Add stdin support with explicit opt-in flag

[A909M]

Hey team,

This brings back stdin support from #390, but with an explicit --stdin flag to avoid the
breaking changes that caused the revert.

The Problem

The original implementation would automatically read from stdin if it was available, which
broke VSCode and PHPStorm extensions since they were inadvertently leaving stdin open when
calling pint.

What Changed

Now you need to explicitly pass --stdin to enable stdin mode. This means existing tools
won't break, and editors can opt-in when they're ready.

You can also pass a file path along with --stdin for better config resolution:

# Basic usage
cat file.php | pint --stdin
# With file path (useful for editors like Zed)
pint app/Models/User.php --stdin < app/Models/User.php

In stdin mode, pint outputs only the formatted code to stdout (no summary), which is what
editors expect.

Testing

Added comprehensive tests covering:

• Basic stdin formatting
• Works with --silent, --test, --format flags
• Path argument for config resolution
• Empty stdin handling

All existing tests still pass.

Zed Integration Example

"languages": {
    "PHP": {
      "format_on_save": "on",
      "formatter": {
        "external": {
          "command": "vendor/bin/pint",
          "arguments": ["{buffer_path}", "--stdin"]
        }
      }
    }
  }

Fixes the issues raised in #402 and implements the solution suggested in #390.

[A909M]

@crynobone

[taylorotwell]

Why is there so much more code than the original PR?

[A909M]

Why is there so much more code than the original PR?

Ha, yeah... I definitely over-engineered that. My bad.

Started fresh with the original PR and just swapped the auto-detection for the flag check.
Kept it simple this time - added the --stdin option and updated tests to use it.

Ready for review!

[taylorotwell]

@calebdw any feedback on this? 🙏

[calebdw]

This is fine I suppose, there's many ways to go about this.

It's also pretty standard to read from STDIN when - is passed as the filename. Black also allows a --stdin-filename to allow passing what the filename should be (to respect any ignores) when passing in the data on stdin

Not saying we have to do all that, just food for thought.

[taylorotwell]

I like the idea of using stdin if - is passed as the file name. cc @A909M

[calebdw]

If we're going with - for stdin, then likely need --stdin-filename so that files that should be ignored will be ignored

[A909M]

Sounds good! I'll update it to use - for stdin and add --stdin-filename for the path
context. Working on it now.

[A909M]

@calebdw @taylorotwell Done! Using - for stdin with --stdin-filename option as suggested.

Re: exclusions - Stdin input is formatted regardless of exclusion patterns (like
Black/Prettier). --stdin-filename provides context for config and error messages, which is
what editors need.

Zed editor example:

{
  "languages": {
    "PHP": {
      "formatter": {
        "external": {
          "command": "vendor/bin/pint",
          "arguments": ["--stdin-filename", "{buffer_path}"]
        }
      }
    }
  }
}