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Added std::type_info formatter #3978

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May 28, 2024
Merged

Added std::type_info formatter #3978

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150 changes: 94 additions & 56 deletions include/fmt/std.h
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Original file line number Diff line number Diff line change
Expand Up @@ -416,6 +416,95 @@ template <typename Char> struct formatter<std::error_code, Char> {
}
};

#if FMT_USE_RTTI
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namespace detail {

template <typename Char, typename OutputIt>
auto write_demangled_name(OutputIt out, const std::type_info& ti) -> OutputIt {
# ifdef FMT_HAS_ABI_CXA_DEMANGLE
int status = 0;
std::size_t size = 0;
std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);

string_view demangled_name_view;
if (demangled_name_ptr) {
demangled_name_view = demangled_name_ptr.get();

// Normalization of stdlib inline namespace names.
// libc++ inline namespaces.
// std::__1::* -> std::*
// std::__1::__fs::* -> std::*
// libstdc++ inline namespaces.
// std::__cxx11::* -> std::*
// std::filesystem::__cxx11::* -> std::filesystem::*
if (demangled_name_view.starts_with("std::")) {
char* begin = demangled_name_ptr.get();
char* to = begin + 5; // std::
for (char *from = to, *end = begin + demangled_name_view.size();
from < end;) {
// This is safe, because demangled_name is NUL-terminated.
if (from[0] == '_' && from[1] == '_') {
char* next = from + 1;
while (next < end && *next != ':') next++;
if (next[0] == ':' && next[1] == ':') {
from = next + 2;
continue;
}
}
*to++ = *from++;
}
demangled_name_view = {begin, detail::to_unsigned(to - begin)};
}
} else {
demangled_name_view = string_view(ti.name());
}
return detail::write_bytes<Char>(out, demangled_name_view);
# elif FMT_MSC_VERSION
const string_view demangled_name(ti.name());
for (std::size_t i = 0; i < demangled_name.size(); ++i) {
auto sub = demangled_name;
sub.remove_prefix(i);
if (sub.starts_with("enum ")) {
i += 4;
continue;
}
if (sub.starts_with("class ") || sub.starts_with("union ")) {
i += 5;
continue;
}
if (sub.starts_with("struct ")) {
i += 6;
continue;
}
if (*sub.begin() != ' ') *out++ = *sub.begin();
}
return out;
# else
return detail::write_bytes<Char>(out, string_view(ti.name()));
# endif
}

} // namespace detail

FMT_EXPORT
template <typename Char>
struct formatter<std::type_info, Char // DEPRECATED! Mixing code unit types.
> {
public:
FMT_CONSTEXPR auto parse(basic_format_parse_context<Char>& ctx)
-> decltype(ctx.begin()) {
return ctx.begin();
}

template <typename Context>
auto format(const std::type_info& ti, Context& ctx) const
-> decltype(ctx.out()) {
return detail::write_demangled_name<Char>(ctx.out(), ti);
}
};
#endif

FMT_EXPORT
template <typename T, typename Char>
struct formatter<
Expand All @@ -441,65 +530,14 @@ struct formatter<
auto format(const std::exception& ex, Context& ctx) const
-> decltype(ctx.out()) {
auto out = ctx.out();
if (!with_typename_)
return detail::write_bytes<Char>(out, string_view(ex.what()));

#if FMT_USE_RTTI
const std::type_info& ti = typeid(ex);
# ifdef FMT_HAS_ABI_CXA_DEMANGLE
int status = 0;
std::size_t size = 0;
std::unique_ptr<char, void (*)(void*)> demangled_name_ptr(
abi::__cxa_demangle(ti.name(), nullptr, &size, &status), &std::free);

string_view demangled_name_view;
if (demangled_name_ptr) {
demangled_name_view = demangled_name_ptr.get();

// Normalization of stdlib inline namespace names.
// libc++ inline namespaces.
// std::__1::* -> std::*
// std::__1::__fs::* -> std::*
// libstdc++ inline namespaces.
// std::__cxx11::* -> std::*
// std::filesystem::__cxx11::* -> std::filesystem::*
if (demangled_name_view.starts_with("std::")) {
char* begin = demangled_name_ptr.get();
char* to = begin + 5; // std::
for (char *from = to, *end = begin + demangled_name_view.size();
from < end;) {
// This is safe, because demangled_name is NUL-terminated.
if (from[0] == '_' && from[1] == '_') {
char* next = from + 1;
while (next < end && *next != ':') next++;
if (next[0] == ':' && next[1] == ':') {
from = next + 2;
continue;
}
}
*to++ = *from++;
}
demangled_name_view = {begin, detail::to_unsigned(to - begin)};
}
} else {
demangled_name_view = string_view(ti.name());
if (with_typename_) {
out = detail::write_demangled_name<Char>(out, typeid(ex));
*out++ = ':';
*out++ = ' ';
}
out = detail::write_bytes<Char>(out, demangled_name_view);
# elif FMT_MSC_VERSION
string_view demangled_name_view(ti.name());
if (demangled_name_view.starts_with("class "))
demangled_name_view.remove_prefix(6);
else if (demangled_name_view.starts_with("struct "))
demangled_name_view.remove_prefix(7);
out = detail::write_bytes<Char>(out, demangled_name_view);
# else
out = detail::write_bytes<Char>(out, string_view(ti.name())
});
# endif
*out++ = ':';
*out++ = ' ';
return detail::write_bytes<Char>(out, string_view(ex.what()));
#endif
return detail::write_bytes<Char>(out, string_view(ex.what()));
}
};

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7 changes: 7 additions & 0 deletions test/std-test.cc
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Original file line number Diff line number Diff line change
Expand Up @@ -300,6 +300,13 @@ TEST(std_test, exception) {
#endif
}

#if FMT_USE_RTTI
TEST(std_test, type_info) {
EXPECT_EQ(fmt::format("{}", typeid(std::runtime_error)),
"std::runtime_error");
}
Comment on lines +304 to +307
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I think this should be wrapped in FMT_USE_RTTI check.

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Note

EXPECT_EQ("std::runtime_error: Test Exception", fmt::format("{:t}", ex));
EXPECT_THAT(fmt::format("{:t}", ex), StartsWith("std::system_error: "));
EXPECT_THAT(fmt::format("{:t}", ex),
                StartsWith("std::filesystem::filesystem_error: "));

None of these tests would succeed without FMT_USE_RTTI, which is not used as guard in std-test.cc.

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This looks like a bug.

#endif

TEST(std_test, format_bit_reference) {
std::bitset<2> bs(1);
EXPECT_EQ(fmt::format("{} {}", bs[0], bs[1]), "true false");
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