[cmake-developers] option to prevent in-source builds

[Brad King]

On 11/09/2018 05:34 AM, Joachim Wuttke wrote:
> include(PreventInSourceBuilds)
> 
> to protect users (and myself) from unintentionally running CMake
> in the source directory.
> 
> Would you consider adding this little module to the CMake code base?

If we are going to offer an upstream solution for this I think
it should be done in a way that avoids ever creating any files
(like CMakeCache.txt or CMakeFiles) in the first place.  This
could be achieved by looking for a `.cmake/init.json` file
at the top of the source tree with declarative information
about the project's preferences.  One of those settings could
reject in-source builds.

-Brad