feat: support explicit object parameters

grammar.js

@@ -146,7 +146,11 @@ module.exports = grammar(C, {
     // Types
 
     placeholder_type_specifier: $ => prec(1, seq(
-      field('constraint', optional($.type_specifier)),
+      field('constraint', optional(choice(
+        alias($.qualified_type_identifier, $.qualified_identifier),
+        $.template_type,
+        $._type_identifier,
+      ))),
       choice($.auto, alias($.decltype_auto, $.decltype)),
     )),
 
@@ -448,6 +452,7 @@ module.exports = grammar(C, {
       '(',
       commaSep(choice(
         $.parameter_declaration,
+        $.explicit_object_parameter_declaration,
         $.optional_parameter_declaration,
         $.variadic_parameter_declaration,
         '...',
@@ -455,6 +460,11 @@ module.exports = grammar(C, {
       ')',
     ),
 
+    explicit_object_parameter_declaration: $ => seq(
+      $.this,
+      $.parameter_declaration,
+    ),
+
     optional_parameter_declaration: $ => seq(
       $._declaration_specifiers,
       field('declarator', optional(choice($._declarator, $.abstract_reference_declarator))),

test/corpus/declarations.txt

@@ -253,6 +253,7 @@ struct S {
   S() : f(0) {}
 
  private:
+  int getF0(this S &self) { return self.f; }
   int getF1() const { return f; }
   int getF2() const try { throw 1; } catch (...) { return f; }
 };
@@ -277,6 +278,22 @@ struct S {
               (number_literal))))
         (compound_statement))
       (access_specifier)
+      (function_definition
+        (primitive_type)
+        (function_declarator
+          (field_identifier)
+          (parameter_list
+            (explicit_object_parameter_declaration
+              (this)
+              (parameter_declaration
+                (type_identifier)
+                (reference_declarator
+                  (identifier))))))
+        (compound_statement
+          (return_statement
+            (field_expression
+              (identifier)
+              (field_identifier)))))
       (function_definition
         (primitive_type)
         (function_declarator