Fix 'transpose-regions' when LEAVE-MARKERS arg is non-nil

* src/insdel.c (adjust_markers_bytepos): New function.
* src/lisp.h (adjust_markers_bytepos): Add prototype.
* src/insdel.c (replace_range, replace_range_2):
* src/editfns.c (Ftranspose_regions): Call
adjust_markers_bytepos.  (Bug#5131)

* test/src/editfns-tests.el (transpose-test-reverse-word)
(transpose-test-get-byte-positions): New functions.
(transpose-ascii-regions-test)
(transpose-nonascii-regions-test-1)
(transpose-nonascii-regions-test-2): New tests.

3 files changed, 108 insertions, 4 deletions

diff --git a/src/editfns.c b/src/editfns.c
index 4c8336b8c82..aed884ebe1c 100644
--- a/src/editfns.c
+++ b/src/editfns.c
@@ -5058,6 +5058,14 @@ Transposing beyond buffer boundaries is an error.  */)
                          start2_byte, start2_byte + len2_byte);
       fix_start_end_in_overlays (start1, end2);
     }
+  else
+    {
+      /* The character positions of the markers remain intact, but we
+         still need to update their byte positions, because the
+         transposed regions might include multibyte sequences which
+         make some original byte positions of the markers invalid.  */
+      adjust_markers_bytepos (start1, start1_byte, end2, end2_byte, 0);
+    }
 
   signal_after_change (start1, end2 - start1, end2 - start1);
   return Qnil;
diff --git a/src/insdel.c b/src/insdel.c
index 4ad1074f5f7..ec7bbb3e715 100644
--- a/src/insdel.c
+++ b/src/insdel.c
@@ -364,6 +364,78 @@ adjust_markers_for_replace (ptrdiff_t from, ptrdiff_t from_byte,
   check_markers ();
 }
 
+/* Starting at POS (BYTEPOS), find the byte position corresponding to
+   ENDPOS, which could be either before or after POS.  */
+static ptrdiff_t
+count_bytes (ptrdiff_t pos, ptrdiff_t bytepos, ptrdiff_t endpos)
+{
+  eassert (BEG_BYTE <= bytepos && bytepos <= Z_BYTE
+           && BEG <= endpos && endpos <= Z);
+
+  if (pos <= endpos)
+    for ( ; pos < endpos; pos++)
+      INC_POS (bytepos);
+  else
+    for ( ; pos > endpos; pos--)
+      DEC_POS (bytepos);
+
+  return bytepos;
+}
+
+/* Adjust byte positions of markers when their character positions
+   didn't change.  This is used in several places that replace text,
+   but keep the character positions of the markers unchanged -- the
+   byte positions could still change due to different numbers of bytes
+   in the new text.
+
+   FROM (FROM_BYTE) and TO (TO_BYTE) specify the region of text where
+   changes have been done.  TO_Z, if non-zero, means all the markers
+   whose positions are after TO should also be adjusted.  */
+void
+adjust_markers_bytepos (ptrdiff_t from, ptrdiff_t from_byte,
+                        ptrdiff_t to, ptrdiff_t to_byte, int to_z)
+{
+  register struct Lisp_Marker *m;
+  ptrdiff_t beg = from, begbyte = from_byte;
+
+  adjust_suspend_auto_hscroll (from, to);
+
+  if (Z == Z_BYTE || (!to_z && to == to_byte))
+    {
+      /* Make sure each affected marker's bytepos is equal to
+         its charpos.  */
+      for (m = BUF_MARKERS (current_buffer); m; m = m->next)
+        {
+          if (m->bytepos > from_byte
+              && (to_z || m->bytepos <= to_byte))
+            m->bytepos = m->charpos;
+        }
+    }
+  else
+    {
+      for (m = BUF_MARKERS (current_buffer); m; m = m->next)
+        {
+          /* Recompute each affected marker's bytepos.  */
+          if (m->bytepos > from_byte
+              && (to_z || m->bytepos <= to_byte))
+            {
+              if (m->charpos < beg
+                  && beg - m->charpos > m->charpos - from)
+                {
+                  beg = from;
+                  begbyte = from_byte;
+                }
+              m->bytepos = count_bytes (beg, begbyte, m->charpos);
+              beg = m->charpos;
+              begbyte = m->bytepos;
+            }
+        }
+    }
+
+  /* Make sure cached charpos/bytepos is invalid.  */
+  clear_charpos_cache (current_buffer);
+}
+
 
 void
 buffer_overflow (void)
@@ -1397,6 +1469,16 @@ replace_range (ptrdiff_t from, ptrdiff_t to, Lisp_Object new,
   if (markers)
     adjust_markers_for_replace (from, from_byte, nchars_del, nbytes_del,
                                 inschars, outgoing_insbytes);
+  else
+    {
+      /* The character positions of the markers remain intact, but we
+         still need to update their byte positions, because the
+         deleted and the inserted text might have multibyte sequences
+         which make the original byte positions of the markers
+         invalid.  */
+      adjust_markers_bytepos (from, from_byte, from + inschars,
+                              from_byte + outgoing_insbytes, 1);
+    }
 
   /* Adjust the overlay center as needed.  This must be done after
      adjusting the markers that bound the overlays.  */
@@ -1509,10 +1591,22 @@ replace_range_2 (ptrdiff_t from, ptrdiff_t from_byte,
   eassert (GPT <= GPT_BYTE);
 
   /* Adjust markers for the deletion and the insertion.  */
-  if (markers
-      && ! (nchars_del == 1 && inschars == 1 && nbytes_del == insbytes))
-    adjust_markers_for_replace (from, from_byte, nchars_del, nbytes_del,
-                                inschars, insbytes);
+  if (! (nchars_del == 1 && inschars == 1 && nbytes_del == insbytes))
+    {
+      if (markers)
+        adjust_markers_for_replace (from, from_byte, nchars_del, nbytes_del,
+                                    inschars, insbytes);
+      else
+        {
+          /* The character positions of the markers remain intact, but
+             we still need to update their byte positions, because the
+             deleted and the inserted text might have multibyte
+             sequences which make the original byte positions of the
+             markers invalid.  */
+          adjust_markers_bytepos (from, from_byte, from + inschars,
+                                  from_byte + insbytes, 1);
+        }
+    }
 
   /* Adjust the overlay center as needed.  This must be done after
      adjusting the markers that bound the overlays.  */
diff --git a/src/lisp.h b/src/lisp.h
index e0eb52a84ea..48c27281643 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -3528,6 +3528,8 @@ extern void adjust_after_insert (ptrdiff_t, ptrdiff_t, ptrdiff_t,
                                  ptrdiff_t, ptrdiff_t);
 extern void adjust_markers_for_delete (ptrdiff_t, ptrdiff_t,
                                        ptrdiff_t, ptrdiff_t);
+extern void adjust_markers_bytepos (ptrdiff_t, ptrdiff_t,
+                                    ptrdiff_t, ptrdiff_t, int);
 extern void replace_range (ptrdiff_t, ptrdiff_t, Lisp_Object, bool, bool, bool);
 extern void replace_range_2 (ptrdiff_t, ptrdiff_t, ptrdiff_t, ptrdiff_t,
                              const char *, ptrdiff_t, ptrdiff_t, bool);