Calling functions in .dir-locals in Emacs

Question

I'm trying to activate flycheck-mode by default when opening any file in my project's directory. I'm a bit of an elisp newbie, my .dir-locals.el file looks like this:

((nil . (mode . flycheck-mode))
 ((cmake-ide-dir . "~/workspace/Samira3D"))
 ((cmake-ide-build-dir . "~/workspace/Samira3D/build/")))

And the error I'm getting is

Invalid function: (nil mode . flycheck-mode)

How would I go about solving this?

Answer 1

1. Your list nesting is wrong.
2. You need to use the eval pseudo-variable to evaluate expressions / call functions.
3. Using mode to set a minor mode is deprecated. That's now for major modes only, and minor modes are enabled via eval.

I think you wanted this:

((nil . ((eval . (flycheck-mode 1))
         (cmake-ide-dir . "~/workspace/Samira3D")
         (cmake-ide-build-dir . "~/workspace/Samira3D/build/"))))

Also have a read of this:

C-hig (elisp) Dotted Pair Notation RET

Sometimes you'll see examples of .dir-locals.el files using fewer dots and parentheses, and the difference (or indeed equivalence) between the different ways of formatting them might be confusing, so that will hopefully clarify the matter.