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https://issues.apache.org/jira/browse/GROOVY-12251?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul King resolved GROOVY-12251.
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Fix Version/s: 6.0.0-beta-2
Resolution: Fixed
> NullChecker: check @NonNull fields are definitely initialized (strict mode)
> ---------------------------------------------------------------------------
>
> Key: GROOVY-12251
> URL: https://issues.apache.org/jira/browse/GROOVY-12251
> Project: Groovy
> Issue Type: Improvement
> Components: groovy-typecheckers
> Reporter: Paul King
> Assignee: Paul King
> Priority: Major
> Fix For: 6.0.0-beta-2
>
>
> The {{NullChecker}} type-checking extension catches _assigning_ null to a
> {{@NonNull}} field, but a {{@NonNull}} field that is simply *never
> initialized* passes silently — and is then trusted as non-null at every
> dereference, so the one field guaranteed to hold null is the one the checker
> never warns about. Definite-initialization checking of non-null fields is a
> core check in comparable tools (NullAway, the Checker Framework's nullness
> checker).
> This issue adds, in flow-sensitive mode ({{NullChecker(strict: true)}}), a
> check that each explicitly-annotated {{@NonNull}} instance field is
> definitely initialized in one of the accepted ways:
> * at its declaration ({{@NonNull String name = 'unknown'}})
> * in an instance initializer block
> * by *every* declared constructor — a constructor delegating via
> {{this(...)}} relies on its delegate
> A class with no declared constructor reports {{@NonNull field 'name' is not
> initialized}}; a class where some but not all constructors assign the field
> reports {{@NonNull field 'name' is not initialized by all constructors}}.
> Example:
> {code:groovy}
> import groovy.transform.TypeChecked
> @TypeChecked(extensions = 'groovy.typecheckers.NullChecker(strict: true)')
> class Library {
> @NonNull String catalog // never assigned
> Library(String catalog) { } // oops — forgot this.catalog =
> catalog
> }
> {code}
> {noformat}
> [Static type checking] - @NonNull field 'catalog' is not initialized by all
> constructors
> {noformat}
> Deliberate scoping, to keep the check noise-free for idiomatic Groovy:
> * *Strict mode only.* The lenient checker's contract is incremental adoption;
> enabling this there would immediately flag existing {{@NonNull}} property
> classes constructed via named arguments ({{new Foo(name: 'x')}} initializes
> the property _after_ default construction). Strict mode is documented as the
> "full coverage" tier, which is where a definite-initialization guarantee
> belongs. Promoting it to lenient mode later remains open for discussion.
> * *Explicitly-annotated fields only.* Fields that are merely non-null by
> default (under {{@NullMarked}} / {{@NonNullByDefault}} without their own
> annotation) are not checked, for the same named-argument-bean reason.
> * *Exclusions:* {{@MonotonicNonNull}} and {{@Lazy}} fields (deliberately
> initialized late), primitives, and interfaces. Static fields are deferred for
> now.
> * *Not path-sensitive:* an assignment anywhere in a constructor counts;
> per-path definite-assignment analysis could tighten this later.
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