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Re: [jdt-dev] Null Annotations / EEA
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Sorry, Jan for not responding sooner. I wasn't subscribed to jdt-dev.
Work on null analysis in JDT has slowed down, partly because most of it is
pretty stable, partly for lack of energy / people (some call it "resources").
Still you might be interested in one particular option that was added recently:
https://www.eclipse.org/eclipse/news/4.21/jdt.php#external_annotations_all_locations
:)
I readily admit, that the set of annotations supported is not "complete" in
several senses. Yet, supporting a new annotation is one of the heavy weight
options of improving the tool.
Example: For some time we discussed another addition: @LazyNonNull. I was
convinced of its benefit, because it addresses a fundamental problem regarding
Object initialization. Just from mixed feedback I wasn't sure it would really
carry its own weight. Still that annotation (or smth similar) would have been my
next candidate.
Regarding @PolyNull I personally am less sure. Is it just an issue of
retrofitting existing API into a null-annotated world, or is there an intrinsic
design problem behind it, that doesn't have a satisfactory solution with the
existing annotations?
If I were a frequent user of methods like Optional.orElse (which I'm not), I'd
probably annotate argument and return as @NonNull. With this I would forgo the
option to invoke it with a null argument, perhaps I would have to code
differently in some few situations, but then everything could be checked in a
suitable & safe way, no?
If you still think, something like @PolyNull should be the next addition to this
tool, feel free to file an enhancement request in bugzilla (and post the link
here for reference). That request would first need some backing by other users.
If during that discussion some volunteer comes forward, I would be more than
happy to guide him/her to the suitable code locations for implementation this
feature.
best,
Stephan
From: "Jan N. Klug via jdt-dev" <jdt-dev@xxxxxxxxxxx>
Date: 17/07/2021 11:26 PM
Subject: [jdt-dev] Null Annotations / EEA
--------------------------------------------------------------------------------
Good evening,
you may know that there is a project named LastNPE that provides EEA for a bunch
of libraries.
Recently a discussion was brought up how to correctly model the annotations for
methods like Optional.orElse or Map.computeIfAbsent
In both cases we need to make the return value @Nullable, because the argument
is allowed to be null and in that case the return value is also null.
However this creates the need for a lot of unnecessary null-checks, if the value
is guaranteed to be non-null, e.g. if used like Map.computeIfAbsent(key, k ->
new Foo()).
So what we would need to have is something to express „same nullness like
argument“ (like @PolyNull in checkerframework) or the option to have two
annotations, one for a @Nullable argument and one for a @NonNull argument. Both
need support in the compiler.
That‘s why I‘m writing here. I couldn’t find a discussion for that. WDYT?
Jan (GitHub: J-N-K)
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