Added nosupertype annotation for subtyping exclusion (RFC 54).

src/libponyc/pass/syntax.c

@@ -398,9 +398,17 @@ static ast_result_t syntax_entity(pass_opt_t* opt, ast_t* ast,
   if(entity_def_index != DEF_TYPEALIAS)
   {
     // Check referenced traits
-    if(ast_id(provides) != TK_NONE &&
-      !check_provides_type(opt, provides, "provides"))
-      r = AST_ERROR;
+    if(ast_id(provides) != TK_NONE)
+    {
+      if(ast_has_annotation(ast, "nosupertype"))
+      {
+        ast_error(opt->check.errors, provides,
+          "a 'nosupertype' type cannot specify a provides list");
+        r = AST_ERROR;
+      } else if(!check_provides_type(opt, provides, "provides")) {
+        r = AST_ERROR;
+      }
+    }
   }
   else
   {
@@ -1261,6 +1269,21 @@ static bool check_annotation_location(pass_opt_t* opt, ast_t* ast,
         "a 'packed' annotation can only appear on a struct declaration");
       return false;
     }
+  } else if(strcmp(str, "nosupertype") == 0) {
+    switch(ast_id(ast_parent(ast)))
+    {
+      case TK_CLASS:
+      case TK_ACTOR:
+      case TK_PRIMITIVE:
+      case TK_STRUCT:
+        break;
+
+      default:
+        ast_error(opt->check.errors, loc,
+          "a 'nosupertype' annotation can only appear on a concrete type "
+          "declaration");
+        return false;
+    }
   }
 
   return true;
@@ -1417,8 +1440,15 @@ ast_result_t pass_syntax(ast_t** astp, pass_opt_t* options)
   }
 
   ast_t* annotation = ast_annotation(ast);
+
   if(annotation != NULL)
-    r = ast_visit(&annotation, pass_syntax, NULL, options, PASS_SYNTAX);
+  {
+    ast_result_t r2 = ast_visit(&annotation, pass_syntax, NULL, options,
+      PASS_SYNTAX);
+
+    if(r2 > r)
+      r = r2;
+  }
 
   return r;
 }

src/libponyc/type/subtype.c

@@ -837,6 +837,18 @@ static bool is_nominal_sub_structural(ast_t* sub, ast_t* super,
   pony_assert((sub_pass >= PASS_TRAITS) && (super_pass >= PASS_TRAITS));
   (void)sub_pass; (void)super_pass;
 
+  if(ast_has_annotation(sub_def, "nosupertype"))
+  {
+    if(errorf != NULL)
+    {
+      ast_error_frame(errorf, sub,
+        "%s is not a subtype of %s: it is marked 'nosupertype'",
+        ast_print_type(sub), ast_print_type(super));
+    }
+
+    return false;
+  }
+
   if(is_bare(sub) != is_bare(super))
   {
     if(errorf != NULL)

test/libponyc/badpony.cc

@@ -1004,3 +1004,13 @@ TEST_F(BadPonyTest, TypeErrorDuringArrayLiteralInference)
     "    ExpectX[C].trigger([C; C].values())";
   TEST_ERRORS_1(src, "type argument is outside its constraint");
 }
+
+TEST_F(BadPonyTest, NosupertypeAnnotationProvides)
+{
+  const char* src =
+    "trait T\n"
+
+    "primitive \\nosupertype\\ P is T";
+
+  TEST_ERRORS_1(src, "a 'nosupertype' type cannot specify a provides list");
+}

test/libponyc/type_check_subtype.cc

@@ -558,6 +558,25 @@ TEST_F(SubTypeTest, IsSubTypeCap)
 }
 
 
+TEST_F(SubTypeTest, IsSubTypeNosupertypeInterface)
+{
+  const char* src =
+    "primitive \\nosupertype\\ P\n"
+
+    "interface Test\n"
+    "  fun z(p: P, a: Any val)";
+
+  TEST_COMPILE(src);
+
+  pass_opt_t opt;
+  pass_opt_init(&opt);
+
+  ASSERT_FALSE(is_subtype(type_of("p"), type_of("a"), NULL, &opt));
+
+  pass_opt_init(&opt);
+}
+
+
 TEST_F(SubTypeTest, IsEqType)
 {
   const char* src =