Per-project indexing setting

[amake]

I have a git project that contains a very large build dependency as a submodule. When I navigate by projectile-find-file in that project I would like to ignore files in that submodule.

Currently the best way I can find to achieve this is to set a .projectile file with an ignore entry for the submodule, and switch to hybrid indexing.

However I also work with very large projects in other contexts, so I would like to stick to alien indexing by default, and only use hybrid for the project described above.

To that end, I can set projectile-indexing-method to alien via dir local variables, but then I get yelled at about unsafe dir-locals very frequently.

Would you accept a PR that marks projectile-indexing-method as safe if it conforms to (lambda (x) (memq x '(native hybrid alien)))? Is there a scenario where an attacker controlling this variable could be unsafe? (Controlling the alien commands themselves would be unsafe, but that is not the case here.)

[bbatsov]

I don't see a problem making projectile-indexing-method safe.