Narrower data type and sign conversion warnings in qt_sinks.h

[davidebeatrici]

include/spdlog/sinks/qt_sinks.h: In instantiation of ‘void spdlog::sinks::qt_color_sink<Mutex>::sink_it_(const spdlog::details::log_msg&) [with Mutex = spdlog::details::null_mutex]’:
include/spdlog/sinks/qt_sinks.h:150:10:   required from here
  150 |     void sink_it_(const details::log_msg &msg) override {
      |          ^~~~~~~~
include/spdlog/sinks/qt_sinks.h:163:71: error: conversion to ‘qsizetype’ {aka ‘long long int’} from ‘size_t’ {aka ‘long unsigned int’} may change the sign of the result [-Werror=sign-conversion]
  163 |                 color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
      |                                                                   ~~~~^~~~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:163:94: error: conversion from ‘qsizetype’ {aka ‘long long int’} to ‘int’ may change value [-Werror=conversion]
  163 |                 color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
      |                                     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
include/spdlog/sinks/qt_sinks.h:164:69: error: conversion to ‘qsizetype’ {aka ‘long long int’} from ‘size_t’ {aka ‘long unsigned int’} may change the sign of the result [-Werror=sign-conversion]
  164 |                 color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
      |                                                                 ~~~~^~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:164:90: error: conversion from ‘qsizetype’ {aka ‘long long int’} to ‘int’ may change value [-Werror=conversion]
  164 |                 color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
      |                                   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~

[gabime]

Which compiler and version?

[davidebeatrici]

Sorry for the delay.

gcc (GCC) 14.2.0 20240801 (OpenMandriva)

With Clang:

OpenMandriva 19.1.6-1 clang version 19.1.6 (/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-llvmorg-19.1.6/clang 1cc1c8b2641ccba94c7b90b5e4c4e500729f7556)

include/spdlog/sinks/qt_sinks.h:163:71: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'qsizetype' (aka 'long long') [-Werror,-Wsign-conversion]
  163 |                 color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
      |                                     ~~~~~~~                       ~~~~^~~~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:164:69: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'qsizetype' (aka 'long long') [-Werror,-Wsign-conversion]
  164 |                 color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
      |                                   ~~~~~~~                       ~~~~^~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:163:71: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'qsizetype' (aka 'long long') [-Werror,-Wsign-conversion]
  163 |                 color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
      |                                     ~~~~~~~                       ~~~~^~~~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:68:5: note: in instantiation of member function 'spdlog::sinks::qt_color_sink<spdlog::details::null_mutex>::sink_it_' requested here
   68 |     qt_color_sink(QTextEdit *qt_text_edit,
      |     ^
include/spdlog/sinks/qt_sinks.h:164:69: error: implicit conversion changes signedness: 'size_t' (aka 'unsigned long') to 'qsizetype' (aka 'long long') [-Werror,-Wsign-conversion]
  164 |                 color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
      |                                   ~~~~~~~                       ~~~~^~~~~~~~~~~~~~~
include/spdlog/sinks/qt_sinks.h:174:45: error: implicit conversion changes signedness: 'const level::level_enum' to 'size_type' (aka 'unsigned long') [-Werror,-Wsign-conversion]
  174 |                              colors_.at(msg.level),  // color to apply
      |                                      ~~ ~~~~^~~~~
include/spdlog/sinks/qt_sinks.h:163:90: error: implicit conversion loses integer precision: 'qsizetype' (aka 'long long') to 'int' [-Werror,-Wshorten-64-to-32]
  163 |                 color_range_start = QString::fromUtf8(str.data(), msg.color_range_start).size();
      |                                   ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~
include/spdlog/sinks/qt_sinks.h:164:86: error: implicit conversion loses integer precision: 'qsizetype' (aka 'long long') to 'int' [-Werror,-Wshorten-64-to-32]
  164 |                 color_range_end = QString::fromUtf8(str.data(), msg.color_range_end).size();
      |                                 ~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~

[tt4g]

This is due to the design of the qsizetype used for the size of the QString being a signed integer.
However, the Qt documentation states that “This type is guaranteed to be the same size as a size_t on all platforms supported by Qt.”: (https://doc.qt.io/qt-6/qttypes.html#qsizetype-typedef)

Integral type providing Posix' ssize_t for all platforms.

This type is guaranteed to be the same size as a size_t on all platforms supported by Qt.

Note that qsizetype is signed. Use size_t for unsigned values.

In order to print values of this type by using formatted-output facilities such as printf(), qDebug(), QString::asprintf() and so on, you can use the PRIdQSIZETYPE and PRIiQSIZETYPE macros as format specifiers. They will both print the value as a base 10 number.

@davidebeatrici If you trust Qt, you can avoid the warning by sending a PR that casts two types with static_cast.

[davidebeatrici]

This is due to the design of the qsizetype used for the size of the QString being a signed integer. However, the Qt documentation states that “This type is guaranteed to be the same size as a size_t on all platforms supported by Qt.”: (doc.qt.io/qt-6/qttypes.html#qsizetype-typedef)

The same size, not the same type. The documentation is correct.

Qt's size type used to be a 32 bit signed integer (int) until Qt 6, now it's a 64 bit signed integer (ssize_t).

If you trust Qt, you can avoid the warning by sending a PR that casts two types with static_cast.

Yeah. Let's wait for @gabime's feedback though.

[gabime]

PR is welcome. But please check sure it won't crash if the casted size_t is huge and casts to negative