"One of these files should be removed from the classpath" should be removed

[eed3si9n]

Steps

See #17394, which was reported in May 2023
See also sbt/sbt#7726

Problem

Under -Wunused:imports Scala 3 reports false warnings:

[warn] Unable to find a link for Id(Project) in extraProjects: dotty.tools.dotc.core.TypeError$$anon$1:
Toplevel definition overrideConfigs is defined in
[warn]   /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-sbt/main_3/2.0.0-M2/main_3-2.0.0-M2.jar(sbt/BuildCommon.class)
[warn] and also in
[warn]   /home/runner/.cache/coursier/v1/https/repo1.maven.org/maven2/org/scala-sbt/main_3/2.0.0-M2/main_3-2.0.0-M2.jar(sbt/ProjectExtra.class)
[warn] One of these files should be removed from the classpath.

Expectation

I have not looked into the details, but it seems like there's a feature interference between the -Wunused:imports linter and "One of these files should be removed from the classpath" error in dropStale (

scala3/compiler/src/dotty/tools/dotc/core/SymDenotations.scala

Lines 2546 to 2557 in cc4a324

	// pick the variant(s) from the youngest class file
	val lastModDate = assocFiles.map(_.lastModified).max
	val youngest = assocFiles.filter(_.lastModified == lastModDate)
	val chosen = youngest.head
	def ambiguousFilesMsg(f: AbstractFile) =
	i"""Toplevel definition $name is defined in
	| $chosen
	|and also in
	| $f"""
	if youngest.size > 1 then
	throw TypeError(em"""${ambiguousFilesMsg(youngest.tail.head)}
	|One of these files should be removed from the classpath.""")

). Given that we want to take the linters seriously, for example by paying attention, or turning them into -Werror, I suggest one of the two features to be removed in the short-term, assuming removal of a linter is relatively easy thing to do.

If someone has the bandwidth to fix the interference, then the linter can always come back.