From f33caca7eb611a388f1e852e67556612a0657b51 Mon Sep 17 00:00:00 2001
From: CreeperFace <165158232+dy-tea@users.noreply.github.com>
Date: Thu, 13 Nov 2025 08:07:29 +0000
Subject: [PATCH] cgen: correct function definitions for callbacks in imported
 modules (fix #25700) (#25719)

---
 vlib/v/gen/c/cgen.v                               |  2 +-
 vlib/v/gen/c/fn.v                                 |  4 ++--
 .../callback_consumer_test.v                      |  7 +++++++
 .../tests/modules/callback_consumer_module/main.v |  8 ++++++++
 .../callback_consumer_module/mod1/faulty.v        | 15 +++++++++++++++
 .../callback_consumer_module/mod2/faulty.v        | 15 +++++++++++++++
 .../tests/modules/callback_consumer_module/v.mod  |  0
 7 files changed, 48 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/tests/modules/callback_consumer_module/callback_consumer_test.v
 create mode 100644 vlib/v/tests/modules/callback_consumer_module/main.v
 create mode 100644 vlib/v/tests/modules/callback_consumer_module/mod1/faulty.v
 create mode 100644 vlib/v/tests/modules/callback_consumer_module/mod2/faulty.v
 create mode 100644 vlib/v/tests/modules/callback_consumer_module/v.mod

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index d8d542505..18cee342e 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -1980,7 +1980,7 @@ pub fn (mut g Gen) write_fn_typesymbol_declaration(sym ast.TypeSymbol) {
 			''
 		}
 		ret_typ :=
-			if !func.return_type.has_flag(.option) && g.table.sym(func.return_type).kind == .array_fixed { '_v_' } else { '' } +
+			if !func.return_type.has_flag(.option) && !func.return_type.has_flag(.result) && g.table.sym(func.return_type).kind == .array_fixed { '_v_' } else { '' } +
 			g.styp(func.return_type)
 		g.type_definitions.write_string('typedef ${ret_typ} (${msvc_call_conv}*${fn_name})(')
 		for i, param in func.params {
diff --git a/vlib/v/gen/c/fn.v b/vlib/v/gen/c/fn.v
index 07e51a1a2..eafb592f9 100644
--- a/vlib/v/gen/c/fn.v
+++ b/vlib/v/gen/c/fn.v
@@ -791,9 +791,9 @@ fn (mut g Gen) fn_decl_params(params []ast.Param, scope &ast.Scope, is_variadic
 			info := param_type_sym.info as ast.FnType
 			func := info.func
 			if !g.inside_c_extern {
-				g.write('${g.styp(func.return_type)} (*${caname})(')
+				g.write('${g.ret_styp(func.return_type)} (*${caname})(')
 			}
-			g.definitions.write_string('${g.styp(func.return_type)} (*${caname})(')
+			g.definitions.write_string('${g.ret_styp(func.return_type)} (*${caname})(')
 			g.fn_decl_params(func.params, unsafe { nil }, func.is_variadic, func.is_c_variadic)
 			if !g.inside_c_extern {
 				g.write(')')
diff --git a/vlib/v/tests/modules/callback_consumer_module/callback_consumer_test.v b/vlib/v/tests/modules/callback_consumer_module/callback_consumer_test.v
new file mode 100644
index 000000000..353ba9360
--- /dev/null
+++ b/vlib/v/tests/modules/callback_consumer_module/callback_consumer_test.v
@@ -0,0 +1,7 @@
+import mod1
+import mod2
+
+fn test_main() {
+	mod1.function()!
+	mod2.function()
+}
diff --git a/vlib/v/tests/modules/callback_consumer_module/main.v b/vlib/v/tests/modules/callback_consumer_module/main.v
new file mode 100644
index 000000000..a4c4f84aa
--- /dev/null
+++ b/vlib/v/tests/modules/callback_consumer_module/main.v
@@ -0,0 +1,8 @@
+module main
+
+import mod1
+import mod2
+
+fn main() {
+	dump('main')
+}
diff --git a/vlib/v/tests/modules/callback_consumer_module/mod1/faulty.v b/vlib/v/tests/modules/callback_consumer_module/mod1/faulty.v
new file mode 100644
index 000000000..dd68f3181
--- /dev/null
+++ b/vlib/v/tests/modules/callback_consumer_module/mod1/faulty.v
@@ -0,0 +1,15 @@
+module mod1
+
+pub fn function() ! {
+	callback_consumer(callback_fn)!
+}
+
+type CallbackType = fn () ![4]u8
+
+fn callback_consumer(callback CallbackType) ! {
+	callback()!
+}
+
+fn callback_fn() ![4]u8 {
+	return [u8(1), 2, 3, 255]!
+}
diff --git a/vlib/v/tests/modules/callback_consumer_module/mod2/faulty.v b/vlib/v/tests/modules/callback_consumer_module/mod2/faulty.v
new file mode 100644
index 000000000..8bf4ad227
--- /dev/null
+++ b/vlib/v/tests/modules/callback_consumer_module/mod2/faulty.v
@@ -0,0 +1,15 @@
+module mod2
+
+pub fn function() {
+	callback_consumer(callback_fn)
+}
+
+type CallbackType = fn () [4]u8
+
+fn callback_consumer(callback CallbackType) {
+	callback()
+}
+
+fn callback_fn() [4]u8 {
+	return [u8(1), 2, 3, 255]!
+}
diff --git a/vlib/v/tests/modules/callback_consumer_module/v.mod b/vlib/v/tests/modules/callback_consumer_module/v.mod
new file mode 100644
index 000000000..e69de29bb
-- 
2.39.5