[LANG-1700] Improve handling of parameterized types and variable unrolling #1549
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garydgregory
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Dec 31, 2025
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Hello @isaric
Please rebase on git master to pick the latest changes, including your other PR.
Thank you!
Enhanced `TypeUtils` to correctly handle parameterized types with nested generic arguments and improve unrolling of type variables. Updated `unrollVariables` to prevent infinite recursion by handling visited `TypeVariable` instances. Modified argument cloning to avoid in-place mutations. Added unit tests to validate behavior against complex parameterized types and ensure accurate assignability checks.
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@garydgregory You're welcome! Rebased off master. |
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Summary
Fixes incorrect assignability checks for parameterized types with nested generic arguments.
Problem
TypeUtils.isAssignable()incorrectly returnedtruewhen checking ifMyComparator<Iterable<MyNonTransientException>>is assignable toMyComparator<? super MyNonTransientException>. This happened because the type variable unrolling logic ingetTypeArguments()didn't properly resolve nested generic arguments when traversing the inheritance hierarchy.Changes
getTypeArguments(): When walking up the inheritance hierarchy, now properly unrolls type variables in parameterized parent types before recursing, ensuring nested generic arguments are correctly resolvedunrollVariables(): Added avisitedset to track already-visitedTypeVariableinstances, preventing infinite loops when circular type variable references existtest_LANG_1700()validates the fix with a complex parameterized type hierarchyTest Case
The test verifies that
LexOrdering<MyNonTransientException>(which implementsMyComparator<Iterable<MyNonTransientException>>) is correctly identified as not assignable toMyComparator<? super MyNonTransientException>, sinceIterable<MyNonTransientException>is not a supertype ofMyNonTransientException.