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Avoid dangling-reference warning in several places
This new warning in gcc 13 is annoying because it happens in certain parts of our code where it is harmless to pass a temporary variable to a function that returns a reference. This patch introduces a new pair of macros, LYX_BEGIN_MUTE_GCC_WARNING(warn) and LYX_END_MUTE_GCC_WARNING, which can be used to define a block of code where a given GCC warning is disabled. The macros are no-ops with compilers other than gcc, although some compilers that pretend to be GCC make be mis-detected. The worse that can happen AFAIU is a bunch of warnings. The macro relies on an intimidating set of for nested macros. The goal of these macros is to build a nested string bit by bit. Here is how it works: PRAGMA_IGNORE(dangling-reference) => PRAGMA_IGNORE_1(-Wdangling-reference) => PRAGMA_IGNORE_2("-Wdangling-reference") => PRAGMA_IGNORE_3(GCC diagnostic ignored "-Wdangling-reference") => _Pragma("GCC diagnostic ignored \""-Wdangling-reference\"") The next question is: what is _Pragma() good for? Well, it is a version of #pragma that can be used in a macro. And finally, what are those pragmas good for? The 'push' and 'pop' ones make changes to warnings local. The 'ignored' ones allow to disable some warnings. And disabling -Wpragmas ensures that we do not have a warning if we try to disable a warning that is not supported by the compiler.
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3698281943
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c2653e451c
27
configure.ac
27
configure.ac
@ -313,6 +313,33 @@ char * strerror(int n);
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# define USE_WCHAR_T
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#endif
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#if defined(__GNUC__) && !defined(__clang__)
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/* This macro can be used to stipulate that a given GCC warning is not
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* relevant in a given block.
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*
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* The -Wpragmas bit takes care of the case where -W<warn> is not implemented
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*
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* The idea for PRAGMA_IGNORE has been stolen from
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* https://stackoverflow.com/questions/45762357/how-to-concatenate-strings-in-the-arguments-of-pragma#comment124444258_45783809
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* The difficulty is to put the <warn> value inside nested quotes; it is done
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* using nested macros.
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*/
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# define PRAGMA_IGNORE(x) PRAGMA_IGNORE_1(-W##x)
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# define PRAGMA_IGNORE_1(x) PRAGMA_IGNORE_2(#x)
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# define PRAGMA_IGNORE_2(x) PRAGMA_IGNORE_3(GCC diagnostic ignored x)
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# define PRAGMA_IGNORE_3(x) _Pragma(#x)
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# define LYX_BEGIN_MUTE_GCC_WARNING(warn) \
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_Pragma("GCC diagnostic push") \
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_Pragma("GCC diagnostic ignored \"-Wpragmas\"") \
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PRAGMA_IGNORE(warn)
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# define LYX_END_MUTE_GCC_WARNING \
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_Pragma("GCC diagnostic pop")
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#else
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# define LYX_BEGIN_MUTE_GCC_WARNING(warn)
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# define LYX_END_MUTE_GCC_WARNING
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#endif
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#endif
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])
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@ -181,8 +181,10 @@ private:
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extern Movers & theMovers();
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LYX_BEGIN_MUTE_GCC_WARNING(dangling-reference)
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/// @c returns the Mover registered for format @c fmt.
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extern Mover const & getMover(std::string const & fmt);
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LYX_END_MUTE_GCC_WARNING
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/** Register a specialised @c command to be used to copy a file
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* of format @c fmt.
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*/
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@ -36,7 +36,9 @@ private:
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std::unique_ptr<Impl> d;
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};
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LYX_BEGIN_MUTE_GCC_WARNING(dangling-reference)
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WordList & theWordList(std::string const & lang);
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LYX_END_MUTE_GCC_WARNING
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} // namespace lyx
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@ -177,8 +177,12 @@ class Font;
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class FontInfo;
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/// Implementation is in Application.cpp
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LYX_BEGIN_MUTE_GCC_WARNING(dangling-reference)
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frontend::FontMetrics const & theFontMetrics(Font const & f);
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frontend::FontMetrics const & theFontMetrics(FontInfo const & fi);
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LYX_END_MUTE_GCC_WARNING
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} // namespace lyx
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