Scala language support

[jkschneider]

Summary

Scala 3 language support for OpenRewrite, enabling automated refactoring of Scala source code using the existing Java recipe ecosystem.

Parser

• Parses Scala 3 source files via the Dotty compiler into OpenRewrite's Lossless Semantic Tree (LST)
• Maps Scala syntax to J (Java) LST types wherever possible, with Scala-specific S types only where Java has no equivalent (S.CompilationUnit, S.TuplePattern, S.Wildcard, S.BlockExpression)
• Scala-specific markers for constructs that map structurally to Java but print differently (SObject, InfixNotation, FunctionApplication, ScalaForLoop, etc.)
• Full printer (ScalaPrinter) that round-trips Scala syntax faithfully (square bracket type params, val/var, trait, => lambdas, etc.)

Type Attribution

• Batch compilation through the Dotty typer phase for type information
• ScalaTypeMapping maps Dotty types/symbols to OpenRewrite's JavaType model
• Span-based lookup from the untyped tree into the typed tree via TreeTraverser
• Name-based fallback for identifiers and method names
• ShallowClass for library types to avoid deep recursive type hierarchies
• Companion object $ suffix stripping for Java recipe compatibility

Recipe Compatibility

Proven working with standard Java recipes on Scala code:

• FindTypes — find type references by FQN pattern
• FindMethods — find method invocations (including static calls like Collections.emptyList())
• ChangeMethodName — rename methods across Scala source
• ChangeType — change type references (including java.lang types)
• OrderImports — alphabetical import ordering

Test Coverage

• 329 tests, 0 failures, 0 disabled
• 261 parser/printer round-trip tests covering all major Scala constructs
• 5 type attribution assertion tests
• 9 recipe compatibility tests
• Tests for classes, objects, traits, vals, vars, methods, lambdas, pattern matching, for-comprehensions, imports, annotations, generics, and more

Test plan

• ./gradlew :rewrite-scala:test — all 329 tests pass
• Recipe compatibility verified: FindTypes, FindMethods, ChangeMethodName, ChangeType, OrderImports
• Type attribution verified: identifiers, class declarations, method invocations, NewClass, field access

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