From eb45cc9521e25dc685bdfb4a6b7926c244fbf259 Mon Sep 17 00:00:00 2001
From: Lars Ingebrigtsen <larsi@gnus.org>
Date: Fri, 26 Jul 2019 09:58:23 +0200
Subject: [PATCH] Add new macro `ignore-error'

* doc/lispref/control.texi (Handling Errors): Document
`ignore-error'.
* lisp/subr.el (ignore-error): New macro.

* lisp/progmodes/elisp-mode.el (elisp-completion-at-point):
Provide completion for `ignore-error'.
---
 doc/lispref/control.texi     | 12 ++++++++++++
 etc/NEWS                     |  5 +++++
 lisp/progmodes/elisp-mode.el | 26 +++++++++++++++++++++-----
 lisp/subr.el                 |  8 ++++++++
 test/lisp/subr-tests.el      | 10 ++++++++++
 5 files changed, 56 insertions(+), 5 deletions(-)

diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi
index de6cd9301ff..e98daf66e98 100644
--- a/doc/lispref/control.texi
+++ b/doc/lispref/control.texi
@@ -2154,6 +2154,18 @@ Here's the example at the beginning of this subsection rewritten using
 @end example
 @end defmac
 
+@defmac ignore-error condition body@dots{}
+This macro is like @code{ignore-errors}, but will only ignore the
+specific error condition specified.
+
+@example
+  (ignore-error end-of-file
+    (read ""))
+@end example
+
+@var{condition} can also be a list of error conditions.
+@end defmac
+
 @defmac with-demoted-errors format body@dots{}
 This macro is like a milder version of @code{ignore-errors}.  Rather
 than suppressing errors altogether, it converts them into messages.
diff --git a/etc/NEWS b/etc/NEWS
index 44a69213899..5673fc1b42d 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1937,6 +1937,11 @@ buffer-local.  `permanent' also sets the variable's
 ** The new macro `with-suppressed-warnings' can be used to suppress
 specific byte-compile warnings.
 
++++
+** The new macro `ignore-error' is like `ignore-errors', but takes a
+specific error condition, and will only ignore that condition.  (This
+can also be a list of conditions.)
+
 ---
 ** The new function `byte-compile-info-message' can be used to output
 informational messages that look pleasing during the Emacs build.
diff --git a/lisp/progmodes/elisp-mode.el b/lisp/progmodes/elisp-mode.el
index da7a731ec22..1babb2f9094 100644
--- a/lisp/progmodes/elisp-mode.el
+++ b/lisp/progmodes/elisp-mode.el
@@ -500,16 +500,27 @@ functions are annotated with \"<f>\" via the
 		(scan-error pos))))
            ;; t if in function position.
            (funpos (eq (char-before beg) ?\())
-           (quoted (elisp--form-quoted-p beg)))
+           (quoted (elisp--form-quoted-p beg))
+           (fun-sym (condition-case nil
+                        (save-excursion
+                          (up-list -1)
+                          (forward-char 1)
+                          (and (memq (char-syntax (char-after)) '(?w ?_))
+                               (read (current-buffer))))
+                      (error nil))))
+      (message "sym: %s %s %s %s" fun-sym funpos beg end)
       (when (and end (or (not (nth 8 (syntax-ppss)))
                          (memq (char-before beg) '(?` ?‘))))
         (let ((table-etc
                (if (or (not funpos) quoted)
-                   ;; FIXME: We could look at the first element of the list and
-                   ;; use it to provide a more specific completion table in some
-                   ;; cases.  E.g. filter out keywords that are not understood by
-                   ;; the macro/function being called.
                    (cond
+                    ;; FIXME: We could look at the first element of
+                    ;; the current form and use it to provide a more
+                    ;; specific completion table in more cases.
+                    ((eq fun-sym 'ignore-error)
+                     (list t obarray
+                           :predicate (lambda (sym)
+                                        (get sym 'error-conditions))))
                     ((elisp--expect-function-p beg)
                      (list nil obarray
                            :predicate #'fboundp
@@ -568,6 +579,11 @@ functions are annotated with \"<f>\" via the
                                         (< (point) beg)))))
                         (list t obarray
                               :predicate (lambda (sym) (get sym 'error-conditions))))
+                       ;; `ignore-error' with a list CONDITION parameter.
+                       ('ignore-error
+                        (list t obarray
+                              :predicate (lambda (sym)
+                                           (get sym 'error-conditions))))
                        ((and (or ?\( 'let 'let*)
                              (guard (save-excursion
                                       (goto-char (1- beg))
diff --git a/lisp/subr.el b/lisp/subr.el
index f1a4e8bb292..eea4e045dde 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -302,6 +302,14 @@ See also `with-demoted-errors' that does something similar
 without silencing all errors."
   (declare (debug t) (indent 0))
   `(condition-case nil (progn ,@body) (error nil)))
+
+(defmacro ignore-error (condition &rest body)
+  "Execute BODY; if the error CONDITION occurs, return nil.
+Otherwise, return result of last form in BODY.
+
+CONDITION can also be a list of error conditions."
+  (declare (debug t) (indent 1))
+  `(condition-case nil (progn ,@body) (,condition nil)))
 
 ;;;; Basic Lisp functions.
 
diff --git a/test/lisp/subr-tests.el b/test/lisp/subr-tests.el
index 06db8f5c902..0023680738d 100644
--- a/test/lisp/subr-tests.el
+++ b/test/lisp/subr-tests.el
@@ -400,5 +400,15 @@ See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=19350."
   (should (equal subr-tests--hook '(f5 f10 f9 f6 f2 f1 f4 f3 f7 f8)))
   )
 
+(ert-deftest ignore-error-tests ()
+  (should (equal (ignore-error (end-of-file)
+                   (read ""))
+                 nil))
+  (should (equal (ignore-error end-of-file
+                   (read ""))
+                 nil))
+  (should-error (ignore-error foo
+                  (read ""))))
+
 (provide 'subr-tests)
 ;;; subr-tests.el ends here
-- 
2.39.2