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

[Brad King]

On 11/09/2018 07:28 AM, Taylor Holberton wrote:
> A lot of projects that use CMake already have a `./cmake` directory,
> I would think `./cmake/init.json` would fit nicer as opposed to the
> hidden directory.

We could have a list of supported places so projects can choose.

> I would prefer an init file be written as a CMake file instead of JSON.

We need to be able to load the file without initializing much.
If it is a CMake language file then people will try to write `if`
conditions to check things that we wouldn't provide access to at
that point.  The idea of this file is to have a purely declarative
specification.  A format like JSON will work well for that.

-Brad