[cmake-developers] Setting environment variables for builds

[David Cole]

On Thu, Aug 11, 2011 at 3:51 PM, Alexander Neundorf <neundorf at kde.org>wrote:

> On Monday 08 August 2011, Brad King wrote:
> > On 8/8/2011 4:24 AM, Johan Björk wrote:
> > > This has been discussed a billion times, so I'll keep it short.
> > >
> > > Problem: Some parts of the build requires a environment variable to be
> > > set Solution: Several workarounds, use custom commands, wrapper scripts
> > > etc.
> > >
> > > While the solution works fine for basic stuff, I have several
> toolchains
> > >
> >  > etc that requires environment variables to be installed for them to
> >  > work.
> >
> > CMake has always assumed that the environment is setup correctly for the
> > desired toolchain before either cmake or make runs.  Typically developers
> > have dealt with this by naming the build tree after the toolchain needed
> > as a reminder of the environment needed.  I'm sure an alternative would
> > be welcomed by many.
> >
> > > Since I'm using cmake --build for all my building, I am thinking about
> > >
> >  > creating a new command in cmake that will store certain environment
> >  > variables in the cache, and if building using cmake --build, they will
> >  > be set before the build starts.
> >
> > This sounds like a great compromise.  I don't think the cache is the
> > right place to put this though.  I think you can create your own file
> > like CMakeFiles/cmake--build.env and give it a format customized for
> > this purpose (like one line per variable or something).
>
> In the Eclipse project generator, I do something similar.
> Depending on the used compiler, a set of env.variables are stored in the
> cache
> and written into the project file, so they will be set when Eclipse invokes
> make.
> E.g. for the Intel compiler that's the license-related one, for MSVC it's
> LIBDIR or something like this.
>
> Alex
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You could have a "--with-env env.cmake" for the --build stuff.

And in the env.cmake file, you could simply have commands of the form:

  set(ENV{abc} "abc val")
  set(ENV{xyz} "xyz val")

As long as the script is processed in the same CMake process that runs the
--build, the environment settings should stick around for the duration of
the build.

Of course, there's not an easy, existing way to prevent other non-env
commands from being executed in such a script. This may or may not be deemed
a "good idea," but I figured I had to throw it out there: rather than
inventing a whole new way of expressing environment variables in a file,
let's use some existing mechanism...
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