Add Reassignable trait - #8175
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A syntactic check that an expression could be the target of a plain assignment without introducing a compile error. Handles two shapes: - a J.Identifier referring to a non-final local declared in an enclosing block (method parameters are excluded because reassigning a parameter silently drops the caller's expected mutation). - a J.FieldAccess whose target is a bare J.Identifier and whose field is non-final. Array-element writes, parenthesized targets, method-chain receivers, and multi-hop qualified field access are intentionally not matched. Effectively-final semantics are not modelled.
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July 3, 2026 21:13
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Can you scan the codebase for places this could be used? I know there's the one in your recipe PR, but before we finalize the API it would be good to make sure this trait is applicable/handles variations
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What
A new incubating
Reassignabletrait underorg.openrewrite.java.traitthat answers a syntactic question recipes tend to re-invent locally: could this expression be the target of a plain assignmenttarget = ...without introducing a compile error?Why
x.setFoo(...)shapes intox = x.rebuild()....build()— or any other transformation that needs to reassign a receiver — currently either duplicate the walk-up-the-cursor-and-check-flags logic each time, or silently skip cases where the receiver is a field access. Concrete example: theReassignable-shaped guard that landed inrewrite-jackson#153(MigrateMapperSettersToBuilder#isReassignableReceiver).Extracting the check as a trait gives future recipes a one-liner and gives us one place to sharpen the semantics.
Scope for v1
Deliberately narrow, matching the jackson recipe's semantics:
J.Identifierreferring to a non-final local declared in an enclosing block, and aJ.FieldAccesswhose target is a bareJ.Identifierand whose field is non-final.a.b.c), array-element writes, parenthesized targets, and method-chain receivers.Follow-up: migrate the jackson recipe to use the trait once this lands.
Test plan
./gradlew :rewrite-java:test --tests 'org.openrewrite.java.trait.ReassignableTest'— 5 cases (non-final local ✓, final local ✗, method parameter ✗, non-finalthis.field✓, finalthis.field✗)../gradlew :rewrite-java:test --tests 'org.openrewrite.java.trait.*'— no regression in other trait tests.