Preserve spliterator characteristics in collection views #8182
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Fix CollectSpliterators.filter() to preserve IMMUTABLE and CONCURRENT characteristics from the source spliterator, matching JDK Stream.filter() behavior which only clears SIZED. Add spliterator() overrides to Lists inner classes (OnePlusArrayList, TwoPlusArrayList, CharSequenceAsList, AbstractListWrapper) and Maps inner classes (KeySet, Values) so that collection views properly report their characteristics rather than falling back to AbstractList defaults. Fixes google#8165
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This was referenced Jan 30, 2026
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Fixes #8165
Summary
CollectSpliterators.filter(): PreserveIMMUTABLEandCONCURRENTcharacteristics from the source spliterator. These describe the source, not the elements, so filtering does not invalidate them. This aligns with JDKStream.filter(), which only clearsSIZED.Listsinner classes: Addspliterator()overrides toOnePlusArrayList,TwoPlusArrayList,CharSequenceAsList, andAbstractListWrapperso they report accurate characteristics (ORDERED,SIZED,IMMUTABLEwhere applicable) instead of falling back toAbstractListdefaults.Mapsinner classes: Addspliterator()overrides toKeySet(propagatesDISTINCTviaCollectSpliterators.map()) andValues(propagates source characteristics viaCollectSpliterators.map()).Test plan
testFilterPreservesImmutableCharacteristicandtestFilterDropsSizedtoCollectSpliteratorsTesttestAsListSpliteratorIsImmutable,testAsListTwoSpliteratorIsImmutable,testCharactersOfSpliteratorCharacteristics, andtestAbstractListWrapperSpliteratorDelegatestoListsTesttestKeySetSpliteratorIsDistinctandtestValuesSpliteratorPreservesCharacteristicstoMapsTestCollections2Test,SetsTest) pass locally