vim-patch:8.2.{4692,4691,4690}: fix Insert mode <LeftDrag> mapping bug (#17999)

vim-patch:8.2.4692: no test for what 8.2.4691 fixes

Problem:    No test for what 8.2.4691 fixes.
Solution:   Add a test.  Use a more generic sotlution. (closes vim/vim#10090)
https://github.com/vim/vim/commit/0f68e6c07aaf62c034a242f183b93c1bb44e7f93

Test cannot be used because it must use test_setmouse(). Use a Lua test.

Reverted patches:

vim-patch:8.2.4691: solution for <Cmd> in a mapping causes trouble

Problem:    Solution for <Cmd> in a mapping causes trouble.
Solution:   Use another solution: put back CTRL-O after reading the <Cmd>
            sequence.
https://github.com/vim/vim/commit/ca9d8d2cb9fc6b9240f2a74ccd36f9d966488294

vim-patch:8.2.4689: using <Cmd> in a mapping does not work for mouse keys

Problem:    Using <Cmd> in a mapping does not work for mouse keys in Insert
            mode. (Sergey Vlasov)
Solution:   When reading the <Cmd> argument do not use the stuff buffer.
            (closes vim/vim#10080)
https://github.com/vim/vim/commit/d0fb2d804183c2786578b4c32ba5b92938f93d0e

3 files changed, 53 insertions, 6 deletions

diff --git a/src/nvim/getchar.c b/src/nvim/getchar.c
index 669d181364..eddd5ccd14 100644
--- a/src/nvim/getchar.c
+++ b/src/nvim/getchar.c
@@ -1253,7 +1253,14 @@ static int old_mod_mask;    // mod_mask for ungotten character
 static int old_mouse_grid;  // mouse_grid related to old_char
 static int old_mouse_row;   // mouse_row related to old_char
 static int old_mouse_col;   // mouse_col related to old_char
+static int old_KeyStuffed;  // whether old_char was stuffed
 
+static bool can_get_old_char(void)
+{
+    // If the old character was not stuffed and characters have been added to
+    // the stuff buffer, need to first get the stuffed characters instead.
+    return old_char != -1 && (old_KeyStuffed || stuff_empty());
+}
 
 /*
  * Save all three kinds of typeahead, so that the user must type at a prompt.
@@ -1454,7 +1461,7 @@ int vgetc(void)
    * If a character was put back with vungetc, it was already processed.
    * Return it directly.
    */
-  if (old_char != -1) {
+  if (can_get_old_char()) {
     c = old_char;
     old_char = -1;
     mod_mask = old_mod_mask;
@@ -1660,7 +1667,7 @@ int plain_vgetc(void)
  */
 int vpeekc(void)
 {
-  if (old_char != -1) {
+  if (can_get_old_char()) {
     return old_char;
   }
   return vgetorpeek(false);
@@ -2052,7 +2059,9 @@ static int handle_mapping(int *keylenp, bool *timedout, int *mapdepth)
   return map_result_nomatch;
 }
 
-// unget one character (can only be done once!)
+/// unget one character (can only be done once!)
+/// If the character was stuffed, vgetc() will get it next time it was called.
+/// Otherwise vgetc() will only get it when the stuff buffer is empty.
 void vungetc(int c)
 {
   old_char = c;
@@ -2060,6 +2069,7 @@ void vungetc(int c)
   old_mouse_grid = mouse_grid;
   old_mouse_row = mouse_row;
   old_mouse_col = mouse_col;
+  old_KeyStuffed = KeyStuffed;
 }
 
 /// Gets a byte:
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 5e46bd468d..9cee2de0c5 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1517,9 +1517,12 @@ bool do_mouse(oparg_T *oap, int c, int dir, long count, bool fixindent)
   for (;;) {
     which_button = get_mouse_button(KEY2TERMCAP1(c), &is_click, &is_drag);
     if (is_drag) {
-      /* If the next character is the same mouse event then use that
-       * one. Speeds up dragging the status line. */
-      if (vpeekc() != NUL) {
+      // If the next character is the same mouse event then use that
+      // one. Speeds up dragging the status line.
+      // Note: Since characters added to the stuff buffer in the code
+      // below need to come before the next character, do not do this
+      // when the current character was stuffed.
+      if (!KeyStuffed && vpeekc() != NUL) {
         int nc;
         int save_mouse_grid = mouse_grid;
         int save_mouse_row = mouse_row;
diff --git a/src/nvim/testdir/test_mapping.vim b/src/nvim/testdir/test_mapping.vim
index 98440ccdd7..a8dd0ca286 100644
--- a/src/nvim/testdir/test_mapping.vim
+++ b/src/nvim/testdir/test_mapping.vim
@@ -676,4 +676,38 @@ func Test_plug_remap()
   %bw!
 endfunc
 
+" Test for mapping <LeftDrag> in Insert mode
+func Test_mouse_drag_insert_map()
+  CheckFunction test_setmouse
+  set mouse=a
+  func ClickExpr()
+    call test_setmouse(1, 1)
+    return "\<LeftMouse>"
+  endfunc
+  func DragExpr()
+    call test_setmouse(1, 2)
+    return "\<LeftDrag>"
+  endfunc
+  inoremap <expr> <F2> ClickExpr()
+  imap <expr> <F3> DragExpr()
+
+  inoremap <LeftDrag> <LeftDrag><Cmd>let g:dragged = 1<CR>
+  exe "normal i\<F2>\<F3>"
+  call assert_equal(1, g:dragged)
+  call assert_equal('v', mode())
+  exe "normal! \<C-\>\<C-N>"
+  unlet g:dragged
+
+  inoremap <LeftDrag> <LeftDrag><C-\><C-N>
+  exe "normal i\<F2>\<F3>"
+  call assert_equal('n', mode())
+
+  iunmap <LeftDrag>
+  iunmap <F2>
+  iunmap <F3>
+  delfunc ClickExpr
+  delfunc DragExpr
+  set mouse&
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab