RemoveUnusedImports creating ambiguous imports

[knutwannheden]

RemoveUnusedImports creating ambiguous imports

Problem

The RemoveUnusedImports recipe was incorrectly creating ambiguous imports by unfolding wildcard imports for
types that were only used in fully qualified form. For example, when java.util.Date was used as new java.util.Date(), the wildcard import import java.util.*; would be replaced with import java.util.Date;
instead of being removed entirely.

Root Cause

The original implementation lacked proper detection of qualified vs unqualified type references. During
wildcard import unfolding, the recipe would add imports for all types found in the typesInUse collection
without checking whether those types were actually used in unqualified form or only in fully qualified form.

Solution

Enhanced the RemoveUnusedImports recipe in
/rewrite-java/src/main/java/org/openrewrite/java/RemoveUnusedImports.java with:

1. Efficient Unqualified Reference Collection

• Added collectUnqualifiedTypeNames() method: Performs a single AST traversal to collect all fully
  qualified names of types used in unqualified form
• Performance optimization: Changed from O(n*m) complexity to O(m + n) by replacing multiple AST traversals
  with a single pass and fast set lookups
• Smart qualified reference detection: Uses isPartOfQualifiedReference() helper to walk up the AST cursor
  and detect when an identifier is part of a J.FieldAccess chain

2. Improved Wildcard Unfolding Logic

• Line 246-247: Modified wildcard unfolding to filter types using
  unqualifiedTypeNames.contains(fqType.getFullyQualifiedName())
• Lines 258-262: Enhanced logic to completely remove wildcard imports when no types are used unqualified
• Lines 282-284, 317: Added defensive checks to prevent IndexOutOfBoundsException

3. Edge Case Handling

• Added test case: keepImportWhenBothQualifiedAndUnqualifiedUsageExists() verifies that imports are
  preserved when a type is used both qualified and unqualified in the same file
• Mixed usage support: Correctly handles scenarios where Date and java.util.Date appear in the same
  file

Key Changes

RemoveUnusedImports.java:

• Lines 87-88: Added upfront collection of unqualified type names
• Lines 473-528: New collectUnqualifiedTypeNames() method with AST traversal logic
• Lines 502-524: Helper method isPartOfQualifiedReference() for qualified reference detection
• Line 246: Replaced inefficient per-type checking with fast set lookup

RemoveUnusedImportsTest.java:

• Lines 2215-2230: Added edge case test for mixed qualified/unqualified usage

Verification

• ✅ Original failing test onlyFullyQualifiedUsageShouldRemoveWildcard() now passes
• ✅ New edge case test keepImportWhenBothQualifiedAndUnqualifiedUsageExists() passes
• ✅ All 63 existing RemoveUnusedImports tests continue to pass with no regressions
• ✅ Significant performance improvement for files with multiple wildcard imports

Test Cases Covered

1. Fully qualified only: java.util.Date usage → wildcard import removed entirely
2. Unqualified only: Date usage → wildcard import unfolded to specific import
3. Mixed usage: Both Date and java.util.Date → import preserved due to unqualified reference
4. Conflicting names: Multiple packages with same class name → correct import precedence maintained

• Fixes RemoveUnusedImports creating ambiguous imports when there's explicit imports accompanying wildcards #5703

[timtebeek]

Nice to see some of these longer standing issues resolved! I've applied the recipe here as well, and seems like we can now safely enable it going forward. Great!