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

[Dylan Baker]

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.

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.

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
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