bug#20144: 25.0.50; Functions using fboundp not known to be defined

bug#20144: 25.0.50; Functions using fboundp not known to be defined

[Philipp Stephani]

Byte-compiling the following file:

(if (fboundp 'car)
    (defalias 'mycar 'car)
  (defun mycar (_l) (error "what")))

(defun foo ()
  (mycar nil))

results in the byte compiler warning

  Warning: the function `mycar' is not known to be defined.

However, the function is clearly always defined.  Since this trick is
rather common, the byte compiler should know about it.



In GNU Emacs 25.0.50.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.8)
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bug#20144: 25.0.50; Functions using fboundp not known to be defined

[Glenn Morris]

Philipp Stephani wrote:

> However, the function is clearly always defined.  Since this trick is
> rather common, the byte compiler should know about it.

This issue has existed "forever". I really doubt it will ever change.

Eg http://lists.gnu.org/archive/html/emacs-devel/2007-09/msg02316.html

bug#20144: 25.0.50; Functions using fboundp not known to be defined

[Glenn Morris]

This is a dupe of http://debbugs.gnu.org/8140 .

bug#20144: 25.0.50; Functions using fboundp not known to be defined

[Stefan Monnier]

severity 20144 wishlist
thanks

> (if (fboundp 'car)
>     (defalias 'mycar 'car)
>   (defun mycar (_l) (error "what")))

   (defalias 'mycar
             (if (fboundp 'car) 'car (lambda (_l) (error "what"))))

The difference is one of the two versions requires reasoning
(simple/trivial for you, but beyond the reach of the simple
byte-compiler we're using), whereas the other doesn't.

Admittedly, when you need to define two versions of a *set* of
functions, depending on a single test, the above trick of sinking the
testing into the `defalias' ends up being a bit ugly/inconvenient.


        Stefan