https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70129
Maxim Cournoyer changed:
What|Removed |Added
CC||maxim.cournoyer at gmail dot
com
--- Comment #9 from Maxim Cournoyer ---
(In reply to Jonathan Wakely from comment #8)
> (In reply to chuck cranor from comment #3)
> > I think you'll find most build systems that do "-isystem /usr/include"
> > instead of "-I /usr/include" are only using "-isystem" for the change
> > in the warning behavior. The change in the include path order is not
> > wanted...
>
> Then they should stop (mis)using -isystem, since it's clearly documented to
> affect the order directories are searched:
>
> If a standard system include directory, or a directory specified with
> -isystem, is also specified with -I, the -I option is ignored. The
> directory
> is still searched but as a system directory at its normal position in the
> system include chain. This is to ensure that GCC's procedure to fix buggy
> system headers and the ordering for the "#include_next" directive are not
> inadvertently changed. If you really need to change the search order for
> system directories, use the -nostdinc and/or -isystem options.
>
> The corollary is that you shouldn't use it unless you really need to change
> the search order for system directories!
About not using it: sure, this works, but now how can a project enable warnings
just for their own headers and not those of the whole system? This seems to be
a valid use case.
In GNU Guix, we worked around the new behavior described here for GCC >= 6 by
searching headers in CPATH rather than CPLUS_INCLUDE_PATH, because using
CPLUS_INCLUDE_PATH would have the headers treated as system headers and break
the required ordering of GCC's own headers. The annoyance with using CPATH is
that now warnings are issued for the whole collection of headers rather than
just for those of the project being built.
I experimented with using CPLUS_INCLUDE_PATH and recommendations found here
about making sure none of GCC's internal include paths were being duplicated
through CPLUS_INCLUDE_PATH (e.g., those of glib and gcc) but the compilation
still failed like this:
cd
/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/build/src/libnrtype
&& /gnu/store/br4id28zs2nx3p2r8nr5kfnk3qway45k-gcc-7.5.0/bin/c++
-DHAVE_CONFIG_H -DWITH_CSSBLEND -DWITH_CSSCOMPOSITE -DWITH_MESH -DWITH_SVG2
-I/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/build/src/libnrtype
-I/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/inkscape-1.0beta2_2019-12-03_2b71d25d45/src/libnrtype
-I/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/inkscape-1.0beta2_2019-12-03_2b71d25d45
-I/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/inkscape-1.0beta2_2019-12-03_2b71d25d45/src
-I/tmp/guix-build-inkscape-1.0beta2_2019-12-03_2b71d25d45.drv-0/build/include
-isystem
/gnu/store/6081r9b5hdrwwfqljwsqsjqn8qvf18qz-libpng-1.6.37/include/libpng16
-isystem
/gnu/store/vsba1vjxy0g47251mrrxrhlpqchlmgr3-libxml2-2.9.10/include/libxml2
-isystem
/gnu/store/7y5kcq7pc31rq8y06pfifqi35x3nn0i2-libsoup-minimal-2.68.3/include/libsoup-2.4
-isystem
/gnu/store/khyi8q7glb4h3xv1yaq6vq837z9y3rif-freetype-2.10.1/include/freetype2
-isystem
/gnu/store/0d49ps0g5knrny1h8ijss65sb4i54dab-util-linux-2.34/include/uuid
-isystem
/gnu/store/0d49ps0g5knrny1h8ijss65sb4i54dab-util-linux-2.34/include/libmount
-isystem
/gnu/store/0d49ps0g5knrny1h8ijss65sb4i54dab-util-linux-2.34/include/blkid
-isystem
/gnu/store/1h4jsfampb408fs3kdzchnvjf21vk5jl-pango-1.42.4/include/pango-1.0
-isystem
/gnu/store/rp02xwl91kb42zi2v7pxcc5jrvwixg36-glib-2.62.4/include/glib-2.0
-isystem
/gnu/store/rp02xwl91kb42zi2v7pxcc5jrvwixg36-glib-2.62.4/lib/glib-2.0/include
-isystem /gnu/store/3vkqx4lxlv09gr1674jw01akipvx9h9f-cairo-1.16.0/include/cairo
-isystem
/gnu/store/jj5a0qzzh556v8kis0xba69rsdg9v3n1-harfbuzz-2.6.4/include/harfbuzz
-isystem
/gnu/store/fdvbnbif5giqimfnmlza6ji8jax4lp9z-fribidi-1.0.7/include/fribidi
-isystem
/gnu/store/i9fi2nwynsigjis0gzlba3jl7s0wygwm-pixman-0.38.4/include/pixman-1
-isystem /gnu/store/01r2pxnkgsi039na193pfnz60di5lwln-libgc-7.6.12/include/gc
-isystem
/gnu/store/192b5i8pilw4kaysy8d6zsrcvfjaz8k7-poppler-0.83.0/include/poppler
-isystem
/gnu/store/llg2s8pqpsg4zprzvx0xcdrsaffvap5s-gdl-minimal-3.34.0/include/libgdl-3.0
-isystem
/gnu/store/7lqlc6r8nmwavjhra4f3b4rfa8pkix1r-gtkmm-3.24.2/include/gtkmm-3.0
-isystem
/gnu/store/7lqlc6r8nmwavjhra4f3b4rfa8pkix1r-gtkmm-3.24.2/lib/gtkmm-3.0/include
-isystem
/gnu/store/7lqlc6r8nmwavjhra4f3b4rfa8pkix1r-gtkmm-3.24.2/include/gdkmm-3.0
-isystem
/gnu/store/7lqlc6r8nmwavjhra4f3b4rfa8pkix1r-gtkmm-3.24.2/lib/gdkmm-3.0/include
-isystem
/gnu/store/n
