Add condition-case success handler (bug#47677)

Allow a condition-case handler on the form (:success BODY) to be
specified as the success continuation of the protected form, with
the specified variable bound to its result.

* src/eval.c (Fcondition_case): Update the doc string.
(internal_lisp_condition_case): Implement in interpreter.
(syms_of_eval): Defsym :success.
* lisp/emacs-lisp/bytecomp.el (byte-compile-condition-case):
Implement in byte-compiler.
* lisp/emacs-lisp/cl-macs.el (cl--self-tco): Allow self-TCO
from success handler.
* doc/lispref/control.texi (Handling Errors): Update manual.
* etc/NEWS: Announce.
* test/lisp/emacs-lisp/bytecomp-tests.el (bytecomp-tests--test-cases)
(bytecomp-condition-case-success):
* test/lisp/emacs-lisp/cl-macs-tests.el (cl-macs--labels):
Add test cases.

1 files changed, 5 insertions, 4 deletions

diff --git a/test/lisp/emacs-lisp/cl-macs-tests.el b/test/lisp/emacs-lisp/cl-macs-tests.el
index 5c3e603b92e..f4e2e46a019 100644
--- a/test/lisp/emacs-lisp/cl-macs-tests.el
+++ b/test/lisp/emacs-lisp/cl-macs-tests.el
@@ -630,12 +630,13 @@ collection clause."
                             (and xs
                                  (progn (setq n1 (1+ n))
                                         (len2 (cdr xs) n1))))))
-         ;; Tail call in error handler.
+         ;; Tail calls in error and success handlers.
          (len3 (xs n)
                (if xs
-                   (condition-case nil
-                       (/ 1 0)
-                     (arith-error (len3 (cdr xs) (1+ n))))
+                   (condition-case k
+                       (/ 1 (logand n 1))
+                     (arith-error (len3 (cdr xs) (1+ n)))
+                     (:success (len3 (cdr xs) (+ n k))))
                  n)))
       (should (equal (len nil 0) 0))
       (should (equal (len2 nil 0) 0))