My phone uses dotted underline to indicate errors; that seems nice, a bit
less aggressive than curly. Unfortunately dotted underlines are not as well
supported in terminal emulators; sometimes they are barely visible. So it's
unlikely that we want to use --underline=dotted for an important theme.
Add double and dashed too I guess, even though I don't have a concrete
use case..
Old versions of ConHost and Putty can't parse DCS sequences.
For this reason, we briefly switch to the alternate screen buffer while sending
DCS-format (e.g. XTGETTCAP) queries. For extra paranoia, we wrapped this
procedure in a synchronized update. This doesn't seem to be needed; neither
ConHost nor Putty show glitches when the synchronized update is omitted.
As of today, every terminal that implements XTGETTCAP also implements
synchronized updates but that might change.
Let's remove it, to reduce surprise for users and terminal developers.
As a bonus, this also fixes a glitch on Terminal.app which fails to parse
the synchronized-update query (`printf '\x1b[?2026$p'`) and echoes the "p"
(bug report ID FB17141059). Else we could work around this with another
alternate screen buffer.
Unfortunately, this change surfaces two issues with GNU screen. For one,
they don't allow apps to use the alternate screen features (the user may
allow it with "altscreen on"). Second, screen unconditionally echoes
the payload of DCS commands. A possible fix has been suggested at
https://lists.gnu.org/archive/html/screen-devel/2025-04/msg00010.html
I think this combination of behaviors is unique among terminals. I'm sure
there are more terminals that don't parse DCS commands yet, but I think almost
all terminals implement alternate screen buffer. Probably only terminal
multiplexers are prone to this issue. AFAICT very few multiplexers exists,
so we can work around those until they are fixed.
Disable XTGETTCAP queries for GNU screen specifically. Unfortunately screen
does not implement XTVERSION, so I don't know how to reliably identify
it. Instead, check STY and some commonly-used values TERM values.
This has false negatives in some edge cases.
But the worst thing that happens is that "+q696e646e" will be echoed once
at startup, which is easy to ignore, or work around with something like
function workaround --on-event fish_prompt
commandline -f repaint
functions --erase workaround
end
which I don't think we should apply by default, because it can mask other
issues.
We should give screen more time to respond. I guess I'll open an issue so
we don't forget. In doubt, we can always go back to the previous approach
(but implement it in fish script).
Alternative workaround: instead of the alternative screen buffer, we could
try something like clr_eol/clr_bol to erase the spuriously echoed text. I
tried to do this in various ways but (surprisingly) failed.
"set_color --background=normal" resets all attributes. I don't expect anyone
relied on this behavior. Let's remove it, to reduce surprise. This also
improves consistency with "set_color --underline-color=normal".
As suggested in
https://github.com/fish-shell/fish-shell/issues/11417#issuecomment-2825023522
For backwards compatibility reasons, "set_color normal" still resets
everything though. In future we could make "set_color --foreground=normal"
reset only foreground.
Closes#11418
Add a new underline-color option to set_color (instead of adding an optional
color argument to --underline); this allows to set the underline color
independently of underline style (line, curly, etc.). I don't think this
flexibility is very important but this approach is probably the least hacky.
Note that there are two variants:
1. \e[58:5:1m
2. \e[58;5;1m
Variant 1 breaks:
breakage from colon-variant for colored underlines
- cool-retro-term makes text blink
- GNU screen (goes into bold mode)
- terminology (goes into bold mode)
Variant 2 would break:
- mintty (Cygwin terminal) -- it enables bold font instead.
- Windows Terminal (where it paints the foreground yellow)
- JetBrains terminals echo the colons instead of consuming them
- putty
- GNU screen (goes into bold mode)
- st
- urxvt
- xterm
- etc.
So choose variant 1.
Closes#11388Closes#7619
set_color --underline=curly outputs \e[4:3m which breaks the following
terminals:
- Terminal.app interprets it as yellow background
- abduco and dvtm interpret it as green foreground
- JetBrains terminals interprets it as yellow background
- urxvt interprets it as yellow background
terminals that interpret curly as single underline:
- tmux [1]
- emacs ansi-term [2]
- emacs vterm
- GNU screen (also wrongly turns on italic mode)
- terminology (also wrongly turns on italic mode)
- Vim's :terminal
[1]: https://github.com/orgs/tmux/discussions/4477
[2]: https://lists.gnu.org/archive/html/bug-gnu-emacs/2025-04/msg01093.htmlCloses#10957
We have a a workaround with a comment saying
> We don't know if exit_attribute_mode resets colors, so we set it to
> something known.
I'm pretty sure fish (and other software) makes this assumption.
I'd be very surprised if a relevant terminal behaves differently.
Let's remove our attempt to work around around this.
While at it, extract a function to be used in two other places
(but don't change their behavior yet).
While at it, also document the command to reset the shape to the default,
which we should probably use. See foot commit 49034bb7 (csi: let CSI 0 q mean
"switch to user configured cursor style", 2019-07-22).
As of today, the XTerm documentation is a not clear on this; in
XTerm itself, CSI 0 q may actually change the cursor because they have an
additional default cursor is configured differently..
Our use of the terminfo database in /usr/share/terminfo/$TERM is both
1. a way for users to configure app behavior in their terminal (by
setting TERM, copying around and modifying terminfo files)
2. a way for terminal emulator developers to advertise support for
backwards-incompatible features that are not otherwise easily observable.
To 1: this is not ideal (it's very easy to break things). There's not many
things that realistically need configuration; let's use shell variables
instead.
To 2: in practice, feature-probing via terminfo is often wrong. There's not
many backwards-incompatible features that need this; for the ones that do
we can still use terminfo capabilities but query the terminal via XTGETTCAP
directly, skipping the file (which may not exist on the same system as
the terminal).
---
Get rid of terminfo. If anyone finds a $TERM where we need different behavior,
we can hardcode that into fish.
* Allow to override this with `fish_features=no-ignore-terminfo fish`
Not sure if we should document this, since it's supposed to be removed soon,
and if someone needs this (which we don't expect), we'd like to know.
* This is supported on a best-effort basis; it doesn't match the previous
behavior exactly. For simplicity of implementation, it will not change
the fact that we now:
* use parm_left_cursor (CSI Ps D) instead of cursor_left (CSI D) if
terminfo claims the former is supported
* no longer support eat_newline_glitch, which seems no longer present
on today's ConEmu and ConHost
* Tested as described in https://github.com/fish-shell/fish-shell/pull/11345#discussion_r2030121580
* add `man fish-terminal-compatibility` to state our assumptions.
This could help terminal emulator developers.
* assume `parm_up_cursor` is supported if the terminal supports XTGETTCAP
* Extract all control sequences to src/terminal_command.rs.
* Remove the "\x1b(B" prefix from EXIT_ATTRIBUTE_MODE. I doubt it's really
needed.
* assume it's generally okay to output 256 colors
Things have improved since commit 3669805627 (Improve compatibility with
0-16 color terminals., 2016-07-21).
Apparently almost every actively developed terminal supports it, including
Terminal.app and GNU screen.
* That is, we default `fish_term256` to true and keep it only as a way to
opt out of the the full 256 palette (e.g. switching to the 16-color
palette).
* `TERM=xterm-16color` has the same opt-out effect.
* `TERM` is generally ignored but add back basic compatiblity by turning
off color for "ansi-m", "linux-m" and "xterm-mono"; these are probably
not set accidentally.
* Since `TERM` is (mostly) ignored, we don't need the magic "xterm" in
tests. Unset it instead.
* Note that our pexpect tests used a dumb terminal because:
1. it makes fish do a full redraw of the commandline everytime, making it
easier to write assertions.
2. it disables all control sequences for colors, etc, which we usually
don't want to test explicitly.
I don't think TERM=dumb has any other use, so it would be better
to print escape sequences unconditionally, and strip them in
the test driver (leaving this for later, since it's a bit more involved).
Closes#11344Closes#11345
