(replace-region-contents): Improve and promote (bug#76313)

Swap the role of `replace-region-contents` and `replace-buffer-contents`,
so `replace-region-contents` is the main function, implemented in C,
and `replace-buffer-contents` is a mere wrapper (marked as obsolete).
Also remove the need to rely on narrowing and on describing the
new text as a function.
Finally, allow MAX-SECS==0 to require a cheap replacement, and
add an INHERIT argument.

* src/editfns.c: Include `coding.h`.
(Freplace_region_contents): Rename from `Freplace_buffer_contents`.
Change calling convention to that of `replace-region-contents`.
Add more options for the SOURCE argument.  Add INHERIT argument.
Skip the costly algorithm if MAX-SECS is 0.
* src/insdel.c (replace_range): Allow NEW to be a buffer.

* lisp/subr.el (replace-buffer-contents): New implementation.
* lisp/emacs-lisp/subr-x.el (replace-region-contents): Delete.

* doc/lispref/text.texi (Replacing): Document new API for
`replace-region-contents`.  Remove documentation of
`replace-buffer-contents`.

* test/src/editfns-tests.el (replace-buffer-contents-1)
(replace-buffer-contents-2, replace-buffer-contents-bug31837):
Use `replace-region-contents`.
(editfns--replace-region): Delete.
(editfns-tests--replace-region): Use `replace-region-contents`.
Adds tests for new types of SOURCE args.

8 files changed, 204 insertions, 151 deletions

diff --git a/doc/lispref/text.texi b/doc/lispref/text.texi
index 18ed71fd1f5..954979a00e6 100644
--- a/doc/lispref/text.texi
+++ b/doc/lispref/text.texi
@@ -4776,30 +4776,42 @@ all markers unrelocated.
 @node Replacing
 @section Replacing Buffer Text
 
-  You can use the following function to replace the text of one buffer
-with the text of another buffer:
+  You can use the following function to replace some the text of the
+current buffer:
 
-@deffn Command replace-buffer-contents source &optional max-secs max-costs
-This function replaces the accessible portion of the current buffer
-with the accessible portion of the buffer @var{source}.  @var{source}
-may either be a buffer object or the name of a buffer.  When
-@code{replace-buffer-contents} succeeds, the text of the accessible
-portion of the current buffer will be equal to the text of the
-accessible portion of the @var{source} buffer.
+@defun replace-region-contents beg end source &optional max-secs max-costs inherit
+This function replaces the region between @var{beg} and @var{end}
+of the current buffer with the text found in @var{source} which
+is usually a string or a buffer, in which case it will use the
+accessible portion of that buffer.
 
 This function attempts to keep point, markers, text properties, and
 overlays in the current buffer intact.  One potential case where this
-behavior is useful is external code formatting programs: they
-typically write the reformatted text into a temporary buffer or file,
-and using @code{delete-region} and @code{insert-buffer-substring}
-would destroy these properties.  However, the latter combination is
-typically faster (@xref{Deletion}, and @ref{Insertion}).
-
-For its working, @code{replace-buffer-contents} needs to compare the
-contents of the original buffer with that of @var{source} which is a
-costly operation if the buffers are huge and there is a high number of
-differences between them.  In order to keep
-@code{replace-buffer-contents}'s runtime in bounds, it has two
+behavior is useful is external code formatting programs: they typically
+write the reformatted text into a temporary buffer or file, and using
+@code{insert} and @code{delete-region} would destroy these properties.
+
+However, in order to do that, @code{replace-region-contents} needs to
+compare the contents of the original buffer with that of @var{source},
+using a costly algorithm which makes the operation much slower than
+a simple @code{insert} and @code{delete-region}.  In many cases, you may
+not need that refinement, and you will then want to pass 0 as
+@var{max-secs} argument, so as to short-circuit that costly algorithm:
+It will then be just as fast as @code{insert} and @code{delete-region}
+while still preserving point and markers marginally better.
+
+Beyond that basic usage, if you need to use as source a subset of the
+accessible portion of a buffer, @var{source} can also be a vector
+@code{[@var{sbuf} @var{sbeg} @var{send}]} where the region between
+@var{sbeg} and @var{send} in buffer @var{sbuf} is the text
+you want to use as source.
+
+If you need the inserted text to inherit text-properties
+from the adjoining text, you can pass a non-@code{nil} value as
+@var{inherit} argument.
+
+When you do want the costly refined replacement, in order to keep
+@code{replace-region-contents}'s runtime in bounds, it has two
 optional arguments.
 
 @var{max-secs} defines a hard boundary in terms of seconds.  If given
@@ -4810,26 +4822,14 @@ and exceeded, it will fall back to @code{delete-region} and
 the actual costs exceed this limit, heuristics are used to provide a
 faster but suboptimal solution.  The default value is 1000000.
 
-@code{replace-buffer-contents} returns @code{t} if a non-destructive
+@code{replace-region-contents} returns @code{t} if a non-destructive
 replacement could be performed.  Otherwise, i.e., if @var{max-secs}
 was exceeded, it returns @code{nil}.
-@end deffn
 
-@defun replace-region-contents beg end replace-fn &optional max-secs max-costs
-This function replaces the region between @var{beg} and @var{end}
-using the given @var{replace-fn}.  The function @var{replace-fn} is
-run in the current buffer narrowed to the specified region and it
-should return either a string or a buffer replacing the region.
-
-The replacement is performed using @code{replace-buffer-contents} (see
-above) which also describes the @var{max-secs} and @var{max-costs}
-arguments and the return value.
-
-Note: If the replacement is a string, it will be placed in a temporary
-buffer so that @code{replace-buffer-contents} can operate on it.
-Therefore, if you already have the replacement in a buffer, it makes
-no sense to convert it to a string using @code{buffer-substring} or
-similar.
+Note: When using the refined replacement algorithm, if the replacement
+is a string, it will be internally copied to a temporary buffer.
+Therefore, all else being equal, it is preferable to pass a buffer than
+a string as @var{source} argument.
 @end defun
 
 @node Decompression
diff --git a/etc/NEWS b/etc/NEWS
index 33a2b3fd07a..f0b84385510 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1733,6 +1733,13 @@ Previously, its argument was always evaluated using dynamic binding.
 * Lisp Changes in Emacs 31.1
 
 +++
+** Improve 'replace-region-contents' to accept more forms of sources.
+It has been promoted from 'subr-x' to the C code.
+You can now directly pass it a string or a buffer rather than a function.
+Actually passing it a function is now deprecated.
+'replace-buffer-contents' is also marked as obsolete.
+
++++
 ** New macros 'static-when' and 'static-unless'.
 Like 'static-if', these macros evaluate their condition at
 macro-expansion time and are useful for writing code that can work
diff --git a/lisp/emacs-lisp/subr-x.el b/lisp/emacs-lisp/subr-x.el
index 6414ecab394..eaa8119ead7 100644
--- a/lisp/emacs-lisp/subr-x.el
+++ b/lisp/emacs-lisp/subr-x.el
@@ -281,35 +281,6 @@ the string."
   (declare (pure t) (side-effect-free t))
   (string-remove-suffix "\n" string))
 
-(defun replace-region-contents (beg end replace-fn
-                                    &optional max-secs max-costs)
-  "Replace the region between BEG and END using REPLACE-FN.
-REPLACE-FN runs on the current buffer narrowed to the region.  It
-should return either a string or a buffer replacing the region.
-
-The replacement is performed using `replace-buffer-contents'
-which also describes the MAX-SECS and MAX-COSTS arguments and the
-return value.
-
-Note: If the replacement is a string, it'll be placed in a
-temporary buffer so that `replace-buffer-contents' can operate on
-it.  Therefore, if you already have the replacement in a buffer,
-it makes no sense to convert it to a string using
-`buffer-substring' or similar."
-  (save-excursion
-    (save-restriction
-      (narrow-to-region beg end)
-      (goto-char (point-min))
-      (let ((repl (funcall replace-fn)))
-        (if (bufferp repl)
-            (replace-buffer-contents repl max-secs max-costs)
-          (let ((source-buffer (current-buffer)))
-            (with-temp-buffer
-              (insert repl)
-              (let ((tmp-buffer (current-buffer)))
-                (set-buffer source-buffer)
-                (replace-buffer-contents tmp-buffer max-secs max-costs)))))))))
-
 ;;;###autoload
 (defmacro named-let (name bindings &rest body)
   "Looping construct taken from Scheme.
diff --git a/lisp/subr.el b/lisp/subr.el
index 8c1e6f657a6..66b73cbf6cc 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -4762,6 +4762,19 @@ Point in BUFFER will be placed after the inserted text."
     (with-current-buffer buffer
       (insert-buffer-substring current start end))))
 
+(defun replace-buffer-contents (source &optional max-secs max-costs)
+  "Replace accessible portion of current buffer with that of SOURCE.
+SOURCE can be a buffer or a string that names a buffer.
+Interactively, prompt for SOURCE.
+
+The replacement is performed using `replace-region-contents'
+which also describes the MAX-SECS and MAX-COSTS arguments and the
+return value."
+  (declare (obsolete replace-region-contents "31.1"))
+  (interactive "bSource buffer: ")
+  (replace-region-contents (point-min) (point-max) (get-buffer source)
+                           max-secs max-costs))
+
 (defun replace-string-in-region (string replacement &optional start end)
   "Replace STRING with REPLACEMENT in the region from START to END.
 The number of replaced occurrences are returned, or nil if STRING
diff --git a/src/coding.c b/src/coding.c
index b0bd5d3a9ab..63b0dbeb18b 100644
--- a/src/coding.c
+++ b/src/coding.c
@@ -7898,6 +7898,8 @@ code_conversion_save (bool with_work_buf, bool multibyte)
       bset_enable_multibyte_characters (current_buffer, multibyte ? Qt : Qnil);
       if (EQ (workbuf, Vcode_conversion_reused_workbuf))
         reused_workbuf_in_use = true;
+      /* FIXME: Maybe we should stay in the new workbuf, because we often
+         switch right back to it anyway in order to initialize it further.  */
       set_buffer_internal (current);
     }
 
diff --git a/src/editfns.c b/src/editfns.c
index 53d6cce7c82..25625793c42 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -54,6 +54,7 @@ along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.  */
 #include "buffer.h"
 #include "window.h"
 #include "blockinput.h"
+#include "coding.h"
 
 #ifdef WINDOWSNT
 # include "w32common.h"
@@ -1914,11 +1915,14 @@ static bool compareseq_early_abort (struct context *);
 #include "minmax.h"
 #include "diffseq.h"
 
-DEFUN ("replace-buffer-contents", Freplace_buffer_contents,
-       Sreplace_buffer_contents, 1, 3, "bSource buffer: ",
-       doc: /* Replace accessible portion of current buffer with that of SOURCE.
-SOURCE can be a buffer or a string that names a buffer.
-Interactively, prompt for SOURCE.
+DEFUN ("replace-region-contents", Freplace_region_contents,
+       Sreplace_region_contents, 3, 6, 0,
+       doc: /* Replace the region between BEG and END with that of SOURCE.
+SOURCE can be a buffer, a string, or a vector [SBUF SBEG SEND]
+denoting the subtring SBEG..SEND of buffer SBUF.
+
+If optional argument INHERIT is non-nil, the inserted text will inherit
+properties from adjoining text.
 
 As far as possible the replacement is non-destructive, i.e. existing
 buffer contents, markers, properties, and overlays in the current
@@ -1940,18 +1944,85 @@ computation.  If the actual costs exceed this limit, heuristics are
 used to provide a faster but suboptimal solution.  The default value
 is 1000000.
 
+Note: If the replacement is a string, it’ll usually be placed internally
+in a temporary buffer.  Therefore, all else being equal, it is preferable
+to pass a buffer rather than a string as SOURCE argument.
+
 This function returns t if a non-destructive replacement could be
 performed.  Otherwise, i.e., if MAX-SECS was exceeded, it returns
-nil.  */)
-  (Lisp_Object source, Lisp_Object max_secs, Lisp_Object max_costs)
+nil.
+
+SOURCE can also be a function that will be called with no arguments
+and with current buffer narrowed to BEG..END, and should return
+a buffer or a string.  But this is deprecated.  */)
+  (Lisp_Object beg, Lisp_Object end, Lisp_Object source,
+   Lisp_Object max_secs, Lisp_Object max_costs, Lisp_Object inherit)
 {
-  struct buffer *a = current_buffer;
-  Lisp_Object source_buffer = Fget_buffer (source);
-  if (NILP (source_buffer))
-    nsberror (source);
-  struct buffer *b = XBUFFER (source_buffer);
-  if (! BUFFER_LIVE_P (b))
+  validate_region (&beg, &end);
+  ptrdiff_t min_a = XFIXNUM (beg);
+  ptrdiff_t size_a = XFIXNUM (end) - min_a;
+  eassume (size_a >= 0);
+  bool a_empty = size_a == 0;
+  bool inh = !NILP (inherit);
+
+  if (FUNCTIONP (source))
+    {
+      specpdl_ref count = SPECPDL_INDEX ();
+      record_unwind_protect (save_restriction_restore,
+                             save_restriction_save ());
+      Fnarrow_to_region (beg, end);
+      source = calln (source);
+      unbind_to (count, Qnil);
+      }
+  ptrdiff_t min_b, size_b;
+  struct buffer *b;
+  if (STRINGP (source))
+    {
+      min_b = BEG;              /* Assuming we'll copy it into a buffer.  */
+      size_b = SCHARS (source);
+      b = NULL;
+    }
+  else if (BUFFERP (source))
+    {
+      b = XBUFFER (source);
+      min_b = BUF_BEGV (b);
+      size_b = BUF_ZV (b) - min_b;
+    }
+  else
+    {
+      CHECK_TYPE (VECTORP (source),
+                  list (Qor, Qstring, Qbuffer, Qvector), source);
+      /* Let `Faref' signal an error if it's too small.  */
+      Lisp_Object send = Faref (source, make_fixnum (2));
+      Lisp_Object sbeg = AREF (source, 1);
+      CHECK_BUFFER (AREF (source, 0));
+      b = XBUFFER (AREF (source, 0));
+      specpdl_ref count = SPECPDL_INDEX ();
+      record_unwind_current_buffer ();
+      set_buffer_internal (b);
+      validate_region (&sbeg, &send);
+      unbind_to (count, Qnil);
+      min_b = XFIXNUM (sbeg);
+      size_b = XFIXNUM (send) - min_b;
+    }
+  bool b_empty = size_b == 0;
+  if (b && !BUFFER_LIVE_P (b))
     error ("Selecting deleted buffer");
+
+  /* Handle trivial cases where at least one accessible portion is
+     empty.  */
+
+  if (a_empty && b_empty)
+    return Qt;
+  else if (a_empty || b_empty
+           || EQ (max_secs, make_fixnum (0))
+           || EQ (max_costs, make_fixnum (0)))
+    {
+      replace_range (min_a, min_a + size_a, source, true, false, inh);
+      return Qt;
+    }
+
+  struct buffer *a = current_buffer;
   if (a == b)
     error ("Cannot replace a buffer with itself");
 
@@ -1977,36 +2048,8 @@ nil.  */)
         time_limit = tlim;
     }
 
-  ptrdiff_t min_a = BEGV;
-  ptrdiff_t min_b = BUF_BEGV (b);
-  ptrdiff_t size_a = ZV - min_a;
-  ptrdiff_t size_b = BUF_ZV (b) - min_b;
-  eassume (size_a >= 0);
-  eassume (size_b >= 0);
-  bool a_empty = size_a == 0;
-  bool b_empty = size_b == 0;
-
-  /* Handle trivial cases where at least one accessible portion is
-     empty.  */
-
-  if (a_empty && b_empty)
-    return Qt;
-
-  if (a_empty)
-    {
-      Finsert_buffer_substring (source, Qnil, Qnil);
-      return Qt;
-    }
-
-  if (b_empty)
-    {
-      del_range_both (BEGV, BEGV_BYTE, ZV, ZV_BYTE, true);
-      return Qt;
-    }
-
   specpdl_ref count = SPECPDL_INDEX ();
 
-
   ptrdiff_t diags = size_a + size_b + 3;
   ptrdiff_t del_bytes = size_a / CHAR_BIT + 1;
   ptrdiff_t ins_bytes = size_b / CHAR_BIT + 1;
@@ -2020,6 +2063,18 @@ nil.  */)
   unsigned char *deletions_insertions = memset (buffer + 2 * diags, 0,
                                                 del_bytes + ins_bytes);
 
+  /* The rest of the code is not prepared to handle a string SOURCE.  */
+  if (!b)
+    {
+      Lisp_Object workbuf
+        = code_conversion_save (true, STRING_MULTIBYTE (source));
+      b = XBUFFER (workbuf);
+      set_buffer_internal (b);
+      CALLN (Finsert, source);
+      set_buffer_internal (a);
+    }
+  Lisp_Object source_buffer = make_lisp_ptr (b, Lisp_Vectorlike);
+
   /* FIXME: It is not documented how to initialize the contents of the
      context structure.  This code cargo-cults from the existing
      caller in src/analyze.c of GNU Diffutils, which appears to
@@ -2053,7 +2108,7 @@ nil.  */)
       Lisp_Object src = CALLN (Fvector, source_buffer,
                                make_fixnum (BUF_BEGV (b)),
                                make_fixnum (BUF_ZV (b)));
-      replace_range (BEGV, ZV, src, true, false, false);
+      replace_range (min_a, min_a + size_a, src, true, false, inh);
       SAFE_FREE_UNBIND_TO (count, Qnil);
       return Qnil;
     }
@@ -2069,7 +2124,7 @@ nil.  */)
      modification hooks, because then they don't want that.  */
   if (!inhibit_modification_hooks)
     {
-      prepare_to_modify_buffer (BEGV, ZV, NULL);
+      prepare_to_modify_buffer (min_a, min_a + size_a, NULL);
       specbind (Qinhibit_modification_hooks, Qt);
       modification_hooks_inhibited = true;
     }
@@ -2102,10 +2157,9 @@ nil.  */)
           eassert (beg_a <= end_a);
           eassert (beg_b <= end_b);
           eassert (beg_a < end_a || beg_b < end_b);
-          /* FIXME: Use 'replace_range'!  */
           ASET (src, 1, make_fixed_natnum (beg_b));
           ASET (src, 2, make_fixed_natnum (end_b));
-          replace_range (beg_a, end_a, src, true, false, false);
+          replace_range (beg_a, end_a, src, true, false, inh);
         }
       --i;
       --j;
@@ -2115,8 +2169,8 @@ nil.  */)
 
   if (modification_hooks_inhibited)
     {
-      signal_after_change (BEGV, size_a, ZV - BEGV);
-      update_compositions (BEGV, ZV, CHECK_INSIDE);
+      signal_after_change (min_a, size_a, size_b);
+      update_compositions (min_a, min_a + size_b, CHECK_INSIDE);
       /* We've locked the buffer's file above in
          prepare_to_modify_buffer; if the buffer is unchanged at this
          point, i.e. no insertions or deletions have been made, unlock
@@ -4787,7 +4841,7 @@ it to be non-nil.  */);
 
   defsubr (&Sinsert_buffer_substring);
   defsubr (&Scompare_buffer_substrings);
-  defsubr (&Sreplace_buffer_contents);
+  defsubr (&Sreplace_region_contents);
   defsubr (&Ssubst_char_in_region);
   defsubr (&Stranslate_region_internal);
   defsubr (&Sdelete_region);
diff --git a/src/insdel.c b/src/insdel.c
index 9b770725971..20267265ab8 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -1409,9 +1409,9 @@ adjust_after_insert (ptrdiff_t from, ptrdiff_t from_byte,
   adjust_after_replace (from, from_byte, Qnil, newlen, len_byte);
 }
 
-/* Replace the text from character positions FROM to TO with NEW.
-   NEW could either be a string, the replacement text, or a vector
-   [BUFFER BEG END], where BUFFER is the buffer with the replacement
+/* Replace the text from character positions FROM to TO with the
+   replacement text NEW.  NEW could either be a string, a buffer, or
+   a vector [BUFFER BEG END], where BUFFER is the buffer with the replacement
    text and BEG and END are buffer positions in BUFFER that give the
    replacement text beginning and end.
    If PREPARE, call prepare_to_modify_buffer.
@@ -1439,6 +1439,12 @@ replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
       insbeg = 0;
       inschars = SCHARS (new);
     }
+  else if (BUFFERP (new))
+    {
+      insbuf = XBUFFER (new);
+      insbeg = BUF_BEGV (insbuf);
+      inschars = BUF_ZV (insbuf) - insbeg;
+    }
   else
     {
       CHECK_VECTOR (new);
diff --git a/test/src/editfns-tests.el b/test/src/editfns-tests.el
index c3f825c6149..3da9d4e8acd 100644
--- a/test/src/editfns-tests.el
+++ b/test/src/editfns-tests.el
@@ -289,7 +289,7 @@
             (narrow-to-region 8 13)
             (goto-char 12)
             (should (looking-at " \\'"))
-            (replace-buffer-contents source)
+            (replace-region-contents (point-min) (point-max) source)
             (should (looking-at " \\'")))
           (should (equal (marker-buffer marker) (current-buffer)))
           (should (equal (marker-position marker) 16)))
@@ -306,7 +306,7 @@
     (let ((source (current-buffer)))
       (with-temp-buffer
         (insert "foo BAR baz qux")
-        (replace-buffer-contents source)
+        (replace-region-contents (point-min) (point-max) source)
         (should (equal-including-properties
                  (buffer-string)
                  "foo bar baz qux"))))))
@@ -318,44 +318,44 @@
   (switch-to-buffer "b")
   (insert-char (char-from-name "SMILE"))
   (insert "5678")
-  (replace-buffer-contents "a")
+  (replace-region-contents (point-min) (point-max) (get-buffer "a"))
   (should (equal (buffer-substring-no-properties (point-min) (point-max))
                  (concat (string (char-from-name "SMILE")) "1234"))))
 
-(defun editfns--replace-region (from to string)
-  (save-excursion
-    (save-restriction
-      (narrow-to-region from to)
-      (let ((buf (current-buffer)))
-        (with-temp-buffer
-          (let ((str-buf (current-buffer)))
-            (insert string)
-            (with-current-buffer buf
-              (replace-buffer-contents str-buf))))))))
-
 (ert-deftest editfns-tests--replace-region ()
   ;; :expected-result :failed
   (with-temp-buffer
-    (insert "here is some text")
-    (let ((m5n (copy-marker (+ (point-min) 5)))
-          (m5a (copy-marker (+ (point-min) 5) t))
-          (m6n (copy-marker (+ (point-min) 6)))
-          (m6a (copy-marker (+ (point-min) 6) t))
-          (m7n (copy-marker (+ (point-min) 7)))
-          (m7a (copy-marker (+ (point-min) 7) t)))
-      (editfns--replace-region (+ (point-min) 5) (+ (point-min) 7) "be")
-      (should (equal (buffer-string) "here be some text"))
-      (should (equal (point) (point-max)))
-      ;; Markers before the replaced text stay before.
-      (should (= m5n (+ (point-min) 5)))
-      (should (= m5a (+ (point-min) 5)))
-      ;; Markers in the replaced text can end up at either end, depending
-      ;; on whether they're advance-after-insert or not.
-      (should (= m6n (+ (point-min) 5)))
-      (should (<= (+ (point-min) 5) m6a (+ (point-min) 7)))
-      ;; Markers after the replaced text stay after.
-      (should (= m7n (+ (point-min) 7)))
-      (should (= m7a (+ (point-min) 7))))))
+    (let ((tmpbuf (current-buffer)))
+      (insert "  be  ")
+      (narrow-to-region (+ (point-min) 2) (- (point-max) 2))
+      (dolist (args `((,tmpbuf)
+                      (,(vector tmpbuf (point-min) (point-max)))
+                      (,"be")
+                      (,(vector tmpbuf (point-min) (point-max)) 0)
+                      (,"be" 0)))
+        (with-temp-buffer
+          (insert "here is some text")
+          (let ((m5n (copy-marker (+ (point-min) 5)))
+                (m5a (copy-marker (+ (point-min) 5) t))
+                (m6n (copy-marker (+ (point-min) 6)))
+                (m6a (copy-marker (+ (point-min) 6) t))
+                (m7n (copy-marker (+ (point-min) 7)))
+                (m7a (copy-marker (+ (point-min) 7) t)))
+            (apply #'replace-region-contents
+                   (+ (point-min) 5) (+ (point-min) 7) args)
+            (should (equal (buffer-string) "here be some text"))
+            (should (equal (point) (point-max)))
+            ;; Markers before the replaced text stay before.
+            (should (= m5n (+ (point-min) 5)))
+            (should (= m5a (+ (point-min) 5)))
+            ;; Markers in the replaced text can end up at either end, depending
+            ;; on whether they're advance-after-insert or not.
+            (should (= m6n (+ (point-min) 5)))
+            (should (<= (+ (point-min) 5) m6a (+ (point-min) 7)))
+            ;; Markers after the replaced text stay after.
+            (should (= m7n (+ (point-min) 7)))
+            (should (= m7a (+ (point-min) 7)))))
+        (widen)))))
 
 (ert-deftest delete-region-undo-markers-1 ()
   "Make sure we don't end up with freed markers reachable from Lisp."