procyberian/emacs
2
0
Fork 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Add byte-compiler warning about useless trailing cond clauses

Browse source 
Warn about clauses after the default clause, as in

    (cond ((= x 0) (say "none"))
          (t (say "some"))
          (say "goodbye"))

because they are very much an indicator of a mistake (such as
misplaced brackets), and since they are deleted by the optimiser, any
other warnings there are lost and the user wouldn't know that
something is wrong otherwise.

* lisp/emacs-lisp/macroexp.el (macroexp--expand-all): Add warning.
* etc/NEWS: Announce.
* test/lisp/emacs-lisp/bytecomp-tests.el
(bytecomp-test--with-suppressed-warnings): Add test case.
This commit is contained in:
Mattias Engdegård 2023-09-09 13:04:54 +02:00
parent 176b7dad71
commit c137b5195b
3 changed files with 52 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

29
lisp/emacs-lisp/macroexp.el
View file

@ -330,7 +330,34 @@ Assumes the caller has bound `macroexpand-all-environment'."
(let ((fn (car-safe form)))
(pcase form
(`(cond . ,clauses)
(macroexp--cons fn (macroexp--all-clauses clauses) form))
;; Check for rubbish clauses at the end before macro-expansion,
;; to avoid nuisance warnings from clauses that become
;; unconditional through that process.
;; FIXME: this strategy is defeated by forced `macroexpand-all',
;; such as in `cl-flet'. Haven't seen that in the wild, though.
(let ((default-tail nil)
(n 0)
(rest clauses))
(while rest
(let ((c (car-safe (car rest))))
(when (cond ((consp c) (and (memq (car c) '(quote function))
(cadr c)))
((symbolp c) (or (eq c t) (keywordp c)))
(t t))
;; This is unquestionably a default clause.
(setq default-tail (cdr rest))
(setq clauses (take (1+ n) clauses)) ; trim the tail
(setq rest nil)))
(setq n (1+ n))
(setq rest (cdr rest)))
(let ((expanded-form
(macroexp--cons fn (macroexp--all-clauses clauses) form)))
(if default-tail
(macroexp-warn-and-return
(format-message
"Useless clause following default `cond' clause")
expanded-form '(suspicious cond) t default-tail)
expanded-form))))
(`(condition-case . ,(or `(,err ,body . ,handlers) pcase--dontcare))
(let ((exp-body (macroexp--expand-all body)))
(if handlers