parse default const parameters

Author: m4rch3n1ng

grammar.js

@@ -566,6 +566,19 @@ module.exports = grammar({
       field('name', $.identifier),
       ':',
       field('type', $._type),
+      optional(
+        seq(
+          '=',
+          field('value',
+            choice(
+              $.block,
+              $.identifier,
+              $._literal,
+              $.negative_literal,
+            ),
+          ),
+        ),
+      ),
     ),
 
     constrained_type_parameter: $ => seq(

test/corpus/declarations.txt

@@ -2413,3 +2413,29 @@ where
             (type_arguments
               (type_identifier))))))
     (block)))
+
+================================================================================
+Const generics with default
+================================================================================
+
+pub struct Loaf<T: Sized, const N: usize = 1>([T; N]);
+
+--------------------------------------------------------------------------------
+
+(source_file
+  (struct_item
+    (visibility_modifier)
+    (type_identifier)
+    (type_parameters
+      (constrained_type_parameter
+        (type_identifier)
+        (trait_bounds
+          (type_identifier)))
+      (const_parameter
+        (identifier)
+        (primitive_type)
+        (integer_literal)))
+    (ordered_field_declaration_list
+      (array_type
+        (type_identifier)
+        (identifier)))))