Re: emacs-26: `with-eval-after-load' docstring omission

[Clément Pit-Claudel]

On 2018-02-28 18:22, Stefan Monnier wrote:
> You should not use `eval-after-load` nowadays, you should only use
> `with-eval-after-load`, so you'd write something like
> 
>     (with-eval-after-load 'flycheck
>       ;; Use eval+quote to delay macro expansion.
>       (eval '(flycheck-define-command ...)))

I got bitten by this again today, this time with this:

  (with-eval-after-load 'flycheck
    (push "npx" (flycheck-checker-get 'javascript-eslint 'command)))

… which failed with this message when Flycheck was actually loaded:

  Debugger entered--Lisp error: (void-function \(setf\ flycheck-checker-get\))
    (\(setf\ flycheck-checker-get\) (cons "npx" (flycheck-checker-get 
'javascript-eslint 'command)) 'javascript-eslint 'command)

I'm slowly developing the habit of writing  (with-eval-after-load 'flycheck 
(eval '(…))), but I'm really not a fan of this pattern :/

What do we gain from byte-compiling the bodies of with-eval-after-load forms?  
Byte-compilation warnings for undefined variables, but these are usually false 
positives (precisely because the variables in a with-eval-after-load are often 
defined by the package in question).  And some performance, but 
with-eval-after-load is discouraged in packages and its body typically runs 
once (or very few times?), so its performance should be essentially irrelevant.

Maybe we can find a way to prevent macro-expansion issues and make the behavior 
more intuitive?

Cheers,
Clément.