False positive unused warnings in 3.7 nightly on implicits in method overrides

[mrdziuban]

Compiler version

3.7.1-RC1-bin-20250328-d519790-NIGHTLY

Minimized code

trait Test[F[_], Ev] {
  def apply[A, B](fa: F[A])(f: A => B)(using ev: Ev): F[B]
}

given testId: Test[[a] =>> a, Unit] =
  new Test[[a] =>> a, Unit] {
    def apply[A, B](fa: A)(f: A => B)(using ev: Unit): B = f(fa)
  }

Output

[warn] -- [E198] Unused Symbol Warning: /Users/matt/scala3.7-nightly-unused/src/main/scala/example/Test.scala:7:44
[warn] 7 |    def apply[A, B](fa: A)(f: A => B)(using ev: Unit): B = f(fa)
[warn]   |                                            ^^
[warn]   |                                            unused implicit parameter

Expectation

The parameter should not be reported unused since it's required to satisfy the apply method override.

This is similar to #22742 which @som-snytt fixed in #22757 by suppressing unused warnings for explicit params in overrides -- could the same be done for implicits?

[Gedochao]

Last good release: 3.7.0-RC1-bin-20250127-89c20f8-NIGHTLY
First bad release: 3.7.0-RC1-bin-20250128-9cb97ec-NIGHTLY

The first bad commit is one of:

• c65d45d
• a5d9e25

(my money's on c65d45d)

This is technically a minor regression, but I have mixed feelings if we should treat it as such.
Still, adding the label.

@som-snytt, will you find the time to work on this?

[som-snytt]

Sorry I missed that on the previous ticket. Scala 2 has the expected behavior.

Not sure why sbt did this in the middle of session:

[success] Total time: 15 s, completed Apr 1, 2025, 8:37:04 AM
sbt:scala3> testCompilation 15503
[info] compiling 4 Java sources to /home/amarki/projects/dotty/sbt-bridge/src/target/classes ...
[info] Test run dotty.tools.dotc.CompilationTests started

[som-snytt]

Also thanks @mrdziuban for the nifty test cases, it really spruces up the test suite.