vim -w or -W records K_SPECIAL sequence from xterm version string in script
Josh Triplett
an xterm or another terminal that supports requesting the terminal
version, vim will do so, and process the resulting version response to
set a few options. In the process of doing so, it ends up recording
three extra bytes at the beginning of the script file:
/tmp$ vim -u /dev/null -N -W foo
/tmp$ hd foo
00000000 80 fd 35 5a 5a |..5ZZ|
00000005
This affected quite a few people playing on vimgolf.com.
After some adventures through vim's source, I think I've tracked down exactly
what happens to cause the problem:
- Vim asks the terminal for its version string when it starts, in the
may_req_termresponse function, by sending the kPRV string from the
terminfo record, and then calling vpeekc_nomap.
- That reads the response from stdin into typebuf, and eventually ends
up in check_termcode, which handles terminal escape sequences.
- check_termcode finds the version response, and if it manages to
extract an xterm version number, it sets various features based on
that version number.
- check_termcode then translates the escape sequence into the key_name
array as KS_EXTRA and KE_IGNORE, which match the second and third
bytes of the escape sequence.
- Towards the end of check_termcode (near the comment "Add any modifier
codes to our string."), this becomes a three-byte sequence K_SPECIAL
KS_EXTRA KE_IGNORE, which matches the three bytes that appear in the
script file.
- check_termcode then puts this sequence into the typebuf, and doesn't
seem to set anything to make vim treat this sequence as something not
typed by the user.
- Later on, this character gets read, and ends up in vgetorpeek. Near
the comment "get a character: 2. from the typeahead buffer",
vgetorpeek ends up considering this character a typed character, and
feeds it to gotchars, which calls updatescript on each character to
write it to the script file.
I don't know the correct fix. Possibly something should set tb_maplen
to mark the character as the result of a map, or possibly the character
shouldn't get re-inserted into typebuf at all.
- Josh Triplett