@ typecheck(Node **np, int top)
 	int et, op;
 	Node *n, *l, *r;
 	NodeList *args;
-	int lno, ok, ntop, ct;
+	int lno, ok, ntop;
 	Type *t;
 	Sym *sym;
 	Val v;

src/cmd/gc/walk.c

@@ -115,11 +115,25 @@ gettype(Node **np, NodeList **init)
 		dump("after gettype", *np);
 }
 
-void
+static int nwalkdeftype;
-walkdeflist(NodeList *l)
+static NodeList *methodqueue;
+
+static void
+domethod(Node *n)
 {
-	for(; l; l=l->next)
+	Node *nt;
-		walkdef(l->n);
+	
+	nt = n->type->nod;
+	typecheck(&nt, Etype);
+	if(nt->type == T) {
+		// type check failed; leave empty func
+		n->type->etype = TFUNC;
+		n->type->nod = N;
+		return;
+	}
+	*n->type = *nt->type;
+	n->type->nod = N;
+	checkwidth(n->type);
 }
 
 static void
@@ -127,7 +141,9 @@ walkdeftype(Node *n)
 {
 	int maplineno, embedlineno, lno;
 	Type *t;
+	NodeList *l;
 	
+	nwalkdeftype++;
 	lno = lineno;
 	setlineno(n);
 	n->type->sym = n->sym;
@@ -168,6 +184,28 @@ walkdeftype(Node *n)
 
 ret:
 	lineno = lno;
+	
+	// if there are no type definitions going on, it's safe to
+	// try to resolve the method types for the interfaces
+	// we just read.
+	if(nwalkdeftype == 1) {
+		while((l = methodqueue) != nil) {
+			methodqueue = nil;
+			for(; l; l=l->next)
+				domethod(l->n);
+		}
+	}
+	nwalkdeftype--;
+}
+
+void
+queuemethod(Node *n)
+{
+	if(nwalkdeftype == 0) {
+		domethod(n);
+		return;
+	}
+	methodqueue = list(methodqueue, n);
 }
 
 void

test/fixedbugs/bug251.go

@@ -8,14 +8,14 @@ package main
 
 type I1 interface {
 	m() I2
-	I2	// ERROR "loop|interface"
+	I2
 }
 
 type I2 interface {
-	I1
+	I1	// ERROR "loop|interface"
 }
 
 
-var i1 I1 = i2
+var i1 I1 = i2	// ERROR "need type assertion"
 var i2 I2
 var i2a I2 = i1

test/golden.out

@@ -150,17 +150,3 @@ throw: interface conversion
 panic PC=xxx
 
 == bugs/
-
-=========== bugs/bug250.go
-bugs/bug250.go:14: interface type loop involving I1
-bugs/bug250.go:17: need type assertion to use I2 as I1
-	missing m() I2
-BUG: bug250
-
-=========== bugs/bug251.go
-BUG: errchk: bugs/bug251.go:11: missing expected error: 'loop|interface'
-errchk: bugs/bug251.go: unmatched error messages:
-==================================================
-bugs/bug251.go:15: interface type loop involving I1
-bugs/bug251.go:19: need type assertion to use I2 as I1
-==================================================