Allow explicit constructors

Co-Authored-By: Thomas Johansen <thomasjo@gmail.com>

corpus/definitions.txt

@@ -50,6 +50,34 @@ T::T() : f1(0), f2(1, 2) {
     (compound_statement
       (expression_statement (call_expression (identifier) (argument_list (string_literal)))))))
 
+=====================================
+Explicit constructor definitions
+=====================================
+
+class C {
+  explicit C(int f) : f_(f) {}
+
+ private:
+  int f_;
+};
+
+---
+
+(translation_unit
+  (class_specifier
+    (type_identifier)
+    (field_declaration_list
+      (function_definition
+        (type_qualifier)
+        (function_declarator
+          (identifier)
+          (parameter_list (parameter_declaration (primitive_type) (identifier))))
+        (field_initializer_list
+          (field_initializer (field_identifier) (argument_list (identifier))))
+        (compound_statement))
+      (access_specifier)
+        (field_declaration (primitive_type) (field_identifier)))))
+
 =====================================
 Destructor definitions
 =====================================

grammar.js

@@ -221,7 +221,8 @@ module.exports = grammar(C, {
         $.friend_declaration,
         $.access_specifier,
         $.alias_declaration,
-        $.using_declaration
+        $.using_declaration,
+        $.type_definition
       )),
       '}'
     ),
@@ -233,6 +234,10 @@ module.exports = grammar(C, {
     ),
 
     constructor_or_destructor_definition: $ => seq(
+      repeat(choice(
+        $.storage_class_specifier,
+        $.type_qualifier
+      )),
       prec(1, seq(
         $.function_declarator,
         optional($.field_initializer_list)

src/grammar.json

@@ -2278,6 +2278,10 @@
               {
                 "type": "SYMBOL",
                 "name": "using_declaration"
+              },
+              {
+                "type": "SYMBOL",
+                "name": "type_definition"
               }
             ]
           }
@@ -5026,6 +5030,22 @@
     "constructor_or_destructor_definition": {
       "type": "SEQ",
       "members": [
+        {
+          "type": "REPEAT",
+          "content": {
+            "type": "CHOICE",
+            "members": [
+              {
+                "type": "SYMBOL",
+                "name": "storage_class_specifier"
+              },
+              {
+                "type": "SYMBOL",
+                "name": "type_qualifier"
+              }
+            ]
+          }
+        },
         {
           "type": "PREC",
           "value": 1,