From d5ce91a5eb9751528b54c0bae6690041d30d5f21 Mon Sep 17 00:00:00 2001
From: Alexander Medvednikov <alexander@medvednikov.com>
Date: Wed, 25 Mar 2026 16:42:26 +0300
Subject: [PATCH] cgen: fix static array unknown type c issue (fixes #24164)

---
 vlib/v/gen/c/cgen.v                           | 44 ++++++++++++++-----
 ..._array_enum_fn_type_dependency.c.must_have |  1 +
 .../fixed_array_enum_fn_type_dependency.vv    |  9 ++++
 .../fixed_array_enum_submodule_test.c.v       | 10 +++++
 .../c_function/some_module/some_module.v      |  5 +++
 5 files changed, 59 insertions(+), 10 deletions(-)
 create mode 100644 vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.c.must_have
 create mode 100644 vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.vv
 create mode 100644 vlib/v/tests/c_function/fixed_array_enum_submodule_test.c.v
 create mode 100644 vlib/v/tests/c_function/some_module/some_module.v

diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 8522d0f80..17f5f0c6d 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -2403,13 +2403,7 @@ pub fn (mut g Gen) write_fn_typesymbol_declaration(sym ast.TypeSymbol) {
 			g.styp(func.return_type)
 		g.type_definitions.write_string('typedef ${ret_typ} (${msvc_call_conv}*${fn_name})(')
 		for i, param in func.params {
-			const_prefix := if param.typ.is_any_kind_of_pointer() && !param.is_mut
-				&& param.name.starts_with('const_') {
-				'const '
-			} else {
-				''
-			}
-			g.type_definitions.write_string('${const_prefix}${g.styp(param.typ)}')
+			g.type_definitions.write_string(g.fn_param_type_decl(param.typ, ''))
 			if i < func.params.len - 1 {
 				g.type_definitions.write_string(',')
 			}
@@ -2418,6 +2412,38 @@ pub fn (mut g Gen) write_fn_typesymbol_declaration(sym ast.TypeSymbol) {
 	}
 }
 
+// fn_param_type_decl emits fixed-array parameters as direct C array declarators so
+// function type definitions do not depend on later fixed-array typedef ordering.
+fn (mut g Gen) fn_param_type_decl(typ ast.Type, name string) string {
+	styp := g.styp(typ)
+	if typ.is_ptr() || typ.has_flag(.option) || typ.has_flag(.result) {
+		return if name == '' { styp } else { '${styp} ${name}' }
+	}
+	mut current_typ := g.table.unaliased_type(typ)
+	mut current_sym := g.table.sym(current_typ)
+	if current_sym.kind != .array_fixed {
+		return if name == '' { styp } else { '${styp} ${name}' }
+	}
+	mut dims := []string{}
+	for current_sym.kind == .array_fixed {
+		info := current_sym.info as ast.ArrayFixed
+		dims << '[${info.size}]'
+		if info.elem_type.is_ptr() || info.elem_type.has_flag(.option)
+			|| info.elem_type.has_flag(.result) {
+			base_styp := g.styp(info.elem_type)
+			decl := if name == '' { dims.join('') } else { '${name}${dims.join('')}' }
+			return '${base_styp} ${decl}'
+		}
+		current_typ = g.table.unaliased_type(info.elem_type)
+		current_sym = g.table.sym(current_typ)
+	}
+	if current_sym.info is ast.FnType {
+		return if name == '' { styp } else { '${styp} ${name}' }
+	}
+	decl := if name == '' { dims.join('') } else { '${name}${dims.join('')}' }
+	return '${g.styp(current_typ)} ${decl}'
+}
+
 pub fn (mut g Gen) write_array_fixed_return_types() {
 	fixed_arr_wrappers := g.table.type_symbols.filter(it.info is ast.ArrayFixed
 		&& !it.info.elem_type.has_flag(.generic))
@@ -4425,9 +4451,7 @@ fn (mut g Gen) write_fn_ptr_decl(func &ast.FnType, ptr_name string) {
 	g.write('${ret_styp} (*${ptr_name}) (')
 	arg_len := func.func.params.len
 	for i, arg in func.func.params {
-		arg_styp := g.styp(arg.typ)
-		g.write(arg_styp)
-		g.write(' ${arg.name}')
+		g.write(g.fn_param_type_decl(arg.typ, arg.name))
 		if i < arg_len - 1 {
 			g.write(', ')
 		}
diff --git a/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.c.must_have b/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.c.must_have
new file mode 100644
index 000000000..f8a87ca14
--- /dev/null
+++ b/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.c.must_have
@@ -0,0 +1 @@
+typedef void (*fixedarr__Callback)(voidptr,fixedarr__FlagBits [2]);
diff --git a/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.vv b/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.vv
new file mode 100644
index 000000000..b024a2bba
--- /dev/null
+++ b/vlib/v/gen/c/testdata/fixed_array_enum_fn_type_dependency.vv
@@ -0,0 +1,9 @@
+// vtest vflags: -shared
+module fixedarr
+
+enum FlagBits {
+	dsntmatter
+}
+
+@[markused]
+pub type Callback = fn (voidptr, [2]FlagBits)
diff --git a/vlib/v/tests/c_function/fixed_array_enum_submodule_test.c.v b/vlib/v/tests/c_function/fixed_array_enum_submodule_test.c.v
new file mode 100644
index 000000000..7a3c0116f
--- /dev/null
+++ b/vlib/v/tests/c_function/fixed_array_enum_submodule_test.c.v
@@ -0,0 +1,10 @@
+module main
+
+import some_module as sm
+
+@[markused]
+type PFN_set_enum_array_submodule = fn (voidptr, [2]sm.Flag_bits2)
+
+fn test_fn_type_with_submodule_enum_fixed_array_second_param() {
+	assert true
+}
diff --git a/vlib/v/tests/c_function/some_module/some_module.v b/vlib/v/tests/c_function/some_module/some_module.v
new file mode 100644
index 000000000..5d8688dd3
--- /dev/null
+++ b/vlib/v/tests/c_function/some_module/some_module.v
@@ -0,0 +1,5 @@
+module some_module
+
+pub enum Flag_bits2 {
+	dsntmatter2
+}
-- 
2.39.5