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feat: add external break signal for read_line interruption and mark Signal as non_exhaustive#1035

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fdncred merged 3 commits intonushell:mainfrom
eitsupi:feat/external-break-signal
Mar 12, 2026
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feat: add external break signal for read_line interruption and mark Signal as non_exhaustive#1035
fdncred merged 3 commits intonushell:mainfrom
eitsupi:feat/external-break-signal

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@eitsupi eitsupi commented Mar 11, 2026 •
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Add a break signal that allows external threads to interrupt read_line(), causing it to return a new Signal::ExternalBreak(String) variant with the current buffer contents.

Motivation

Applications that embed a REPL alongside external control systems (e.g., AI agents) need a way to interrupt read_line() from another thread.
For example, an AI agent controlling the console may need to inject input while the user is at the prompt — but read_line() is a blocking loop with no external interruption mechanism.

Currently, there is no way for an external thread to cause read_line() to return.
The external_printer feature can print messages above the prompt, but cannot break out of the input loop.
The idle_callback feature (#1015) allows periodic processing but also cannot cause an early return.

Design

The break signal check is placed in the read_line_helper loop alongside idle_callback and external_printer.
When break_signal is configured, needs_polling is set to true so read_line() uses poll() instead of blocking indefinitely on crossterm::event::read().

API

use std::sync::{atomic::AtomicBool, Arc};

let break_signal = Arc::new(AtomicBool::new(false));
let mut editor = Reedline::create()
    .with_break_signal(break_signal.clone());

// From another thread:
break_signal.store(true, Ordering::Relaxed);

// read_line() returns:
// Ok(Signal::ExternalBreak(buffer_contents))

Note

Signal is now #[non_exhaustive].
Downstream match arms on Signal will need a wildcard _ pattern.
This is a one-time change that prevents future additions from being breaking.

@eitsupi eitsupi changed the title feat!: add external break signal for read_line interruption and mark Signal as non_exhaustive feat: add external break signal for read_line interruption and mark Signal as non_exhaustive Mar 11, 2026
@eitsupi eitsupi mentioned this pull request Mar 11, 2026
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fdncred commented Mar 11, 2026

Is there any way to test this automatically and/or manually?

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eitsupi commented Mar 12, 2026

Is there any way to test this automatically and/or manually?

I've added an example so you can test it manually.

Automated testing requires a terminal, which is tested in arf test suite (eitsupi/arf#113) using https://github.com/doy/vt100-rust (unfortunately not compatible with Windows).

@fdncred fdncred merged commit 5c2f105 into nushell:main Mar 12, 2026
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fdncred commented Mar 12, 2026

Thanks!

@Juhan280
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Juhan280 commented Mar 12, 2026

Hi. I was bumping reedline in nushell. How should nushell handle this? Should it just ignore it? Both nusehll repl and the input command uses it.

@Juhan280 Juhan280 mentioned this pull request Mar 12, 2026
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fdncred commented Mar 12, 2026

@Juhan280 For now it can be ignored but in the future it would be cool to have proper support for it.

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Juhan280 commented Mar 12, 2026

Ok

@eitsupi eitsupi deleted the feat/external-break-signal branch March 12, 2026 15:05
@eitsupi eitsupi mentioned this pull request Mar 19, 2026
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eitsupi added a commit to eitsupi/arf that referenced this pull request Mar 19, 2026
@eitsupi
feat: add experimental JSON-RPC IPC server for external tool access (#…
24fe4b3 
…113)

## Summary

Add an experimental JSON-RPC 2.0 IPC server for AI agents, IDE extensions, and other external tools to interact with a running arf R session.

### Features

- **Transport**: Unix domain sockets (Linux/macOS), Windows named pipes
- **Protocol**: JSON-RPC 2.0 over HTTP (curl-compatible) or raw JSON
- **`evaluate` method**: Silent or visible evaluation with captured stdout/value/error via WriteConsoleEx interception
- **`user_input` method**: Inject code into the REPL via reedline's `ExternalBreak` signal (nushell/reedline#1035), with full echo, history, spinner, and duration tracking
- **`send` method**: Alias for `user_input`
- **`:ipc` meta command**: Start/stop/check server status at runtime
- **`arf ipc` subcommand**: CLI client for eval/send/list/status from another terminal
- **Session discovery**: `~/.cache/arf/sessions/<pid>.json`, cleaned up on exit

### Safety

- Mutual exclusion with console input: IPC requests are rejected with `USER_IS_TYPING` (-32003) when the user has typed something in the buffer
- Alternate screen modes (help pager, history browser, shell mode): IPC requests are rejected immediately with `R_NOT_AT_PROMPT` (-32001)
- Prompt position is preserved after rejected ExternalBreak (reedline fix: nushell/reedline#1042)

### Tests

- 7 cross-platform IPC unit tests (protocol, evaluate, user_input)
- 6 PTY integration tests (evaluate capture, visible/silent modes, user_input, rejection, prompt position)
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3 participants

@eitsupi @fdncred @Juhan280