shortenFullyQualifiedTypes can change type resolution for inherited nested types #3117

Summary

shortenFullyQualifiedTypes can change the meaning of a qualified type when the simple name is also an inherited nested type.

The formatter avoids some collisions with types declared in the same compilation unit, but does not appear to account for member types inherited from a superclass or interface.

Reproducer

Spotless Gradle plugin 8.10.3, with shortenFullyQualifiedTypes() as the only configured Java step:

The complete Gradle project is available here:

https://gist.github.com/MattAlp/a50100bc9d712c470ded424c36e8f315

The reproducer contains:

• Base, which declares nested type Type
• Child, which extends Base
• external.Type, which is referenced by fully qualified name

Before formatting, Child contains:

public static String use(external.Type value) {
    return value.externalOnly();
}

The project compiles successfully. After running:

./gradlew spotlessApply

Spotless adds import external.Type; and changes the code to:

public static String use(Type value) {
    return value.externalOnly();
}

The unqualified Type resolves to the inherited Base.Type, not external.Type. Compilation then fails:

cannot find symbol
  method externalOnly()
  location: variable value of type Type

Suggested behavior

Leave a qualified reference alone when its simple name can resolve to an inherited member type. If this cannot be determined without a classpath, the conservative behavior should be to leave the qualification intact.

Related work

This appears related to:

• shortenFullyQualifiedTypes produces uncompilable code when the simple name collides with a type in the same compilation unit #3033 — same-compilation-unit type collisions
• shortenFullyQualifiedTypes: skip FQNs whose simple name clashes with types declared in the same file #3031 — collisions with types declared in the same file
• shortenFullyQualifiedTypes: preserve unqualified type resolution #3037 — preserving existing unqualified type resolution