Development

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Developing a compiler is complex. Testing it well is expensive, so we focus on getting as wide testing as possible for the time spent. For that reason we have a few levels of testing:

Unit tests

Only really used for the parser, but utterly necessary to write one. All changes to the parser should come with a corresponding unit test.

ImporterTest

Built in the same spirit as the scala compiler's partest, this takes smallish pieces of typescript code and run it through the entire pipeline, including scalac. These are relatively cheap (~30 seconds for all tests if they all recompile), and covers a lot of ground. If you're making changes, you'll get quite a few answers here.

Note that for non-CI machines we update the checked in conversion results directly, as long as scalac is happy. This means that after successfully running the test, the next step is to review the git changes in importer/src/test/resources/*/check. In CI it's enforced that the checked in results are current, so we know which commit introduces which change.

Demo set

Do your changes look good when running ImporterTest? The next step is to run the demo set.

See Running for more information about the parameters.

A good command to run might be:

sbt:ScalablyTypedConverter> importer/runMain org.scalablytyped.converter.Main -softWrites -parseCache -offline -dontCleanProject -forceCommit -demoSet

Does any library fail? Fix it.

Does all libraries convert successfully? Inspect git changes.

Full set

Did you make small innocent change and passed the demo set without problems? Skip this, it takes an hour or two, depending.

Larger change? Run the command for demo set without the -demoSet option and go for a walk.

Pull request.

All changes go through a PR.