From 7893945cc8f9421d0be5b07b9ed404bdf25ce140 Mon Sep 17 00:00:00 2001
From: Mattias Engdegård <mattiase@acm.org>
Date: Wed, 7 Apr 2021 11:31:07 +0200
Subject: 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.
---
 lisp/emacs-lisp/bytecomp.el | 63 ++++++++++++++++++++++++++++-----------------
 1 file changed, 39 insertions(+), 24 deletions(-)

(limited to 'lisp/emacs-lisp/bytecomp.el')

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 0babbbb978d..4f91f0d5dea 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -4621,10 +4621,15 @@ binding slots have been popped."
 (defun byte-compile-condition-case (form)
   (let* ((var (nth 1 form))
          (body (nth 2 form))
+         (handlers (nthcdr 3 form))
          (depth byte-compile-depth)
+         (success-handler (assq :success handlers))
+         (failure-handlers (if success-handler
+                               (remq success-handler handlers)
+                             handlers))
          (clauses (mapcar (lambda (clause)
                             (cons (byte-compile-make-tag) clause))
-                          (nthcdr 3 form)))
+                          failure-handlers))
          (endtag (byte-compile-make-tag)))
     (byte-compile-set-symbol-position 'condition-case)
     (unless (symbolp var)
@@ -4650,30 +4655,40 @@ binding slots have been popped."
 
     (byte-compile-form body) ;; byte-compile--for-effect
     (dolist (_ clauses) (byte-compile-out 'byte-pophandler))
-    (byte-compile-goto 'byte-goto endtag)
 
-    (while clauses
-      (let ((clause (pop clauses))
-            (byte-compile-bound-variables byte-compile-bound-variables)
-            (byte-compile--lexical-environment
-             byte-compile--lexical-environment))
-        (setq byte-compile-depth (1+ depth))
-        (byte-compile-out-tag (pop clause))
-        (dolist (_ clauses) (byte-compile-out 'byte-pophandler))
-        (cond
-         ((null var) (byte-compile-discard))
-         (lexical-binding
-          (push (cons var (1- byte-compile-depth))
-                byte-compile--lexical-environment))
-         (t (byte-compile-dynamic-variable-bind var)))
-        (byte-compile-body (cdr clause)) ;; byte-compile--for-effect
-        (cond
-         ((null var) nil)
-         (lexical-binding (byte-compile-discard 1 'preserve-tos))
-         (t (byte-compile-out 'byte-unbind 1)))
-        (byte-compile-goto 'byte-goto endtag)))
-
-    (byte-compile-out-tag endtag)))
+    (let ((compile-handler-body
+           (lambda (body)
+             (let ((byte-compile-bound-variables byte-compile-bound-variables)
+                   (byte-compile--lexical-environment
+                    byte-compile--lexical-environment))
+               (cond
+                ((null var) (byte-compile-discard))
+                (lexical-binding
+                 (push (cons var (1- byte-compile-depth))
+                       byte-compile--lexical-environment))
+                (t (byte-compile-dynamic-variable-bind var)))
+
+               (byte-compile-body body) ;; byte-compile--for-effect
+
+               (cond
+                ((null var))
+                (lexical-binding (byte-compile-discard 1 'preserve-tos))
+                (t (byte-compile-out 'byte-unbind 1)))))))
+
+      (when success-handler
+        (funcall compile-handler-body (cdr success-handler)))
+
+      (byte-compile-goto 'byte-goto endtag)
+
+      (while clauses
+        (let ((clause (pop clauses)))
+          (setq byte-compile-depth (1+ depth))
+          (byte-compile-out-tag (pop clause))
+          (dolist (_ clauses) (byte-compile-out 'byte-pophandler))
+          (funcall compile-handler-body (cdr clause))
+          (byte-compile-goto 'byte-goto endtag)))
+
+      (byte-compile-out-tag endtag))))
 
 (defun byte-compile-save-excursion (form)
   (if (and (eq 'set-buffer (car-safe (car-safe (cdr form))))
-- 
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