vim-patch:8.2.3430: no generic way to trigger an autocommand on mode change

Problem:    No generic way to trigger an autocommand on mode change.
Solution:   Add the ModeChanged autocommand event. (Magnus Gross, closes vim/vim#8856)
https://github.com/vim/vim/commit/f1e8876fa2359b572d262772747405d3616db670

N/A patches for version.c:

vim-patch:8.2.3434: function prototype for trigger_modechanged() is incomplete

Problem:    Function prototype for trigger_modechanged() is incomplete.
Solution:   Add "void".
https://github.com/vim/vim/commit/28e591dd5080bbcd0f468f9d9597cedb716e28c9

Fixes #4399.
Fixes #7416.

12 files changed, 85 insertions, 7 deletions

diff --git a/src/nvim/auevents.lua b/src/nvim/auevents.lua
index 6be51c504c..bd30966acf 100644
--- a/src/nvim/auevents.lua
+++ b/src/nvim/auevents.lua
@@ -69,6 +69,7 @@ return {
     'InsertLeave',            -- just after leaving Insert mode
     'InsertLeavePre',         -- just before leaving Insert mode
     'MenuPopup',              -- just before popup menu is displayed
+    'ModeChanged',            -- after changing the mode
     'OptionSet',              -- after setting any option
     'QuickFixCmdPost',        -- after :make, :grep etc.
     'QuickFixCmdPre',         -- before :make, :grep etc.
diff --git a/src/nvim/autocmd.c b/src/nvim/autocmd.c
index 2d0c0f3fd5..ae81b6a808 100644
--- a/src/nvim/autocmd.c
+++ b/src/nvim/autocmd.c
@@ -1440,7 +1440,7 @@ static bool apply_autocmds_group(event_T event, char_u *fname, char_u *fname_io,
   // invalid.
   if (fname_io == NULL) {
     if (event == EVENT_COLORSCHEME || event == EVENT_COLORSCHEMEPRE
-        || event == EVENT_OPTIONSET) {
+        || event == EVENT_OPTIONSET || event == EVENT_MODECHANGED) {
       autocmd_fname = NULL;
     } else if (fname != NULL && !ends_excmd(*fname)) {
       autocmd_fname = fname;
@@ -1494,11 +1494,12 @@ static bool apply_autocmds_group(event_T event, char_u *fname, char_u *fname_io,
         || event == EVENT_CMDWINLEAVE || event == EVENT_CMDUNDEFINED
         || event == EVENT_COLORSCHEME || event == EVENT_COLORSCHEMEPRE
         || event == EVENT_DIRCHANGED || event == EVENT_FILETYPE
-        || event == EVENT_FUNCUNDEFINED || event == EVENT_OPTIONSET
-        || event == EVENT_QUICKFIXCMDPOST || event == EVENT_QUICKFIXCMDPRE
-        || event == EVENT_REMOTEREPLY || event == EVENT_SPELLFILEMISSING
-        || event == EVENT_SYNTAX || event == EVENT_SIGNAL
-        || event == EVENT_TABCLOSED || event == EVENT_WINCLOSED) {
+        || event == EVENT_FUNCUNDEFINED || event == EVENT_MODECHANGED
+        || event == EVENT_OPTIONSET || event == EVENT_QUICKFIXCMDPOST
+        || event == EVENT_QUICKFIXCMDPRE || event == EVENT_REMOTEREPLY
+        || event == EVENT_SPELLFILEMISSING || event == EVENT_SYNTAX
+        || event == EVENT_SIGNAL || event == EVENT_TABCLOSED
+        || event == EVENT_WINCLOSED) {
       fname = vim_strsave(fname);
     } else {
       fname = (char_u *)FullName_save((char *)fname, false);
diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 7a24ee1b32..cbb93c88ee 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -385,6 +385,7 @@ static void insert_enter(InsertState *s)
     State = INSERT;
   }
 
+  trigger_modechanged();
   stop_insert_mode = false;
 
   // Need to recompute the cursor position, it might move when the cursor is
@@ -7965,6 +7966,7 @@ static bool ins_esc(long *count, int cmdchar, bool nomove)
 
 
   State = NORMAL;
+  trigger_modechanged();
   // need to position cursor again (e.g. when on a TAB )
   changed_cline_bef_curs();
 
@@ -8066,6 +8068,7 @@ static void ins_insert(int replaceState)
   } else {
     State = replaceState | (State & LANGMAP);
   }
+  trigger_modechanged();
   AppendCharToRedobuff(K_INS);
   showmode();
   ui_cursor_shape();            // may show different cursor shape
diff --git a/src/nvim/ex_docmd.c b/src/nvim/ex_docmd.c
index e622a2a68f..03d85ea888 100644
--- a/src/nvim/ex_docmd.c
+++ b/src/nvim/ex_docmd.c
@@ -196,6 +196,7 @@ void do_exmode(void)
 
   exmode_active = true;
   State = NORMAL;
+  trigger_modechanged();
 
   // When using ":global /pat/ visual" and then "Q" we return to continue
   // the :global command.
diff --git a/src/nvim/ex_getln.c b/src/nvim/ex_getln.c
index 0716b5445d..09f379d0b9 100644
--- a/src/nvim/ex_getln.c
+++ b/src/nvim/ex_getln.c
@@ -906,6 +906,7 @@ static uint8_t *command_line_enter(int firstc, long count, int indent)
     }
     tl_ret = true;
   }
+  trigger_modechanged();
 
   state_enter(&s->state);
 
@@ -6547,6 +6548,7 @@ static int open_cmdwin(void)
   cmdmsg_rl = save_cmdmsg_rl;
 
   State = save_State;
+  trigger_modechanged();
   setmouse();
 
   return cmdwin_result;
diff --git a/src/nvim/globals.h b/src/nvim/globals.h
index e2d3378402..9f0f19024b 100644
--- a/src/nvim/globals.h
+++ b/src/nvim/globals.h
@@ -727,6 +727,7 @@ EXTERN bool listcmd_busy INIT(= false);     // set when :argdo, :windo or
                                             // :bufdo is executing
 EXTERN bool need_start_insertmode INIT(= false);
 // start insert mode soon
+EXTERN char *last_mode INIT(= NULL);
 EXTERN char_u *last_cmdline INIT(= NULL);      // last command line (for ":)
 EXTERN char_u *repeat_cmdline INIT(= NULL);    // command line for "."
 EXTERN char_u *new_last_cmdline INIT(= NULL);  // new value for last_cmdline
diff --git a/src/nvim/memory.c b/src/nvim/memory.c
index 547a9015b7..85140e4c64 100644
--- a/src/nvim/memory.c
+++ b/src/nvim/memory.c
@@ -632,6 +632,7 @@ void free_all_mem(void)
   clear_sb_text(true);            // free any scrollback text
 
   // Free some global vars.
+  xfree(last_mode);
   xfree(last_cmdline);
   xfree(new_last_cmdline);
   set_keep_msg(NULL, 0);
diff --git a/src/nvim/misc1.c b/src/nvim/misc1.c
index 5ecd4ca431..4c495ee9db 100644
--- a/src/nvim/misc1.c
+++ b/src/nvim/misc1.c
@@ -1059,3 +1059,32 @@ void add_time(char_u *buf, size_t buflen, time_t tt)
                  seconds);
   }
 }
+
+/// Fires a ModeChanged autocmd.
+void trigger_modechanged(void)
+{
+  if (!has_event(EVENT_MODECHANGED)) {
+    return;
+  }
+
+  dict_T *v_event = get_vim_var_dict(VV_EVENT);
+
+  char *mode = get_mode();
+  if (last_mode == NULL) {
+    last_mode = (char *)vim_strsave((char_u *)"n");
+  }
+  tv_dict_add_str(v_event, S_LEN("new_mode"), mode);
+  tv_dict_add_str(v_event, S_LEN("old_mode"), last_mode);
+
+  char_u *pat_pre = concat_str((char_u *)last_mode, (char_u *)":");
+  char_u *pat = concat_str(pat_pre, (char_u *)mode);
+  xfree(pat_pre);
+
+  apply_autocmds(EVENT_MODECHANGED, pat, NULL, false, curbuf);
+  xfree(last_mode);
+  last_mode = mode;
+
+  xfree(pat);
+  tv_dict_free_contents(v_event);
+  hash_init(&v_event->dv_hashtab);
+}
diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index 1effeefd32..81e8251361 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -3050,6 +3050,7 @@ static int get_mouse_class(char_u *p)
 void end_visual_mode(void)
 {
   VIsual_active = false;
+  trigger_modechanged();
   setmouse();
   mouse_dragging = 0;
 
@@ -6680,6 +6681,7 @@ static void nv_visual(cmdarg_T *cap)
                                               //           or char/line mode
       VIsual_mode = cap->cmdchar;
       showmode();
+      trigger_modechanged();
     }
     redraw_curbuf_later(INVERTED);          // update the inversion
   } else {                // start Visual mode
@@ -6782,6 +6784,7 @@ static void n_start_visual_mode(int c)
   VIsual_mode = c;
   VIsual_active = true;
   VIsual_reselect = true;
+  trigger_modechanged();
   // Corner case: the 0 position in a tab may change when going into
   // virtualedit.  Recalculate curwin->w_cursor to avoid bad highlighting.
   //
diff --git a/src/nvim/state.c b/src/nvim/state.c
index 4eb0073873..71db25664f 100644
--- a/src/nvim/state.c
+++ b/src/nvim/state.c
@@ -136,7 +136,7 @@ int get_real_state(void)
 /// @returns[allocated] mode string
 char *get_mode(void)
 {
-  char *buf = xcalloc(4, sizeof(char));
+  char *buf = xcalloc(MODE_MAX_LENGTH, sizeof(char));
 
   if (VIsual_active) {
     if (VIsual_select) {
diff --git a/src/nvim/testdir/test_edit.vim b/src/nvim/testdir/test_edit.vim
index 23ad8dbfc5..75e30502b8 100644
--- a/src/nvim/testdir/test_edit.vim
+++ b/src/nvim/testdir/test_edit.vim
@@ -1644,4 +1644,38 @@ func Test_read_invalid()
   set encoding=utf-8
 endfunc
 
+" Test for ModeChanged pattern
+func Test_mode_changes()
+  let g:count = 0
+  func! DoIt()
+    let g:count += 1
+  endfunc
+  let g:index = 0
+  let g:mode_seq = ['n', 'i', 'n', 'v', 'V', 'n', 'V', 'v', 'n']
+  func! TestMode()
+    call assert_equal(g:mode_seq[g:index], get(v:event, "old_mode"))
+    call assert_equal(g:mode_seq[g:index + 1], get(v:event, "new_mode"))
+    call assert_equal(mode(), get(v:event, "new_mode"))
+    let g:index += 1
+  endfunc
+
+  au ModeChanged * :call TestMode()
+  au ModeChanged n:* :call DoIt()
+  call feedkeys("i\<esc>vV\<esc>", 'tnix')
+  call assert_equal(2, g:count)
+
+  au ModeChanged V:v :call DoIt()
+  call feedkeys("Vv\<esc>", 'tnix')
+  call assert_equal(4, g:count)
+
+  call assert_equal(len(g:mode_seq) - 1, g:index)
+
+  au! ModeChanged
+  delfunc TestMode
+  unlet! g:mode_seq
+  unlet! g:index
+  delfunc DoIt
+  unlet! g:count
+endfunc
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/src/nvim/vim.h b/src/nvim/vim.h
index 726670f082..e3539c1a57 100644
--- a/src/nvim/vim.h
+++ b/src/nvim/vim.h
@@ -72,6 +72,8 @@ enum { NUMBUFLEN = 65, };
 #define TERM_FOCUS      0x2000  // Terminal focus mode
 #define CMDPREVIEW      0x4000  // Showing 'inccommand' command "live" preview.
 
+#define MODE_MAX_LENGTH 4       // max mode length returned in mode()
+
 // all mode bits used for mapping
 #define MAP_ALL_MODES   (0x3f | SELECTMODE | TERM_FOCUS)