Alias types use memoized hashCode for collections

[schlosna]

Before this PR

Generated alias types did not memoize hashCode, potentially leading to expensive hash code computations when the aliased type is an immutable collection or map.

A hypothetical example CompositeKey alias for Map<Field, Value> currently generates:

@Generated("com.palantir.conjure.java.types.AliasGenerator")
public final class CompositeKey {
    private static final CompositeKey EMPTY = new CompositeKey();

    private final Map<Field, Value> value;

    private CompositeKey(@Nonnull Map<Field, Value> value) {
        this.value = Preconditions.checkNotNull(value, "value cannot be null");
    }

    private CompositeKey() {
        this(Collections.emptyMap());
    }

    @JsonValue
    public Map<Field, Value> get() {
        return value;
    }

    @Override
    public String toString() {
        return value.toString();
    }

    @Override
    public boolean equals(@Nullable Object other) {
        return this == other
                || (other instanceof CompositeKey && this.value.equals(((CompositeKey) other).value));
    }

    @Override
    public int hashCode() {
        return value.hashCode();
    }

    @JsonCreator(mode = JsonCreator.Mode.DELEGATING)
    public static CompositeKey of(@Nonnull Map<Field, Value> value) {
        return new CompositeKey(value);
    }

    public static CompositeKey empty() {
        return EMPTY;
    }
}

After this PR

==COMMIT_MSG==
Alias types use memoized hashCode for collections
==COMMIT_MSG==

Possible downsides?

[changelog-app]

Generate changelog in changelog/@unreleased

What do the change types mean?

• feature: A new feature of the service.
• improvement: An incremental improvement in the functionality or operation of the service.
• fix: Remedies the incorrect behaviour of a component of the service in a backwards-compatible way.
• break: Has the potential to break consumers of this service's API, inclusive of both Palantir services
  and external consumers of the service's API (e.g. customer-written software or integrations).
• deprecation: Advertises the intention to remove service functionality without any change to the
  operation of the service itself.
• manualTask: Requires the possibility of manual intervention (running a script, eyeballing configuration,
  performing database surgery, ...) at the time of upgrade for it to succeed.
• migration: A fully automatic upgrade migration task with no engineer input required.

Note: only one type should be chosen.

How are new versions calculated?

• ❗The break and manual task changelog types will result in a major release!
• 🐛 The fix changelog type will result in a minor release in most cases, and a patch release version for patch branches. This behaviour is configurable in autorelease.
• ✨ All others will result in a minor version release.

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Alias types use memoized hashCode for collections

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[carterkozak]

lgtm, thanks!

[svc-autorelease]

Released 8.19.0