Mapping sometimes works but sometimes not

Question

What I tried:

 :nnoremap <C-w>n <Enter>

Expected result:

• When pressing Ctrl+w then n, just an Enter is simulated rather than horizontally splitting a window.

Actual result:

• The mapping sometimes works but sometimes not.

What I noticed:

• When lhs of :map is of the form <C-X>Y where X and Y are arbitrary characteres, mapping works only when you press Ctrl+X and then rapidly press Y. If there is a delay (maybe hundreds milliseconds or so) before pressing Y, mapping does not work and original key-binding is used. By "original key-binding", I mean the un-mapped version of Ctrl+X + Y, not just Y. So it seems this strange behavior doesn't come from time-out of Ctrl+X. (If so, it would be natural that un-mapped version of just Y is simulated.)

Environment:

~ $ vi --version
VIM - Vi IMproved 8.2 (2019 Dec 12, compiled Feb 15 2020 13:52:40)
Included patches: 1-259

How can I map to Ctrl+w n? Or does the behavior natural?

Answer 1

So, first, the breakdown on mappings and "timing out":

'timeout'       boolean (default on)
'ttimeout'      boolean (default off, set in |defaults.vim|)
    These two options together determine the behavior when part of a
    mapped key sequence or keyboard code has been received:

    'timeout'    'ttimeout'     action
       off      off             do not time out
       on       on or off       time out on :mappings and key codes
       off      on              time out on key codes

    [snipped]

Essentially, by default, vim will time out on :mapped sequences and special key codes (like the <Esc>. that is the equivalent of pressing <A-.>).

You can control the length of said timeout with timeoutlen and ttimeoutlen:

'timeoutlen'    number  (default 1000)
'ttimeoutlen'   number  (default -1, set to 100 in |defaults.vim|)
    The time in milliseconds that is waited for a key code or mapped key
    sequence to complete.  Also used for CTRL-\ CTRL-N and CTRL-\ CTRL-G
    when part of a command has been typed.
    Normally only 'timeoutlen' is used and 'ttimeoutlen' is -1.  When a
    different timeout value for key codes is desired set 'ttimeoutlen' to
    a non-negative number.

        ttimeoutlen mapping delay      key code delay
           < 0      'timeoutlen'       'timeoutlen'
          >= 0      'timeoutlen'       'ttimeoutlen'

    The timeout only happens when the 'timeout' and 'ttimeout' options
    tell so.  A useful setting would be
        :set timeout timeoutlen=3000 ttimeoutlen=100
    (time out on mapping after three seconds, time out on key codes after
    a tenth of a second).

So it sounds like by default, you should get at least 1 second for mappings and key-codes alike, unless you're using the line from defaults.vim such that key-codes only get 100s.

---

Options for a solution

1. Disable timeouts entirely (set notimeout nottimeout)—personally, I don't recommend this, but YMMV.
2. Enable timeouts on mappings as longer, and keycodes as shorter (set timeoutlen=3000 ttimeoutlen=100)—this is what I've been using and I've not had any issues. Your mapping works for me with this setup.

---

Understanding where the issue might be

Try running

verbose set timeout? ttimeout? timeoutlen? ttimeoutlen?

The results should be informative.