From 4c3cb92b4bad6716394eea398f1ce5ee3f4a2d00 Mon Sep 17 00:00:00 2001
From: Eugene Yokota <eed3si9n@gmail.com>
Date: Sat, 14 Jan 2023 15:37:55 -0500
Subject: [PATCH] Singleton type

Problem
-------
Currently singleton types are treated as `stable_type_identifier`.

Solution
--------
This adds `singleton_type`.
---
 corpus/types.txt | 17 +++++++++++++++++
 grammar.js       |  7 +++++++
 2 files changed, 24 insertions(+)

diff --git a/corpus/types.txt b/corpus/types.txt
index 82494f67a..f9ccd4d4d 100644
--- a/corpus/types.txt
+++ b/corpus/types.txt
@@ -293,6 +293,23 @@ class Test(d: "hello", b: 25)
         (literal_type
           (integer_literal))))))
 
+==================================
+Singleton Types
+==================================
+
+class A:
+  def foobar: this.type = this
+  type X = A.B.type
+
+---
+
+(compilation_unit
+  (class_definition
+    (identifier)
+    (template_body
+      (function_definition (identifier) (singleton_type (identifier)) (identifier))
+      (type_definition (type_identifier) (singleton_type (stable_identifier (identifier) (identifier)))))))
+
 ==================================
 Opaque type aliases (Scala 3)
 ==================================
diff --git a/grammar.js b/grammar.js
index d1520c86c..9b2ed8604 100644
--- a/grammar.js
+++ b/grammar.js
@@ -682,6 +682,7 @@ module.exports = grammar({
       $.generic_type,
       $.projected_type,
       $.tuple_type,
+      $.singleton_type,
       $.stable_type_identifier,
       $._type_identifier,
       $.wildcard,
@@ -705,6 +706,12 @@ module.exports = grammar({
       ')',
     ),
 
+    singleton_type: $ => prec.left(PREC.stable_type_id, seq(
+      choice($._identifier, $.stable_identifier),
+      '.',
+      'type',
+    )),
+
     stable_type_identifier: $ => prec.left(PREC.stable_type_id, seq(
       choice($._identifier, $.stable_identifier),
       '.',