cgen: fix array fixed initialization on struct from call (#21568)

vlib/v/gen/c/cgen.v

@@ -2455,6 +2455,20 @@ fn (mut g Gen) call_cfn_for_casting_expr(fname string, expr ast.Expr, exp_is_ptr
 	g.write(')'.repeat(rparen_n))
 }
 
+// use instead of expr() when you need a var to use as reference
+fn (mut g Gen) expr_with_var(expr ast.Expr, got_type_raw ast.Type, expected_type ast.Type) string {
+	stmt_str := g.go_before_last_stmt().trim_space()
+	g.empty_line = true
+	tmp_var := g.new_tmp_var()
+	styp := g.typ(expected_type)
+	g.writeln('${styp} ${tmp_var};')
+	g.write('memcpy(&${tmp_var}, ')
+	g.expr(expr)
+	g.writeln(', sizeof(${styp}));')
+	g.write(stmt_str)
+	return tmp_var
+}
+
 // use instead of expr() when you need to cast to a different type
 fn (mut g Gen) expr_with_cast(expr ast.Expr, got_type_raw ast.Type, expected_type ast.Type) {
 	got_type := ast.mktyp(got_type_raw)

vlib/v/gen/c/struct.v

@@ -652,6 +652,10 @@ fn (mut g Gen) struct_init_field(sfield ast.StructInitField, language ast.Langua
 			info := field_unwrap_sym.info as ast.ArrayFixed
 			g.fixed_array_var_init(g.expr_string(sfield.expr), sfield.expr.is_auto_deref_var(),
 				info.elem_type, info.size)
+		} else if field_unwrap_sym.kind == .array_fixed && sfield.expr is ast.CallExpr {
+			info := field_unwrap_sym.info as ast.ArrayFixed
+			tmp_var := g.expr_with_var(sfield.expr, sfield.typ, sfield.expected_type)
+			g.fixed_array_var_init(tmp_var, false, info.elem_type, info.size)
 		} else {
 			if sfield.typ != ast.voidptr_type && sfield.typ != ast.nil_type
 				&& (sfield.expected_type.is_ptr() && !sfield.expected_type.has_flag(.shared_f))

vlib/v/tests/array_fixed_struct_field_test.v

@@ -0,0 +1,17 @@
+struct Args {
+	bytes [2]int
+}
+
+fn test_main() {
+	make_args() or { assert err.msg() == 'a' }
+}
+
+fn make_args() !Args {
+	return Args{
+		bytes: get_range() or { return error('a') }
+	}
+}
+
+fn get_range() ![2]int {
+	return error('')
+}