bug#50222: Advising a function pollutes its docstring

[Clément Pit-Claudel]

Hi all,

Advising a function changes the first line of its docstring, which breaks 
packages that use the first line of the docstring to display a short piece of 
information about a function.  I noticed this issue while playing with the 
"shortdoc" feature. For example:

M-x shortdoc-display-group RET process:

  (make-process &rest args)
    Start a program in a subprocess.  Return the process object for it.
    (make-process :name "foo" :command '("cat" "/tmp/foo"))

But after running (advice-add 'make-process :before (lambda (&rest args))):

  (make-process &rest args)
    This function has :before advice: No documentation
    (make-process :name "foo" :command '("cat" "/tmp/foo"))
      eg. ⇒ #<process foo>

It would be nice to place the bit of text about advice somewhere else — maybe 
with the indented paragraph of the docs that says when the function was 
introduced and which group contains the relevant docs?

  (make-process &rest ARGS)

    Other relevant functions are documented in the process group.
    Probably introduced at or before Emacs version 25.1.
    // HERE? //

  This function has :before advice: No documentation

  Start a program in a subprocess.  Return the process object for it.

Clément.

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