From 5c1662d234d8c884b8fba3828e9852f3967d7e6e Mon Sep 17 00:00:00 2001
From: Felipe Pena <felipensp@gmail.com>
Date: Sun, 9 Nov 2025 13:56:35 -0300
Subject: [PATCH] cgen: fix codegen for if comptime and array fixed (fix
 #25691) (#25697)

---
 vlib/v/gen/c/comptime.v                       | 14 +++++++++++--
 vlib/v/gen/c/consts_and_globals.v             |  3 ++-
 .../tests/consts/const_if_fixed_array_test.v  | 21 +++++++++++++++++++
 3 files changed, 35 insertions(+), 3 deletions(-)
 create mode 100644 vlib/v/tests/consts/const_if_fixed_array_test.v

diff --git a/vlib/v/gen/c/comptime.v b/vlib/v/gen/c/comptime.v
index d905566cf..2388304ed 100644
--- a/vlib/v/gen/c/comptime.v
+++ b/vlib/v/gen/c/comptime.v
@@ -393,6 +393,7 @@ fn (mut g Gen) comptime_if(node ast.IfExpr) {
 	}
 	tmp_var := g.new_tmp_var()
 	is_opt_or_result := node.typ.has_option_or_result()
+	is_array_fixed := g.table.final_sym(node.typ).kind == .array_fixed
 	line := if node.is_expr {
 		stmt_str := g.go_before_last_stmt()
 		g.write(util.tabs(g.indent))
@@ -485,10 +486,19 @@ fn (mut g Gen) comptime_if(node ast.IfExpr) {
 					g.skip_stmt_pos = true
 					if is_opt_or_result {
 						tmp_var2 := g.new_tmp_var()
-						g.write('{ ${g.base_type(node.typ)} ${tmp_var2} = ')
+						base_styp := g.base_type(node.typ)
+						g.write('{ ${base_styp} ${tmp_var2} = ')
 						g.stmt(last)
-						g.writeln('builtin___result_ok(&(${g.base_type(node.typ)}[]) { ${tmp_var2} }, (_result*)(&${tmp_var}), sizeof(${g.base_type(node.typ)}));')
+						g.writeln('builtin___result_ok(&(${base_styp}[]) { ${tmp_var2} }, (_result*)(&${tmp_var}), sizeof(${base_styp}));')
 						g.writeln('}')
+					} else if is_array_fixed {
+						base_styp := g.base_type(node.typ)
+						g.write('memcpy(&${tmp_var}, (${base_styp})')
+						g.stmt(last)
+						if g.out.last_n(2).contains(';') {
+							g.go_back(2)
+						}
+						g.write(', sizeof(${base_styp}))')
 					} else {
 						g.write('${tmp_var} = ')
 						g.stmt(last)
diff --git a/vlib/v/gen/c/consts_and_globals.v b/vlib/v/gen/c/consts_and_globals.v
index d44f049eb..fc42934ab 100644
--- a/vlib/v/gen/c/consts_and_globals.v
+++ b/vlib/v/gen/c/consts_and_globals.v
@@ -319,7 +319,8 @@ fn (mut g Gen) const_decl_init_later(mod string, name string, cname string, expr
 	if surround_cbr {
 		init.writeln('{')
 	}
-	if expr is ast.ArrayInit && (expr as ast.ArrayInit).has_index {
+	if (expr is ast.ArrayInit && expr.has_index)
+		|| (expr is ast.IfExpr && g.table.type_kind(expr.typ) == .array_fixed) {
 		init.writeln(g.expr_string_surround('\tmemcpy(&${cname}, &', expr, ', sizeof(${styp}));'))
 	} else if expr is ast.CallExpr
 		&& g.table.final_sym(g.unwrap_generic((expr as ast.CallExpr).return_type)).kind == .array_fixed {
diff --git a/vlib/v/tests/consts/const_if_fixed_array_test.v b/vlib/v/tests/consts/const_if_fixed_array_test.v
new file mode 100644
index 000000000..570b40ae6
--- /dev/null
+++ b/vlib/v/tests/consts/const_if_fixed_array_test.v
@@ -0,0 +1,21 @@
+// vtest vflags: -d some_other_define
+pub const fixed_sized_comptime_array_const = $if some_other_define ? {
+	[u8(0x01), 0x02]!
+} $else $if some_other_define_2 ? {
+	[u8(0x01), 0x02, 0x03]!
+} $else {
+	[u8(0)]!
+}
+
+pub const fixed_sized_comptime_array_const2 = $if some_other_define_2 ? {
+	[u8(0x01), 0x02, 0x03]!
+} $else $if some_other_define ? {
+	[u8(0x01), 0x02]!
+} $else {
+	[u8(0)]!
+}
+
+fn test_main() {
+	assert fixed_sized_comptime_array_const == [u8(1), 2]!
+	assert fixed_sized_comptime_array_const2 == [u8(1), 2]!
+}
-- 
2.39.5