bug#20784: 25.0.50; pcase documentation on t and nil

[Stefan Monnier]

How 'bout the following patch?


        Stefan


   * lisp/emacs-lisp/pcase.el (pcase): Reword the SELFQUOTING case.
   (pcase--split-pred, pcase--self-quoting-p): Restrict selfquoting
   numbers to integers.
   (pcase--u1): Deprecate t patterns.  Reject nil as an invalid pattern.


diff --git a/lisp/emacs-lisp/pcase.el b/lisp/emacs-lisp/pcase.el
index ab82b7e..a6994a6 100644
--- a/lisp/emacs-lisp/pcase.el
+++ b/lisp/emacs-lisp/pcase.el
@@ -112,11 +112,12 @@ CASES is a list of elements of the form (PATTERN CODE...).
 
 Patterns can take the following forms:
   _            matches anything.
-  SELFQUOTING  matches itself.  This includes keywords, numbers, and strings.
   SYMBOL       matches anything and binds it to SYMBOL.
   (or PAT...)  matches if any of the patterns matches.
   (and PAT...) matches if all the patterns match.
   'VAL         matches if the object is `equal' to VAL
+  SELFQUOTING  is a shorthand for 'SELFQUOTING.
+               SELFQUOTING can be a keyword, an integer, or a string.
   (pred FUN)   matches if FUN applied to the object returns non-nil.
   (guard BOOLEXP)      matches if BOOLEXP evaluates to non-nil.
   (let PAT EXP)        matches if EXP matches PAT.
@@ -620,7 +621,7 @@ MATCH is the pattern that needs to be matched, of the form:
      ((and (eq 'pred (car upat))
            (eq 'quote (car-safe pat))
            (symbolp (cadr upat))
-           (or (symbolp (cadr pat)) (stringp (cadr pat)) (numberp (cadr pat)))
+           (or (symbolp (cadr pat)) (stringp (cadr pat)) (integerp (cadr pat)))
            (get (cadr upat) 'side-effect-free)
            (ignore-errors
              (setq test (list (funcall (cadr upat) (cadr pat))))))
@@ -638,7 +639,7 @@ MATCH is the pattern that needs to be matched, of the form:
     res))
 
 (defun pcase--self-quoting-p (upat)
-  (or (keywordp upat) (numberp upat) (stringp upat)))
+  (or (keywordp upat) (integerp upat) (stringp upat)))
 
 (defun pcase--app-subst-match (match sym fun nsym)
   (cond
@@ -770,7 +771,12 @@ Otherwise, it defers to REST which is a list of branches 
of the form
            (sym (car cdrpopmatches))
            (upat (cdr cdrpopmatches)))
       (cond
-       ((memq upat '(t _)) (pcase--u1 matches code vars rest))
+       ((memq upat '(t _))
+        (let ((code (pcase--u1 matches code vars rest)))
+          (if (eq upat '_) code
+            (macroexp--warn-and-return
+             "Pattern t is deprecated.  Use `_' instead"
+             code))))
        ((eq upat 'pcase--dontcare) :pcase--dontcare)
        ((memq (car-safe upat) '(guard pred))
         (if (eq (car upat) 'pred) (pcase--mark-used sym))
@@ -784,7 +790,7 @@ Otherwise, it defers to REST which is a list of branches of 
the form
                        (pcase--eval (cadr upat) vars))
                      (pcase--u1 matches code vars then-rest)
                      (pcase--u else-rest))))
-       ((symbolp upat)
+       ((and (symbolp upat) upat)
         (pcase--mark-used sym)
         (if (not (assq upat vars))
             (pcase--u1 matches code (cons (cons upat sym) vars) rest)
@@ -854,7 +860,7 @@ Otherwise, it defers to REST which is a list of branches of 
the form
                      (pcase--u rest))
                    vars
                    (list `((and . ,matches) ,code . ,vars))))
-       (t (error "Unknown internal pattern `%S'" upat)))))
+       (t (error "Unknown pattern `%S'" upat)))))
    (t (error "Incorrect MATCH %S" (car matches)))))
 
 (def-edebug-spec