fix(edit.c): indentkeys double indent after "!" #12894

which is both unexpected and different from the Vim behaviour.

Indent was triggered once by the '!' check in insert_execute(), and
inserting the char was correctly skipped, but then triggered again in
insert_check() (provided that cindent was not being ignored after manual
indentation, i.e. `can_cindent == true`).

While this is the smallest fix, another solution would be to remove
VimState#check and instead move that to *_enter()/-_execute(), since the
control flow is pretty unnecessarily convoluted as is. That would also
have the benefit of differing less from the Vim source code.

2 files changed, 16 insertions, 7 deletions

diff --git a/src/nvim/edit.c b/src/nvim/edit.c
index 6583ac8584..dc856f01fe 100644
--- a/src/nvim/edit.c
+++ b/src/nvim/edit.c
@@ -624,16 +624,17 @@ static int insert_execute(VimState *state, int key)
   }
 
   if (cindent_on() && ctrl_x_mode_none()) {
+    s->line_is_white = inindent(0);
     // A key name preceded by a bang means this key is not to be
     // inserted.  Skip ahead to the re-indenting below.
-    // A key name preceded by a star means that indenting has to be
-    // done before inserting the key.
-    s->line_is_white = inindent(0);
-    if (in_cinkeys(s->c, '!', s->line_is_white)) {
-      insert_do_cindent(s);
+    if (in_cinkeys(s->c, '!', s->line_is_white)
+        && stop_arrow() == OK) {
+      do_c_expr_indent();
       return 1;  // continue
     }
 
+    // A key name preceded by a star means that indenting has to be
+    // done before inserting the key.
     if (can_cindent && in_cinkeys(s->c, '*', s->line_is_white)
         && stop_arrow() == OK) {
       do_c_expr_indent();
@@ -3657,7 +3658,7 @@ void fix_indent(void)
 /// Check that "cinkeys" contains the key "keytyped",
 /// when == '*': Only if key is preceded with '*' (indent before insert)
 /// when == '!': Only if key is preceded with '!' (don't insert)
-/// when == ' ': Only if key is not preceded with '*' (indent afterwards)
+/// when == ' ': Only if key is not preceded with '*' or '!' (indent afterwards)
 ///
 /// "keytyped" can have a few special values:
 /// KEY_OPEN_FORW :
@@ -3697,7 +3698,7 @@ bool in_cinkeys(int keytyped, int when, bool line_is_empty)
     case '!':
       try_match = (*look == '!'); break;
     default:
-      try_match = (*look != '*'); break;
+      try_match = (*look != '*') && (*look != '!'); break;
     }
     if (*look == '*' || *look == '!') {
       look++;
diff --git a/test/functional/editor/mode_insert_spec.lua b/test/functional/editor/mode_insert_spec.lua
index e3d3cdbd85..cd51a65be3 100644
--- a/test/functional/editor/mode_insert_spec.lua
+++ b/test/functional/editor/mode_insert_spec.lua
@@ -6,12 +6,20 @@ local expect = helpers.expect
 local command = helpers.command
 local eq = helpers.eq
 local eval = helpers.eval
+local curbuf_contents = helpers.curbuf_contents
 
 describe('insert-mode', function()
   before_each(function()
     clear()
   end)
 
+  it('indents only once after "!" keys #12894', function()
+    command('let counter = []')
+    command('set indentexpr=len(add(counter,0))')
+    feed('i<C-F>x')
+    eq(' x', curbuf_contents())
+  end)
+
   it('CTRL-@', function()
     -- Inserts last-inserted text, leaves insert-mode.
     insert('hello')