12 files changed, 595 insertions, 131 deletions

diff --git a/src/Makefile.in b/src/Makefile.in
index 92a8790efdc..a7024bda461 100644
--- a/src/Makefile.in
+++ b/src/Makefile.in
@@ -845,7 +845,6 @@ ifeq ($(HAVE_NATIVE_COMP):$(NATIVE_DISABLED),yes:)
 ## List of *.eln files we need to produce in addition to the preloaded
 ## ones in $(lisp).
 elnlisp := \
-        emacs-lisp/autoload.eln \
         emacs-lisp/byte-opt.eln \
         emacs-lisp/bytecomp.eln \
         emacs-lisp/cconv.eln \
diff --git a/src/buffer.c b/src/buffer.c
index e5601af5051..98066a2eb60 100644
--- a/src/buffer.c
+++ b/src/buffer.c
@@ -1160,7 +1160,8 @@ is first appended to NAME, to speed up finding a non-existent buffer.  */)
     genbase = name;
   else
     {
-      char number[sizeof "-999999"];
+      enum { bug_52711 = true };  /* https://bugs.gnu.org/57211 */
+      char number[bug_52711 ? INT_BUFSIZE_BOUND (int) + 1 : sizeof "-999999"];
       EMACS_INT r = get_random ();
       eassume (0 <= r);
       int i = r % 1000000;
@@ -6442,6 +6443,24 @@ If nil, these display shortcuts will always remain disabled.
 There is no reason to change that value except for debugging purposes.  */);
   XSETFASTINT (Vlong_line_threshold, 10000);
 
+  DEFVAR_INT ("large-hscroll-threshold", large_hscroll_threshold,
+    doc: /* Horizontal scroll of truncated lines above which to use redisplay shortcuts.
+
+The value should be a positive integer.
+
+Shortcuts in the display code intended to speed up redisplay for long
+and truncated lines will automatically be enabled when a line's
+horizontal scroll amount is or about to become larger than the value
+of this variable.
+
+This variable has effect only in buffers which contain one or more
+lines whose length is above `long-line-threshold', which see.
+To disable redisplay shortcuts for long truncated line, set this
+variable to `most-positive-fixnum'.
+
+There is no reason to change that value except for debugging purposes.  */);
+  large_hscroll_threshold = 10000;
+
   defsubr (&Sbuffer_live_p);
   defsubr (&Sbuffer_list);
   defsubr (&Sget_buffer);
diff --git a/src/eval.c b/src/eval.c
index d82d05797b2..56b42966623 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -57,6 +57,12 @@ Lisp_Object Vrun_hooks;
 /* FIXME: We should probably get rid of this!  */
 Lisp_Object Vsignaling_function;
 
+/* The handler structure which will catch errors in Lisp hooks called
+   from redisplay.  We do not use it for this; we compare it with the
+   handler which is about to be used in signal_or_quit, and if it
+   matches, cause a backtrace to be generated.  */
+static struct handler *redisplay_deep_handler;
+
 /* These would ordinarily be static, but they need to be visible to GDB.  */
 bool backtrace_p (union specbinding *) EXTERNALLY_VISIBLE;
 Lisp_Object *backtrace_args (union specbinding *) EXTERNALLY_VISIBLE;
@@ -246,6 +252,7 @@ init_eval (void)
   lisp_eval_depth = 0;
   /* This is less than the initial value of num_nonmacro_input_events.  */
   when_entered_debugger = -1;
+  redisplay_deep_handler = NULL;
 }
 
 /* Ensure that *M is at least A + B if possible, or is its maximum
@@ -333,7 +340,8 @@ call_debugger (Lisp_Object arg)
   /* Interrupting redisplay and resuming it later is not safe under
      all circumstances.  So, when the debugger returns, abort the
      interrupted redisplay by going back to the top-level.  */
-  if (debug_while_redisplaying)
+  if (debug_while_redisplaying
+      && !EQ (Vdebugger, Qdebug_early))
     Ftop_level ();
 
   return unbind_to (count, val);
@@ -1556,12 +1564,16 @@ internal_condition_case_n (Lisp_Object (*bfun) (ptrdiff_t, Lisp_Object *),
                                                 ptrdiff_t nargs,
                                                 Lisp_Object *args))
 {
+  struct handler *old_deep = redisplay_deep_handler;
   struct handler *c = push_handler (handlers, CONDITION_CASE);
+  if (redisplaying_p)
+    redisplay_deep_handler = c;
   if (sys_setjmp (c->jmp))
     {
       Lisp_Object val = handlerlist->val;
       clobbered_eassert (handlerlist == c);
       handlerlist = handlerlist->next;
+      redisplay_deep_handler = old_deep;
       return hfun (val, nargs, args);
     }
   else
@@ -1569,6 +1581,7 @@ internal_condition_case_n (Lisp_Object (*bfun) (ptrdiff_t, Lisp_Object *),
       Lisp_Object val = bfun (nargs, args);
       eassert (handlerlist == c);
       handlerlist = c->next;
+      redisplay_deep_handler = old_deep;
       return val;
     }
 }
@@ -1701,6 +1714,11 @@ quit (void)
   return signal_or_quit (Qquit, Qnil, true);
 }
 
+/* Has an error in redisplay giving rise to a backtrace occurred as
+   yet in the current command?  This gets reset in the command
+   loop.  */
+bool backtrace_yet = false;
+
 /* Signal an error, or quit.  ERROR_SYMBOL and DATA are as with Fsignal.
    If KEYBOARD_QUIT, this is a quit; ERROR_SYMBOL should be
    Qquit and DATA should be Qnil, and this function may return.
@@ -1816,6 +1834,40 @@ signal_or_quit (Lisp_Object error_symbol, Lisp_Object data, bool keyboard_quit)
       unbind_to (count, Qnil);
     }
 
+  /* If an error is signalled during a Lisp hook in redisplay, write a
+     backtrace into the buffer *Redisplay-trace*.  */
+  if (!debugger_called && !NILP (error_symbol)
+      && backtrace_on_redisplay_error
+      && (NILP (clause) || h == redisplay_deep_handler)
+      && NILP (Vinhibit_debugger)
+      && !NILP (Ffboundp (Qdebug_early)))
+    {
+      max_ensure_room (&max_lisp_eval_depth, lisp_eval_depth, 100);
+      specpdl_ref count = SPECPDL_INDEX ();
+      ptrdiff_t counti = specpdl_ref_to_count (count);
+      AUTO_STRING (redisplay_trace, "*Redisplay_trace*");
+      Lisp_Object redisplay_trace_buffer;
+      AUTO_STRING (gap, "\n\n\n\n"); /* Separates things in *Redisplay-trace* */
+      Lisp_Object delayed_warning;
+      max_ensure_room (&max_specpdl_size, counti, 200);
+      redisplay_trace_buffer = Fget_buffer_create (redisplay_trace, Qnil);
+      current_buffer = XBUFFER (redisplay_trace_buffer);
+      if (!backtrace_yet) /* Are we on the first backtrace of the command?  */
+        Ferase_buffer ();
+      else
+        Finsert (1, &gap);
+      backtrace_yet = true;
+      specbind (Qstandard_output, redisplay_trace_buffer);
+      specbind (Qdebugger, Qdebug_early);
+      call_debugger (list2 (Qerror, Fcons (error_symbol, data)));
+      unbind_to (count, Qnil);
+      delayed_warning = make_string
+        ("Error in a redisplay Lisp hook.  See buffer *Redisplay_trace*", 61);
+
+      Vdelayed_warnings_list = Fcons (list2 (Qerror, delayed_warning),
+                                      Vdelayed_warnings_list);
+    }
+
   if (!NILP (clause))
     {
       Lisp_Object unwind_data
@@ -4278,6 +4330,11 @@ Does not apply if quit is handled by a `condition-case'.  */);
   DEFVAR_BOOL ("debug-on-next-call", debug_on_next_call,
                doc: /* Non-nil means enter debugger before next `eval', `apply' or `funcall'.  */);
 
+  DEFVAR_BOOL ("backtrace-on-redisplay-error", backtrace_on_redisplay_error,
+               doc: /* Non-nil means create a backtrace if a lisp error occurs in redisplay.
+The backtrace is written to buffer *Redisplay-trace*.  */);
+  backtrace_on_redisplay_error = false;
+
   DEFVAR_BOOL ("debugger-may-continue", debugger_may_continue,
                doc: /* Non-nil means debugger may continue execution.
 This is nil when the debugger is called under circumstances where it
diff --git a/src/ftcrfont.c b/src/ftcrfont.c
index 119ec284094..e089f9dea85 100644
--- a/src/ftcrfont.c
+++ b/src/ftcrfont.c
@@ -677,7 +677,11 @@ ftcrhbfont_begin_hb_font (struct font *font, double *position_unit)
 
   ftcrfont_info->ft_size = ft_face->size;
   hb_font_t *hb_font = fthbfont_begin_hb_font (font, position_unit);
-  if (ftcrfont_info->bitmap_position_unit)
+  /* HarfBuzz 5 correctly scales bitmap-only fonts without position
+     unit adjustment.
+     (https://github.com/harfbuzz/harfbuzz/issues/489) */
+  if (!hb_version_atleast (5, 0, 0)
+      && ftcrfont_info->bitmap_position_unit)
     *position_unit = ftcrfont_info->bitmap_position_unit;
 
   return hb_font;
diff --git a/src/indent.c b/src/indent.c
index d2dfaee254e..cb368024d97 100644
--- a/src/indent.c
+++ b/src/indent.c
@@ -306,8 +306,8 @@ and point (e.g., control characters will have a width of 2 or 4, tabs
 will have a variable width).
 Ignores finite width of frame, which means that this function may return
 values greater than (frame-width).
-In a buffer with very long lines, the value can be zero, because calculating
-the exact number is very expensive.
+In a buffer with very long lines, the value will be an approximation,
+because calculating the exact number is very expensive.
 Whether the line is visible (if `selective-display' is t) has no effect;
 however, ^M is treated as end of line when `selective-display' is t.
 Text that has an invisible property is considered as having width 0, unless
@@ -316,8 +316,6 @@ Text that has an invisible property is considered as having width 0, unless
 {
   Lisp_Object temp;
 
-  if (current_buffer->long_line_optimizations_p)
-    return make_fixnum (0);
   XSETFASTINT (temp, current_column ());
   return temp;
 }
@@ -346,6 +344,14 @@ current_column (void)
       && MODIFF == last_known_column_modified)
     return last_known_column;
 
+  ptrdiff_t line_beg = find_newline (PT, PT_BYTE, BEGV, BEGV_BYTE, -1,
+                                     NULL, NULL, 1);
+
+  /* Avoid becoming abysmally slow for very long lines.  */
+  if (current_buffer->long_line_optimizations_p
+      && !NILP (Vlong_line_threshold)
+      && PT - line_beg > XFIXNUM (Vlong_line_threshold))
+    return PT - line_beg;       /* this is an approximation! */
   /* If the buffer has overlays, text properties,
      or multibyte characters, use a more general algorithm.  */
   if (buffer_intervals (current_buffer)
@@ -561,13 +567,53 @@ scan_for_column (ptrdiff_t *endpos, EMACS_INT *goalcol,
   ptrdiff_t scan, scan_byte, next_boundary, prev_pos, prev_bpos;
 
   scan = find_newline (PT, PT_BYTE, BEGV, BEGV_BYTE, -1, NULL, &scan_byte, 1);
-  next_boundary = scan;
-  prev_pos = scan;
-  prev_bpos = scan_byte;
 
   window = Fget_buffer_window (Fcurrent_buffer (), Qnil);
   w = ! NILP (window) ? XWINDOW (window) : NULL;
 
+  if (current_buffer->long_line_optimizations_p)
+    {
+      bool lines_truncated = false;
+
+      if (!NILP (BVAR (current_buffer, truncate_lines)))
+        lines_truncated = true;
+      else if (w && FIXNUMP (Vtruncate_partial_width_windows))
+        lines_truncated =
+          w->total_cols < XFIXNAT (Vtruncate_partial_width_windows);
+      else if (w && !NILP (Vtruncate_partial_width_windows))
+        lines_truncated =
+          w->total_cols < FRAME_COLS (XFRAME (WINDOW_FRAME (w)));
+      /* Special optimization for buffers with long and truncated
+         lines: assumes that each character is a single column.  */
+      if (lines_truncated)
+        {
+          ptrdiff_t bolpos = scan;
+          /* The newline which ends this line or ZV.  */
+          ptrdiff_t eolpos =
+            find_newline (PT, PT_BYTE, ZV, ZV_BYTE, 1, NULL, NULL, 1);
+
+          scan = bolpos + goal;
+          if (scan > end)
+            scan = end;
+          if (scan > eolpos)
+            scan = (eolpos == ZV ? ZV : eolpos - 1);
+          col = scan - bolpos;
+          if (col > large_hscroll_threshold)
+            {
+              prev_col = col - 1;
+              prev_pos = scan - 1;
+              prev_bpos = CHAR_TO_BYTE (scan);
+              goto endloop;
+            }
+          /* Restore the values we've overwritten above.  */
+          scan = bolpos;
+          col = 0;
+        }
+    }
+  next_boundary = scan;
+  prev_pos = scan;
+  prev_bpos = scan_byte;
+
   memset (&cmp_it, 0, sizeof cmp_it);
   cmp_it.id = -1;
   composition_compute_stop_pos (&cmp_it, scan, scan_byte, end, Qnil);
diff --git a/src/keyboard.c b/src/keyboard.c
index 4ad6e4e6bd1..8a2b7d58c4b 100644
--- a/src/keyboard.c
+++ b/src/keyboard.c
@@ -1331,6 +1331,7 @@ command_loop_1 (void)
         display_malloc_warning ();
 
       Vdeactivate_mark = Qnil;
+      backtrace_yet = false;
 
       /* Don't ignore mouse movements for more than a single command
          loop.  (This flag is set in xdisp.c whenever the tool bar is
@@ -1841,7 +1842,7 @@ safe_run_hooks_1 (ptrdiff_t nargs, Lisp_Object *args)
 static Lisp_Object
 safe_run_hooks_error (Lisp_Object error, ptrdiff_t nargs, Lisp_Object *args)
 {
-  eassert (nargs == 2);
+  eassert (nargs >= 2 && nargs <= 4);
   AUTO_STRING (format, "Error in %s (%S): %S");
   Lisp_Object hook = args[0];
   Lisp_Object fun = args[1];
@@ -1915,6 +1916,17 @@ safe_run_hooks_maybe_narrowed (Lisp_Object hook, struct window *w)
   unbind_to (count, Qnil);
 }
 
+void
+safe_run_hooks_2 (Lisp_Object hook, Lisp_Object arg1, Lisp_Object arg2)
+{
+  specpdl_ref count = SPECPDL_INDEX ();
+
+  specbind (Qinhibit_quit, Qt);
+  run_hook_with_args (4, ((Lisp_Object []) {hook, hook, arg1, arg2}),
+                      safe_run_hook_funcall);
+  unbind_to (count, Qnil);
+}
+
 
 /* Nonzero means polling for input is temporarily suppressed.  */
 
@@ -12638,10 +12650,17 @@ cancels any modification.  */);
 
   DEFSYM (Qdeactivate_mark, "deactivate-mark");
   DEFVAR_LISP ("deactivate-mark", Vdeactivate_mark,
-               doc: /* If an editing command sets this to t, deactivate the mark afterward.
+    doc: /* Whether to deactivate the mark after an editing command.
 The command loop sets this to nil before each command,
 and tests the value when the command returns.
-Buffer modification stores t in this variable.  */);
+If an editing command sets this non-nil, deactivate the mark after
+the command returns.
+
+Buffer modifications store t in this variable.
+
+By default, deactivating the mark will save the contents of the region
+according to `select-active-regions', unless this is set to the symbol
+`dont-save'.  */);
   Vdeactivate_mark = Qnil;
   Fmake_variable_buffer_local (Qdeactivate_mark);
 
diff --git a/src/lisp.h b/src/lisp.h
index fe6e98843d1..2f73ba4c617 100644
--- a/src/lisp.h
+++ b/src/lisp.h
@@ -4530,6 +4530,7 @@ extern Lisp_Object Vrun_hooks;
 extern Lisp_Object Vsignaling_function;
 extern Lisp_Object inhibit_lisp_code;
 extern bool signal_quit_p (Lisp_Object);
+extern bool backtrace_yet;
 
 /* To run a normal hook, use the appropriate function from the list below.
    The calling convention:
@@ -4831,6 +4832,7 @@ extern bool detect_input_pending_ignore_squeezables (void);
 extern bool detect_input_pending_run_timers (bool);
 extern void safe_run_hooks (Lisp_Object);
 extern void safe_run_hooks_maybe_narrowed (Lisp_Object, struct window *);
+extern void safe_run_hooks_2 (Lisp_Object, Lisp_Object, Lisp_Object);
 extern void cmd_error_internal (Lisp_Object, const char *);
 extern Lisp_Object command_loop_2 (Lisp_Object);
 extern Lisp_Object read_menu_command (void);
diff --git a/src/timefns.c b/src/timefns.c
index 1112f174763..eed2edf1cc0 100644
--- a/src/timefns.c
+++ b/src/timefns.c
@@ -401,6 +401,10 @@ decode_float_time (double t, struct lisp_time *result)
   else
     {
       int scale = double_integer_scale (t);
+      /* FIXME: `double_integer_scale` often returns values that are
+         "pessimistic" (i.e. larger than necessary), so 3.5 gets converted
+         to (7881299347898368 . 2251799813685248) rather than (7 . 2).
+         On 64bit systems, this should not matter very much, tho.  */
       eassume (scale < flt_radix_power_size);
 
       if (scale < 0)
@@ -818,17 +822,6 @@ decode_lisp_time (Lisp_Object specified_time, bool decode_secs_only,
 
   if (NILP (specified_time))
     form = TIMEFORM_NIL;
-  else if (FLOATP (specified_time))
-    {
-      double d = XFLOAT_DATA (specified_time);
-      if (!isfinite (d))
-        time_error (isnan (d) ? EDOM : EOVERFLOW);
-      if (result)
-        decode_float_time (d, result);
-      else
-        *dresult = d;
-      return TIMEFORM_FLOAT;
-    }
   else if (CONSP (specified_time))
     {
       high = XCAR (specified_time);
@@ -868,6 +861,22 @@ decode_lisp_time (Lisp_Object specified_time, bool decode_secs_only,
       if (! INTEGERP (low))
         form = TIMEFORM_INVALID;
     }
+  else if (FASTER_TIMEFNS && INTEGERP (specified_time))
+    {
+      decode_ticks_hz (specified_time, make_fixnum (1), result, dresult);
+      return form;
+    }
+  else if (FLOATP (specified_time))
+    {
+      double d = XFLOAT_DATA (specified_time);
+      if (!isfinite (d))
+        time_error (isnan (d) ? EDOM : EOVERFLOW);
+      if (result)
+        decode_float_time (d, result);
+      else
+        *dresult = d;
+      return TIMEFORM_FLOAT;
+    }
 
   int err = decode_time_components (form, high, low, usec, psec,
                                     result, dresult);
@@ -1202,10 +1211,16 @@ time_cmp (Lisp_Object a, Lisp_Object b)
     return 0;
 
   /* Compare (X . Z) to (Y . Z) quickly if X and Y are fixnums.
-     Do not inspect Z, as it is OK to not signal if A and B are invalid.  */
-  if (FASTER_TIMEFNS && CONSP (a) && CONSP (b) && BASE_EQ (XCDR (a), XCDR (b))
-      && FIXNUMP (XCAR (a)) && FIXNUMP (XCAR (b)))
-    return XFIXNUM (XCAR (a)) - XFIXNUM (XCAR (b));
+     Do not inspect Z, as it is OK to not signal if A and B are invalid.
+     Also, compare X to Y quickly if X and Y are fixnums.  */
+  if (FASTER_TIMEFNS)
+    {
+      Lisp_Object x = a, y = b;
+      if (CONSP (a) && CONSP (b) && BASE_EQ (XCDR (a), XCDR (b)))
+        x = XCAR (a), y = XCAR (b);
+      if (FIXNUMP (x) && FIXNUMP (y))
+        return XFIXNUM (x) - XFIXNUM (y);
+    }
 
   /* Compare (ATICKS . AZ) to (BTICKS . BHZ) by comparing
      ATICKS * BHZ to BTICKS * AHZ.  */
@@ -1714,21 +1729,29 @@ usage: (encode-time TIME &rest OBSOLESCENT-ARGUMENTS)  */)
 }
 
 DEFUN ("time-convert", Ftime_convert, Stime_convert, 1, 2, 0,
-       doc: /* Convert TIME value to a Lisp timestamp.
-With optional FORM, convert to that timestamp form.
+       doc: /* Convert TIME value to a Lisp timestamp of the given FORM.
 Truncate the returned value toward minus infinity.
 
-If FORM is nil (the default), return the same form as `current-time'.
 If FORM is a positive integer, return a pair of integers (TICKS . FORM),
 where TICKS is the number of clock ticks and FORM is the clock frequency
-in ticks per second.  If FORM is t, return (TICKS . PHZ), where
-PHZ is a suitable clock frequency in ticks per second.  If FORM is
-`integer', return an integer count of seconds.  If FORM is `list',
-return an integer list (HIGH LOW USEC PSEC), where HIGH has the most
-significant bits of the seconds, LOW has the least significant 16
-bits, and USEC and PSEC are the microsecond and picosecond counts.  */)
+in ticks per second.
+
+If FORM is t, return (TICKS . PHZ), where PHZ is a suitable clock
+frequency in ticks per second.
+
+If FORM is `integer', return an integer count of seconds.
+
+If FORM is `list', return an integer list (HIGH LOW USEC PSEC), where
+HIGH has the most significant bits of the seconds, LOW has the least
+significant 16 bits, and USEC and PSEC are the microsecond and
+picosecond counts.
+
+If FORM is nil, the behavior depends on `current-time-list',
+but new code should not rely on it.  */)
      (Lisp_Object time, Lisp_Object form)
 {
+  /* FIXME: Any reason why we don't offer a `float` output format option as
+     well, since we accept it as input?  */
   struct lisp_time t;
   enum timeform input_form = decode_lisp_time (time, false, &t, 0);
   if (NILP (form))
diff --git a/src/window.c b/src/window.c
index afb8f75537b..c8fcb3a607f 100644
--- a/src/window.c
+++ b/src/window.c
@@ -6575,9 +6575,12 @@ and redisplay normally--don't erase and redraw the frame.  */)
      in case scroll_margin is buffer-local.  */
   this_scroll_margin = window_scroll_margin (w, MARGIN_IN_LINES);
 
-  /* Don't use redisplay code for initial frames, as the necessary
-     data structures might not be set up yet then.  */
-  if (!FRAME_INITIAL_P (XFRAME (w->frame)))
+  /* Don't use the display code for initial frames, as the necessary
+     data structures might not be set up yet then.  Also don't use it
+     for buffers with very long lines, as it tremdously slows down
+     redisplay, especially when lines are truncated.  */
+  if (!FRAME_INITIAL_P (XFRAME (w->frame))
+      && !current_buffer->long_line_optimizations_p)
     {
       specpdl_ref count = SPECPDL_INDEX ();
 
diff --git a/src/xdisp.c b/src/xdisp.c
index 1fcff2c2e3b..1e8f70b2db9 100644
--- a/src/xdisp.c
+++ b/src/xdisp.c
@@ -11040,6 +11040,15 @@ move_it_by_lines (struct it *it, ptrdiff_t dvpos)
 int
 partial_line_height (struct it *it_origin)
 {
+  /* In a buffer with very long and truncated lines, we ignore the
+     possibly-partial height of the last line in the window: it is too
+     expensive to compute that (since in most cases that involves
+     going all the way to ZV), and the effect of ignoring it is
+     relatively minor.  */
+  if (XBUFFER (it_origin->w->contents)->long_line_optimizations_p
+      && it_origin->line_wrap == TRUNCATE)
+    return 0;
+
   int partial_height;
   void *it_data = NULL;
   struct it it;
@@ -11063,6 +11072,51 @@ partial_line_height (struct it *it_origin)
   return partial_height;
 }
 
+/* Approximate move_it_in_display_line_to for very long and truncated
+   display lines, when moving horizontally.  This is used when the
+   buffer's long_line_optimizations_p flag is set.  It ignores various
+   complications, like different font sizes, invisible text, display
+   and overlay strings, and, to some degree, bidirectional text.  So
+   caveat emptor!
+
+   Starting from IT's position, reseat IT after skipping NCHARS
+   characters or to the next newline/ZV, whichever comes first.  Return
+   what move_it_in_display_line_to would have returned in this case.  */
+
+static enum move_it_result
+fast_move_it_horizontally (struct it *it, ptrdiff_t nchars)
+{
+  ptrdiff_t nl_bytepos;
+  ptrdiff_t nl_pos = find_newline_no_quit (IT_CHARPOS (*it), IT_BYTEPOS (*it),
+                                           1, &nl_bytepos);
+  struct text_pos new_pos;
+  enum move_it_result move_result;
+
+  if (nl_pos - IT_CHARPOS (*it) > nchars)
+    {
+      SET_TEXT_POS (new_pos,
+                    IT_CHARPOS (*it) + nchars,
+                    CHAR_TO_BYTE (IT_CHARPOS (*it) + nchars));
+      move_result = MOVE_X_REACHED;
+    }
+  else
+    {
+      if (nl_bytepos < ZV_BYTE
+          || (nl_bytepos > BEGV_BYTE
+              && FETCH_BYTE (nl_bytepos - 1) == '\n'))
+        {
+          nl_pos--;
+          nl_bytepos--;
+          move_result = MOVE_NEWLINE_OR_CR;
+        }
+      else
+        move_result = MOVE_POS_MATCH_OR_ZV;
+      SET_TEXT_POS (new_pos, nl_pos, nl_bytepos);
+    }
+  reseat (it, new_pos, false);
+  return move_result;
+}
+
 /* Return true if IT points into the middle of a display vector.  */
 
 bool
@@ -13106,8 +13160,7 @@ mode_line_update_needed (struct window *w)
 {
   return (w->column_number_displayed != -1
           && !(PT == w->last_point && !window_outdated (w))
-          && (!current_buffer->long_line_optimizations_p
-              && w->column_number_displayed != current_column ()));
+          && (w->column_number_displayed != current_column ()));
 }
 
 /* True if window start of W is frozen and may not be changed during
@@ -15776,7 +15829,20 @@ hscroll_window_tree (Lisp_Object window)
                 it.first_visible_x = window_hscroll_limited (w, it.f)
                                      * FRAME_COLUMN_WIDTH (it.f);
               it.last_visible_x = DISP_INFINITY;
-              move_it_in_display_line_to (&it, pt, -1, MOVE_TO_POS);
+
+              ptrdiff_t nchars = pt - IT_CHARPOS (it);
+              if (current_buffer->long_line_optimizations_p
+                  && nchars > large_hscroll_threshold)
+                {
+                  /* Special optimization for very long and truncated
+                     lines which need to be hscrolled far to the left:
+                     jump directly to the (approximate) first position
+                     that is visible, instead of slowly walking there.  */
+                  fast_move_it_horizontally (&it, nchars);
+                  it.current_x += nchars * FRAME_COLUMN_WIDTH (it.f);
+                }
+              else
+                move_it_in_display_line_to (&it, pt, -1, MOVE_TO_POS);
               /* If the line ends in an overlay string with a newline,
                  we might infloop, because displaying the window will
                  want to put the cursor after the overlay, i.e. at X
@@ -15789,7 +15855,14 @@ hscroll_window_tree (Lisp_Object window)
                   if (hscl)
                     it.first_visible_x = (window_hscroll_limited (w, it.f)
                                           * FRAME_COLUMN_WIDTH (it.f));
-                  move_it_in_display_line_to (&it, pt - 1, -1, MOVE_TO_POS);
+                  if (current_buffer->long_line_optimizations_p
+                      && nchars > large_hscroll_threshold)
+                    {
+                      fast_move_it_horizontally (&it, nchars - 1);
+                      it.current_x += (nchars - 1) * FRAME_COLUMN_WIDTH (it.f);
+                    }
+                  else
+                    move_it_in_display_line_to (&it, pt - 1, -1, MOVE_TO_POS);
                 }
               current_buffer = saved_current_buffer;
 
@@ -16727,9 +16800,23 @@ redisplay_internal (void)
           it.current_y = this_line_y;
           it.vpos = this_line_vpos;
 
-          /* The call to move_it_to stops in front of PT, but
-             moves over before-strings.  */
-          move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
+          if (current_buffer->long_line_optimizations_p
+              && it.line_wrap == TRUNCATE
+              && PT - CHARPOS (tlbufpos) > large_hscroll_threshold)
+            {
+              /* When lines are very long and truncated, jumping to
+                 the next visible line is much faster than slowly
+                 iterating there.  */
+              reseat_at_next_visible_line_start (&it, false);
+              if (IT_CHARPOS (it) <= PT) /* point moved off this line */
+                it.vpos = this_line_vpos + 1;
+            }
+          else
+            {
+              /* The call to move_it_to stops in front of PT, but
+                 moves over before-strings.  */
+              move_it_to (&it, PT, -1, -1, -1, MOVE_TO_POS);
+            }
 
           if (it.vpos == this_line_vpos
               && (row = MATRIX_ROW (w->current_matrix, this_line_vpos),
@@ -18119,8 +18206,8 @@ run_window_scroll_functions (Lisp_Object window, struct text_pos startp)
     {
       specpdl_ref count = SPECPDL_INDEX ();
       specbind (Qinhibit_quit, Qt);
-      run_hook_with_args_2 (Qwindow_scroll_functions, window,
-                            make_fixnum (CHARPOS (startp)));
+      safe_run_hooks_2
+        (Qwindow_scroll_functions, window, make_fixnum (CHARPOS (startp)));
       unbind_to (count, Qnil);
       SET_TEXT_POS_FROM_MARKER (startp, w->start);
       /* In case the hook functions switch buffers.  */
@@ -19229,6 +19316,16 @@ window_start_acceptable_p (Lisp_Object window, ptrdiff_t startp)
   return true;
 }
 
+DEFUN ("long-line-optimizations-p", Flong_line_optimizations_p, Slong_line_optimizations_p,
+       0, 0, 0,
+       doc: /* Return non-nil if long-line optimizations are in effect in current buffer.
+See `long-line-threshold' and `large-hscroll-threshold' for what these
+optimizations mean and when they are in effect.  */)
+  (void)
+{
+  return current_buffer->long_line_optimizations_p ? Qt : Qnil;
+}
+
 /* Redisplay leaf window WINDOW.  JUST_THIS_ONE_P means only
    selected_window is redisplayed.
 
@@ -19504,33 +19601,36 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
       ptrdiff_t it_charpos;
 
       w->optional_new_start = false;
-      start_display (&it, w, startp);
-      move_it_to (&it, PT, 0, it.last_visible_y, -1,
-                  MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
-      /* Record IT's position now, since line_bottom_y might change
-         that.  */
-      it_charpos = IT_CHARPOS (it);
-      /* Make sure we set the force_start flag only if the cursor row
-         will be fully visible.  Otherwise, the code under force_start
-         label below will try to move point back into view, which is
-         not what the code which sets optional_new_start wants.  */
-      if ((it.current_y == 0 || line_bottom_y (&it) < it.last_visible_y)
-          && !w->force_start)
-        {
-          if (it_charpos == PT)
-            w->force_start = true;
-          /* IT may overshoot PT if text at PT is invisible.  */
-          else if (it_charpos > PT && CHARPOS (startp) <= PT)
-            w->force_start = true;
+      if (!w->force_start)
+        {
+          start_display (&it, w, startp);
+          move_it_to (&it, PT, 0, it.last_visible_y, -1,
+                      MOVE_TO_POS | MOVE_TO_X | MOVE_TO_Y);
+          /* Record IT's position now, since line_bottom_y might
+             change that.  */
+          it_charpos = IT_CHARPOS (it);
+          /* Make sure we set the force_start flag only if the cursor
+             row will be fully visible.  Otherwise, the code under
+             force_start label below will try to move point back into
+             view, which is not what the code which sets
+             optional_new_start wants.  */
+          if (it.current_y == 0 || line_bottom_y (&it) < it.last_visible_y)
+            {
+              if (it_charpos == PT)
+                w->force_start = true;
+              /* IT may overshoot PT if text at PT is invisible.  */
+              else if (it_charpos > PT && CHARPOS (startp) <= PT)
+                w->force_start = true;
 #ifdef GLYPH_DEBUG
-          if (w->force_start)
-            {
-              if (window_frozen_p (w))
-                debug_method_add (w, "set force_start from frozen window start");
-              else
-                debug_method_add (w, "set force_start from optional_new_start");
-            }
+              if (w->force_start)
+                {
+                  if (window_frozen_p (w))
+                    debug_method_add (w, "set force_start from frozen window start");
+                  else
+                    debug_method_add (w, "set force_start from optional_new_start");
+                }
 #endif
+            }
         }
     }
 
@@ -20256,7 +20356,6 @@ redisplay_window (Lisp_Object window, bool just_this_one_p)
        || w->base_line_pos > 0
        /* Column number is displayed and different from the one displayed.  */
        || (w->column_number_displayed != -1
-           && !current_buffer->long_line_optimizations_p
            && (w->column_number_displayed != current_column ())))
       /* This means that the window has a mode line.  */
       && (window_wants_mode_line (w)
@@ -24496,8 +24595,26 @@ display_line (struct it *it, int cursor_vpos)
           it->first_visible_x += x_incr;
           it->last_visible_x  += x_incr;
         }
-      move_result = move_it_in_display_line_to (it, ZV, it->first_visible_x,
-                                                MOVE_TO_POS | MOVE_TO_X);
+      if (current_buffer->long_line_optimizations_p
+          && it->line_wrap == TRUNCATE
+          && window_hscroll_limited (it->w, it->f) > large_hscroll_threshold)
+        {
+          /* Special optimization for very long and truncated lines
+             which are hscrolled far to the left: jump directly to the
+             (approximate) position that is visible, instead of slowly
+             walking there.  */
+          ptrdiff_t chars_to_skip =
+            it->first_visible_x / FRAME_COLUMN_WIDTH (it->f);
+          move_result = fast_move_it_horizontally (it, chars_to_skip);
+
+          if (move_result == MOVE_X_REACHED)
+            it->current_x = it->first_visible_x;
+          else  /* use arbitrary value < first_visible_x */
+            it->current_x = it->first_visible_x - FRAME_COLUMN_WIDTH (it->f);
+        }
+      else
+        move_result = move_it_in_display_line_to (it, ZV, it->first_visible_x,
+                                                  MOVE_TO_POS | MOVE_TO_X);
       /* If we are under a large hscroll, move_it_in_display_line_to
          could hit the end of the line without reaching
          first_visible_x.  Pretend that we did reach it.  This is
@@ -27758,17 +27875,6 @@ decode_mode_spec (struct window *w, register int c, int field_width,
          even crash emacs.)  */
       if (mode_line_target == MODE_LINE_TITLE)
         return "";
-      else if (b->long_line_optimizations_p)
-        {
-          char *p = decode_mode_spec_buf;
-          int pad = width - 2;
-          while (pad-- > 0)
-            *p++ = ' ';
-          *p++ = '?';
-          *p++ = '?';
-          *p = '\0';
-          return decode_mode_spec_buf;
-        }
       else
         {
           ptrdiff_t col = current_column ();
@@ -36112,6 +36218,7 @@ be let-bound around code that needs to disable messages temporarily. */);
   defsubr (&Sbidi_find_overridden_directionality);
   defsubr (&Sdisplay__line_is_continued_p);
   defsubr (&Sget_display_property);
+  defsubr (&Slong_line_optimizations_p);
 
   DEFSYM (Qmenu_bar_update_hook, "menu-bar-update-hook");
   DEFSYM (Qoverriding_terminal_local_map, "overriding-terminal-local-map");
diff --git a/src/xfns.c b/src/xfns.c
index 2845ecca6a9..6ed93ee42ca 100644
--- a/src/xfns.c
+++ b/src/xfns.c
@@ -6851,17 +6851,16 @@ The coordinates X and Y are interpreted in pixels relative to a position
 #ifdef HAVE_XINPUT2
   int deviceid;
 
-  if (FRAME_DISPLAY_INFO (f)->supports_xi2)
+  deviceid = FRAME_DISPLAY_INFO (f)->client_pointer_device;
+
+  if (FRAME_DISPLAY_INFO (f)->supports_xi2
+      && deviceid != -1)
     {
-      XGrabServer (FRAME_X_DISPLAY (f));
-      if (XIGetClientPointer (FRAME_X_DISPLAY (f), FRAME_X_WINDOW (f),
-                              &deviceid))
-        {
-          XIWarpPointer (FRAME_X_DISPLAY (f), deviceid, None,
-                         FRAME_DISPLAY_INFO (f)->root_window,
-                         0, 0, 0, 0, xval, yval);
-        }
-      XUngrabServer (FRAME_X_DISPLAY (f));
+      x_catch_errors_for_lisp (FRAME_DISPLAY_INFO (f));
+      XIWarpPointer (FRAME_X_DISPLAY (f), deviceid, None,
+                     FRAME_DISPLAY_INFO (f)->root_window,
+                     0, 0, 0, 0, xval, yval);
+      x_uncatch_errors_for_lisp (FRAME_DISPLAY_INFO (f));
     }
   else
 #endif
diff --git a/src/xterm.c b/src/xterm.c
index ab43a8ec517..5047f3066be 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1398,6 +1398,15 @@ static int x_dnd_last_tooltip_x, x_dnd_last_tooltip_y;
 /* Whether or not those values are actually known yet.  */
 static bool x_dnd_last_tooltip_valid;
 
+#ifdef HAVE_XINPUT2
+/* The master pointer device being used for the drag-and-drop
+   operation.  */
+static int x_dnd_pointer_device;
+
+/* The keyboard device attached to that pointer device.  */
+static int x_dnd_keyboard_device;
+#endif
+
 /* Structure describing a single window that can be the target of
    drag-and-drop operations.  */
 struct x_client_list_window
@@ -4705,6 +4714,67 @@ x_restore_events_after_dnd (struct frame *f, XWindowAttributes *wa)
                      dpyinfo->Xatom_XdndTypeList);
 }
 
+#ifdef HAVE_XINPUT2
+
+/* Cancel the current drag-and-drop operation, sending leave messages
+   to any relevant toplevels.  This is called from the event loop when
+   an event is received telling Emacs to gracefully cancel the
+   drag-and-drop operation.  */
+
+static void
+x_dnd_cancel_dnd_early (void)
+{
+  struct frame *f;
+  xm_drop_start_message dmsg;
+
+  eassert (x_dnd_frame && x_dnd_in_progress);
+
+  f = x_dnd_frame;
+
+  if (x_dnd_last_seen_window != None
+      && x_dnd_last_protocol_version != -1)
+    x_dnd_send_leave (x_dnd_frame,
+                      x_dnd_last_seen_window);
+  else if (x_dnd_last_seen_window != None
+           && !XM_DRAG_STYLE_IS_DROP_ONLY (x_dnd_last_motif_style)
+           && x_dnd_last_motif_style != XM_DRAG_STYLE_NONE
+           && x_dnd_motif_setup_p)
+    {
+      dmsg.reason = XM_DRAG_REASON (XM_DRAG_ORIGINATOR_INITIATOR,
+                                    XM_DRAG_REASON_DROP_START);
+      dmsg.byte_order = XM_BYTE_ORDER_CUR_FIRST;
+      dmsg.timestamp = FRAME_DISPLAY_INFO (f)->last_user_time;
+      dmsg.side_effects
+        = XM_DRAG_SIDE_EFFECT (xm_side_effect_from_action (FRAME_DISPLAY_INFO (f),
+                                                           x_dnd_wanted_action),
+                               XM_DROP_SITE_VALID, x_dnd_motif_operations,
+                               XM_DROP_ACTION_DROP_CANCEL);
+      dmsg.x = 0;
+      dmsg.y = 0;
+      dmsg.index_atom = x_dnd_motif_atom;
+      dmsg.source_window = FRAME_X_WINDOW (f);
+
+      x_dnd_send_xm_leave_for_drop (FRAME_DISPLAY_INFO (f), f,
+                                    x_dnd_last_seen_window,
+                                    FRAME_DISPLAY_INFO (f)->last_user_time);
+      xm_send_drop_message (FRAME_DISPLAY_INFO (f), FRAME_X_WINDOW (f),
+                            x_dnd_last_seen_window, &dmsg);
+    }
+
+  x_dnd_last_seen_window = None;
+  x_dnd_last_seen_toplevel = None;
+  x_dnd_in_progress = false;
+  x_dnd_waiting_for_finish = false;
+  x_dnd_return_frame_object = NULL;
+  x_dnd_movement_frame = NULL;
+  x_dnd_wheel_frame = NULL;
+  x_dnd_frame = NULL;
+  x_dnd_action = None;
+  x_dnd_action_symbol = Qnil;
+}
+
+#endif
+
 static void
 x_dnd_cleanup_drag_and_drop (void *frame)
 {
@@ -11909,6 +11979,9 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, Atom xaction,
   struct x_display_info *event_display;
 #endif
   unsigned int additional_mask;
+#ifdef HAVE_XINPUT2
+  struct xi_device_t *device;
+#endif
 
   base = SPECPDL_INDEX ();
 
@@ -12089,6 +12162,33 @@ x_dnd_begin_drag_and_drop (struct frame *f, Time time, Atom xaction,
   x_dnd_wheel_frame = NULL;
   x_dnd_init_type_lists = false;
   x_dnd_need_send_drop = false;
+
+#ifdef HAVE_XINPUT2
+
+  if (FRAME_DISPLAY_INFO (f)->supports_xi2)
+    {
+      /* Only accept input from the last master pointer to have interacted
+         with Emacs.  This prevents another pointer device getting our
+         idea of the button state messed up.  */
+      if (FRAME_DISPLAY_INFO (f)->client_pointer_device != -1)
+        x_dnd_pointer_device
+          = FRAME_DISPLAY_INFO (f)->client_pointer_device;
+      else
+        /* This returns Bool but cannot actually fail.  */
+        XIGetClientPointer (FRAME_X_DISPLAY (f), None,
+                            &x_dnd_pointer_device);
+
+      x_dnd_keyboard_device = -1;
+
+      device = xi_device_from_id (FRAME_DISPLAY_INFO (f),
+                                  x_dnd_pointer_device);
+
+      if (device)
+        x_dnd_keyboard_device = device->attachment;
+    }
+
+#endif
+
 #ifdef HAVE_XKB
   x_dnd_keyboard_state = 0;
 
@@ -12882,6 +12982,13 @@ xi_disable_devices (struct x_display_info *dpyinfo,
         {
           if (to_disable[j] == dpyinfo->devices[i].device_id)
             {
+              if (x_dnd_in_progress
+                  /* If the drag-and-drop pointer device is being
+                     disabled, then cancel the drag and drop
+                     operation.  */
+                  && to_disable[j] == x_dnd_pointer_device)
+                x_dnd_cancel_dnd_early ();
+
               /* Free any scroll valuators that might be on this
                  device.  */
 #ifdef HAVE_XINPUT2_1
@@ -14164,11 +14271,13 @@ x_send_scroll_bar_event (Lisp_Object window, enum scroll_bar_part part,
   ev->window = FRAME_X_WINDOW (f);
   ev->format = 32;
 
-  /* A 32-bit X client on a 64-bit X server can pass a window pointer
-     as-is.  A 64-bit client on a 32-bit X server is in trouble
-     because a pointer does not fit and would be truncated while
-     passing through the server.  So use two slots and hope that X12
-     will resolve such issues someday.  */
+  /* A 32-bit X client can pass a window pointer through the X server
+     as-is.
+
+     A 64-bit client is in trouble because a pointer does not fit in
+     the 32 bits given for ClientMessage data and will be truncated by
+     Xlib.  So use two slots and hope that X12 will resolve such
+     issues someday.  */
   ev->data.l[0] = iw >> 31 >> 1;
   ev->data.l[1] = sign_shift <= 0 ? iw : iw << sign_shift >> sign_shift;
   ev->data.l[2] = part;
@@ -17316,6 +17425,10 @@ handle_one_xevent (struct x_display_info *dpyinfo,
   union buffered_input_event inev;
   int count = 0;
   int do_help = 0;
+#ifdef HAVE_XINPUT2
+  struct xi_device_t *gen_help_device;
+  Time gen_help_time;
+#endif
   ptrdiff_t nbytes = 0;
   struct frame *any, *f = NULL;
   Mouse_HLInfo *hlinfo = &dpyinfo->mouse_highlight;
@@ -17345,6 +17458,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
   EVENT_INIT (inev.ie);
   inev.ie.kind = NO_EVENT;
   inev.ie.arg = Qnil;
+#ifdef HAVE_XINPUT2
+  gen_help_device = NULL;
+#endif
 
   /* Ignore events coming from various extensions, such as XFIXES and
      XKB.  */
@@ -17870,6 +17986,12 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       if (!x_window_to_frame (dpyinfo, event->xselection.requestor))
         goto OTHER;
 #endif /* not USE_X_TOOLKIT and not USE_GTK */
+#ifdef HAVE_GTK3
+      /* GTK 3 apparently chokes on these events since they have no
+         associated device.  (bug#56869, another bug as well that I
+         can't find) */
+      *finish = X_EVENT_DROP;
+#endif
       x_handle_selection_notify (&event->xselection);
       break;
 
@@ -17878,6 +18000,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       if (!x_window_to_frame (dpyinfo, event->xselectionclear.window))
         goto OTHER;
 #endif /* not USE_X_TOOLKIT and not USE_GTK */
+#ifdef HAVE_GTK3
+      *finish = X_EVENT_DROP;
+#endif
       {
         const XSelectionClearEvent *eventp = &event->xselectionclear;
 
@@ -17904,6 +18029,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       if (!x_window_to_frame (dpyinfo, event->xselectionrequest.owner))
         goto OTHER;
 #endif /* USE_X_TOOLKIT */
+#ifdef HAVE_GTK3
+      *finish = X_EVENT_DROP;
+#endif
       {
         const XSelectionRequestEvent *eventp = &event->xselectionrequest;
 
@@ -18446,6 +18574,11 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 #endif
 
       if (x_dnd_in_progress
+          /* When _NET_WM_CLIENT_LIST stacking is being used, changes
+             in that property are watched for, and it's not necessary
+             to update the state in response to ordinary window
+             substructure events.  */
+          && !x_dnd_use_toplevels
           && dpyinfo == FRAME_DISPLAY_INFO (x_dnd_frame))
         x_dnd_update_state (dpyinfo, dpyinfo->last_user_time);
 
@@ -20280,6 +20413,11 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 
     case CirculateNotify:
       if (x_dnd_in_progress
+          /* When _NET_WM_CLIENT_LIST stacking is being used, changes
+             in that property are watched for, and it's not necessary
+             to update the state in response to ordinary window
+             substructure events.  */
+          && !x_dnd_use_toplevels
           && dpyinfo == FRAME_DISPLAY_INFO (x_dnd_frame))
         x_dnd_update_state (dpyinfo, dpyinfo->last_user_time);
       goto OTHER;
@@ -20876,6 +21014,12 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                          operation, don't send an event.  We only have
                          to set the user time.  */
                       if (x_dnd_in_progress
+                          /* If another master device moved the
+                             pointer, we should put a wheel event on
+                             the keyboard buffer as usual.  It will be
+                             run once the drag-and-drop operation
+                             completes.  */
+                          && xev->deviceid == x_dnd_pointer_device
                           && (command_loop_level + minibuf_level
                               <= x_dnd_recursion_depth)
                           && dpyinfo == FRAME_DISPLAY_INFO (x_dnd_frame))
@@ -20968,6 +21112,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                      `x-dnd-movement-function`.  */
                   && (command_loop_level + minibuf_level
                       <= x_dnd_recursion_depth)
+                  && xev->deviceid == x_dnd_pointer_device
                   && dpyinfo == FRAME_DISPLAY_INFO (x_dnd_frame))
                 {
                   Window target, toplevel;
@@ -21270,7 +21415,15 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                  has changed, generate a HELP_EVENT.  */
               if (!NILP (help_echo_string)
                   || !NILP (previous_help_echo_string))
-                do_help = 1;
+                {
+                  /* Also allow the focus and client pointer to be
+                     adjusted accordingly, in case a help tooltip is
+                     shown.  */
+                  gen_help_device = device;
+                  gen_help_time = xev->time;
+
+                  do_help = 1;
+                }
               goto XI_OTHER;
             }
 
@@ -21294,6 +21447,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
               if (x_dnd_in_progress
                   && (command_loop_level + minibuf_level
                       <= x_dnd_recursion_depth)
+                  && xev->deviceid == x_dnd_pointer_device
                   && dpyinfo == FRAME_DISPLAY_INFO (x_dnd_frame))
                 {
                   f = mouse_or_wdesc_frame (dpyinfo, xev->event);
@@ -21333,6 +21487,10 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                     }
 #endif
 
+                  if (f && device)
+                    xi_handle_interaction (dpyinfo, f, device,
+                                           xev->time);
+
                   if (xev->evtype == XI_ButtonPress
                       && x_dnd_last_seen_window != None)
                     {
@@ -21579,11 +21737,19 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                                               xev->send_event);
 
               source = xi_device_from_id (dpyinfo, xev->sourceid);
+              device = xi_device_from_id (dpyinfo, xev->deviceid);
 
 #ifdef HAVE_XWIDGETS
               xvw = xwidget_view_from_window (xev->event);
               if (xvw)
                 {
+                  /* If the user interacts with a frame that's focused
+                     on another device, but not the current focus
+                     frame, make it the focus frame.  */
+                  if (device)
+                    xi_handle_interaction (dpyinfo, xvw->frame,
+                                           device, xev->time);
+
                   xwidget_button (xvw, xev->evtype == XI_ButtonPress,
                                   lrint (xev->event_x), lrint (xev->event_y),
                                   xev->detail, xi_convert_event_state (xev),
@@ -21603,8 +21769,6 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                 }
 #endif
 
-              device = xi_device_from_id (dpyinfo, xev->deviceid);
-
               if (!device)
                 goto XI_OTHER;
 
@@ -22162,7 +22326,9 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                   inev.ie.modifiers = x_x_to_emacs_modifiers (dpyinfo, state);
 
 #ifdef XK_F1
-                  if (x_dnd_in_progress && keysym == XK_F1)
+                  if (x_dnd_in_progress
+                      && xev->deviceid == x_dnd_keyboard_device
+                      && keysym == XK_F1)
                     {
                       x_dnd_xm_use_help = true;
                       goto xi_done_keysym;
@@ -22426,11 +22592,14 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 
           case XI_HierarchyChanged:
             {
-              XIHierarchyEvent *hev = (XIHierarchyEvent *) xi_event;
+              XIHierarchyEvent *hev;
               XIDeviceInfo *info;
               int i, ndevices, n_disabled, *disabled;
               struct xi_device_t *device;
+              bool any_changed;
 
+              any_changed = false;
+              hev = (XIHierarchyEvent *) xi_event;
               disabled = SAFE_ALLOCA (sizeof *disabled * hev->num_info);
               n_disabled = 0;
 
@@ -22440,8 +22609,17 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                     {
                       /* Handle all disabled devices now, to prevent
                          things happening out-of-order later.  */
-                      xi_disable_devices (dpyinfo, disabled, n_disabled);
-                      n_disabled = 0;
+
+                      if (ndevices)
+                        {
+                          xi_disable_devices (dpyinfo, disabled, n_disabled);
+                          n_disabled = 0;
+
+                          /* This flag really just means that disabled
+                             devices were handled early and should be
+                             used in conjunction with n_disabled.  */
+                          any_changed = true;
+                        }
 
                       x_catch_errors (dpyinfo->display);
                       info = XIQueryDevice (dpyinfo->display, hev->info[i].deviceid,
@@ -22492,9 +22670,12 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                  event.  */
               xi_disable_devices (dpyinfo, disabled, n_disabled);
 
-              /* Now that the device hierarchy has been changed,
-                 recompute focus.  */
-              xi_handle_focus_change (dpyinfo);
+              /* If the device hierarchy has been changed, recompute
+                 focus.  This might seem like a micro-optimization but
+                 it actually keeps the focus from changing in some
+                 cases where it would be undesierable.  */
+              if (any_changed || n_disabled)
+                xi_handle_focus_change (dpyinfo);
 
               goto XI_OTHER;
             }
@@ -23182,6 +23363,12 @@ handle_one_xevent (struct x_display_info *dpyinfo,
       if (do_help > 0)
         {
           any_help_event_p = true;
+#ifdef HAVE_XINPUT2
+          if (gen_help_device)
+            xi_handle_interaction (dpyinfo, f,
+                                   gen_help_device,
+                                   gen_help_time);
+#endif
           gen_help_event (help_echo_string, frame, help_echo_window,
                           help_echo_object, help_echo_pos);
         }
@@ -25947,27 +26134,25 @@ x_set_window_size (struct frame *f, bool change_gravity,
 void
 frame_set_mouse_pixel_position (struct frame *f, int pix_x, int pix_y)
 {
-  block_input ();
 #ifdef HAVE_XINPUT2
   int deviceid;
 
-  if (FRAME_DISPLAY_INFO (f)->supports_xi2)
+  deviceid = FRAME_DISPLAY_INFO (f)->client_pointer_device;
+
+  if (FRAME_DISPLAY_INFO (f)->supports_xi2
+      && deviceid != -1)
     {
-      if (XIGetClientPointer (FRAME_X_DISPLAY (f),
-                              FRAME_X_WINDOW (f),
-                              &deviceid))
-        {
-          x_ignore_errors_for_next_request (FRAME_DISPLAY_INFO (f));
-          XIWarpPointer (FRAME_X_DISPLAY (f), deviceid, None,
-                         FRAME_X_WINDOW (f), 0, 0, 0, 0, pix_x, pix_y);
-          x_stop_ignoring_errors (FRAME_DISPLAY_INFO (f));
-        }
+      block_input ();
+      x_ignore_errors_for_next_request (FRAME_DISPLAY_INFO (f));
+      XIWarpPointer (FRAME_X_DISPLAY (f), deviceid, None,
+                     FRAME_X_WINDOW (f), 0, 0, 0, 0, pix_x, pix_y);
+      x_stop_ignoring_errors (FRAME_DISPLAY_INFO (f));
+      unblock_input ();
     }
   else
 #endif
     XWarpPointer (FRAME_X_DISPLAY (f), None, FRAME_X_WINDOW (f),
                   0, 0, 0, 0, pix_x, pix_y);
-  unblock_input ();
 }
 
 /* Raise frame F.  */
@@ -28955,7 +29140,7 @@ void
 x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
                        Lisp_Object current_owner)
 {
-  Lisp_Object tail, frame, new_owner, tem;
+  Lisp_Object tail, frame, new_owner;
   Time timestamp;
   Window *owners;
   Atom *names;
@@ -28985,7 +29170,7 @@ x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
 
   FOR_EACH_TAIL_SAFE (tail)
     {
-      tem = XCAR (tail);
+      Lisp_Object tem = XCAR (tail);
       ++nowners;
 
       /* The selection is really lost (since we cannot find a new
@@ -29019,7 +29204,7 @@ x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
 
       FOR_EACH_TAIL_SAFE (tail)
         {
-          tem = XCAR (tail);
+          Lisp_Object tem = XCAR (tail);
 
           /* Now check if we still don't own that selection, which can
              happen if another program set itself as the owner.  */
@@ -29039,9 +29224,10 @@ x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
 
       FOR_EACH_TAIL_SAFE (tail)
         {
+          Lisp_Object tem = XCAR (tail);
+
           reply = xcb_get_selection_owner_reply (dpyinfo->xcb_connection,
                                                  cookies[nowners++], &error);
-
           if (reply)
             owners[nowners - 1] = reply->owner;
           else
@@ -29071,7 +29257,7 @@ x_preserve_selections (struct x_display_info *dpyinfo, Lisp_Object lost,
 
       FOR_EACH_TAIL_SAFE (tail)
         {
-          tem = XCAR (tail);
+          Lisp_Object tem = XCAR (tail);
 
           /* If the selection isn't owned by us anymore, note that the
              selection was lost.  */