From 7c50fb16557dcd82a895bcfdc90df14f5f610502 Mon Sep 17 00:00:00 2001
From: Delyan Angelov <delian66@gmail.com>
Date: Wed, 21 May 2025 11:35:00 +0300
Subject: [PATCH] checker: reallow passing closures as voidptr parameters with
 no warning, to enable convenient interfacing with C libs

---
 vlib/v/checker/fn.v                           |  2 +-
 ..._method_passed_to_voidptr_parameter_test.v | 62 +++++++++++++++++++
 2 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 vlib/v/tests/fns/closure_of_instance_method_passed_to_voidptr_parameter_test.v

diff --git a/vlib/v/checker/fn.v b/vlib/v/checker/fn.v
index ec7426012..f6f0f3144 100644
--- a/vlib/v/checker/fn.v
+++ b/vlib/v/checker/fn.v
@@ -1783,7 +1783,7 @@ fn (mut c Checker) fn_call(mut node ast.CallExpr, mut continue_check &bool) ast.
 			else if param.typ == ast.voidptr_type && func.language == .v
 				&& arg_typ !in [ast.voidptr_type, ast.nil_type] && arg_typ.nr_muls() == 0
 				&& func.name !in ['isnil', 'ptr_str'] && !func.name.starts_with('json.')
-				&& arg_typ_sym.kind !in [.float_literal, .int_literal, .charptr]
+				&& arg_typ_sym.kind !in [.float_literal, .int_literal, .charptr, .function]
 				&& !c.pref.backend.is_js() {
 				c.warn('automatic ${arg_typ_sym.name} referencing/dereferencing into voidptr is deprecated and will be removed soon; use `foo(&x)` instead of `foo(x)`',
 					call_arg.pos)
diff --git a/vlib/v/tests/fns/closure_of_instance_method_passed_to_voidptr_parameter_test.v b/vlib/v/tests/fns/closure_of_instance_method_passed_to_voidptr_parameter_test.v
new file mode 100644
index 000000000..ff0577041
--- /dev/null
+++ b/vlib/v/tests/fns/closure_of_instance_method_passed_to_voidptr_parameter_test.v
@@ -0,0 +1,62 @@
+type AudioCallback = fn (buffer voidptr, frames u32)
+
+@[heap]
+struct App {
+mut:
+	id int
+}
+
+fn (mut app App) callback(buffer voidptr, frames u32) {
+	assert voidptr(app) != unsafe { nil }
+	assert buffer != unsafe { nil }
+	assert frames == 256
+
+	assert app.id == 12345
+	app.id = 98765
+
+	unsafe {
+		p := &u8(buffer)
+		assert p[0] == 59
+		assert p[1] == 58
+		assert p[2] == 51
+		assert p[3] == 52
+		p[0] = 12
+		p[1] = 22
+		p[2] = 32
+		p[3] = 42
+	}
+}
+
+fn set_audio_callback(p voidptr) {
+	println(p)
+	cb := AudioCallback(p)
+	mut buf := [1024]u8{}
+	buf[0] = 59
+	buf[1] = 58
+	buf[2] = 51
+	buf[3] = 52
+	cb(&buf[0], 256)
+	assert buf[0] == 12
+	assert buf[1] == 22
+	assert buf[2] == 32
+	assert buf[3] == 42
+}
+
+fn test_creating_a_closure_from_instance_method_through_explicit_cast_works() {
+	mut app := &App{
+		id: 12345
+	}
+	audio_closure := AudioCallback(app.callback)
+	set_audio_callback(audio_closure)
+	assert app.id == 98765
+}
+
+fn test_creating_a_closure_from_instance_method_passed_to_voidptr_fn_parameter_works() {
+	mut app := &App{
+		id: 12345
+	}
+	// TODO: the code below should work, but does not yet, because it just passes the fn address
+	// of the method implementation itself, without creating a closure to wrap the instance.
+	// set_audio_callback(app.callback)
+	// assert app.id == 98765
+}
-- 
2.39.5