gephi / graphstore / #571

91%

push

Make graph attributes iteration order canonical (#286)

GraphAttributesImpl backed its map with a java.util.HashMap, and
Serialization.serializeGraphAttributes iterates that map's entrySet()
straight into the byte stream. HashMap iteration order is an
implementation detail, so the serialized bytes were a function of
insertion history rather than of content alone.

Switch the field to a TreeMap so iteration is sorted by key and the
output bytes become a pure function of the content. This is a
prerequisite for byte-pinned serialization fixtures.

TreeMap rejects null keys where HashMap accepted them, and throws NPE
from deep inside the map on get(null)/containsKey(null) where HashMap
returned null/false. Add explicit Objects.requireNonNull(key, "key")
guards to every public method taking a key so the failure is
intentional and well-messaged.

deepHashCode and deepEquals are unchanged and remain correct:
Map.hashCode() is specified as the order-independent sum of entry hash
codes, and deepEquals goes through MapDeepEquals which compares by key
lookup.

The read path is unaffected -- deserializeGraphAttributes just puts
entries into the map -- so previously written files still load
identically. Only the order of newly written graph-attribute entries
changes; the format itself is untouched and Serialization.VERSION is
not bumped.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

10 of 10 new or added lines in 1 file covered. (100.0%)

11800 of 12938 relevant lines covered (91.2%)

0.91 hits per line