[Mesa-dev] [PATCH] docs: add documentation for building with meson

[Dylan Baker]

Quoting Nicolai Hähnle (2017-10-17 13:40:00)
> On 17.10.2017 22:33, Dylan Baker wrote:
> > Quoting Nicolai Hähnle (2017-10-17 13:05:12)
> >> On 17.10.2017 21:21, Dylan Baker wrote:
> >>> +<dt><code>CC, CFLAGS, CXX, CXXFLAGS</code></dt>
> >>> +<dd><p>These environment variables
> >>> +control the C and C++ compilers used during the build. The default compilers
> >>> +depends on your operating system. Meson supports GCC, Clang, and MSVC as first
> >>> +class compilers. There is some support for the Intel ICC compiler. No other
> >>> +C/C++ compilers are currently supported.
> >>> +</dd>
> >>> +
> >>> +<dt><code>PKG_CONFIG_PATH</code></dt>
> >>> +<dd><p>The
> >>> +<code>pkg-config</code> utility is a hard requirement for configuring and
> >>> +building mesa. It is used to search for external libraries
> >>> +on the system. This environment variable is used to control the search
> >>> +path for <code>pkg-config</code>. For instance, setting
> >>> +<code>PKG_CONFIG_PATH=/usr/X11R6/lib/pkgconfig</code> will search for
> >>> +package metadata in <code>/usr/X11R6</code> before the standard
> >>> +directories.</p>
> >>> +</dd>
> >>> +</dl>
> >>
> >> Not knowing Meson, how do environment variables like CFLAGS, CC, etc.
> >> work? Are they "latched" when calling `meson $builddir`? When calling
> >> `meson configure`? Both? Does setting them have an effect when calling
> >> `ninja`?
> > 
> > I'll update this document as well, but for your edification: they are "latched"
> > by meson and stored in it's configuration information, they can be overwritten
> > when meson is initialized or re-initialized. That means that passing them to
> > "meson configure" won't change anything, since meson configure just touches
> > stored variables, but doesn't re-initialize. Passing them to ninja will only do
> > something if ninja decides that it needs to re-initialize, say if you touch a
> > meson.build file.
> 
> Thanks!
> 
> 
> > examples:
> >      CC=clang CXX=clang++ meson build-clang
> >      CC=notacompiler CXX=notacompiler ninja -C build
> > will result in building with clang/clang++
> > 
> >      touch meson.build
> >      CC=notacompiler CXX=notacompiler ninja -C build
> > nothing works, since ninja will re-initialize meson and it will read the
> > environment and set the compiler to notacompiler and fail.
> 
> :(
> 
> Presumably at least it doesn't break if CC and CXX are unset? In the 
> sense that the old values are kept?

Yes, if any of these are unset on subsequent re-initializations the previous
value is retained.
so:
      CC=clang CXX=clang++ meson build-clang
      CC=notacompiler CXX=notacompiler ninja -C build-clang clean
      touch meson.build
      ninja -C build-clang

Would build with clang, clean, and build with clang again.

Dylan

> 
> Cheers,
> Nicolai
> 
> 
> > 
> > I'll also add this to the documentation, but meson remembers options, and meson
> > configure only changes options that you supply so:
> >      meson build --prefix=/tmp
> >      meson configure build -Ddri-drivers=i965
> > will not reset the prefix.
> > 
> > Dylan
> > 
> 
> 
> -- 
> Lerne, wie die Welt wirklich ist,
> Aber vergiss niemals, wie sie sein sollte.
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