patch 8.2.4723: the ModeChanged autocmd event is inefficient

Problem:    The ModeChanged autocmd event is inefficient.
Solution:   Avoid allocating memory. (closes #10134)  Rename
            trigger_modechanged() to may_trigger_modechanged().

src/autocmd.c

@@ -1240,17 +1240,7 @@ do_autocmd_event(
 		// need to initialize last_mode for the first ModeChanged
 		// autocmd
 		if (event == EVENT_MODECHANGED && !has_modechanged())
-		{
-		    typval_T rettv;
-		    typval_T tv[2];
-
-		    tv[0].v_type = VAR_NUMBER;
-		    tv[0].vval.v_number = 1;
-		    tv[1].v_type = VAR_UNKNOWN;
-		    f_mode(tv, &rettv);
-		    STRCPY(last_mode, rettv.vval.v_string);
-		    vim_free(rettv.vval.v_string);
-		}
+		    get_mode(last_mode);
 #endif
 		// Initialize the fields checked by the WinScrolled trigger to
 		// stop it from firing right after the first autocmd is defined.

src/edit.c

@@ -284,7 +284,7 @@ edit(
     else
 	State = INSERT;
 
-    trigger_modechanged();
+    may_trigger_modechanged();
     stop_insert_mode = FALSE;
 
 #ifdef FEAT_CONCEAL
@@ -3701,7 +3701,7 @@ ins_esc(
 #endif
 
     State = NORMAL;
-    trigger_modechanged();
+    may_trigger_modechanged();
     // need to position cursor again when on a TAB
     if (gchar_cursor() == TAB)
 	curwin->w_valid &= ~(VALID_WROW|VALID_WCOL|VALID_VIRTCOL);
@@ -3838,7 +3838,7 @@ ins_insert(int replaceState)
 	State = INSERT | (State & LANGMAP);
     else
 	State = replaceState | (State & LANGMAP);
-    trigger_modechanged();
+    may_trigger_modechanged();
     AppendCharToRedobuff(K_INS);
     showmode();
 #ifdef CURSOR_SHAPE

src/ex_docmd.c

@@ -477,7 +477,7 @@ do_exmode(
     else
 	exmode_active = EXMODE_NORMAL;
     State = NORMAL;
-    trigger_modechanged();
+    may_trigger_modechanged();
 
     // When using ":global /pat/ visual" and then "Q" we return to continue
     // the :global command.

src/ex_getln.c

@@ -1714,7 +1714,7 @@ getcmdline_int(
     trigger_cmd_autocmd(cmdline_type, EVENT_CMDLINEENTER);
 #ifdef FEAT_EVAL
     if (!debug_mode)
-	trigger_modechanged();
+	may_trigger_modechanged();
 #endif
 
     init_history();
@@ -2555,7 +2555,7 @@ getcmdline_int(
 
 #ifdef FEAT_EVAL
     if (!debug_mode)
-	trigger_modechanged();
+	may_trigger_modechanged();
 #endif
 
 #ifdef HAVE_INPUT_METHOD

src/insexpand.c

@@ -257,7 +257,7 @@ ins_ctrl_x(void)
 	// CTRL-V look like CTRL-N
 	ctrl_x_mode = CTRL_X_CMDLINE_CTRL_X;
 
-    trigger_modechanged();
+    may_trigger_modechanged();
 }
 
 /*
@@ -2381,7 +2381,7 @@ ins_compl_prep(int c)
 	// upon the (possibly failed) completion.
 	ins_apply_autocmds(EVENT_COMPLETEDONE);
 
-    trigger_modechanged();
+    may_trigger_modechanged();
 
     // reset continue_* if we left expansion-mode, if we stay they'll be
     // (re)set properly in ins_complete()
@@ -2865,7 +2865,7 @@ set_completion(colnr_T startcol, list_T *list)
     // Lazily show the popup menu, unless we got interrupted.
     if (!compl_interrupted)
 	show_pum(save_w_wrow, save_w_leftcol);
-    trigger_modechanged();
+    may_trigger_modechanged();
     out_flush();
 }
 
@@ -3818,7 +3818,7 @@ ins_compl_get_exp(pos_T *ini)
 	if (compl_curr_match == NULL)
 	    compl_curr_match = compl_old_match;
     }
-    trigger_modechanged();
+    may_trigger_modechanged();
 
     return i;
 }

src/misc1.c

@@ -625,105 +625,119 @@ ask_yesno(char_u *str, int direct)
 #if defined(FEAT_EVAL) || defined(PROTO)
 
 /*
- * "mode()" function
+ * Returns the current mode as a string in "buf[MODE_MAX_LENGTH]", NUL
+ * terminated.
+ * The first character represents the major mode, the following ones the minor
+ * ones.
  */
     void
-f_mode(typval_T *argvars, typval_T *rettv)
+get_mode(char_u *buf)
 {
-    char_u	buf[MODE_MAX_LENGTH];
-
-    if (in_vim9script() && check_for_opt_bool_arg(argvars, 0) == FAIL)
-	return;
-
-    CLEAR_FIELD(buf);
+    int		i = 0;
 
     if (time_for_testing == 93784)
     {
 	// Testing the two-character code.
-	buf[0] = 'x';
-	buf[1] = '!';
+	buf[i++] = 'x';
+	buf[i++] = '!';
     }
 #ifdef FEAT_TERMINAL
     else if (term_use_loop())
-	buf[0] = 't';
+	buf[i++] = 't';
 #endif
     else if (VIsual_active)
     {
 	if (VIsual_select)
-	    buf[0] = VIsual_mode + 's' - 'v';
+	    buf[i++] = VIsual_mode + 's' - 'v';
 	else
 	{
-	    buf[0] = VIsual_mode;
+	    buf[i++] = VIsual_mode;
 	    if (restart_VIsual_select)
-	        buf[1] = 's';
+	        buf[i++] = 's';
 	}
     }
     else if (State == HITRETURN || State == ASKMORE || State == SETWSIZE
 		|| State == CONFIRM)
     {
-	buf[0] = 'r';
+	buf[i++] = 'r';
 	if (State == ASKMORE)
-	    buf[1] = 'm';
+	    buf[i++] = 'm';
 	else if (State == CONFIRM)
-	    buf[1] = '?';
+	    buf[i++] = '?';
     }
     else if (State == EXTERNCMD)
-	buf[0] = '!';
+	buf[i++] = '!';
     else if (State & INSERT)
     {
 	if (State & VREPLACE_FLAG)
 	{
-	    buf[0] = 'R';
-	    buf[1] = 'v';
+	    buf[i++] = 'R';
+	    buf[i++] = 'v';
 
 	    if (ins_compl_active())
-		buf[2] = 'c';
+		buf[i++] = 'c';
 	    else if (ctrl_x_mode_not_defined_yet())
-		buf[2] = 'x';
+		buf[i++] = 'x';
 	}
 	else
 	{
 	    if (State & REPLACE_FLAG)
-		buf[0] = 'R';
+		buf[i++] = 'R';
 	    else
-		buf[0] = 'i';
+		buf[i++] = 'i';
 
 	    if (ins_compl_active())
-		buf[1] = 'c';
+		buf[i++] = 'c';
 	    else if (ctrl_x_mode_not_defined_yet())
-		buf[1] = 'x';
+		buf[i++] = 'x';
 	}
     }
     else if ((State & CMDLINE) || exmode_active)
     {
-	buf[0] = 'c';
+	buf[i++] = 'c';
 	if (exmode_active == EXMODE_VIM)
-	    buf[1] = 'v';
+	    buf[i++] = 'v';
 	else if (exmode_active == EXMODE_NORMAL)
-	    buf[1] = 'e';
+	    buf[i++] = 'e';
     }
     else
     {
-	buf[0] = 'n';
+	buf[i++] = 'n';
 	if (finish_op)
 	{
-	    buf[1] = 'o';
+	    buf[i++] = 'o';
 	    // to be able to detect force-linewise/blockwise/characterwise
 	    // operations
-	    buf[2] = motion_force;
+	    buf[i++] = motion_force;
 	}
 	else if (restart_edit == 'I' || restart_edit == 'R'
 							|| restart_edit == 'V')
 	{
-	    buf[1] = 'i';
-	    buf[2] = restart_edit;
+	    buf[i++] = 'i';
+	    buf[i++] = restart_edit;
 	}
 #ifdef FEAT_TERMINAL
 	else if (term_in_normal_mode())
-	    buf[1] = 't';
+	    buf[i++] = 't';
 #endif
     }
 
+    buf[i] = NUL;
+}
+
+/*
+ * "mode()" function
+ */
+    void
+f_mode(typval_T *argvars, typval_T *rettv)
+{
+    char_u	buf[MODE_MAX_LENGTH];
+
+    if (in_vim9script() && check_for_opt_bool_arg(argvars, 0) == FAIL)
+	return;
+
+    get_mode(buf);
+
     // Clear out the minor mode when the argument is not a non-zero number or
     // non-empty string.
     if (!non_zero_arg(&argvars[0]))
@@ -2691,47 +2705,36 @@ restore_v_event(dict_T *v_event, save_v_event_T *sve)
 #endif
 
 /*
- * Fires a ModeChanged autocmd
+ * Fires a ModeChanged autocmd event if appropriate.
  */
     void
-trigger_modechanged()
+may_trigger_modechanged()
 {
 #ifdef FEAT_EVAL
     dict_T	    *v_event;
-    typval_T	    rettv;
-    typval_T	    tv[2];
-    char_u	    *pat_pre;
-    char_u	    *pat;
     save_v_event_T  save_v_event;
+    char_u	    curr_mode[MODE_MAX_LENGTH];
+    char_u	    pattern_buf[2 * MODE_MAX_LENGTH];
 
     if (!has_modechanged())
 	return;
 
-    tv[0].v_type = VAR_NUMBER;
-    tv[0].vval.v_number = 1;	    // get full mode
-    tv[1].v_type = VAR_UNKNOWN;
-    f_mode(tv, &rettv);
-    if (STRCMP(rettv.vval.v_string, last_mode) == 0)
-    {
-	vim_free(rettv.vval.v_string);
+    get_mode(curr_mode);
+    if (STRCMP(curr_mode, last_mode) == 0)
 	return;
-    }
 
     v_event = get_v_event(&save_v_event);
-    (void)dict_add_string(v_event, "new_mode", rettv.vval.v_string);
+    (void)dict_add_string(v_event, "new_mode", curr_mode);
     (void)dict_add_string(v_event, "old_mode", last_mode);
     dict_set_items_ro(v_event);
 
     // concatenate modes in format "old_mode:new_mode"
-    pat_pre = concat_str(last_mode, (char_u*)":");
-    pat = concat_str(pat_pre, rettv.vval.v_string);
-    vim_free(pat_pre);
+    vim_snprintf((char *)pattern_buf, sizeof(pattern_buf), "%s:%s", last_mode,
+	    curr_mode);
 
-    apply_autocmds(EVENT_MODECHANGED, pat, NULL, FALSE, curbuf);
-    STRCPY(last_mode, rettv.vval.v_string);
+    apply_autocmds(EVENT_MODECHANGED, pattern_buf, NULL, FALSE, curbuf);
+    STRCPY(last_mode, curr_mode);
 
-    vim_free(pat);
     restore_v_event(v_event, &save_v_event);
-    vim_free(rettv.vval.v_string);
 #endif
 }

src/normal.c

@@ -689,7 +689,7 @@ normal_cmd(
 # endif
     }
 #endif
-    trigger_modechanged();
+    may_trigger_modechanged();
 
     // When not finishing an operator and no register name typed, reset the
     // count.
@@ -971,7 +971,7 @@ normal_cmd(
     c = finish_op;
 #endif
     finish_op = FALSE;
-    trigger_modechanged();
+    may_trigger_modechanged();
 #ifdef CURSOR_SHAPE
     // Redraw the cursor with another shape, if we were in Operator-pending
     // mode or did a replace command.
@@ -1027,7 +1027,7 @@ normal_cmd(
 	if (restart_VIsual_select == 1)
 	{
 	    VIsual_select = TRUE;
-	    trigger_modechanged();
+	    may_trigger_modechanged();
 	    showmode();
 	    restart_VIsual_select = 0;
 	    VIsual_select_reg = 0;
@@ -1151,7 +1151,7 @@ end_visual_mode_keep_button()
     may_clear_cmdline();
 
     adjust_cursor_eol();
-    trigger_modechanged();
+    may_trigger_modechanged();
 }
 
 /*
@@ -3222,7 +3222,7 @@ nv_ctrlg(cmdarg_T *cap)
     if (VIsual_active)	// toggle Selection/Visual mode
     {
 	VIsual_select = !VIsual_select;
-	trigger_modechanged();
+	may_trigger_modechanged();
 	showmode();
     }
     else if (!checkclearop(cap->oap))
@@ -3285,7 +3285,7 @@ nv_ctrlo(cmdarg_T *cap)
     if (VIsual_active && VIsual_select)
     {
 	VIsual_select = FALSE;
-	trigger_modechanged();
+	may_trigger_modechanged();
 	showmode();
 	restart_VIsual_select = 2;	// restart Select mode later
     }
@@ -5422,7 +5422,7 @@ nv_visual(cmdarg_T *cap)
 	{				    //	   or char/line mode
 	    VIsual_mode = cap->cmdchar;
 	    showmode();
-	    trigger_modechanged();
+	    may_trigger_modechanged();
 	}
 	redraw_curbuf_later(INVERTED);	    // update the inversion
     }
@@ -5549,7 +5549,7 @@ n_start_visual_mode(int c)
     foldAdjustVisual();
 #endif
 
-    trigger_modechanged();
+    may_trigger_modechanged();
     setmouse();
 #ifdef FEAT_CONCEAL
     // Check if redraw is needed after changing the state.