gc: correctly handle fields of pointer type to recursive forward references

Previously, whether declaring a type which copied the structure of a type it was referenced in via a pointer field would work depended on whether you declared it before or after the type it copied, e.g. type T2 T1; type T1 struct { F *T2 } would work, however type T1 struct { F *T2 }; type T2 T1 wouldn't.

Fixes #667.

R=rsc
CC=golang-dev
https://golang.org/cl/4313064

src/cmd/gc/dcl.c

@@ -679,15 +679,11 @@ typedcl2(Type *pt, Type *t)
 
 ok:
 	n = pt->nod;
-	*pt = *t;
-	pt->method = nil;
+	copytype(pt->nod, t);
+	// unzero nod
 	pt->nod = n;
-	pt->sym = n->sym;
+
 	pt->sym->lastlineno = parserline();
-	pt->siggen = 0;
-	pt->printed = 0;
-	pt->deferwidth = 0;
-	pt->local = 0;
 	declare(n, PEXTERN);
 
 	checkwidth(pt);

src/cmd/gc/go.h

@@ -1172,9 +1172,12 @@ Node*	unsafenmagic(Node *n);
  */
 Node*	callnew(Type *t);
 Node*	chanfn(char *name, int n, Type *t);
+void	copytype(Node *n, Type *t);
+void	defertypecopy(Node *n, Type *t);
 Node*	mkcall(char *name, Type *t, NodeList **init, ...);
 Node*	mkcall1(Node *fn, Type *t, NodeList **init, ...);
 void	queuemethod(Node *n);
+void	resumetypecopy(void);
 int	vmatch1(Node *l, Node *r);
 void	walk(Node *fn);
 Node*	walkdef(Node *n);

src/cmd/gc/lex.c

@@ -249,6 +249,7 @@ main(int argc, char *argv[])
 	for(l=xtop; l; l=l->next)
 		if(l->n->op == ODCL || l->n->op == OAS)
 			typecheck(&l->n, Etop);
+	resumetypecopy();
 	resumecheckwidth();
 	for(l=xtop; l; l=l->next)
 		if(l->n->op == ODCLFUNC)

src/cmd/gc/typecheck.c

@@ -31,6 +31,7 @@ static void	checkassign(Node*);
 static void	checkassignlist(NodeList*);
 static void stringtoarraylit(Node**);
 static Node* resolve(Node*);
+static Type*	getforwtype(Node*);
 
 /*
  * resolve ONONAME to definition, if any.
@@ -110,7 +111,7 @@ typecheck(Node **np, int top)
 	Node *n, *l, *r;
 	NodeList *args;
 	int lno, ok, ntop;
-	Type *t, *tp, *missing, *have;
+	Type *t, *tp, *ft, *missing, *have;
 	Sym *sym;
 	Val v;
 	char *why;
@@ -153,6 +154,11 @@ typecheck(Node **np, int top)
 			yyerror("use of builtin %S not in function call", n->sym);
 			goto error;
 		}
+
+		// a dance to handle forward-declared recursive pointer types.
+		if(n->op == OTYPE && (ft = getforwtype(n->ntype)) != T)
+			defertypecopy(n, ft);
+
 		walkdef(n);
 		n->realtype = n->type;
 		if(n->op == ONONAME)
@@ -2470,3 +2476,24 @@ stringtoarraylit(Node **np)
 	typecheck(&nn, Erv);
 	*np = nn;
 }
+
+static Type*
+getforwtype(Node *n)
+{
+	Node *f1, *f2;
+
+	for(f1=f2=n; ; n=n->ntype) {
+		if((n = resolve(n)) == N || n->op != OTYPE)
+			return T;
+
+		if(n->type != T && n->type->etype == TFORW)
+			return n->type;
+
+		// Check for ntype cycle.
+		if((f2 = resolve(f2)) != N && (f1 = resolve(f2->ntype)) != N) {
+			f2 = resolve(f1->ntype);
+			if(f1 == n || f2 == n)
+				return T;
+		}
+	}
+}

src/cmd/gc/walk.c

@@ -119,6 +119,62 @@ domethod(Node *n)
 	checkwidth(n->type);
 }
 
+typedef struct NodeTypeList NodeTypeList;
+struct NodeTypeList {
+	Node *n;
+	Type *t;
+	NodeTypeList *next;
+};
+
+static	NodeTypeList	*dntq;
+static	NodeTypeList	*dntend;
+
+void
+defertypecopy(Node *n, Type *t)
+{
+	NodeTypeList *ntl;
+
+	if(n == N || t == T)
+		return;
+
+	ntl = mal(sizeof *ntl);
+	ntl->n = n;
+	ntl->t = t;
+	ntl->next = nil;
+
+	if(dntq == nil)
+		dntq = ntl;
+	else
+		dntend->next = ntl;
+
+	dntend = ntl;
+}
+
+void
+resumetypecopy(void)
+{
+	NodeTypeList *l;
+
+	for(l=dntq; l; l=l->next)
+		copytype(l->n, l->t);
+}
+
+void
+copytype(Node *n, Type *t)
+{
+	*n->type = *t;
+
+	t = n->type;
+	t->sym = n->sym;
+	t->local = n->local;
+	t->vargen = n->vargen;
+	t->siggen = 0;
+	t->method = nil;
+	t->nod = N;
+	t->printed = 0;
+	t->deferwidth = 0;
+}
+
 static void
 walkdeftype(Node *n)
 {
@@ -141,22 +197,14 @@ walkdeftype(Node *n)
 		goto ret;
 	}
 
+	maplineno = n->type->maplineno;
+	embedlineno = n->type->embedlineno;
+
 	// copy new type and clear fields
 	// that don't come along.
 	// anything zeroed here must be zeroed in
 	// typedcl2 too.
-	maplineno = n->type->maplineno;
-	embedlineno = n->type->embedlineno;
-	*n->type = *t;
-	t = n->type;
-	t->sym = n->sym;
-	t->local = n->local;
-	t->vargen = n->vargen;
-	t->siggen = 0;
-	t->method = nil;
-	t->nod = N;
-	t->printed = 0;
-	t->deferwidth = 0;
+	copytype(n, t);
 
 	// double-check use of type as map key.
 	if(maplineno) {

test/fixedbugs/bug336.go

+// $G $D/$F.go && $L $F.$A && ./$A.out
+
+// Copyright 2011 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.
+
+package main
+
+type T1 struct {
+	Next *T2
+}
+
+type T2 T1
+
+type T3 struct {
+	Next *T4
+}
+
+type T4 T5
+type T5 T6
+type T6 T7
+type T7 T8
+type T8 T9
+type T9 T3
+
+type T10 struct {
+	x struct {
+		y ***struct {
+			z *struct {
+				Next *T11
+			}
+		}
+	}
+}
+
+type T11 T10
+
+type T12 struct {
+	F1 *T15
+	F2 *T13
+	F3 *T16
+}
+
+type T13 T14
+type T14 T15
+type T15 T16
+type T16 T17
+type T17 T12
+
+// issue 1672
+type T18 *[10]T19
+type T19 T18
+
+func main() {
+	_ = &T1{&T2{}}
+	_ = &T2{&T2{}}
+	_ = &T3{&T4{}}
+	_ = &T4{&T4{}}
+	_ = &T5{&T4{}}
+	_ = &T6{&T4{}}
+	_ = &T7{&T4{}}
+	_ = &T8{&T4{}}
+	_ = &T9{&T4{}}
+	_ = &T12{&T15{}, &T13{}, &T16{}}
+
+	var (
+		tn    struct{ Next *T11 }
+		tz    struct{ z *struct{ Next *T11 } }
+		tpz   *struct{ z *struct{ Next *T11 } }
+		tppz  **struct{ z *struct{ Next *T11 } }
+		tpppz ***struct{ z *struct{ Next *T11 } }
+		ty    struct {
+			y ***struct{ z *struct{ Next *T11 } }
+		}
+	)
+	tn.Next = &T11{}
+	tz.z = &tn
+	tpz = &tz
+	tppz = &tpz
+	tpppz = &tppz
+	ty.y = tpppz
+	_ = &T10{ty}
+
+	t19s := &[10]T19{}
+	_ = T18(t19s)
+}