Adding NonNull annotations to Observable & Single

[freakomonk]

Adding NonNull annotations in factory methods for improved code compilation

Resolves: #6309

[freakomonk]

#6309 @akarnokd Can you pls take a look at this and review ?

[akarnokd]

Thanks for Contributing. A few points:

• You don't have to keep the welcome text of the PR, that's for telling contributors what to do. See the updated text for future reference.
• Didn't you mean to add @NonNull to the arguments rather than to the return value?

[vanniktech]

I like it. Kotlin currently warns about those since it's not capable of inferring whether they can be null or not.

Annotation order should be the same for all usages. This will mix this up.

Can't we use a nonnull by default kind of annotation since 99 percent of the API only uses non null?

[codecov]

Codecov Report

Merging #6313 into 2.x will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##                2.x    #6313      +/-   ##
============================================
+ Coverage     98.23%   98.26%   +0.03%     
- Complexity     6284     6285       +1     
============================================
  Files           672      672              
  Lines         44992    44992              
  Branches       6223     6223              
============================================
+ Hits          44198    44213      +15     
+ Misses          253      244       -9     
+ Partials        541      535       -6

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/io/reactivex/Flowable.java	100% <ø> (ø)	567 <0> (ø)	⬇️
src/main/java/io/reactivex/Completable.java	100% <ø> (ø)	120 <0> (ø)	⬇️
src/main/java/io/reactivex/Observable.java	100% <ø> (ø)	542 <0> (ø)	⬇️
src/main/java/io/reactivex/Maybe.java	100% <ø> (ø)	172 <0> (ø)	⬇️
src/main/java/io/reactivex/Single.java	100% <ø> (ø)	148 <0> (ø)	⬇️
...tivex/internal/observers/FutureSingleObserver.java	94.33% <0%> (-3.78%)	24% <0%> (-1%)
...rnal/operators/flowable/FlowableFlatMapSingle.java	94.56% <0%> (-1.64%)	2% <0%> (ø)
...ternal/operators/completable/CompletableMerge.java	96.42% <0%> (-1.2%)	2% <0%> (ø)
.../io/reactivex/internal/schedulers/IoScheduler.java	89.36% <0%> (-1.07%)	9% <0%> (ø)
...operators/observable/ObservableMergeWithMaybe.java	99.1% <0%> (-0.9%)	2% <0%> (ø)
... and 20 more

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[akarnokd]

Non-null by default came up in #5341 but not sure what happened. I'd think it was a JSR 305 annotation instead of just a convention thus the IDEs simply wouldn't have supported them.

@freakomonk Did you also want to add these to Maybe, Flowable and Completable static methods?

[freakomonk]

@vanniktech Can you elaborate nonNull by default ?

[freakomonk]

@akarnokd Thanks for the suggestions. Will keep in mind henceforth.

I added the @NonNull annotation to methods with ObjectHelper.requireNonNull check in them. As the input params are being checked for null, I am checking for the return value.

I have updated the Flowable static methods but do not see any Maybe, Completable that do not have already have this annotation.

[vanniktech]

Non-null by default came up in #5341 but not sure what happened. I'd think it was a JSR 305 annotation instead of just a convention thus the IDEs simply wouldn't have supported them.

This @freakomonk. I'm not sure though which annotations works where and what needs to be enabled/disabled or not. Either we look into this or we just use RxJava's NonNull annotation which does the job.

[freakomonk]

@akarnokd Hi David. Is there something else to do to get this PR merged ?

[akarnokd]

@freakomonk I was waiting for you to add them to the other reactive base classes.

[freakomonk]

@akarnokd Added annotation to further methods now. Can you pls check ?

[freakomonk]

@akarnokd Is this now okay to be merged ? Your review pls