quarto emits ANSI cursor-control sequences when stderr is not a terminal

[cderv]

When quarto's stderr is piped, redirected to a file, or consumed by an editor build tool (e.g. Emacs M-x compile, VS Code tasks), progress and spinner helpers still emit ANSI cursor-control sequences. These appear as raw escape bytes in the output buffer:

^[[0G^[[2K^[[J^[[0G^[[2K^[[J^[[0G

Reported in https://github.com/orgs/quarto-dev/discussions/14403

Root cause

src/core/console.ts emits cursor-control bytes without checking whether the output stream is a terminal. Specifically, clearLine() calls ansi.eraseLine.cursorLeft() unconditionally, and spinner() and progressBar() gate their output on runningInCI() but not on whether stderr is actually a TTY. withSpinner()'s cancel path always calls clearLine(), regardless of where output goes.

quarto-cli/src/core/console.ts

Lines 180 to 182 in d5c1f1d

	export function clearLine() {
	info(ansi.eraseLine.cursorLeft(), { newline: false });
	}

quarto-cli/src/core/console.ts

Lines 110 to 124 in d5c1f1d

	const id = setInterval(() => {
	// Display the message
	const char = kSpinnerChars[spin % kSpinnerChars.length];
	const msg = `${spinContainer(char)} ${statusFn()}`;
	// when running in CI only show the first tick
	if (!runningInCI() || spin === 0) {
	info(`\r${msg}`, {
	newline: false,
	});
	}
	// Increment the spin counter
	spin = spin + 1;
	}, timeInterval);

NO_COLOR does not cover this — it governs colors only. --log-format plain governs the log file format, not console output.

The codebase already has the right helper: isInteractiveTerminal() in src/core/platform.ts, which returns Deno.stderr.isTerminal(). It is already used in command/create/cmd.ts and command/publish/cmd.ts to gate interactive prompts, but not in src/core/console.ts.

quarto-cli/src/core/platform.ts

Lines 97 to 99 in d5c1f1d

	export function isInteractiveTerminal() {
	return Deno.stderr.isTerminal();
	}

src/core/log.ts's LogFileHandler.format() already handles this for file output — messages starting with \r are dropped because they are progress lines. The same "progress is terminal-only" notion is not applied to the stderr console handler or to clearLine().

quarto-cli/src/core/log.ts

Lines 232 to 237 in d5c1f1d

	override format(logRecord: LogRecord): string {
	// Messages that start with a carriage return are progress messages
	// that rewrite a line, so just ignore these
	if (logRecord.msg.startsWith("\r")) {
	return "";
	}

Reproduction

Any quarto command that uses withSpinner or progressBar shows this when stderr is piped. The cleanest CLI-only form:

quarto check versions 2>&1 | cat -v
quarto install tinytex 2>&1 | cat -v

leading to something like

$ quarto check versions 2>&1 | cat -v
Quarto 1.10.3
^M[>] Checking versions of quarto binary dependencies...
      Pandoc version 3.8.3: OK
      Dart Sass version 1.87.0: OK
      Deno version 2.4.5: OK
      Typst version 0.14.2: OK
^M[>] Checking versions of quarto dependencies......OK

Or via Emacs M-x compile running quarto render example.qmd --to html, where the compilation buffer is not a TTY.

Suggested direction

Gate clearLine(), spinner(), and progressBar() on isInteractiveTerminal() (extending the !runningInCI() check that is already there to also require a TTY). This matches the idiom already used for interactive prompts in create/publish, and aligns console behavior with the file-handler behavior in log.ts.