atuinsh/atuin · info

writing to a String cannot fail

Error message

writing to a String cannot fail

What it means

`on_scroll` writes vt100 row contents into a `String` buffer via `write_formatted_basic` and unwraps the `Result` with `.expect("writing to a String cannot fail")`. The error type from rmp/vt100-style writers cannot occur when the target is a `String` (no capacity or IO errors), so this is an infallibility assertion, not a real runtime failure.

Solutions

1. Pin/upgrade the `vt100` crate and confirm `write_formatted_basic` still returns an infallible-for-String error type
2. If it can now fail, propagate the error instead of expecting

// infallible in practice; if the vt100 API becomes fallible:
if let Err(e) = contents.write_formatted_basic(&mut self.buffer, &mut self.state) {
    log::warn!("failed to format scroll contents: {e}");
    return;
}

When it happens

Trigger: Only via a library bug: the underlying `write_formatted_basic` implementation returning `Err` despite writing to a `String` (e.g. a breaking change in the vt100 crate's API contract).

Common situations: Effectively never; appears in terminal scrollback rendering inside the TUI when new screen contents are captured.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

• writing to a Vec is infallible
• Atuin running with no parent!
• clone pty reader
• Could not build config
• Could not build default

AI-assisted analysis of atuinsh/atuin@900007c480 (2026-09-19). Data as JSON: /api/errors/ecadee7d9dfe5847. Report an issue: GitHub.

Appendix: source

Thrown at crates/atuin-common/src/ansi.rs:59

                if !std::mem::take(&mut first) {
                    // Trim the end of the line that was pushed in the previous iteration, and add
                    // the newline that we didn't push.
                    plain_contents.trim_end_matches_in_place([' ', '\t']);
                    plain_contents.push('\n');
                }
                plain_contents.push_str(plain_line);
            }
        }
    }

    impl vt100::Callbacks for Capture {
        fn on_scroll(&mut self, contents: vt100::capture::RowContents<'_>, alternate_screen: bool) {
            if alternate_screen {
                return;
            }
            contents
                .write_formatted_basic(&mut self.buffer, &mut self.state)
                .expect("writing to a String cannot fail");
            push_formatted(&mut self.plain_contents, &self.buffer);
            self.buffer.clear();
        }
    }

    if input.is_empty() {
        return String::new();
    }

    let mut parser = vt100::Parser::new_with_callbacks(rows, cols, 0, Capture::default());
    onlcr(input).for_each(|chunk| parser.process(chunk));

    let (screen, capture) = parser.screen_and_callbacks_mut();
    screen
        .write_contents_formatted_basic(
            &mut capture.buffer,
            vt100::capture::BasicFormattedCaptureRange::Full(&mut capture.state),
        )

View on GitHub (pinned to 900007c480)