False positive unused warning in 3.7 nightly on override of overloaded java class member

[mrdziuban]

Compiler version

3.7.1-RC1-bin-20250328-d519790-NIGHTLY

Minimized code

Running scala-cli:

scala-cli -Wunused:privates -S 3.7.1-RC1-bin-20250328-d519790-NIGHTLY --dep software.amazon.kinesis:amazon-kinesis-client:3.0.2

and then compiling this code:

import software.amazon.kinesis.metrics.{MetricsConfig, MetricsLevel}
lazy val c = new MetricsConfig(???, ???) { override val metricsLevel = MetricsLevel.NONE }

Output

-- [E198] Unused Symbol Warning: -----------------------------------------------
1 |lazy val c = new MetricsConfig(???, ???) { override val metricsLevel = MetricsLevel.NONE }
  |                                                        ^^^^^^^^^^^^
  |                                                     unused private member

Expectation

The value should not be reported unused since it overrides the metricsLevel member from the MetricsLevel class.

I don't really understand why I'm allowed to override metricsLevel in the first place since it's private, but perhaps that's a different issue.

[Gedochao]

Last good release: 3.7.0-RC1-bin-20250307-977232c-NIGHTLY
First bad release: 3.7.0-RC1-bin-20250308-133dcb3-NIGHTLY

c880a58 is the first bad commit
cc @som-snytt

While it's a different case, and bisects to a different change, it's yet another minor regression tied to -Wunused... I'm thinking we'll find it hard to squash them all.
... @som-snytt I realise there are many, but would you be willing to take a look at this one, as well?

[som-snytt]

I assume these annotations are implicated.

import lombok.Data;
import lombok.experimental.Accessors;
import software.amazon.awssdk.services.cloudwatch.CloudWatchAsyncClient;

/**
 * Used by KCL to configure the metrics reported by the application.
 */
@Data
@Accessors(fluent = true)
public class MetricsConfig {

[som-snytt]

sym.nextOverriddenSymbol doesn't quite do the job.

Workaround is to write override def metricsLevel().

The fix is to trust the override modifier first, when checking if member of anonymous class is "effectively" private.

[som-snytt]

@Gedochao This is not a regression because 3.6.4 does not warn about members of anonymous classes at all. That feature regression from Scala 2 was #22681