[libcxx-commits] [PATCH] D144325: [NFC][libc++][format] Improves diagnostics.
Mark de Wever via Phabricator via libcxx-commits
libcxx-commits at lists.llvm.org
Sat Feb 18 02:18:14 PST 2023
Mordante created this revision.
Herald added a project: All.
Mordante requested review of this revision.
Herald added a project: libc++.
Herald added a subscriber: libcxx-commits.
Herald added a reviewer: libc++.
While implementing the tests for LWG3720 I noticed the std::format
errors for non-formattable types are not user friendly (and thus hard to
write a .verify test too).
The issue stems from using a deleted function for invalid types. By
using a function that returns an invalid value the diagnostics become a
lot better. Before this change the existing "invalid value"
static_assert could never trigger. Now it can be triggered by user
code, therefore a diagnostic message has been added.
Before this change using a non-formattable type resulted in list of
error messages along the line of
.../include/c++/v1/__format/format_arg_store.h:167:29: error: call to deleted function '__determine_arg_t'
constexpr __arg_t __arg = __determine_arg_t<_Context, remove_cvref_t<_Tp>>();
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
.../include/c++/v1/__format/format_arg_store.h:210:54: note: in instantiation of function template specialization 'std::__format::__create_format_arg<std::format_context, char16_t &>' requested here
basic_format_arg<_Context> __arg = __format::__create_format_arg<_Context>(__args);
^
.../include/c++/v1/__format/format_arg_store.h:246:19: note: in instantiation of function template specialization 'std::__format::__create_packed_storage<std::format_context, int &, char16_t &>' requested here
__format::__create_packed_storage(__storage.__types_, __storage.__values_, __args...);
^
.../include/c++/v1/__format/format_functions.h:73:10: note: in instantiation of member function 'std::__format_arg_store<std::format_context, int &, char16_t &>::__format_arg_store' requested here
return _VSTD::__format_arg_store<_Context, _Args...>(__args...);
^
.../include/c++/v1/__config:664:17: note: expanded from macro '_VSTD'
# define _VSTD std
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:46:50: note: in instantiation of function template specialization 'std::make_format_args<std::format_context, int &, char16_t &>' requested here
TEST_IGNORE_NODISCARD std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...));
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:69:3: note: in instantiation of function template specialization 'test_exception<char, int, char16_t>' requested here
test_exception(SV("{:{}}"), 42, u'0');
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:97:3: note: in instantiation of function template specialization 'test<char>' requested here
test<char>();
^
.../include/c++/v1/__format/format_arg_store.h:154:19: note: candidate function [with _Context = std::format_context, _Tp = char16_t] has been explicitly deleted
consteval __arg_t __determine_arg_t()
^
.../include/c++/v1/__format/format_arg_store.h:148:19: note: candidate function [with _Context = std::format_context, _Tp = char16_t]
consteval __arg_t __determine_arg_t() {
<more errors omitted>
.../include/c++/v1/__format/format_arg_store.h:185:22: note: initializer of '__arg' is not a constant expression
.../include/c++/v1/__format/format_arg_store.h:167:21: note: declared here
constexpr __arg_t __arg = __determine_arg_t<_Context, remove_cvref_t<_Tp>>();
^
.../build/include/c++/v1/__format/format_arg_store.h:194:73: error: member reference base type 'char16_t' is not a structure or union
__arg, basic_string_view<typename _Context::char_type>{__value.data(), __value.size()}};
~~~~~~~^~~~~
11 errors generated.
After the change using the same non-formmatable type gives the following
diagnostics
.../include/c++/v1/__format/format_arg_store.h:168:3: error: static assertion failed due to requirement '__arg != __arg_t::__none': the supplied type is not formattable
static_assert(__arg != __arg_t::__none, "the supplied type is not formattable");
^ ~~~~~~~~~~~~~~~~~~~~~~~~
.../include/c++/v1/__format/format_arg_store.h:210:54: note: in instantiation of function template specialization 'std::__format::__create_format_arg<std::format_context, char16_t &>' requested here
basic_format_arg<_Context> __arg = __format::__create_format_arg<_Context>(__args);
^
.../include/c++/v1/__format/format_arg_store.h:246:19: note: in instantiation of function template specialization 'std::__format::__create_packed_storage<std::format_context, int &, char16_t &>' requested here
__format::__create_packed_storage(__storage.__types_, __storage.__values_, __args...);
^
.../include/c++/v1/__format/format_functions.h:73:10: note: in instantiation of member function 'std::__format_arg_store<std::format_context, int &, char16_t &>::__format_arg_store' requested here
return _VSTD::__format_arg_store<_Context, _Args...>(__args...);
^
.../include/c++/v1/__config:664:17: note: expanded from macro '_VSTD'
# define _VSTD std
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:46:50: note: in instantiation of function template specialization 'std::make_format_args<std::format_context, int &, char16_t &>' requested here
TEST_IGNORE_NODISCARD std::vformat(fmt, std::make_format_args<context_t<CharT>>(args...));
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:69:3: note: in instantiation of function template specialization 'test_exception<char, int, char16_t>' requested here
test_exception(SV("{:{}}"), 42, u'0');
^
.../libcxx/test/std/utilities/format/format.string/format.string.std/lwg3720_arg_id_width_precision_allowed_types.pass.cpp:97:3: note: in instantiation of function template specialization 'test<char>' requested here
test<char>();
^
.../include/c++/v1/__format/format_arg_store.h:168:23: note: expression evaluates to '0 != 0'
static_assert(__arg != __arg_t::__none, "the supplied type is not formattable");
~~~~~~^~~~~~~~~~~~~~~~~~
1 error generated.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D144325
Files:
libcxx/include/__format/format_arg_store.h
Index: libcxx/include/__format/format_arg_store.h
===================================================================
--- libcxx/include/__format/format_arg_store.h
+++ libcxx/include/__format/format_arg_store.h
@@ -142,21 +142,27 @@
//
// Note this version can't be constrained avoiding ambiguous overloads.
// That means it can be instantiated by disabled formatters. To solve this, a
-// constrained version for not formattable formatters is added. That overload
-// is marked as deleted to fail creating a storage type for disabled formatters.
+// constrained version for not formattable formatters is added.
template <class _Context, class _Tp>
consteval __arg_t __determine_arg_t() {
return __arg_t::__handle;
}
+// The overload for not formattable types.
+//
+// Originially this overload was marked as deleted, this resulted in 11 error
+// messages when a non-formattable type was used. Returning the "invalid type"
+// value, reduces this to 1 error message.
template <class _Context, class _Tp>
requires(!__formattable<_Tp, typename _Context::char_type>)
-consteval __arg_t __determine_arg_t() = delete;
+consteval __arg_t __determine_arg_t() {
+ return __arg_t::__none;
+}
template <class _Context, class _Tp>
_LIBCPP_HIDE_FROM_ABI basic_format_arg<_Context> __create_format_arg(_Tp&& __value) noexcept {
constexpr __arg_t __arg = __determine_arg_t<_Context, remove_cvref_t<_Tp>>();
- static_assert(__arg != __arg_t::__none);
+ static_assert(__arg != __arg_t::__none, "the supplied type is not formattable");
// Not all types can be used to directly initialize the
// __basic_format_arg_value. First handle all types needing adjustment, the
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