bug#16567: 24.3.50; pcase should signal an error if no case matches

[Leo Liu]

Stefan,

Which name would you prefer, `epcase' or 'pcasex'? Do you see any
problems with the following patch (assume `pcasex' for now)?

Thanks, Leo

=== modified file 'lisp/emacs-lisp/lisp-mode.el'
--- lisp/emacs-lisp/lisp-mode.el        2014-06-19 14:03:45 +0000
+++ lisp/emacs-lisp/lisp-mode.el        2014-09-12 02:28:44 +0000
@@ -197,7 +197,7 @@
               (el-vdefs '("defconst" "defcustom" "defvaralias" "defvar-local"
                           "defface"))
               (el-tdefs '("defgroup" "deftheme"))
-              (el-kw '("while-no-input" "letrec" "pcase" "pcase-let"
+              (el-kw '("while-no-input" "letrec" "pcase" "pcasex" "pcase-let"
                        "pcase-let*" "save-restriction" "save-excursion"
                        "save-selected-window"
                        ;; "eval-after-load" "eval-next-after-load"

=== modified file 'lisp/emacs-lisp/pcase.el'
--- lisp/emacs-lisp/pcase.el    2014-09-06 00:59:00 +0000
+++ lisp/emacs-lisp/pcase.el    2014-09-10 10:44:59 +0000
@@ -68,6 +68,8 @@
 
 (defconst pcase--dontcare-upats '(t _ pcase--dontcare))
 
+(defvar pcase--dontwarn-upats '(pcase--dontcare))
+
 (def-edebug-spec
   pcase-UPAT
   (&or symbolp
@@ -148,6 +150,15 @@
         ;; (puthash (car cases) `(,exp ,cases ,@expansion) pcase--memoize-2)
         expansion))))
 
+;;;###autoload
+(defmacro pcasex (exp &rest cases)
+  "The exhausitive version of `pcase' (which see)."
+  (declare (indent 1) (debug pcase))
+  (let* ((x (make-symbol "x"))
+         (pcase--dontwarn-upats (cons x pcase--dontwarn-upats)))
+    (pcase--expand
+     exp (append cases `((,x (error "No clause matching `%S'" ,x)))))))
+
 (defun pcase--let* (bindings body)
   (cond
    ((null bindings) (macroexp-progn body))
@@ -280,7 +291,8 @@
                              vars))))
                      cases))))
       (dolist (case cases)
-        (unless (or (memq case used-cases) (eq (car case) 'pcase--dontcare))
+        (unless (or (memq case used-cases)
+                    (memq (car case) pcase--dontwarn-upats))
           (message "Redundant pcase pattern: %S" (car case))))
       (macroexp-let* defs main))))