Investigate issues w. `screen`

[bash]

Bug report in delta: dandavison/delta#1707

Notes

• Sending OSC 10 ; ? + DA1 returns just the response to DA1:

  printf '\e]10;?\e\\\e[c'
  e[c^C

• Sending OSC 11 ; ? + DA1 returns the DA1 response followed by OSC 11. This breaks a core assumption that the order of sequences is respected!

[bash]

Fixed in https://github.com/bash/terminal-colorsaurus/releases/tag/0.4.1 by detecting and bailing out early for screen.

Context:

terminal-colorsaurus/src/xterm/quirks.rs

Lines 18 to 43 in c888fdd

	// Why is GNU Screen unsupported?
	//
	// 1. Screen only supports `OSC 11` (background) and not `OSC 10` (foreground)
	//
	// 2. Screen replies to queries in the incorrect order.
	// We send `OSC 11` + `DA1` and expect the answers to also be in that order.
	// However, as far as I can tell, Screen relays the `OSC 11` query to the underlying terminal,
	// and so we get the `DA1` response back *first*. This is usually an indicator that
	// the terminal doesn't support the `OSC` query.
	//
	// There are two both equally broken workarounds:
	//
	// * Don't send `DA1`, just `OSC 11`. \
	// Since Screen forwards the query to the underlying terminal, we won't get an answer
	// if the underlying terminal doesn't support it. And we don't have a way to detect that
	// => we hit the 1s timeout :/
	//
	// * Send the query (`OSC 11` + `DA1`) to the underlying terminal by wrapping it between `CSI P` and `ST`.
	// (There's a reverted commit that does exactly this: f06206b53d2499e95627ef29e5e35278209725db)
	// * If there's exactly one attached display (underlying terminal)
	// => everything works as usual.
	// * If there's no attached display we don't get an answer to DA1
	// => we hit the 1s timeout :/
	// * If there are multiple displays attached (yes this is supported and quite fun to try) we get back multiple responses
	// => since there's no way to know that we need to expect multiple responses
	// some of them are not consumed by us and end up on the user's screen :/

[bash]

Note to self: Don't try to reproduce this on the version installed from Homebrew.
OSC 11 support in screen is only enabled when compiled with --enable-rxvt_osc. The official Homebrew formula doesn't enable this feature.