HHH-19584 add @CurrentTimestamp(allowMutation)

[gavinking]

[Please describe here what your change is about]

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https://hibernate.atlassian.net/browse/HHH-19584

[gavinking]

@yrodiere This is the only significant thing here.

[yrodiere]

LGTM, thanks, but should we merge this immediately, or do you want someone to have a look at the "manually set the value for inserts" case too?
Asking because that might change the exposed API, if we decide its' better (simpler) to expose a single allowOverride() attribute controlling whether people can manually set the value for both inserts and updates.

[gavinking]

LGTM, thanks, but should we merge this immediately, or do you want someone to have a look at the "manually set the value for inserts" case too?

Well, nobody actually asked for that yet. (Except you 😉)

Asking because that might change the exposed API, if we decide its' better (simpler) to expose a single allowOverride() attribute controlling whether people can manually set the value for both inserts and updates.

It's not linked directly to inserts vs updates, it depends on whether the client can override generation. So I think it's two different things.

All that said, we can't merge this without a test.

[Copilot]

Pull Request Overview

Adds a new allowMutation flag to the @CurrentTimestamp annotation and its generator implementation, controlling whether application code can override generated timestamps outside of generation events.

• Introduces allowMutation attribute in CurrentTimestamp API (default: false).
• Propagates allowMutation through CurrentTimestampAnnotation and CurrentTimestampGeneration.
• Adds accessor in the generator for downstream use.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
hibernate-core/src/main/java/org/hibernate/generator/internal/CurrentTimestampGeneration.java	Added allowMutation field, constructor assignments, and allowMutation() method; refactored delegate lookup formatting.
hibernate-core/src/main/java/org/hibernate/boot/models/annotations/internal/CurrentTimestampAnnotation.java	Added allowMutation field, constructors, getter, and setter.
hibernate-core/src/main/java/org/hibernate/annotations/CurrentTimestamp.java	Extended annotation definition with allowMutation() and Javadoc.

Comments suppressed due to low confidence (3)

hibernate-core/src/main/java/org/hibernate/generator/internal/CurrentTimestampGeneration.java:265

• [nitpick] Consider adding a Javadoc comment for the new allowMutation() method to explain its purpose and usage in the generator.

	@Override

hibernate-core/src/main/java/org/hibernate/generator/internal/CurrentTimestampGeneration.java:82

• The new allowMutation feature should be covered by unit tests to verify its behavior across different event types and ensure regression safety.

	private final boolean allowMutation;

hibernate-core/src/main/java/org/hibernate/generator/internal/CurrentTimestampGeneration.java:233

• [nitpick] The else block is redundant after a return; you can flatten this code by removing the else and decreasing nested indentation for better readability.

				else {