Byte-compiling a file against a package that may or may not be here

Question

I am trying to include support for smartparens in a major-mode package. I want that if a user is using smartparens, then he will get additional pair definitions, and if he isn't, he will not notice anything different.

For that, I am using instructions of the form:

(declare-function sp-with-modes "ext:smartparens.el" t t)
(declare-function sp-local-pair "ext:smartparens.el" t t)

(eval-after-load 'smartparens
  '(sp-with-modes '(test-mode)
     (sp-local-pair "<" ">"
                    :actions '(insert wrap autoskip))))

This works fine if the file is not byte-compiled, or if it is byte-compiled by an emacs with smartparens loaded, or with emacs 24.3. However, with 24.5 (and probably with 24.4, though I cannot easily test it at the moment), and if it is compiled in a vanilla emacs (for example with cask build), it gives an error, stating that the argument (insert wrap autoskip) is not one of the keywords admissible by sp-local-pair (:actions...).

If I remove the call to sp-with-modes, and I replace the definition with

(sp-local-pair 'test-mode "<" ">"
               :actions '(insert wrap autoskip))

then it works fine. The macro sp-with-modes is supposed to loop over its argument (a list), inserting each element as first argument to everything in the body, I suspect that it confuses the byte-compiler at some point.

Is there a way to include this kind of "maybe evaluation" in a byte-compiled file, without confusing the byte-compiler? For example, is it possible to tell the compiler "do not compile this form"?

Or what would be the idiomatic way of achieving this kind of third-party support in a package?

Please note that the question involves smartparens because that's where I noticed the problem, but I suspect that it may happen with a lot of other packages.

---

The rest of the question is a MWE. I assumes that your regular emacs configuration has smartparens installed.

File ~/.emacs.d/tests/test.el

(declare-function sp-with-modes "ext:smartparens.el" t t)
(declare-function sp-local-pair "ext:smartparens.el" t t)

(eval-after-load 'smartparens
  '(sp-with-modes '(test-mode)
     (sp-local-pair "<" ">"
                    :actions '(insert wrap autoskip))))

(define-derived-mode test-mode
  fundamental-mode "Test" "Test mode")

(provide 'test)

File ~/.emacs.d/tests/init.el:

(require 'package)
(setq package-enable-at-startup nil)
(add-to-list 'package-archives '("melpa" . "http://melpa.org/packages/"))

(package-initialize)

(add-to-list 'load-path "~/.emacs.d/tests/")
(require 'test)

(require 'smartparens)
(smartparens-global-mode t)

Run emacs -Q and evaluate

(byte-compile-file "~/.emacs.d/tests/test.el")

then run emacs -Q --load "~/.emacs.d/tests/init.el".

Answer 1

Is there a way to include this kind of "maybe evaluation" in a byte-compiled file, without confusing the byte-compiler? For example, is it possible to tell the compiler "do not compile this form"?

Yes, you can quote it and then eval it: (eval '(sp-whatever ...)). This will not be seen by the compiler and will only be expanded at runtime.

Or what would be the idiomatic way of achieving this kind of third-party support in a package?

Emacs has no dedicated support for optional dependencies ATM. If this would be useful to you, please file a bug. This sort of thing only gets implemented after people ask for it.

Answer 2

To add to what @Malabarba said, I think the problem here is that smartparens should provide an API that does not rely on a macro.

The "normal" way this works with usual packages is that the major mode can just do something like:

(when (boundp 'smartparens-thingies)
  (push mythingies smartparens-thingies))

or even

(setq smartparens-extra-thingies mythingies)

And I think it's likely [beware: I know next to nothing about smartparens] that rather then using eval-after-load and sp-with-modes you can just call sp-local-pair from the major mode function:

(define-derived-mode test-mode parent-mode "doc"
  ...
  (when (fboundp 'sp-local-pair)
    (sp-local-pair "<" ">" :actions '(insert wrap autoskip)))
  ...)

which will solve your problem since it doesn't use a macro that's only available when smartparens is installed.