Givens instance

This implements support for givens instances.

Author: eed3si9n

corpus/definitions.txt

@@ -621,6 +621,64 @@ class A:
         (indented_block
           (val_definition (identifier) (integer_literal)) (val_definition (identifier) (integer_literal)) (infix_expression (identifier) (operator_identifier) (identifier)))))))
 
+=======================================
+Given instance definitions (Scala 3 syntax)
+=======================================
+
+object A:
+  given a: A = x
+
+  given intFoo: CanFoo[Int] with
+    def foo(x: Int): Int = 0
+
+  private given listFoo[A1](using ev: CanFoo[A1]): CanFoo[List[A1]] with
+    def foo(xs: List[A1]): Int = 0
+
+---
+
+(compilation_unit
+  (object_definition
+    (identifier)
+    (template_body
+      (given_definition
+        (identifier)
+        (type_identifier)
+        (identifier))
+      (given_definition
+        (identifier)
+        (generic_type
+          (type_identifier)
+          (type_arguments (type_identifier)))
+        (with_template_body
+          (function_definition
+            (identifier)
+            (parameters
+              (parameter (identifier) (type_identifier)))
+            (type_identifier)
+            (integer_literal)
+          )))
+      (given_definition
+        (modifiers (access_modifier))
+        (identifier)
+        (type_parameters (identifier))
+        (parameters
+          (parameter
+            (identifier)
+            (generic_type (type_identifier) (type_arguments (type_identifier)))))
+        (generic_type
+          (type_identifier)
+          (type_arguments 
+            (generic_type (type_identifier) (type_arguments (type_identifier)))))
+        (with_template_body
+          (function_definition
+            (identifier)
+            (parameters
+              (parameter
+                (identifier)
+                (generic_type (type_identifier) (type_arguments (type_identifier)))))
+            (type_identifier)
+            (integer_literal)))))))
+
 =======================================
 Top-level Definitions (Scala 3 syntax)
 =======================================

grammar.js

@@ -81,6 +81,7 @@ module.exports = grammar({
     ),
 
     _definition: $ => choice(
+      $.given_definition,
       $.class_definition,
       $.import_declaration,
       $.object_definition,
@@ -92,7 +93,7 @@ module.exports = grammar({
       $.var_declaration,
       $.type_definition,
       $.function_definition,
-      $.function_declaration
+      $.function_declaration,
     ),
 
     enum_definition: $ => seq(
@@ -307,6 +308,16 @@ module.exports = grammar({
       ),
     ),
 
+    /*
+     * WithTemplateBody  ::=  <<< [SelfType] TemplateStat {semi TemplateStat} >>>
+     */
+    with_template_body: $ => prec.left(PREC.control, seq(
+      // TODO: self type
+      $._indent,
+      $._block,
+      $._outdent,
+    )),
+
     _end_marker: $ => prec.left(PREC.end_marker, seq(
       'end',
       choice(
@@ -411,6 +422,40 @@ module.exports = grammar({
 
     opaque_modifier: $ => 'opaque',
 
+    /**
+     * GivenDef          ::=  [GivenSig] (AnnotType ['=' Expr] | StructuralInstance)
+     * GivenSig          ::=  [id] [DefTypeParamClause] {UsingParamClause} ':'
+     */
+    given_definition: $ => prec.right(seq(
+      repeat($.annotation),
+      optional($.modifiers),
+      'given',
+      field('name', $.identifier),
+      field('type_parameters', optional($.type_parameters)),
+      field('parameters', repeat($.parameters)),
+      ':',
+      choice(
+        field('return_type', $._structural_instance),
+        seq(
+          field('return_type', $._annotated_type),
+          '=',
+          field('body', $.expression),
+        )
+      ),
+    )),
+
+    /**
+     * StructuralInstance ::=  ConstrApp {'with' ConstrApp} ['with' WithTemplateBody]
+     */
+    _structural_instance: $ => seq(
+      choice(
+        $._annotated_type,
+        $.compound_type,
+      ),
+      'with',
+      field('body', $.with_template_body),
+    ),
+
     modifiers: $ => repeat1(choice(
       'abstract',
       'final',