Add support for asserts in type declarations

Author: guillaumebrunerie

common/corpus/types.txt

@@ -889,7 +889,8 @@ function f(x: any): asserts x {
     (identifier)
     (formal_parameters
       (required_parameter (identifier) (type_annotation (predefined_type))))
-    (asserts (identifier))
+    (asserts_annotation
+      (asserts (identifier)))
     (statement_block)))
 
 =======================================
@@ -915,8 +916,9 @@ function isT(t: T): t is T {
     (formal_parameters
     (required_parameter
       (identifier) (type_annotation (predefined_type))))
-    (asserts
-      (type_predicate (identifier) (predefined_type)))
+    (asserts_annotation
+      (asserts
+        (type_predicate (identifier) (predefined_type))))
     (statement_block))
   (class_declaration
     (type_identifier)
@@ -942,6 +944,45 @@ function isT(t: T): t is T {
         (type_identifier)))
     (statement_block (return_statement (true)))))
 
+=======================================
+Type of an assertion function
+=======================================
+
+declare const f: (x: any) => asserts x;
+declare const g: (x: any) => asserts x is number;
+
+---
+
+(program
+  (ambient_declaration
+    (lexical_declaration
+      (variable_declarator
+        (identifier)
+        (type_annotation
+          (function_type
+            (formal_parameters
+              (required_parameter
+                (identifier)
+                (type_annotation
+                  (predefined_type))))
+            (asserts
+              (identifier)))))))
+  (ambient_declaration
+    (lexical_declaration
+      (variable_declarator
+        (identifier)
+        (type_annotation
+          (function_type
+            (formal_parameters
+              (required_parameter
+                (identifier)
+                (type_annotation
+                  (predefined_type))))
+            (asserts
+              (type_predicate
+                (identifier)
+                (predefined_type)))))))))
+
 ==================================
 Type predicate and predefined types
 ==================================

common/define-grammar.js

@@ -627,11 +627,14 @@ module.exports = function defineGrammar(dialect) {
       type_annotation: $ => seq(':', $._type),
 
       asserts: $ => seq(
-        ':',
         'asserts',
         choice($.type_predicate, $.identifier, $.this)
       ),
 
+      asserts_annotation: $ => seq(
+        seq(':', $.asserts)
+      ),
+
       _type: $ => choice(
         $._primary_type,
         $.function_type,
@@ -882,7 +885,7 @@ module.exports = function defineGrammar(dialect) {
         field('type_parameters', optional($.type_parameters)),
         field('parameters', $.formal_parameters),
         field('return_type', optional(
-          choice($.type_annotation, $.asserts, $.type_predicate_annotation)
+          choice($.type_annotation, $.asserts_annotation, $.type_predicate_annotation)
         ))
       ),
 
@@ -954,7 +957,7 @@ module.exports = function defineGrammar(dialect) {
         field('type_parameters', optional($.type_parameters)),
         field('parameters', $.formal_parameters),
         '=>',
-        field('return_type', choice($._type, $.type_predicate)),
+        field('return_type', choice($._type, $.asserts, $.type_predicate)),
       )),
 
       _type_identifier: $ => alias($.identifier, $.type_identifier),