shithub: mc

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Don't spuriously constrain types.

--- a/parse/infer.c

+++ b/parse/infer.c

@@ -33,7 +33,7 @@

 static void infernode(Node **np, Type *ret, int *sawret);

 static void inferexpr(Node **np, Type *ret, int *sawret);

 static void inferdecl(Node *n);

-static int tryconstrain(Type *ty, Trait *tr);

+static int tryconstrain(Type *ty, Trait *tr, int update);

 static Type *tf(Type *t);

@@ -782,7 +782,7 @@

 		if (!pat->trneed)

 			return 0;

 		for (i = 0; bsiter(pat->trneed, &i); i++)

-			if (!tryconstrain(to, traittab[i]))

+			if (!tryconstrain(to, traittab[i], 0))

 				return -1;

 		return 0;

 	} else if (pat->type == Tyvar) {

@@ -862,7 +862,7 @@

 }

 static int

-tryconstrain(Type *base, Trait *tr)

+tryconstrain(Type *base, Trait *tr, int update)

 {

 	Traitmap *tm;

 	Bitset *bs;

@@ -879,7 +879,8 @@

 			if (ty->type == Tyvar) {

 				if (!ty->trneed)

 					ty->trneed = mkbs();

-				bsput(ty->trneed, tr->uid);

+				if (update)

+					bsput(ty->trneed, tr->uid);

 				return 1;

 			} 

 			if (bshas(tm->traits, tr->uid))

@@ -916,7 +917,7 @@

 static void

 constrain(Node *ctx, Type *base, Trait *tr)

 {

-	if (!tryconstrain(base, tr))

+	if (!tryconstrain(base, tr, 1))

 		fatal(ctx, "%s needs trait %s near %s", tystr(base), namestr(tr->name), ctxstr(ctx));

 }