shortenFullyQualifiedTypes corrupts method references on fields (x.field::m -> bogus import x.field) #3133

Summary

shortenFullyQualifiedTypes() (added in #3005) corrupts a method reference on a field of a local variable. It treats localVar.field::method as if localVar.field were a fully-qualified type, shortens it to field::method, and injects a bogus import localVar.field; — which does not compile.

Because it only manifests on spotlessApply (not the read-only spotlessCheck), a developer runs spotlessApply, commits, and then the project no longer builds.

Version

• com.diffplug.spotless 8.10.3 (Gradle plugin)
• JDK 11 / 17 (reproduces on both)

Minimal reproducer

build.gradle:

plugins {
    id 'java'
    id 'com.diffplug.spotless' version '8.10.3'
}
repositories { mavenCentral() }
spotless { java { shortenFullyQualifiedTypes() } }

src/main/java/Example.java:

import java.util.Map;
import java.util.function.Function;

public class Example {
    static class Catalog {
        Map<String, String> aliases;
    }

    String demo(Catalog catalog) {
        return find(catalog.aliases::get);   // method ref on a field of a local var
    }

    String find(Function<String, String> f) {
        return f.apply("x");
    }
}

Steps

./gradlew spotlessApply
./gradlew compileJava

Actual

spotlessApply rewrites the file to:

import java.util.Map;
import java.util.function.Function;
import catalog.aliases;          // <-- bogus import of a non-existent package/type

public class Example {
    ...
    String demo(Catalog catalog) {
        return find(aliases::get);   // <-- qualifier dropped, now unresolved
    }
    ...
}

and compilation fails:

Example.java: error: package catalog does not exist

Expected

catalog.aliases::get is a method reference on a field access of a local variable, not a fully-qualified type reference. It must be left untouched (no shortening, no import added).

Root cause (guess)

The qualifier-resolution doesn't verify that the left-hand side of a qualified name / method-reference scope actually resolves to a type before shortening. Field accesses on locals/params (x.y, x.y::m, x.y.z) are being misclassified as fully-qualified type names. Checking that the qualifier is a type (not a local variable / field expression) before rewriting should fix it.

Found while enabling the step on a real codebase (jbangdev/jbang), where catalog.aliases::get (a Catalog local + Map field) broke the build.