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Improve error messages.

--- a/parse/infer.c

+++ b/parse/infer.c

@@ -99,7 +99,23 @@

     return s;

 }

+void typeerror(Inferstate *st, Type *a, Type *b, Node *ctx, char *msg)

+{

+    char *t1, *t2, *c;

+    t1 = tystr(a);

+    t2 = tystr(b);

+    c = ctxstr(st, ctx);

+    if (msg)

+        fatal(ctx->line, "Type \"%s\" incompatible with \"%s\" near %s: %s", t1, t2, c, msg);

+    else

+        fatal(ctx->line, "Type \"%s\" incompatible with \"%s\" near %s", t1, t2, c);

+    free(t1);

+    free(t2);

+    free(c);

+}

+

+

 /* Set a scope's enclosing scope up correctly.

  * We don't do this in the parser for some reason. */

 static void setsuper(Stab *st, Stab *super)

@@ -473,7 +489,7 @@

             a->cstrs = mkbs();

         setcstr(a, c);

     } else if (!a->cstrs || !bshas(a->cstrs, c->cid)) {

-            fatal(ctx->line, "%s needs %s near %s", tystr(a), c->name, ctxstr(st, ctx));

+        fatal(ctx->line, "%s needs %s near %s", tystr(a), c->name, ctxstr(st, ctx));

     }

 }

@@ -581,6 +597,7 @@

     Type *t, *r;

     Type *a, *b;

     char *from, *to;

+    char buf[256];

     size_t i;

     /* a ==> b */

@@ -616,20 +633,25 @@

             htput(st->delayed, b, htget(st->delayed, a));

         else if (hthas(st->delayed, b) && !hthas(st->delayed, a))

             htput(st->delayed, a, htget(st->delayed, b));

+    } else if (hthas(st->delayed, a)) {

+        t = htget(st->delayed, a);

+        if (tybase(t)->type != tybase(b)->type)

+            typeerror(st, t, b, ctx, NULL);

     }

     /* Disallow recursive types */

-    if (a->type == Tyvar && b->type != Tyvar) 

+   if (a->type == Tyvar && b->type != Tyvar)  {

         if (occurs(a, b))

-            fatal(ctx->line, "Infinite type %s in %s near %s",

-                  tystr(a), tystr(b), ctxstr(st, ctx));

+            typeerror(st, a, b, ctx, "Infinite type\n");

+   }

     /* if the tyrank of a is 0 (ie, a raw tyvar), just unify.

      * Otherwise, match up subtypes. */

     if ((a->type == b->type || idxhacked(a, b)) && tyrank(a) != 0) {

-        if (a->nsub != b->nsub)

-            fatal(ctx->line, "%s has wrong subtype count for %s (got %d, expected %d) near %s",

-                  tystr(a), tystr(b), a->nsub, b->nsub, ctxstr(st, ctx));

+        if (a->nsub != b->nsub) {

+            snprintf(buf, sizeof buf, "Wrong subtype count - Got %zu, expected %zu", a->nsub, b->nsub);

+            typeerror(st, a, b, ctx, buf);

+        }

         for (i = 0; i < b->nsub; i++)

             unify(st, ctx, a->sub[i], b->sub[i]);

         r = b;

@@ -637,16 +659,13 @@

         /* Only Tygeneric and Tyname should be able to unify. And they

          * should have the same names for this to be true. */

         if (!nameeq(a->name, b->name))

-            fatal(ctx->line, "%s incompatible with %s near %s",

-                  tystr(a), tystr(b), ctxstr(st, ctx));

+            typeerror(st, a, b, ctx, NULL);

         if (a->narg != b->narg)

-            fatal(ctx->line, "%s has wrong parameter list for %s near %s",

-                  tystr(a), tystr(b), ctxstr(st, ctx));

+            typeerror(st, a, b, ctx, "Incompatible parameter lists");

         for (i = 0; i < a->narg; i++)

             unify(st, ctx, a->arg[i], b->arg[i]);

     } else if (a->type != Tyvar) {

-        fatal(ctx->line, "%s incompatible with %s near %s",

-              tystr(a), tystr(b), ctxstr(st, ctx));

+        typeerror(st, a, b, ctx, NULL);

     }

     mergecstrs(st, ctx, a, b);

     membunify(st, ctx, a, b);