build: Add PHP binding

[vanillajonathan]

This patch adds a PHP binding that uses the libprql_lib through PHP's Foreign Function Interface (FFI) extension.

Closes #1844

[max-sixty]

Overall this looks great, thanks a lot @vanillajonathan !

We do need to add a test which runs in GitHub Actions, we add that for everything now. Would you be able to do that? We can use something like test-python.yaml as an example.

[vanillajonathan]

Overall this looks great, thanks a lot @vanillajonathan !

We do need to add a test which runs in GitHub Actions, we add that for everything now. Would you be able to do that? We can use something like test-python.yaml as an example.

I don't know how to do this, but it needs to run Composer which is a package manager for PHP which will install the the PHPUnit test framework which can be ran as ./vendor/bin/phpunit tests.

[max-sixty]

OK. It does look like there lots of examples out there — e.g. https://github.com/php-actions/example-phpunit/blob/master/.github/workflows/ci.yml — does that help?

I appreciate that it might seem less fun than the code (?) But it does mean your contribution will live on forever! Whenever something changes in PRQL, the test confirms that this code still works. If you can run the test locally, getting it to run in GHA should be 10-15 mins maximum, and happy to help with questions if that's helpful.

[max-sixty]

FYI looks like this might be causing the failure: php-actions/composer#95

We can run on just ubuntu in the meantime if that helps

[vanillajonathan]

Thanks! I changed to only run on Ubuntu now and this seems to work a little better, it still fails, but at least now I get a better error message.

Building PHP latest with extensions: FFI ...
Composer could not find a composer.json file in /app
To initialize a project, please create a composer.json file. See https://getcomposer.org/basic-usage
Error: Process completed with exit code 1.

Okay now I managed to get Composer (package manager) working. Now for the unit tests...

[vanillajonathan]

Then I don't know how to get it inside there.

mkdir -p /app/prql-php will fix this error

It's unclear why it's looking for /app/prql-php/, I'm not sure that's a total solution...

Just tried that.

mkdir: cannot create directory ‘/app’: Permission denied

[max-sixty]

mkdir: cannot create directory ‘/app’: Permission denied

We need to create the app directory first! e.g. mkdir /app. Does that make sense?

It looks like we're still seeing errors because of the /app path. I'm not sure why it always goes to the /app path. Is this something to do with PHP? Do we see this behavior locally?

We could ask at https://github.com/php-actions/phpunit/issues if we can't figure it out.

[max-sixty]

@vanillajonathan do I see it working? Great job!!

Let me know when you're ready and I'll have a final look over

[vanillajonathan]

Yes, it is working.

I had some problems, I used the php-actions/phpunit@v3 and when the unit tests ran it would complain that it couldn't find the library file even though I had confirmed that it indeed existed by running ls in the pipeline. It seems php-actions/phpunit@v3 was executing with the project root directory as context, so it would look for the library in src/ instead of prql-php/src/. So instead of using the php-actions/phpunit@v3 GitHub Action I now just run the unit tests via the shell instead just as I do on my local machine. This works. The php-actions/phpunit@v3 would probably work too if prql-php was in a separate repository like the demo-c-program repository.

[max-sixty]

Excellent! A couple of final clean-ups and then we can merge.

I know this has been quite the journey, thanks @vanillajonathan !

[vanillajonathan]

Excellent! A couple of final clean-ups and then we can merge.

I know this has been quite the journey, thanks @vanillajonathan !

Yeah, writing the PHP code was quick, fun and easy. The CI stuff, not so much. 😅️

[max-sixty]

Yeah, writing the PHP code was quick, fun and easy. The CI stuff, not so much. 😅️

Yeah, this did end up being quite laborious for that. I'm surprised PHP isn't better supported by the ecosystem — generally these are as easy as adding an action and it works. But here it the action was worse than running a single command...

From our perspective, without the tests, it's very difficult to manage the project, particularly for things we're not familiar with, like PHP. So really appreciate your patience in pushing through.

[max-sixty]

Merging! Further work could be to update prql-lib to use the latest API, and pushing that change through here.