From 8dd318729c81c7e1fb7b44fae7fbb18864e9878a Mon Sep 17 00:00:00 2001
From: Julien Portalier <julien@portalier.com>
Date: Sat, 8 Jun 2024 19:57:50 +0200
Subject: [PATCH] Add StringLiteral#to_utf16

closes #14670
---
 spec/compiler/macro/macro_methods_spec.cr |  5 +++++
 src/compiler/crystal/macros/methods.cr    | 10 ++++++++++
 2 files changed, 15 insertions(+)

diff --git a/spec/compiler/macro/macro_methods_spec.cr b/spec/compiler/macro/macro_methods_spec.cr
index 493fd070744a..72a60d1e106b 100644
--- a/spec/compiler/macro/macro_methods_spec.cr
+++ b/spec/compiler/macro/macro_methods_spec.cr
@@ -591,6 +591,11 @@ module Crystal
         assert_macro %({{"hello world".titleize}}), %("Hello World")
       end
 
+      it "executes to_utf16" do
+        assert_macro %({{"hello".to_utf16}}), "::Slice(UInt16).literal(104_u16, 101_u16, 108_u16, 108_u16, 111_u16, 0_u16)"
+        assert_macro %({{"TEST 😐🐙 ±∀ の".to_utf16}}), "::Slice(UInt16).literal(84_u16, 69_u16, 83_u16, 84_u16, 32_u16, 55357_u16, 56848_u16, 55357_u16, 56345_u16, 32_u16, 177_u16, 8704_u16, 32_u16, 12398_u16, 0_u16)"
+      end
+
       it "executes to_i" do
         assert_macro %({{"1234".to_i}}), %(1234)
       end
diff --git a/src/compiler/crystal/macros/methods.cr b/src/compiler/crystal/macros/methods.cr
index 2c45f49701fd..c386da998e1e 100644
--- a/src/compiler/crystal/macros/methods.cr
+++ b/src/compiler/crystal/macros/methods.cr
@@ -820,6 +820,16 @@ module Crystal
         else
           raise "StringLiteral#to_i: #{@value} is not an integer"
         end
+      when "to_utf16"
+        interpret_check_args do
+          slice = @value.to_utf16
+          # include the trailing zero that isn't counted in the slice but was
+          # generated by String#to_utf16 so the literal can be passed to C
+          # functions that expect a null terminated UInt16*
+          slice = Slice(UInt16).new(slice.to_unsafe, slice.size + 1)
+          args = slice.to_a { |codepoint| NumberLiteral.new(codepoint).as(ASTNode) }
+          Call.new(Path.global("Slice(UInt16)"), "literal", args)
+        end
       when "tr"
         interpret_check_args do |first, second|
           raise "first argument to StringLiteral#tr must be a string, not #{first.class_desc}" unless first.is_a?(StringLiteral)