cgen: fix c compilation error in nested array declaration (fixes #23818)

(cherry picked from commit ca2bc2023ed24b418cfa4cec09e8c4e40806e8df)

Author: medvednikov

vlib/v/gen/c/if.v

@@ -81,6 +81,16 @@ fn (mut g Gen) need_tmp_var_in_expr(expr ast.Expr) bool {
 	}
 	match expr {
 		ast.ArrayInit {
+			elem_type := g.unwrap_generic(expr.elem_type)
+			elem_kind := if elem_type != 0 {
+				g.table.final_sym(elem_type).kind
+			} else {
+				ast.Kind.placeholder
+			}
+			if expr.has_index || (expr.has_len && (g.struct_has_array_or_map_field(elem_type)
+				|| (elem_kind in [.array, .map] && !expr.has_init))) {
+				return true
+			}
 			if g.need_tmp_var_in_expr(expr.len_expr) {
 				return true
 			}

vlib/v/tests/builtin_arrays/array_init_test.v

@@ -300,3 +300,21 @@ fn test_array_init_from_generic_typ() {
 	assert typeof(ints).name == '[]int'
 	assert ints.len == 0
 }
+
+fn test_nested_array_init_in_if_expr_with_index() {
+	map_test := [][][]int{len: 10, init: if index == 0 || index == 9 {
+		[][]int{len: 10, init: [1]}
+	} else {
+		[][]int{len: 10, init: if index == 0 || index == 9 { [1] } else { [] }}
+	}}
+
+	assert map_test.len == 10
+	assert map_test[0].len == 10
+	assert map_test[0][0] == [1]
+	assert map_test[0][9] == [1]
+	assert map_test[1].len == 10
+	assert map_test[1][0] == [1]
+	assert map_test[1][1] == []int{}
+	assert map_test[1][9] == [1]
+	assert map_test[9][5] == [1]
+}