vim-patch:8.2.4713: plugins cannot track text scrolling

Problem:    Plugins cannot track text scrolling.
Solution:   Add the WinScrolled event. (closes vim/vim#10102)
0937182d49

Skip User event in autocmd.txt, not needed unless #10689 is reverted.

runtime/doc/autocmd.txt

@@ -1084,15 +1084,24 @@ WinLeave			Before leaving a window.  If the window to be
 WinNew				When a new window was created.  Not done for
 				the first window, when Vim has just started.
 				Before WinEnter.
-							*WinScrolled*
-WinScrolled			After scrolling the viewport of the current
-				window.
 
+							*WinScrolled*
+WinScrolled			After scrolling the content of a window or
+				resizing a window.
+				The pattern is matched against the
+				|window-ID|.  Both <amatch> and <afile> are
+				set to the |window-ID|.
+				Non-recursive (the event cannot trigger
+				itself).  However, if the command causes the
+				window to scroll or change size another
+				WinScrolled event will be triggered later.
+				Does not trigger when the command is added,
+				only after the first scroll or resize.
 
 ==============================================================================
 6. Patterns					*autocmd-pattern* *{aupat}*
 
-The {aupat} argument of `:autocmd` can be a comma separated list.  This works
+The {aupat} argument of `:autocmd` can be a comma-separated list.  This works
 as if the command was given with each pattern separately.  Thus this command: >
 	:autocmd BufRead *.txt,*.info set et
 Is equivalent to: >

src/nvim/auevents.lua

@@ -141,6 +141,5 @@ return {
     TermOpen=true,
     UIEnter=true,
     UILeave=true,
-    WinScrolled=true,
   },
 }

src/nvim/autocmd.c

@@ -1092,6 +1092,15 @@ int autocmd_register(int64_t id, event_T event, char_u *pat, int patlen, int gro
       curwin->w_last_cursormoved = curwin->w_cursor;
     }
 
+    // Initialize the fields checked by the WinScrolled trigger to
+    // stop it from firing right after the first autocmd is defined.
+    if (event == EVENT_WINSCROLLED && !has_event(EVENT_WINSCROLLED)) {
+      curwin->w_last_topline = curwin->w_topline;
+      curwin->w_last_leftcol = curwin->w_leftcol;
+      curwin->w_last_width = curwin->w_width;
+      curwin->w_last_height = curwin->w_height;
+    }
+
     ap->cmds = NULL;
     *prev_ap = ap;
     last_autopat[(int)event] = ap;
@@ -1718,7 +1727,7 @@ bool apply_autocmds_group(event_T event, char_u *fname, char_u *fname_io, bool f
         || event == EVENT_REMOTEREPLY || event == EVENT_SPELLFILEMISSING
         || event == EVENT_SYNTAX || event == EVENT_SIGNAL
         || event == EVENT_TABCLOSED || event == EVENT_USER
-        || event == EVENT_WINCLOSED) {
+        || event == EVENT_WINCLOSED || event == EVENT_WINSCROLLED) {
       fname = vim_strsave(fname);
     } else {
       fname = (char_u *)FullName_save((char *)fname, false);

src/nvim/buffer_defs.h

@@ -1269,12 +1269,11 @@ struct window_S {
   colnr_T w_skipcol;                // starting column when a single line
                                     // doesn't fit in the window
 
-  // "w_last_topline" and "w_last_leftcol" are used to determine if
-  // a Scroll autocommand should be emitted.
-  linenr_T w_last_topline;          ///< last known value for topline
-  colnr_T w_last_leftcol;          ///< last known value for leftcol
-  int w_last_width;                 ///< last known value for width
-  int w_last_height;                ///< last known value for height
+  // four fields that are only used when there is a WinScrolled autocommand
+  linenr_T w_last_topline;          ///< last known value for w_topline
+  colnr_T w_last_leftcol;           ///< last known value for w_leftcol
+  int w_last_width;                 ///< last known value for w_width
+  int w_last_height;                ///< last known value for w_height
 
   //
   // Layout of the window in the screen.

src/nvim/edit.c

@@ -1543,10 +1543,9 @@ static void ins_redraw(bool ready)
     }
   }
 
-  // Trigger Scroll if viewport changed.
-  if (ready && has_event(EVENT_WINSCROLLED)
-      && win_did_scroll(curwin)) {
-    do_autocmd_winscrolled(curwin);
+  if (ready) {
+    // Trigger Scroll if viewport changed.
+    may_trigger_winscrolled(curwin);
   }
 
   // Trigger BufModified if b_changed_invalid is set.

src/nvim/normal.c

@@ -1223,10 +1223,9 @@ static void normal_check_interrupt(NormalState *s)
 
 static void normal_check_window_scrolled(NormalState *s)
 {
-  // Trigger Scroll if the viewport changed.
-  if (!finish_op && has_event(EVENT_WINSCROLLED)
-      && win_did_scroll(curwin)) {
-    do_autocmd_winscrolled(curwin);
+  if (!finish_op) {
+    // Trigger Scroll if the viewport changed.
+    may_trigger_winscrolled(curwin);
   }
 }
 
@@ -1353,9 +1352,10 @@ static int normal_check(VimState *state)
   if (skip_redraw || exmode_active) {
     skip_redraw = false;
   } else if (do_redraw || stuff_empty()) {
-    // Need to make sure w_topline and w_leftcol are correct before
-    // normal_check_window_scrolled() is called.
+    // Ensure curwin->w_topline and curwin->w_leftcol are up to date
+    // before triggering a WinScrolled autocommand.
     update_topline(curwin);
+    validate_cursor();
 
     normal_check_cursor_moved(s);
     normal_check_text_changed(s);

src/nvim/testdir/test_autocmd.vim

@@ -3,6 +3,7 @@
 source shared.vim
 source check.vim
 source term_util.vim
+source screendump.vim
 
 func s:cleanup_buffers() abort
   for bnr in range(1, bufnr('$'))
@@ -260,6 +261,60 @@ func Test_win_tab_autocmd()
   unlet g:record
 endfunc
 
+func Test_WinScrolled()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+	set nowrap scrolloff=0
+        for ii in range(1, 18)
+          call setline(ii, repeat(nr2char(96 + ii), ii * 2))
+        endfor
+        let win_id = win_getid()
+        let g:matched = v:false
+        execute 'au WinScrolled' win_id 'let g:matched = v:true'
+        let g:scrolled = 0
+        au WinScrolled * let g:scrolled += 1
+        au WinScrolled * let g:amatch = str2nr(expand('<amatch>'))
+        au WinScrolled * let g:afile = str2nr(expand('<afile>'))
+  END
+  call writefile(lines, 'Xtest_winscrolled')
+  let buf = RunVimInTerminal('-S Xtest_winscrolled', {'rows': 6})
+
+  call term_sendkeys(buf, ":echo g:scrolled\<CR>")
+  call WaitForAssert({-> assert_match('^0 ', term_getline(buf, 6))}, 1000)
+
+  " Scroll left/right in Normal mode.
+  call term_sendkeys(buf, "zlzh:echo g:scrolled\<CR>")
+  call WaitForAssert({-> assert_match('^2 ', term_getline(buf, 6))}, 1000)
+
+  " Scroll up/down in Normal mode.
+  call term_sendkeys(buf, "\<c-e>\<c-y>:echo g:scrolled\<CR>")
+  call WaitForAssert({-> assert_match('^4 ', term_getline(buf, 6))}, 1000)
+
+  " Scroll up/down in Insert mode.
+  call term_sendkeys(buf, "Mi\<c-x>\<c-e>\<Esc>i\<c-x>\<c-y>\<Esc>")
+  call term_sendkeys(buf, ":echo g:scrolled\<CR>")
+  call WaitForAssert({-> assert_match('^6 ', term_getline(buf, 6))}, 1000)
+
+  " Scroll the window horizontally to focus the last letter of the third line
+  " containing only six characters. Moving to the previous and shorter lines
+  " should trigger another autocommand as Vim has to make them visible.
+  call term_sendkeys(buf, "5zl2k")
+  call term_sendkeys(buf, ":echo g:scrolled\<CR>")
+  call WaitForAssert({-> assert_match('^8 ', term_getline(buf, 6))}, 1000)
+
+  " Ensure the command was triggered for the specified window ID.
+  call term_sendkeys(buf, ":echo g:matched\<CR>")
+  call WaitForAssert({-> assert_match('^v:true ', term_getline(buf, 6))}, 1000)
+
+  " Ensure the expansion of <amatch> and <afile> matches the window ID.
+  call term_sendkeys(buf, ":echo g:amatch == win_id && g:afile == win_id\<CR>")
+  call WaitForAssert({-> assert_match('^v:true ', term_getline(buf, 6))}, 1000)
+
+  call StopVimInTerminal(buf)
+  call delete('Xtest_winscrolled')
+endfunc
+
 func Test_WinClosed()
   " Test that the pattern is matched against the closed window's ID, and both
   " <amatch> and <afile> are set to it.

src/nvim/window.c

@@ -2851,7 +2851,7 @@ static void do_autocmd_winclosed(win_T *win)
   }
   recursive = true;
   char_u winid[NUMBUFLEN];
-  vim_snprintf((char *)winid, sizeof(winid), "%i", win->handle);
+  vim_snprintf((char *)winid, sizeof(winid), "%d", win->handle);
   apply_autocmds(EVENT_WINCLOSED, winid, winid, false, win->w_buffer);
   recursive = false;
 }
@@ -5246,25 +5246,31 @@ void shell_new_columns(void)
   win_reconfig_floats();  // The size of floats might change
 }
 
-/// Check if "wp" has scrolled since last time it was checked
-/// @param wp the window to check
-bool win_did_scroll(win_T *wp)
+/// Trigger WinScrolled autocmd if window has scrolled.
+void may_trigger_winscrolled(win_T *wp)
 {
-  return (curwin->w_last_topline != curwin->w_topline
-          || curwin->w_last_leftcol != curwin->w_leftcol
-          || curwin->w_last_width != curwin->w_width
-          || curwin->w_last_height != curwin->w_height);
-}
+  static bool recursive = false;
 
-/// Trigger WinScrolled autocmd
-void do_autocmd_winscrolled(win_T *wp)
-{
-  apply_autocmds(EVENT_WINSCROLLED, NULL, NULL, false, curbuf);
+  if (recursive || !has_event(EVENT_WINSCROLLED)) {
+    return;
+  }
 
-  wp->w_last_topline = wp->w_topline;
-  wp->w_last_leftcol = wp->w_leftcol;
-  wp->w_last_width = wp->w_width;
-  wp->w_last_height = wp->w_height;
+  if (wp->w_last_topline != wp->w_topline
+      || wp->w_last_leftcol != wp->w_leftcol
+      || wp->w_last_width != wp->w_width
+      || wp->w_last_height != wp->w_height) {
+    char_u winid[NUMBUFLEN];
+    vim_snprintf((char *)winid, sizeof(winid), "%d", wp->handle);
+
+    recursive = true;
+    apply_autocmds(EVENT_WINSCROLLED, winid, winid, false, wp->w_buffer);
+    recursive = false;
+
+    wp->w_last_topline = wp->w_topline;
+    wp->w_last_leftcol = wp->w_leftcol;
+    wp->w_last_width = wp->w_width;
+    wp->w_last_height = wp->w_height;
+  }
 }
 
 /*