fix: do not save K_EVENT as lastc in Insert mode

I'm also gonna move some other K_EVENT-related tests to vim_spec.lua

src/nvim/edit.c

@@ -643,7 +643,10 @@ static int insert_check(VimState *state)
   update_curswant();
   s->old_topline = curwin->w_topline;
   s->old_topfill = curwin->w_topfill;
-  s->lastc = s->c;   // remember previous char for CTRL-D
+
+  if (s->c != K_EVENT) {
+    s->lastc = s->c;  // remember previous char for CTRL-D
+  }
 
   // After using CTRL-G U the next cursor key will not break undo.
   if (dont_sync_undo == kNone) {

test/functional/api/vim_spec.lua

@@ -1154,8 +1154,8 @@ describe('API', function()
     end)
   end)
 
-  describe('RPC (K_EVENT) #6166', function()
-    it('does not complete ("interrupt") normal-mode operator-pending', function()
+  describe('RPC (K_EVENT)', function()
+    it('does not complete ("interrupt") normal-mode operator-pending #6166', function()
       helpers.insert([[
         FIRST LINE
         SECOND LINE]])
@@ -1191,7 +1191,7 @@ describe('API', function()
       ]])
     end)
 
-    it('does not complete ("interrupt") normal-mode map-pending', function()
+    it('does not complete ("interrupt") normal-mode map-pending #6166', function()
       command("nnoremap dd :let g:foo='it worked...'<CR>")
       helpers.insert([[
         FIRST LINE
@@ -1207,7 +1207,8 @@ describe('API', function()
         SECOND LINE]])
       eq('it worked...', helpers.eval('g:foo'))
     end)
-    it('does not complete ("interrupt") insert-mode map-pending', function()
+
+    it('does not complete ("interrupt") insert-mode map-pending #6166', function()
       command('inoremap xx foo')
       command('set timeoutlen=9999')
       helpers.insert([[
@@ -1222,6 +1223,37 @@ describe('API', function()
         FIRST LINE
         SECOND LINfooE]])
     end)
+
+    it('does not interrupt Insert mode i_CTRL-O #10035', function()
+      feed('iHello World<c-o>')
+      eq({mode='niI', blocking=false}, meths.get_mode())  -- fast event
+      eq(2, eval('1+1'))  -- causes K_EVENT key
+      eq({mode='niI', blocking=false}, meths.get_mode())  -- still in ctrl-o mode
+      feed('dd')
+      eq({mode='i', blocking=false}, meths.get_mode())  -- left ctrl-o mode
+      expect('') -- executed the command
+    end)
+
+    it('does not interrupt Select mode v_CTRL-O #15688', function()
+      feed('iHello World<esc>gh<c-o>')
+      eq({mode='vs', blocking=false}, meths.get_mode())  -- fast event
+      eq({mode='vs', blocking=false}, meths.get_mode())  -- again #15288
+      eq(2, eval('1+1'))  -- causes K_EVENT key
+      eq({mode='vs', blocking=false}, meths.get_mode())  -- still in ctrl-o mode
+      feed('^')
+      eq({mode='s', blocking=false}, meths.get_mode())  -- left ctrl-o mode
+      feed('h')
+      eq({mode='i', blocking=false}, meths.get_mode())  -- entered insert mode
+      expect('h')  -- selection is the whole line and is replaced
+    end)
+
+    it('does not interrupt Insert mode i_0_CTRL-D #13997', function()
+      command('set timeoutlen=9999')
+      feed('i<Tab><Tab>a0')
+      eq(2, eval('1+1'))  -- causes K_EVENT key
+      feed('<C-D>')
+      expect('a')  -- recognized i_0_CTRL-D
+    end)
   end)
 
   describe('nvim_get_context', function()

test/functional/editor/mode_insert_spec.lua

@@ -6,7 +6,6 @@ local expect = helpers.expect
 local command = helpers.command
 local eq = helpers.eq
 local eval = helpers.eval
-local meths = helpers.meths
 
 describe('insert-mode', function()
   before_each(function()
@@ -75,15 +74,5 @@ describe('insert-mode', function()
       feed('ooo')
       expect('hello oooworld')
     end)
-
-    it("doesn't cancel Ctrl-O mode when processing event", function()
-      feed('iHello World<c-o>')
-      eq({mode='niI', blocking=false}, meths.get_mode()) -- fast event
-      eq(2, eval('1+1'))  -- causes K_EVENT key
-      eq({mode='niI', blocking=false}, meths.get_mode()) -- still in ctrl-o mode
-      feed('dd')
-      eq({mode='i', blocking=false}, meths.get_mode()) -- left ctrl-o mode
-      expect('') -- executed the command
-    end)
   end)
 end)

test/functional/editor/mode_visual_spec.lua

@@ -1,27 +0,0 @@
--- Visual-mode tests.
-
-local helpers = require('test.functional.helpers')(after_each)
-local clear = helpers.clear
-local eq = helpers.eq
-local eval = helpers.eval
-local expect = helpers.expect
-local feed = helpers.feed
-local meths = helpers.meths
-
-describe('visual-mode', function()
-  before_each(clear)
-
-  it("select-mode Ctrl-O doesn't cancel Ctrl-O mode when processing event #15688", function()
-    feed('iHello World<esc>gh<c-o>')
-    eq({mode='vs', blocking=false}, meths.get_mode()) -- fast event
-    eq({mode='vs', blocking=false}, meths.get_mode()) -- again #15288
-    eq(2, eval('1+1'))  -- causes K_EVENT key
-    eq({mode='vs', blocking=false}, meths.get_mode()) -- still in ctrl-o mode
-    feed('^')
-    eq({mode='s', blocking=false}, meths.get_mode()) -- left ctrl-o mode
-    feed('h')
-    eq({mode='i', blocking=false}, meths.get_mode()) -- entered insert mode
-    expect('h') -- selection is the whole line and is replaced
-  end)
-end)
-