Implement a failing test for InternCache churn on map keys

[carterkozak]

This is based on the investigation described here: FasterXML/jackson-core#946 (comment)

[carterkozak]

This fails with:

AssertionFailedError: Arbitrary map key values should not be added to the InternCache because map keys may have greater cardinality than the InternCache expects 
Expected :{}
Actual   :{1st=1st, 2nd=2nd}

[cowtowncoder]

Um, no. This is incorrect -- due to the way interning/canonicalization works it will canonicalize EVERY JSON Object key, by design. It's a feature not bug.
Streaming parser has no knowledge of the ultimate usage of Object keys, whether for POJOs or Maps.

Jackson 3.0 improves things slightly by reducing needs/benefits of canonicalization (BeanDeserializers will create NameMatchers that do not rely on canonicalization but act as "mini" symbol tables). But there's no way to start to only use canonicalization for some keys regardless.

[carterkozak]

I see, sorry for my misunderstanding -- the change in 3.x sounds great!

[cowtowncoder]

@carterkozak understandable. It'd be nice if canonicalization could be avoided for Map key cases etc.