vim src/submodule/frontend/frobnicate2.c

In Ex commands, at places where a file name can be used, the following
characters have a special meaning.  These can also be used in the expression
function `expand()`.

        %       Is replaced with the current file name.           :_% c_%

:edit %.orig

:edit file/in/a/deeply/nested/subdirectory/here.txt
:edit %:h/in_same_dir_as_above.txt

:edit %:h:h:h/file.txt

set path=./**

cnoremap <a-q> <c-c>:let @a=expand('%')<CR>:<Up><c-r>a

expand('%:p')