CloseableIterator.stream() reports improper Spliterator size

[sanha]

Stream.toList() was added in Java 16.
In here, Nodes.builder(…) decides to generate a fixed size node or a variable size node.
The result of AbstractPipeline.exactOutputSizeIfKnown() is used as the size, and the method checks the characteristics flags of a source spliterator.

The default implementation of CloseableIterator.stream() in Spring data seems to create a source spliterator with characteristic representing fixed size of 0.

Because of this, Nodes.builder(...) generates a fixed size node builder with size 0.
After, when Stream.toList() try to put an element to this node builder, it throws an exception in FixedNodeBuilder.accept(T) with message 
Accept exceeded fixed size of 0
.

You can reproduce this issue using the code below.

val springIterator = object : CloseableIterator<Int>, Iterator<Int> by (0..10).iterator() {
    override fun remove() = Unit
    override fun close() = Unit
}

val list = springIterator.stream().toList()

It would be nice to resolve this collision.

Tested with

• 
Zulu JDK 17.0.1
• 
Spring data commons 2.6.0

[mp911de]

Thanks for reporting the issue. The size value of 0 was considered as size hint and although we didn't specify the SIZED characteristic, the stream used the size hint for count, toList and other operators.