fix(autocmd): dot-repeat triggers InsertCharPre #41806

Problem:
InsertCharPre is triggered for stuffed text (".", i_CTRL-R, i_CTRL-A).
But that text was already transformed when it was typed: the `v:char`
result is appended to the redo buffer literally (`redo_append_lit()`).
So "." transforms it again, e.g. an autopair handler turns "()" into
"())".

Solution:
Skip InsertCharPre for stuffed text.

Precedent: `vgetorpeek()` disables abbreviations for stuffed text for
the same reason (it is post-expansion).

Macros are unaffected.

runtime/doc/autocmd.txt

@@ -903,6 +903,8 @@ InsertCharPre			When a character is typed in Insert mode,
 				to more than one character this text is
 				inserted literally.
 
+				Not triggered for |.| redo, |i_CTRL-R|, |i_CTRL-A|.
+
 				Cannot change the text. |textlock|
 
 							*InsertEnter*

runtime/doc/vim_diff.txt

@@ -349,6 +349,8 @@ Editor:
 
 Events (autocommands):
 - Fixed inconsistent behavior in execution of nested autocommands #23368
+- |InsertCharPre| is not triggered for stuffed text (|.| redo, |i_CTRL-R|,
+  |i_CTRL-A|), which also skips mappings and abbreviations.
 - |OptionSet| is triggered for 'modified' when writing a file, undoing changes,
   or using |:set| modified.
 - |Progress|

src/nvim/insert.c

@@ -4384,14 +4384,14 @@ static char *do_insert_char_pre(int c)
   char buf[MB_MAXBYTES + 1];
   const int save_State = State;
 
-  if (c == Ctrl_RSB) {
+  if (c == Ctrl_RSB  // i_CTRL-] only triggers abbreviations.
+      // Stuffed text was transformed when typed and appended to redobuf (redo_append_lit).
+      // Like abbreviations (vgetorpeek()), don't transform it again.
+      || KeyStuffed
+      || !has_event(EVENT_INSERTCHARPRE)) {
     return NULL;
   }
 
-  // Return quickly when there is nothing to do.
-  if (!has_event(EVENT_INSERTCHARPRE)) {
-    return NULL;
-  }
   size_t buflen = (size_t)utf_char2bytes(c, buf);
   buf[buflen] = NUL;
 

test/functional/editor/mode_insert_spec.lua

@@ -49,6 +49,56 @@ describe('insert-mode', function()
     expect('hellhellhellhelloxo')
   end)
 
+  it('InsertCharPre is not triggered for stuffed text (redo/dot-repeat) #25296', function()
+    n.exec_lua([[
+      _G.n = 0
+      vim.api.nvim_create_autocmd('InsertCharPre', {
+        callback = function()
+          _G.n = _G.n + 1
+          if vim.v.char == '(' then
+            vim.v.char = '()'
+          end
+        end,
+      })
+    ]])
+    local function calls()
+      return n.exec_lua('return _G.n')
+    end
+    api.nvim_buf_set_lines(0, 0, -1, true, { 'a', 'b', 'c', 'd' })
+    feed('gg0i(<Esc>')
+    eq(1, calls())
+
+    -- Dot-repeat ("redo") inserts literally (no InsertCharPre).
+    feed('j.')
+    expect([[
+      ()a
+      ()b
+      c
+      d]])
+    eq(1, calls())
+
+    -- i_CTRL-R, i_CTRL-A inserts as stuffed text (no InsertCharPre).
+    n.fn.setreg('a', '(')
+    feed('ji<C-R>a<Esc>')
+    feed('ji<C-A><Esc>')
+    expect([[
+      ()a
+      ()b
+      (c
+      (d]])
+    eq(1, calls())
+
+    -- Macro keys are typeahead, not stuffed, thus trigger InsertCharPre.
+    n.fn.setreg('q', 'A(\27')
+    feed('gg@q')
+    expect([[
+      ()a()
+      ()b
+      (c
+      (d]])
+    eq(2, calls())
+  end)
+
   describe('Ctrl-R', function()
     it('works', function()
       command("let @@ = 'test'")