implement scroll autocommand

src/nvim/auevents.lua

@@ -72,6 +72,7 @@ return {
     'QuickFixCmdPre',         -- before :make, :grep etc.
     'QuitPre',                -- before :quit
     'RemoteReply',            -- upon string reception from a remote vim
+    'Scroll',                 -- after scrolling
     'SessionLoadPost',        -- after loading a session file
     'ShellCmdPost',           -- after ":!cmd"
     'ShellFilterPost',        -- after ":1,2!cmd", ":w !cmd", ":r !cmd".
@@ -123,6 +124,7 @@ return {
   -- syntax file
   nvim_specific = {
     DirChanged=true,
+    Scroll=true,
     Signal=true,
     TabClosed=true,
     TabNew=true,

src/nvim/buffer_defs.h

@@ -1204,6 +1204,9 @@ struct window_S {
   colnr_T w_skipcol;                // starting column when a single line
                                     // doesn't fit in the window
 
+  linenr_T w_last_topline;          ///< last known value for topline
+  colnr_T w_last_leftcol;           ///< last known value for leftcol
+
   //
   // Layout of the window in the screen.
   // May need to add "msg_scrolled" to "w_winrow" in rare situations.

src/nvim/edit.c

@@ -1482,6 +1482,31 @@ static void ins_redraw(
     }
   }
 
+  if (ready && has_event(EVENT_SCROLL)
+      && (curwin->w_last_topline != curwin->w_topline ||
+          curwin->w_last_leftcol != curwin->w_leftcol)) {
+
+    // XXX is the buf changedtick thing necessary?
+    // XXX apply_autocmds vs ins_apply_autocmds?
+    // XXX why can't we re-use normal_check_window_scrolled()?
+
+    aco_save_T aco;
+    varnumber_T tick = buf_get_changedtick(curbuf);
+
+    // save and restore curwin and curbuf, in case the autocmd changes them
+    aucmd_prepbuf(&aco, curbuf);
+    apply_autocmds(EVENT_SCROLL, NULL, NULL, false, curbuf);
+    aucmd_restbuf(&aco);
+    curbuf->b_last_changedtick_pum = buf_get_changedtick(curbuf);
+    if (tick != buf_get_changedtick(curbuf)) {  // see ins_apply_autocmds()
+      u_save(curwin->w_cursor.lnum,
+             (linenr_T)(curwin->w_cursor.lnum + 1));
+    }
+
+    curwin->w_last_topline = curwin->w_topline;
+    curwin->w_last_leftcol = curwin->w_leftcol;
+  }
+
   if (curwin->w_p_cole > 0 && conceal_cursor_line(curwin)
       && conceal_cursor_moved) {
     redrawWinline(curwin, curwin->w_cursor.lnum);

src/nvim/normal.c

@@ -1193,6 +1193,22 @@ static void normal_check_interrupt(NormalState *s)
   }
 }
 
+static void normal_check_window_scrolled(NormalState *s)
+{
+  // XXX why is has_event necessary?
+
+  // Trigger Scroll if the window moved.
+  if (!finish_op && has_event(EVENT_SCROLL)
+      && (curwin->w_last_topline != curwin->w_topline ||
+          curwin->w_last_leftcol != curwin->w_leftcol)) {
+
+    apply_autocmds(EVENT_SCROLL, NULL, NULL, false, curbuf);
+
+    curwin->w_last_topline = curwin->w_topline;
+    curwin->w_last_leftcol = curwin->w_leftcol;
+  }
+}
+
 static void normal_check_cursor_moved(NormalState *s)
 {
   // Trigger CursorMoved if the cursor moved.
@@ -1279,6 +1295,7 @@ static void normal_redraw(NormalState *s)
     xfree(p);
   }
 
+
   // show fileinfo after redraw
   if (need_fileinfo && !shortmess(SHM_FILEINFO)) {
     fileinfo(false, true, false);
@@ -1318,6 +1335,7 @@ static int normal_check(VimState *state)
   } else if (do_redraw || stuff_empty()) {
     normal_check_cursor_moved(s);
     normal_check_text_changed(s);
+    normal_check_window_scrolled(s);
 
     // Updating diffs from changed() does not always work properly,
     // esp. updating folds.  Do an update just before redrawing if