Add 'required' keyword for properties + fields.

Author: damieng

README.md

@@ -57,6 +57,7 @@ Comprehensive supports C# 1 through 10.0 with the following exceptions:
 - [x] Newlines in string interpolations
 - [x] List patterns
 - [x] Slice pattern
+- [x] Required members
 - [ ] Raw string literals
 
 ### References

corpus/type-fields.txt

@@ -242,7 +242,7 @@ class A {
           (variable_declarator (identifier)))))))
 
 =======================================
-Native interger types
+Native integer types
 =======================================
 
 class A {
@@ -264,3 +264,26 @@ class A {
         (variable_declaration
           (predefined_type)
           (variable_declarator (identifier)))))))
+
+
+=======================================
+Required fields
+=======================================
+
+class A {
+  public required int B;
+}
+
+---
+
+(compilation_unit
+  (class_declaration
+    (identifier)
+      (declaration_list
+        (field_declaration
+          (modifier)
+          (modifier)
+          (variable_declaration
+            (predefined_type)
+            (variable_declarator
+              (identifier)))))))

corpus/type-properties.txt

@@ -194,3 +194,27 @@ class Foo: IFoo {
         (explicit_interface_specifier (identifier))
         (identifier)
         (accessor_list (accessor_declaration))))))
+
+
+=======================================
+Required properties
+=======================================
+
+class A {
+  public required int B { get; set; }
+}
+
+---
+
+(compilation_unit
+  (class_declaration
+    (identifier)
+      (declaration_list
+        (property_declaration
+          (modifier)
+          (modifier)
+          (predefined_type)
+          (identifier)
+          (accessor_list
+            (accessor_declaration)
+            (accessor_declaration))))))

grammar.js

@@ -259,6 +259,7 @@ module.exports = grammar({
       'protected',
       'public',
       'readonly',
+      'required',
       prec(1, 'ref'), //make sure that 'ref' is treated as a modifier for local variable declarations instead of as a ref expression
       'sealed',
       'static',
@@ -935,7 +936,7 @@ module.exports = grammar({
 
     list_pattern: $ => seq(
       '[',
-      optional(seq(commaSep(choice($._pattern, $.slice_pattern)), optional(','))),
+      optional(seq(commaSep1(choice($._pattern, $.slice_pattern)), optional(','))),
       ']'
     ),