Sending two keys in series during autocompletion confirmation

Question

I have the following mapping:

inoremap <expr><CR> pumvisible() && complete_info().selected != -1? "\<C-y>" : "\<CR>"
inoremap <expr><Space> pumvisible() && complete_info().selected != -1? "\<C-y>" : "\<Space>"

The idea here is that if I have a completion menu open & and item selected, then pressing Enter or Space will select that item from the completion menu. Notice that <C-y> is the built-in combination to confirm a selection. This works fine.

Now, I want to expand the functionality of this so that whenever I press Space, it will select an item from the list and type a literal whitespace. I tried the following:

inoremap <expr><Space> pumvisible() && complete_info().selected != -1? "\<C-y>\<Space>" : "\<Space>"

This does not work (it behaves as if only space was pressed), & I suspect it's because the keys are sent simultaneously. I tried using a regular space character instead of the symbol and it behaved the same way. What can I do?

EDIT: Just to make my question clearer, here is what happens when I select an autocompletion option using the Enter key:

No problems here, all works as intended. What I want to do now is that if I had pressed Space instead of Enter, then it would do the exact same thing as it did before, but also add a whitespace at the end. With the current settings I am using, this is what happens instead:

Answer 1

One can use a timer to prevent keys from being pressed simultaneously. For example,

inoremap <C-a> <C-y><Esc>:call timer_start(100, {-> feedkeys("a ")})<CR>

will send <C-y><Esc> followed by a<Space> after 100ms.

Instead of 100ms, one can specify any delay, even 0ms.

Adding the above to the expr mapping for Space, we get

inoremap <expr><Space> pumvisible() && complete_info().selected != -1? '<C-y><Esc>:call timer_start(0, {-> feedkeys("a ")})<CR>' : '<Space>'

On my machine, this spits out the selected option, and after a tiny delay, adds a space.

Answer 2

The problem with your code is that in a mapping command, you do not need to escape <keys>. This is because they are already interpreted by the inoremap.

inoremap <expr><Space> pumvisible() && complete_info().selected != -1? '<C-y><Space>' : '<Space>'