[Webkit-unassigned] [Bug 282275] New: C compiler flags improperly used when compiling libpas source files as C++

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=282275

            Bug ID: 282275
           Summary: C compiler flags improperly used when compiling libpas
                    source files as C++
           Product: WebKit
           Version: Other
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: bmalloc
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: mcatanzaro at redhat.com
                CC: berto at igalia.com, ggaren at apple.com, ysuzuki at apple.com

Berto is complaining about this warning when compiling e.g. bmalloc_heap_config.c:

/usr/bin/cc -DBUILDING_GTK__=1 -DBUILDING_WEBKIT=1 -DBUILDING_WITH_CMAKE=1 -DBUILDING_bmalloc -DBWRAP_EXECUTABLE=\"/usr/bin/bwrap\" -DDBUS_PROXY_EXECUTABLE=\"/usr/bin/xdg-dbus-proxy\" -DGETTEXT_PACKAGE=\"WebKitGTK-4.1\" -DHAVE_CONFIG_H=1 -DJSC_GLIB_API_ENABLED -DPAS_BMALLOC=1 -D_GNU_SOURCE -I/tmp/webkit2gtk-2.47.1/Source/bmalloc -I/tmp/webkit2gtk-2.47.1/Source/bmalloc/bmalloc -I/tmp/webkit2gtk-2.47.1/Source/bmalloc/libpas/src/libpas -fdiagnostics-color=always -Wextra -Wall -pipe -fmax-errors=20 -Wno-expansion-to-defined -Wno-psabi -Wno-misleading-indentation -Wno-maybe-uninitialized -Wundef -Wpointer-arith -Wmissing-format-attribute -Wformat-security -Wcast-align -Wno-tautological-compare -g1 -O2 -Werror=implicit-function-declaration -ffile-prefix-map=/tmp/webkit2gtk-2.47.1=. -fstack-protector-strong -fstack-clash-protection -Wformat -Werror=format-security -fcf-protection -Wdate-time -D_FORTIFY_SOURCE=2 -DNDEBUG -DG_DISABLE_CAST_CHECKS -fno-strict-aliasing -fno-exceptions -ffunction-sections -fdata-sections -fPIC -fvisibility=hidden -Wno-missing-field-initializers -Wno-cast-align -xc++ -std=c++2b -MD -MT Source/bmalloc/CMakeFiles/bmalloc.dir/libpas/src/libpas/bmalloc_heap_config.c.o -MF Source/bmalloc/CMakeFiles/bmalloc.dir/libpas/src/libpas/bmalloc_heap_config.c.o.d -o Source/bmalloc/CMakeFiles/bmalloc.dir/libpas/src/libpas/bmalloc_heap_config.c.o -c /tmp/webkit2gtk-2.47.1/Source/bmalloc/libpas/src/libpas/bmalloc_heap_config.c
cc1plus: warning: ‘-Werror=’ argument ‘-Werror=implicit-function-declaration’ is not valid for C++

Problem is a few libpas files are manually compiled with -xc++ -std=c++2b, but CMake doesn't know about this so it uses CFLAGS and CMAKE_C_FLAGS rather than CXXFLAGS and CMAKE_CXX_FLAGS. We can simply tell CMake to change the programming language rather than attempt to change this by passing -xc++ to the C compiler. This works since CMake 3.20, which is conveniently the minimum version that we support. (And we already set CMAKE_CXX_STANDARD to 23, so no need for -std=c++2b anymore either.)

I wonder why C++ is used at all. It's quite unusual to compile C source files as C++ without some explanation in the code or build system for why this is done. The code clearly does not use any C++. But I assume there's some good reason for this?

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