WIP: Read the terminal colour scheme on REPL startup by tecosaur · Pull Request #59958 · JuliaLang/julia

tecosaur · 2025-10-26T18:41:41Z

Wouldn't it be nice if Julia/the REPL knew what your terminal colours were, and displayed content appropriately?

useful description coming soon-ish

Sneak peek:

Query durations

initial query on a local machine: ~0.1s (which I suspect is due to other work that gets scheduled before the response is read)
subsequent queries on a local machine: <0.01s
initial query over SSH (100ms latency): ~0.3s

Important

This is asynchronous, and does not impact startup latency

Tested terminals

Test script

using StyledStrings
let (; FACES, SimpleColor, rgbcolor) = StyledStrings  # Grab some private API
    colors = Iterators.flatten((c, Symbol("bright_" * String(c))) for c in
        [:black, :green, :cyan, :blue, :magenta, :red, :yellow, :white])
    println(styled"{bold:    Swatch test  Read  Actual}\n ", '━'^30)
    termfg, termbg = @. SimpleColor(rgbcolor((:foreground, :background)))
    println(styled"     foreground  {(bg=$termfg):  }    {inverse:  }")
    println(styled"     background {light,grey:▕{(bg=$termbg):  }▏  ▕{:  }▏}")
    for color in colors
        termc = SimpleColor(FACES.basecolors[color])
        println(styled" $(lpad(color, 14))  {(bg=$termc):  }    {(bg=$color):  }")
    end
    print(styled"\n {bold:Platform:} {emphasis:$(Sys.KERNEL){grey:/}$(ENV[\"TERM\"])} {grey:(truecolor }")
    println(if Base.ttyhastruecolor() styled"{green,bold:✓}" else styled"{red,bold:✕}" end, styled"{grey:)}")
    println(styled" Do the swatches match?")
end

Everything works

Linux
- Kitty
- Wezterm
- Foot
- Ghostty
- Xterm
- Alacritty
- St (Suckless)
- Ubuntu terminal (Gnome terminal?)
- Tilix
Mac
- Terminal.app
- iTerm2
- WezTerm
- Alacritty
- Ghostty
- Kitty
Windows
- Windows terminal (it messes up inverse video though)
- Windows terminal: WSL

Misbehaving (terminal's fault)

Linux
- Konsole (lies about values)
Emacs
- Eat (doesn't supply colours)
- Vterm (doesn't report anything)
Mac
- iTerm2 + Tmux (doesn't report anything)
Windows
- Wezterm via Ubuntu WSL (doesn't report anything)

Misbehaving (our fault)

Nothing yet 🙂

This is not ready for review yet, I just want CI to build it so that helpful testers on Zulip (:wave:) can try this with juliaup add +pr59958.

topolarity · 2025-10-31T16:45:50Z

iTerm2 + Tmux (doesn't report anything)

Any issue that we can file upstream? This is a fairly common configuration, esp. since iTerm2 has tmux integration

tecosaur · 2025-10-31T17:00:40Z

Any issue that we can file upstream? This is a fairly common configuration, esp. since iTerm2 has tmux integration

Potentially, there seem to be a few closed OSC-related issues on tmux's repo. I'm also not 100% on the performance: it might be passing through fg/bg info, in which case as of some recent (unpushed) improvements we will still be able to set pick light/dark appropriately and set fg/bg colours.

Testing tmux locally myself, I see that it does pass through OSC 10 and OSC 11 codes (these are the fg/bg codes):

~$ printf '\e]10;?\e\\'
10;rgb:bbbb/c2c2/cfcf

~$ printf '\e]11;?\e\\'
11;rgb:2424/2727/3030

~$ printf '\e]4;1;?\e\\'

~$

tecosaur · 2025-11-02T11:13:02Z

I'm not sure what's a good idea to do here in terms of unit testing, since this should be tested against a collection of different terminal emulators.

jakobjpeters · 2025-11-20T08:01:01Z

Wouldn't it be nice if Julia/the REPL knew what your terminal colours were, and displayed content appropriately?

Yes please!

tecosaur · 2026-01-04T08:00:29Z

I now plan on getting this merged after #60527, and have adjusted the PR accordingly.

Keno · 2026-02-26T08:56:20Z

stdlib/REPL/src/term_osc.jl

+end
+
+const PENDING_RESPONSES = OSCResponse[]
+const RESPONSE_POLLERS = Tuple{Function, Timer}[]


Why does this architecture need to be so complicated with the pollers and the timeouts, why not just set the colors when the response comes in whatever time that might be.

Because we want to set the colours all at once after 16 responses have come in, but some terminals only partially respond (and so we'd be waiting forever without a timeout).

So why isn't that an integer that just counts how many you got and runs the function when that integer hits 16.

Because then we'd never apply the partial response (foreground + background only), which is what we rely on the timeout for.

So two integers then. I really don't see the point of the timeout.

How do we know if we should keep on waiting without a timeout?

tecosaur · 2026-02-26T09:16:53Z

Given #61151 and and (my) interest in supporting KKP eventually, it would probably be good to support non-OSC queries too, specifically primary device attributes (DA1: CSI c) and current progressive enhancement status (CSI ? u).

As it is, OSC support lets us query more than just colour: such as clipboard contents (when possible), and OSC 99 support.

This is prepratory work for #61151 and #59958. The key problem is that when we issue informational queries to the terminal emulator, we don't really have any way of knowing when they'll come back. There could be arbitrary amount of actual user input before or after. Thus, any code that would attempt to read from the terminal inline to read OSC responses faces the problem of accidentally getting user input and likewise, the REPL may see delayed OSC responses that are not inteded for it. To avoid all that complication, just put the REPL in charge of OSC response processing. The idea here is that at some point something issues the OSC query (possibly at startup) and whenever the response comes in, the REPL will just process it as if it was user input. This PR intentionally does not define a query interface, which is delagated to the follow on PRs that actually make use of this information. Example: ``` julia> write(stdout, "\e[c") 3 julia> 52 in Base.active_repl.mistate.terminal_properties.da1 true ```

This is prepratory work for #61151 (and could be extended in #59958). The key problem is that when we issue informational queries to the terminal emulator, we don't really have any way of knowing when they'll come back. There could be arbitrary amount of actual user input before or after. Thus, any code that would attempt to read from the terminal inline to read OSC responses faces the problem of accidentally getting user input and likewise, the REPL may see delayed OSC responses that are not inteded for it. To avoid all that complication, just put the REPL in charge of OSC response processing. The idea here is that at some point something issues the OSC query (possibly at startup) and whenever the response comes in, the REPL will just process it as if it was user input. This PR intentionally does not define a query interface, which is delagated to the follow on PRs that actually make use of this information. Example: ``` julia> write(stdout, "\e[c") 3 julia> 52 in Base.active_repl.mistate.terminal_properties.da1 true ```

This is prepratory work for #61151 and #59958. The key problem is that when we issue informational queries to the terminal emulator, we don't really have any way of knowing when they'll come back. There could be arbitrary amount of actual user input before or after. Thus, any code that would attempt to read from the terminal inline to read OSC responses faces the problem of accidentally getting user input and likewise, the REPL may see delayed OSC responses that are not inteded for it. To avoid all that complication, just put the REPL in charge of OSC response processing. The idea here is that at some point something issues the OSC query (possibly at startup) and whenever the response comes in, the REPL will just process it as if it was user input. This PR intentionally does not define a query interface, which is delagated to the follow on PRs that actually make use of this information. Example: ``` julia> write(stdout, "\e[c") 3 julia> 52 in Base.active_repl.mistate.terminal_properties.da1 true ``` Written by Claude.

This is prepratory work for #61151 and #59958. The key problem is that when we issue informational queries to the terminal emulator, we don't really have any way of knowing when they'll come back. There could be arbitrary amount of actual user input before or after. Thus, any code that would attempt to read from the terminal inline to read OSC responses faces the problem of accidentally getting user input and likewise, the REPL may see delayed OSC responses that are not inteded for it. To avoid all that complication, just put the REPL in charge of OSC response processing. The idea here is that at some point something issues the OSC query (possibly at startup) and whenever the response comes in, the REPL will just process it as if it was user input. This PR intentionally does not define a query interface, which is delagated to the follow on PRs that actually make use of this information. Example: ``` julia> write(stdout, "\e[c") 3 julia> 52 in Base.active_repl.mistate.terminal_properties.da1 true ``` Written by Claude. (cherry picked from commit 331421e)

tecosaur added REPL Julia's REPL (Read Eval Print Loop) display and printing Aesthetics and correctness of printed representations of objects. labels Oct 26, 2025

This was referenced Oct 26, 2025

Recolouring support JuliaLang/StyledStrings.jl#129

Merged

FYI: overlapping history work in upstream dalum/Diary.jl#5

Open

tecosaur force-pushed the term-recolour branch 3 times, most recently from 5633335 to 7e22584 Compare October 27, 2025 15:29

tecosaur mentioned this pull request Oct 27, 2025

Stylistically disambiguate julia> in docstrings #55455

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tecosaur force-pushed the term-recolour branch from 7e22584 to c89eef3 Compare October 27, 2025 16:52

tecosaur mentioned this pull request Oct 28, 2025

Make banner size depend on terminal size #51811

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tecosaur force-pushed the term-recolour branch 3 times, most recently from 80b448e to 0c05f5b Compare October 29, 2025 19:12

tecosaur mentioned this pull request Nov 5, 2025

:incomplete detection should properly consider where in the line I am #60017

Open

tecosaur mentioned this pull request Jan 1, 2026

Value-parameterised annotations and Face primacy #60527

Draft

Read the terminal colour scheme on REPL startup

9869f0c

tecosaur force-pushed the term-recolour branch from 0c05f5b to 9869f0c Compare January 4, 2026 07:59

This was referenced Jan 22, 2026

Markdown code highlighting in terminal styling regression: REPL examples blend in too much with code #60541

Open

Interactive history search in Julia 1.13 not readable on light background #60810

Open

tecosaur mentioned this pull request Feb 26, 2026

REPL: add OSC 52 clipboard fallback and graceful degradation #61151

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Keno reviewed Feb 26, 2026

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Keno mentioned this pull request Feb 26, 2026

REPL: Add OSC parsing to the keymap #61181

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andradei mentioned this pull request Mar 30, 2026

delta pager option --detect-dark-light not working. jesseduffield/lazygit#4550

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WIP: Read the terminal colour scheme on REPL startup#59958

WIP: Read the terminal colour scheme on REPL startup#59958
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Query durations

Tested terminals

Everything works

Misbehaving (terminal's fault)

Misbehaving (our fault)

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