Ivan Saric created SOLR-18603:
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Summary: Seal the NamedList class hierarchy (SIP-22 step 4)
Key: SOLR-18603
URL: https://issues.apache.org/jira/browse/SOLR-18603
Project: Solr
Issue Type: Improvement
Components: SolrJ
Reporter: Ivan Saric
This is step 4 of [SIP-22: NamedList
Reduction|https://cwiki.apache.org/confluence/spaces/SOLR/pages/340036504/SIP-22+NamedList+Reduction]:
{quote}Minor: Use Java 17 "sealed classes" to insist the NamedList type
hierarchy is exactly what we want; no surprises.{quote}
Steps 1-3 of the SIP are done (SOLR-17623, SOLR-17635, SOLR-17625). This step
was agreed as the next one on the dev list: [Follow-up work after
SOLR-17600|https://lists.apache.org/thread/2o09q8yjmsx4l9b58mqqk5mgdbv7qf36].
Per that thread, the SIP's "Solr 10" now means Solr 11 ({{main}}), since 10.0
has shipped.
h3. Proposal
Declare {{org.apache.solr.common.util.NamedList}} as {{sealed}} with an
explicit {{permits}} list, so that the set of NamedList subtypes is fixed and
visible in one place. The expected outcome is that {{NamedList}} permits
exactly {{SimpleOrderedMap}}; whether {{SimpleOrderedMap}} itself becomes
{{final}} or stays open is to be decided from the audit below.
Before writing any {{permits}} clause, audit every subclass of {{NamedList}}
across all Gradle modules, including test sources, {{solr/modules/*}} and
anonymous subclasses. Any subclass beyond {{SimpleOrderedMap}} is either
removed or rewritten (if it is internal), or reported here as a finding before
deciding whether to permit it.
No behaviour changes and no public method signature changes. Those are later
SIP-22 steps.
h3. Compatibility
{{NamedList}} is public SolrJ API, so sealing it is a plugin-compatibility
change: a third-party subclass of {{NamedList}} will no longer compile. This is
a {{main}} / 11.0-only change and will be called out in the changelog as an
upgrade note. The SIP already anticipates plugin-compatibility impact.
h3. Out of scope
* Migrating {{new NamedList(...)}} instantiations to {{SimpleOrderedMap}}
(SIP-22 step 5). That will be a separate Jira, per the SIP's "don't combine
with anything else".
* Changing public API signatures away from {{NamedList}} (SIP-22 step 7).
One PR against {{main}}.
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