Re: [Emacs-diffs] emacs-25 d0d9f55: Allow newlines inside cl function arglists

[Dmitry Gutov <dgutov@yandex.ru>]

On 05/10/2016 04:34 AM, Stefan Monnier wrote:

> Why?

Because nobody has proposed a better patch until now.

> This is problematic since it might be difficult to adjust
> help-split-fundoc correspondingly.

We already have this problem with e.g.

   (cl-defgeneric asdasd (&optional (separator "\n")))

because when that is evaluated, ARGLIST passed to help-add-fundoc-usage 
is a form, not a string. I think it's better than not being able to 
define the function at all.

We could escape the newlines in the returned string. What's the best 
place to do that? Do we have a handier function that turns "\n" into 
"\\n", and does the same for \r, \t, and maybe unprintable characters?

This seems to work:

diff --git a/lisp/help.el b/lisp/help.el
index 7289375..4bd9cc1 100644
--- a/lisp/help.el
+++ b/lisp/help.el
@@ -1394,11 +1394,14 @@ help-add-fundoc-usage
  	    (if (string-match "\n?\n\\'" docstring)
  		(if (< (- (match-end 0) (match-beginning 0)) 2) "\n" "")
  	      "\n\n")
-	    (if (stringp arglist)
-                (if (string-match "\\`[^ ]+\\(\\(?:.\\|\n\\)*\\))\\'" 
arglist)
-                    (concat "(fn" (match-string 1 arglist) ")")
-                  (error "Unrecognized usage format"))
-	      (help--make-usage-docstring 'fn arglist)))))
+            (replace-regexp-in-string
+             "\n" "\\n"
+             (if (stringp arglist)
+                 (if (string-match "\\`[^ ]+\\(\\(?:.\\|\n\\)*\\))\\'" 
arglist)
+                     (concat "(fn" (match-string 1 arglist) ")")
+                   (error "Unrecognized usage format"))
+               (help--make-usage-docstring 'fn arglist))
+             t t))))

  (defun help-function-arglist (def &optional preserve-names)
    "Return a formal argument list for the function DEF.