Fix NoGuavaSetsNewHashSet to skip Iterable-only arguments

[timtebeek]

Summary

• Fixes issue Sets.newHashSet(Iterables.filter... is not correctly handed by NoGuavaSetsNewHashSet recipe #881 where Sets.newHashSet(Iterables.filter(...)) was incorrectly transformed
• Implements conservative approach (Option 3 from analysis): skip transformation for Iterable-only cases
• Adds comprehensive test coverage for the bug and edge cases

Problem

The NoGuavaSetsNewHashSet recipe was transforming code like:

Sets.newHashSet(Iterables.filter(myExceptions, ClassCastException.class))

Into broken code:

new HashSet<>(Arrays.asList(Iterables.filter(...)))

This caused compilation errors because:

1. Arrays.asList() doesn't accept Iterable parameters
2. Type inference failed for HashSet<>

Root Cause

The recipe only checked if the argument was assignable to Collection, but Guava's Sets.newHashSet() has three overloads:

• newHashSet() - no args ✓
• newHashSet(E... elements) - varargs ✓
• newHashSet(Iterable<? extends E> elements) - Missing!

When an Iterable (not a Collection) was passed, it fell through to the varargs case and generated invalid code.

Solution

Modified the recipe to:

1. Check if argument is a Collection first → transform to new HashSet<>(collection)
2. Check if argument is only an Iterable → skip transformation (preserve Guava code)
3. Otherwise, treat as varargs → transform to new HashSet<>(Arrays.asList(...))

This conservative approach ensures we never generate broken code.

Test Plan

• ✅ setsNewHashSetWithIterablesFilter: Verifies the reported issue is fixed
• ✅ setsNewHashSetWithCustomIterable: Verifies other Iterable types are skipped
• ✅ setsNewHashSetWithCollectionStillWorks: Verifies Collection transformation still works
• ✅ All existing tests pass

Alternative Approaches Considered

• See issue Sets.newHashSet(Iterables.filter... is not correctly handed by NoGuavaSetsNewHashSet recipe #881 for full analysis of multiple fix options. This PR implements Option 3 (conservative skip) as it:

• Is the safest approach (won't break code)

• Aligns with user expectation ("it could be ignored")

• Follows "do no harm" principle

• Can be enhanced later with Option 1 (StreamSupport) if desired

• Fixes Sets.newHashSet(Iterables.filter... is not correctly handed by NoGuavaSetsNewHashSet recipe #881

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