From 6ab13a870fadddfbb753a351236fd9c9f58d95aa Mon Sep 17 00:00:00 2001
From: GGRei <tontonalex_887@hotmail.com>
Date: Sun, 28 Jan 2024 18:23:36 +0100
Subject: [PATCH] v.gen.js: fix u16 cast handling in the JS backend (#20620)

---
 vlib/v/gen/js/builtin_types.v        | 10 ++++++----
 vlib/v/gen/js/tests/testdata/u16.out |  5 +++++
 vlib/v/gen/js/tests/testdata/u16.v   |  8 ++++++++
 3 files changed, 19 insertions(+), 4 deletions(-)
 create mode 100644 vlib/v/gen/js/tests/testdata/u16.out
 create mode 100644 vlib/v/gen/js/tests/testdata/u16.v

diff --git a/vlib/v/gen/js/builtin_types.v b/vlib/v/gen/js/builtin_types.v
index d7af533ef..69118fcee 100644
--- a/vlib/v/gen/js/builtin_types.v
+++ b/vlib/v/gen/js/builtin_types.v
@@ -335,7 +335,7 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 	for typ_name in v_types {
 		// TODO: JsDoc
 		match typ_name {
-			'i8', 'i16', 'int', 'u16', 'int_literal' {
+			'i8', 'i16', 'int', 'int_literal' {
 				// TODO: Bounds checking
 				g.gen_builtin_prototype(
 					typ_name: typ_name
@@ -348,13 +348,15 @@ fn (mut g JsGen) gen_builtin_type_defs() {
 					to_jsval: '+this'
 				)
 			}
-			// u32 requires special handling in JavaScript to correctly represent it as an unsigned 32-bit integer.
+			// u16 / u32 requires special handling in JavaScript to correctly represent it as an unsigned 32-bit integer.
 			// The '>>> 0' bit operation ensures it is treated as unsigned, covering the full 0 to 2^32-1 range.
-			'u32' {
+			// For u16, '>>> 0' combined with a mask of 0xffff limits it to the 0 to 2^16-1 range, correctly handling values as unsigned 16-bit integers.
+			'u16', 'u32' {
 				g.gen_builtin_prototype(
 					typ_name: typ_name
 					default_value: 'new Number(0)'
-					constructor: 'this.val = Math.floor(Number(val) & 0xffffffff) >>> 0'
+					constructor: "this.val = Math.floor(Number(val) & ('" + typ_name +
+						'\' === "u16" ? 0xffff : 0xffffffff)) >>> 0'
 					value_of: 'Number(this.val)'
 					to_string: 'this.valueOf().toString()'
 					eq: 'new bool(self.valueOf() === other.valueOf())'
diff --git a/vlib/v/gen/js/tests/testdata/u16.out b/vlib/v/gen/js/tests/testdata/u16.out
new file mode 100644
index 000000000..92b3f0780
--- /dev/null
+++ b/vlib/v/gen/js/tests/testdata/u16.out
@@ -0,0 +1,5 @@
+65535
+0
+true
+56000
+65535
\ No newline at end of file
diff --git a/vlib/v/gen/js/tests/testdata/u16.v b/vlib/v/gen/js/tests/testdata/u16.v
new file mode 100644
index 000000000..0244f637f
--- /dev/null
+++ b/vlib/v/gen/js/tests/testdata/u16.v
@@ -0,0 +1,8 @@
+fn main() {
+	println(u16(0xFFFF))
+	println(u16(65535) + 1)
+
+	println(u16(42) == u16(42))
+	println(u16(1000) * 56)
+	println(u16(0xFFFFFFFF))
+}
-- 
2.39.5