feat: use STDERR for console components auxiliary output

[faisuc]

As described in issue #56602, this PR modifies Laravel's console components to write auxiliary output (task progress, prompts, etc.) to STDERR when available, while maintaining full backwards compatibility. This allows commands with --json flags to pipe output without UI contamination.

Currently, console components like task(), progress bars, and prompts write to STDOUT, which contaminates piped output:

# Current behavior - task output breaks JSON
php artisan some:command --json > output.json
$ head -n+3 output.json
Doing work ...................................... 1s DONE  # ← Breaks JSON!
[
  {

Console components now use STDERR for auxiliary output when ConsoleOutputInterface is available:

# New behavior - clean JSON output
php artisan some:command --json > output.json
$ head -n+3 output.json
[
  {
    "nice": "valid JSON!"

[taylorotwell]

I feel almost certain this will be a breaking change for someone.

[shaedrich]

Do we have to use standard streams or would it be perhaps better to use non-standard streams to not abuse STDERR for non-error output?

[faisuc]

Thanks for the review. Two concrete, non‑breaking ways forward:

• Opt‑in toggle (default OFF in 12.x)

  • Per command: add a small opt‑in (e.g. protected bool $componentsToStderr = true or a useErrorOutputForComponents() helper).
  • Global: config/env toggle (e.g. console.components_to_stderr=true) with per‑command override.
  • We can flip the default in the next major.

• Optional “auto” mode (behind config)

  • Only route components to STDERR when STDOUT is not a TTY (i.e., piped). Keeps current behavior for interactive runs; enables clean piping when needed.

On using non‑standard streams: that’s not portable across shells/CI. STDERR is the conventional place for progress/debug output and Symfony explicitly supports this via getErrorStyle(), which is why many tools do it this way. Reference: “Writing to the error output” in Symfony’s console docs (symfony.com/docs/current/console/style.html#writing-to-the-error-output).

I’m happy to update the PR to:

• keep current behavior by default,
• add per‑command and global opt‑in,
• optionally include an “auto when not TTY” mode behind config,
• keep the tests covering both paths.

[Radiergummi]

Do we have to use standard streams or would it be perhaps better to use non-standard streams to not abuse STDERR for non-error output?

That's no abuse; it's the other way around: Standard output is reserved for the result of the command, while standard error takes any other auxiliary output like debug information, warnings, or optional info. If a command has the purpose of carrying out a single action, it shouldn't print any output to stdout at all, and just exit with 0. You can observe this with pretty much all standard Unix CLI tools.

[taylorotwell]

I'm not going to make any changes here on 12.x.