Regression in map implementation

[brandes-pq]

Description of the Problem

Removing entries from a map may throw an exception: The query

map{'aa':1,'bb':2,'cc':3} => map:remove('aa') => map:remove('bb')

crashes with

java.lang.ClassCastException: class org.basex.query.value.map.TrieBranch cannot be cast to class org.basex.query.value.map.TrieLeaf (org.basex.query.value.map.TrieBranch and org.basex.query.value.map.TrieLeaf are in unnamed module of loader 'app')
	at org.basex.query.value.map.XQTrieMap.keysInternal(XQTrieMap.java:72)
...

The problem is that the assumption that TrieNodes of size 1 are always TrieLeafs. This assumption may be broken when removing the second-to-last entry in a TrieBranch (return new TrieBranch(ks, nu, size - 1); when size is 2).

The regression has been introduced with commit bc73d82 and has thus been present since release 11.7.

Expected Behavior

The correct result would be map{'cc':3} and no uncaught exception.

Steps to Reproduce the Behavior

see above

Do you have an idea how to solve the issue?

In TreeBranch::remove, the last line (return new TrieBranch(ks, nu, size - 1);) should probably specially handle the case size == 2

What is your configuration?

Cloned BaseX repository, running with mvn exec:java

[ChristianGruen]

Thanks for the observation. I am optimistic that your previous PR was pretty much the solution to the problem: TrieList and TrieBranch will now both return a single leaf node when there are no other nodes left.

A new snapshot is online.

[brandes-pq]

Wonderful, thank you very much!