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https://issues.apache.org/jira/browse/GROOVY-12208?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King resolved GROOVY-12208.
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Fix Version/s: 6.0.0-beta-1
Assignee: Paul King
Resolution: Fixed
> NullChecker: broaden null-guard recognition
> -------------------------------------------
>
> Key: GROOVY-12208
> URL: https://issues.apache.org/jira/browse/GROOVY-12208
> Project: Groovy
> Issue Type: Improvement
> Components: groovy-typecheckers
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
> Fix For: 6.0.0-beta-1
>
>
> The incubating {{groovy.typecheckers.NullChecker}} currently recognizes a
> limited in-body guard vocabulary: single {{x != null}} / {{x == null}} binary
> comparisons (including identity forms) as {{if}} conditions, and early-exit
> patterns ({{if (x == null) return/throw}}), plus safe navigation.
> (Separately, the groovy-contracts bridge already infers non-nullness from
> {{@Requires}} conditions including conjunctions, via
> {{StaticTypesMarker.INFERRED_NON_NULL}} — this issue is about guard
> recognition inside method bodies, where conjunctions and other idiomatic
> forms are not yet recognized.)
> Idiomatic Groovy uses several other null-guard forms, each currently
> producing false positives that discourage adoption:
> * Groovy-truth guards: {{if (x) { x.foo() } }} — for reference types,
> truthiness implies non-null within the guarded block (Groovy truth being
> false for empty strings/collections does not affect nullness soundness).
> * Boolean conjunctions in conditions: {{if (x != null && x.foo())}}, and
> short-circuit dereferences {{x != null && x.foo()}} in expression position;
> Groovy-truth conjuncts {{x && x.foo()}}.
> * {{instanceof}} checks: {{if (x instanceof Foo)}} implies {{x}} is non-null
> (aligns with the flow typing the static type checker already performs for
> {{instanceof}}).
> * {{Objects.nonNull(x)}} / {{Objects.isNull(x)}} in the positions the binary
> forms are recognized today.
> * {{assert x}} and {{assert x != null}} statements.
> * Guard conditions in {{while}} loops and ternary conditions, mirroring the
> {{if}} handling.
> Each addition removes a class of false positives without changing the
> checker's architecture. Test coverage should include the negated forms and
> else-branch behaviour for each new guard shape, following the existing
> patterns in {{NullCheckerTest}} (cf. {{testNullableWithNotNullGuard}} et al.).
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