From 7f3eb2738f4e2e372fc43e72b28be0685381e7f4 Mon Sep 17 00:00:00 2001
From: Russ Cox <rsc@golang.org>
Date: Fri, 19 Jun 2009 14:00:53 -0700
Subject: [PATCH] implement new spec language regarding conversions

R=ken
OCL=30519
CL=30534
---
 src/cmd/gc/subr.c | 23 +++++++++++++++++++++--
 src/cmd/gc/walk.c | 41 ++++++++++++++++++++++++++---------------
 2 files changed, 47 insertions(+), 17 deletions(-)

diff --git a/src/cmd/gc/subr.c b/src/cmd/gc/subr.c
index 0ff75248b8..43cde4ac4f 100644
--- a/src/cmd/gc/subr.c
+++ b/src/cmd/gc/subr.c
@@ -1723,10 +1723,29 @@ eqtype(Type *t1, Type *t2)
 	return eqtype1(t1, t2, 0, 1);
 }
 
+/*
+ * can we convert from type src to dst with
+ * a trivial conversion (no bits changing)?
+ */
 int
-cvttype(Type *t1, Type *t2)
+cvttype(Type *dst, Type *src)
 {
-	return eqtype1(t1, t2, 0, 0);
+	Sym *ds, *ss;
+	int ret;
+
+	if(eqtype1(dst, src, 0, 0))
+		return 1;
+
+	// Can convert if assignment compatible when
+	// top-level names are ignored.
+	ds = dst->sym;
+	dst->sym = nil;
+	ss = src->sym;
+	src->sym = nil;
+	ret = ascompat(dst, src);
+	dst->sym = ds;
+	src->sym = ss;
+	return ret == 1;
 }
 
 int
diff --git a/src/cmd/gc/walk.c b/src/cmd/gc/walk.c
index e29d608cd8..bcd139f4ba 100644
--- a/src/cmd/gc/walk.c
+++ b/src/cmd/gc/walk.c
@@ -1301,7 +1301,7 @@ walkconv(Node *n)
 		return;
 
 	// no-op conversion
-	if(cvttype(t, l->type)) {
+	if(cvttype(t, l->type) == 1) {
 	nop:
 		if(l->op != ONAME) {
 			indir(n, l);
@@ -2217,7 +2217,8 @@ exportasok(Type *t)
 }
 
 /*
- * can we assign var of type src to var of type dst
+ * can we assign var of type src to var of type dst?
+ * return 0 if not, 1 if conversion is trivial, 2 if conversion is non-trivial.
  */
 int
 ascompat(Type *dst, Type *src)
@@ -2230,6 +2231,28 @@ ascompat(Type *dst, Type *src)
 	if(dst == T || src == T)
 		return 0;
 
+	if(dst->etype == TFORWINTER || dst->etype == TFORWSTRUCT || dst->etype == TFORW)
+		return 0;
+	if(src->etype == TFORWINTER || src->etype == TFORWSTRUCT || src->etype == TFORW)
+		return 0;
+
+	// interfaces go through even if names don't match
+	if(isnilinter(dst) || isnilinter(src))
+		return 2;
+
+	if(isinter(dst) && isinter(src))
+		return 2;
+
+	if(isinter(dst) && methtype(src))
+		return 2;
+
+	if(isinter(src) && methtype(dst))
+		return 2;
+
+	// otherwise, if concrete types have names, they must match
+	if(dst->sym && src->sym && dst != src)
+		return 0;
+
 	if(dst->etype == TCHAN && src->etype == TCHAN) {
 		if(!eqtype(dst->type, src->type))
 			return 0;
@@ -2242,19 +2265,7 @@ ascompat(Type *dst, Type *src)
 	&& isptr[src->etype]
 	&& isfixedarray(src->type)
 	&& eqtype(dst->type, src->type->type))
-		return 1;
-
-	if(isnilinter(dst) || isnilinter(src))
-		return 1;
-
-	if(isinter(dst) && isinter(src))
-		return 1;
-
-	if(isinter(dst) && methtype(src))
-		return 1;
-
-	if(isinter(src) && methtype(dst))
-		return 1;
+		return 2;
 
 	return 0;
 }
-- 
2.48.1