indicatif outputs cursor movement escape sequences even when TERM=dumb and/or NO_COLOR=1 is set, displaying raw ANSI sequences in environments that use pseudo-TTYs but cannot interpret ANSI sequences.

When deciding whether to render progress bars, indicatif checks terminal.is_terminal(), which downstream only checks if stdout/stderr is a TTY (isatty()).

This recently came up in j178/prek#1551 where a user of fugitive.vim -- which sets both TERM=dumb and/or NO_COLOR=1 -- saw raw ANSI sequences from our indicatif spinner.

MRE

cargo.toml:

[dependencies]
indicatif = "0.18.3"

src/main.rs:

use indicatif::ProgressBar;

fn main() {
    let pb = ProgressBar::new_spinner();
    pb.tick();
    pb.finish_with_message("done");
}

Build:

cargo build --release

Run (note, script syntax below is for macOS; Linux syntax varies slightly):

script -q /dev/null creates a pseudo-TTY so isatty() returns true. 1b 5b is hex for ESC[ — the ANSI escape sequence prefix.

# Normal TTY - escape sequences expected
script -q /dev/null ./target/release/mre 2>&1 | xxd | grep '1b 5b'
# Output: 00000050: ... 0d1b 5b32 4b ...  (ESC[2K present)

# With TERM=dumb - escape sequences should be suppressed
TERM=dumb script -q /dev/null ./target/release/mre 2>&1 | xxd | grep '1b 5b'
# Output: (same - ESC[2K still present)

# With NO_COLOR=1 - escape sequences should be suppressed
NO_COLOR=1 script -q /dev/null ./target/release/mre 2>&1 | xxd | grep '1b 5b'
# Output: (same - ESC[2K still present)