JSpecify migrations remove nullability annotations from void methods

[sullis]

What's changed

• New recipe org.openrewrite.java.migrate.jspecify.RemoveAnnotationFromVoidMethod. It removes annotations matching a type pattern (for example org.jetbrains.annotations.*ull*) from methods that return void, wherever they appear in the declaration:

  • before the modifiers: @Nullable public void m()
  • after a modifier: public @Nullable static void m()
  • before type parameters: public static @Nullable <T> void m()
  • directly before the return type: public @Nullable void m()

  The import is removed too when nothing else uses it.

• All seven JSpecify migrations in jspecify.yml (javax, jakarta, JetBrains, Micrometer, Spring, Micronaut, FindBugs) now run this recipe before ChangeType, and before MoveAnnotationToArrayType in the migrations that use it.

  • jakarta, JetBrains, Micrometer, Spring, and Micronaut use the *ull* pattern.
  • javax and FindBugs list the annotations one by one instead (javax: Nullable, CheckForNull, Nonnull; FindBugs: Nullable, CheckForNull, PossiblyNull, NonNull). In those packages *ull* also matches the *ByDefault annotations, such as @ParametersAreNonnullByDefault, which still mean something on a void method and must not be removed.

Why

A nullability annotation on a void method has no meaning. JSpecify's @Nullable is a TYPE_USE annotation, so Java doesn't allow it on a void return. Before this change, ChangeType carried code like @Nullable void foo() over to JSpecify unchanged, and the migrated code failed to compile.

Scope

• Only methods returning primitive void are changed. Methods returning boxed Void keep their annotations, since Void can legitimately be null.
• Annotations on parameters of void methods are left alone.
• Annotations that don't match the pattern, such as @Deprecated, stay in place.
• *ByDefault annotations on void methods are kept, so the existing migrations still handle them (for example, javax @ParametersAreNonnullByDefault still becomes @NullMarked).
• Formatting is preserved: after removal, the declaration keeps its indentation whether it starts with modifiers, type parameters, or the return type.

Tests

• RemoveAnnotationFromVoidMethodTest covers:
  • removing one matching annotation, and several at once
  • keeping annotations that don't match the pattern
  • methods without modifiers, and methods with type parameters
  • annotations after modifiers, before type parameters, and mixed with non-matching annotations
  • leaving non-void methods, parameter annotations, and boxed Void methods unchanged
• JSpecifyBestPracticesTest adds end-to-end cases for:
  • void methods annotated with JetBrains and jakarta @Nullable
  • a void method with javax @Nullable and @ParametersAreNonnullByDefault: @Nullable is removed and @ParametersAreNonnullByDefault becomes @NullMarked
  • a void method with FindBugs @Nullable and @ReturnValuesAreNonnullByDefault: @Nullable is removed and @ReturnValuesAreNonnullByDefault is kept

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