Vim 8.1.0495 (25 октября 2018 г.)

С патчем vim 8.1.0495 команда :filterподдерживает:let

:filter <pattern> let g:

:h :filter

                                                        :filt :filter
:filt[er][!] {pat} {command}
:filt[er][!] /{pat}/ {command}
                        Restrict the output of {command} to lines matching
                        with {pat}.  For example, to list only xml files: 
                                :filter /\.xml$/ oldfiles
                       If the [!] is given, restrict the output of {command}
                        to lines that do NOT match {pat}.

                        {pat} is a Vim search pattern.  Instead of enclosing
                        it in / any non-ID character (see 'isident') can be
                        used, so long as it does not appear in {pat}.  Without
                        the enclosing character the pattern cannot include the
                        bar character.

                        The pattern is matched against the relevant part of
                        the output, not necessarily the whole line. Only some
                        commands support filtering, try it out to check if it
                        works. Some of the commands that support filtering:
                           :#          - filter whole line
                           :clist      - filter by file name or module name
                           :command    - filter by command name
                           :files      - filter by file name
                           :highlight  - filter by highlight group
                           :jumps      - filter by file name
                           :let        - filter by variable name
                           :list       - filter whole line
                           :llist      - filter by file name or module name
                           :marks      - filter by text in the current file,
                                           or file name for other files
                           :oldfiles   - filter by file name
                           :set        - filter by variable name

                        Only normal messages are filtered, error messages are
                        not.