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Interpret precision as display width (#4443)

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Nikhil
2025-05-25 21:12:47 +05:30
committed by GitHub
parent 1ff0b7f5e1
commit 6d79757a38
2 changed files with 45 additions and 2 deletions
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42
include/fmt/format.h
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@ -2109,13 +2109,51 @@ FMT_CONSTEXPR FMT_INLINE auto write(OutputIt out, T value,
return write_int<Char>(out, make_write_int_arg(value, specs.sign()), specs);
}
FMT_INLINE auto count_code_points_with_display_width_precision(
string_view s, size_t display_width_precision) -> size_t {
size_t display_width = 0;
size_t code_points = 0;
// Iterate through the string to compute display width
for_each_codepoint(s, [&](uint32_t, string_view sv) {
// Compute the display width of the current code point
size_t cp_width = compute_width(sv);
if (display_width + cp_width > display_width_precision) {
return false; // Stop iteration when display width exceeds precision
}
display_width += cp_width;
code_points++;
return true;
});
return code_points;
}
template <typename Char>
FMT_CONSTEXPR auto handle_precision(
basic_string_view<Char> s, const format_specs& specs,
FMT_ENABLE_IF(std::is_same<Char, char>::value)) -> size_t {
auto code_points = count_code_points_with_display_width_precision(
s, to_unsigned(specs.precision));
return code_point_index(s, code_points);
}
template <typename Char>
FMT_CONSTEXPR auto handle_precision(
basic_string_view<Char> s, const format_specs&,
FMT_ENABLE_IF(!std::is_same<Char, char>::value)) -> size_t {
return code_point_index(s, s.size());
}
template <typename Char, typename OutputIt>
FMT_CONSTEXPR auto write(OutputIt out, basic_string_view<Char> s,
const format_specs& specs) -> OutputIt {
auto data = s.data();
auto size = s.size();
if (specs.precision >= 0 && to_unsigned(specs.precision) < size)
size = code_point_index(s, to_unsigned(specs.precision));
if (specs.precision >= 0 && to_unsigned(specs.precision) < size) {
size = handle_precision(s, specs);
}
bool is_debug = specs.type() == presentation_type::debug;
if (is_debug) {

5
test/format-test.cc
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@ -6,6 +6,7 @@
// For the license information refer to format.h.
// Check if fmt/format.h compiles with windows.h included before it.
#include <gtest/gtest.h>
#ifdef _WIN32
# include <windows.h>
#endif
@ -552,6 +553,10 @@ TEST(format_test, arg_errors) {
format_error, "argument not found");
}
TEST(format_test, display_width_precision) {
EXPECT_EQ(fmt::format("{:.5}", "🐱🐱🐱"), "🐱🐱");
}
template <int N> struct test_format {
template <typename... T>
static auto format(fmt::string_view fmt, const T&... args) -> std::string {