compat-29: Add with-narrowing

4 files changed, 39 insertions, 0 deletions

diff --git a/NEWS.org b/NEWS.org
index a8ba33d..985fb71 100644
--- a/NEWS.org
+++ b/NEWS.org
@@ -12,6 +12,7 @@
 - compat-29: Add ~plistp~.
 - compat-29: Add ~list-of-strings-p~.
 - compat-29: Add ~delete-line~.
+- compat-29: Add ~with-narrowing~.
 
 * Release of "Compat" Version 29.1.2.0
 
diff --git a/compat-29.el b/compat-29.el
index 9373c0c..4010a9e 100644
--- a/compat-29.el
+++ b/compat-29.el
@@ -187,6 +187,23 @@ This function does not move point.  Also see `line-end-position'."
   "Delete the current line."
   (delete-region (pos-bol) (pos-bol 2)))
 
+(compat-defmacro with-narrowing (start end &rest rest)
+  "Execute BODY with restrictions set to START and END.
+
+The current restrictions, if any, are restored upon return.
+
+With the optional :locked TAG argument, inside BODY,
+`narrow-to-region' and `widen' can be used only within the START
+and END limits, unless the restrictions are unlocked by calling
+`narrowing-unlock' with TAG.  See `narrowing-lock' for a more
+detailed description.
+
+\(fn START END [:locked TAG] BODY)"
+  `(save-restriction
+     (narrow-to-region ,start ,end)
+     ;; Locking is ignored
+     ,@(if (eq (car rest) :locked) (cddr rest) rest)))
+
 (compat-defmacro with-memoization (place &rest code) ;; <compat-tests:with-memoization>
   "Return the value of CODE and stash it in PLACE.
 If PLACE's value is non-nil, then don't bother evaluating CODE
diff --git a/compat-tests.el b/compat-tests.el
index 1b61570..9b787db 100644
--- a/compat-tests.el
+++ b/compat-tests.el
@@ -211,6 +211,16 @@
     (should-equal 'h (get-text-property 2 'help-echo))
     (should-equal 'h (get-text-property 6 'help-echo))))
 
+(ert-deftest with-narrowing ()
+  (with-temp-buffer
+    (insert "abc")
+    (with-narrowing 2 3 :locked 'foo
+      (should-equal "b" (buffer-string)))
+    (should-equal "abc" (buffer-string))
+    (with-narrowing 2 3
+                    (should-equal "b" (buffer-string)))
+    (should-equal "abc" (buffer-string))))
+
 (ert-deftest with-memoization ()
   (let ((x (cons nil nil)) y computed)
     (with-memoization (car x)
diff --git a/compat.texi b/compat.texi
index bb86925..61a9fc7 100644
--- a/compat.texi
+++ b/compat.texi
@@ -2034,6 +2034,17 @@ evaluated and then stashed in @var{place}.  If @var{place}'s value is
 non-@code{nil}, return that value instead of evaluating @var{code}.
 @end defmac
 
+@c based on lisp/subr.el
+@defmac with-narrowing start end [:locked tag] &rest body
+Execute @var{body} with restrictions set to @var{start} and @var{end}.
+The current restrictions, if any, are restored upon return.  With the
+optional :locked @var{tag} argument, inside @var{tag},
+@code{narrow-to-region} and @code{widen} can be used only within the
+@var{start} and @var{end} limits, unless the restrictions are unlocked
+by calling @code{narrowing-unlock} with @var{tag}.  See
+@code{narrowing-lock} for a more detailed description.
+@end defmac
+
 @c copied from lispref/positions.texi
 @defun pos-bol &optional count
 Like @code{line-beginning-position}, but ignores fields (and is more