Implement LWG-3720 Restrict the valid types of arg-id for width and precision in std-format-spec (#3511)

Co-authored-by: A. Jiang <de34@live.cn>

stl/inc/format

@@ -1410,13 +1410,17 @@ _NODISCARD constexpr basic_format_arg<_Context> _Get_arg(const _Context& _Ctx, c
     return _Arg;
 }
 
+template <class _Ty>
+inline constexpr bool _Is_signed_or_unsigned_large_integer_t =
+    _Is_any_of_v<remove_cv_t<_Ty>, int, unsigned int, long, unsigned long, long long, unsigned long long>;
+
 // Checks that the type and value of an argument associated with a dynamic
 // width specifier are valid.
 class _Width_checker {
 public:
     template <class _Ty>
     _NODISCARD constexpr unsigned long long operator()(const _Ty _Value) const {
-        if constexpr (is_integral_v<_Ty>) {
+        if constexpr (_Is_signed_or_unsigned_large_integer_t<_Ty>) {
             if constexpr (is_signed_v<_Ty>) {
                 if (_Value < 0) {
                     _Throw_format_error("Negative width.");
@@ -1435,7 +1439,7 @@ class _Precision_checker {
 public:
     template <class _Ty>
     _NODISCARD constexpr unsigned long long operator()(const _Ty _Value) const {
-        if constexpr (is_integral_v<_Ty>) {
+        if constexpr (_Is_signed_or_unsigned_large_integer_t<_Ty>) {
             if constexpr (is_signed_v<_Ty>) {
                 if (_Value < 0) {
                     _Throw_format_error("Negative precision.");

tests/std/tests/P0645R10_text_formatting_formatting/test.cpp

@@ -1356,10 +1356,13 @@ void libfmt_formatter_test_runtime_width() {
     throw_helper(STR("{0:{1}}"), 0, (int_max + 1u));
     throw_helper(STR("{0:{1}}"), 0, -1l);
     throw_helper(STR("{0:{1}}"), 0, (int_max + 1ul));
-    assert(format(STR("{0:{1}}"), 0, '0')
-           == STR("                                               0")); // behavior differs from libfmt, but conforms
     throw_helper(STR("{0:{1}}"), 0, 0.0);
 
+    // LWG-3720: Restrict the valid types of arg-id for width and precision in std-format-spec
+    throw_helper(STR("{:*^{}}"), 'a', true);
+    throw_helper(STR("{:*^{}}"), 'a', '0');
+    assert(format(STR("{:*^{}}"), 'a', static_cast<signed char>(2)) == STR("a*"));
+
     assert(format(STR("{0:{1}}"), 42, 0) == STR("42")); // LWG-3721: zero dynamic width is OK
 
     assert(format(STR("{0:{1}}"), -42, 4) == STR(" -42"));
@@ -1407,6 +1410,11 @@ void libfmt_formatter_test_runtime_precision() {
     throw_helper(STR("{0:.{1}}"), reinterpret_cast<void*>(0xcafe), 2);
     throw_helper(STR("{0:.{1}f}"), reinterpret_cast<void*>(0xcafe), 2);
     assert(format(STR("{0:.{1}}"), STR("str"), 2) == STR("st"));
+
+    // LWG-3720: Restrict the valid types of arg-id for width and precision in std-format-spec
+    throw_helper(STR("{:.{}f}"), 3.14f, true);
+    throw_helper(STR("{:.{}f}"), 3.14f, '0');
+    assert(format(STR("{:.{}f}"), 3.14f, static_cast<signed char>(2)) == STR("3.14"));
 }
 
 template <class charT>