vim-patch:8.2.4711: when 'insermode' is set :edit from <Cmd> mapping misbehaves

Problem:    When 'insermode' is set :edit from <Cmd> mapping misbehaves.
Solution:   Don't set "need_start_insertmode" when already in Insert mode.
            (closes vim/vim#10116)
3a56b6d405

src/nvim/ex_cmds.c

@@ -2875,7 +2875,7 @@ int do_ecmd(int fnum, char_u *ffname, char_u *sfname, exarg_T *eap, linenr_T new
     redraw_curbuf_later(NOT_VALID);     // redraw this buffer later
   }
 
-  if (p_im) {
+  if (p_im && (State & INSERT) == 0) {
     need_start_insertmode = true;
   }
 

src/nvim/testdir/test_edit.vim

@@ -1627,6 +1627,29 @@ func Test_edit_is_a_directory()
   call delete(dirname, 'rf')
 endfunc
 
+" Using :edit without leaving 'insertmode' should not cause Insert mode to be
+" re-entered immediately after <C-L>
+func Test_edit_insertmode_ex_edit()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+    set insertmode noruler
+    inoremap <C-B> <Cmd>edit Xfoo<CR>
+  END
+  call writefile(lines, 'Xtest_edit_insertmode_ex_edit')
+
+  let buf = RunVimInTerminal('-S Xtest_edit_insertmode_ex_edit', #{rows: 6})
+  call TermWait(buf, 50)
+  call assert_match('^-- INSERT --\s*$', term_getline(buf, 6))
+  call term_sendkeys(buf, "\<C-B>\<C-L>")
+  call TermWait(buf, 50)
+  call assert_notmatch('^-- INSERT --\s*$', term_getline(buf, 6))
+
+  " clean up
+  call StopVimInTerminal(buf)
+  call delete('Xtest_edit_insertmode_ex_edit')
+endfunc
+
 func Test_edit_browse()
   " in the GUI this opens a file picker, we only test the terminal behavior
   CheckNotGui