Under zinc invalidation/recompilation when moving extension method to another file

[FabioPinheiro]

Compiler version

ScalaVersion: 3.0.0 but also on 3.0.2-RC1-bin-20210713-cf6fa97-NIGHTLY
dependency (still): "org.scalameta" %% "munit" % "0.7.27"

Minimized code

File1.scala

package app.fmgp
extension (i: Int) def extensionMethod: String = "hello"

File2.scala

package app.fmgp
// extension (i: Int) def extensionMethod: String = "hello"

TestUtils.scala

import app.fmgp.{extensionMethod}
object TestUtils {
  inline def anInlineMethod: Unit = { 1.extensionMethod; ()}
}

Main.scala

import TestUtils._ //If we copy the code to this file the bug does not happen!

class Test extends A {
  TestUtils.anInlineMethod
}

abstract class A extends B { self =>}
trait B { self: A => }

@main def hello() = 
  println("Hello, world")
  new Test
}

I also create a branch with the minimal amount of code: https://github.com/FabioPinheiro/fmgp-generative-design/tree/dotty_IncrementalCompilation_inconsistent_bug2/src/main/scala

Output

The bug apened when:
1- compile Note all the code in the same module
2- Move the extensionMethod from File1 to File2
3- Run run

sbt:fmgp-geometry> run
[info] compiling 4 Scala sources to /home/fabio/workspace/fmgp-threejs/target/scala-3.0.2-RC1-bin-20210713-cf6fa97-NIGHTLY/classes ...
[error] -- [E008] Not Found Error: /home/fabio/workspace/fmgp-threejs/src/main/scala/TestUtils.scala:4:38 
[error] 4 |  inline def anInlineMethod: Unit = 1.extensionMethod
[error]   |                                    ^^^^^^^^^^^^^^^^^
[error]   |                              value extensionMethod is not a member of Int
[error] one error found
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 0 s, completed Jul 16, 2021 10:32:52 AM

Expectation

The runtime error should not happen

[FabioPinheiro]

I minimize the code a bit more.
It no longer depends on Munit

The Main.scala file looks like

import TestUtils._ //If we copy the code to this file the bug does not happen!

class Test extends A {
  TestUtils.anInlineMethod
}

abstract class A extends B { self =>}
trait B { self: A => }

@main def hello() = 
  println("Hello, world")
  new Test

https://github.com/FabioPinheiro/fmgp-generative-design/tree/dotty_IncrementalCompilation_inconsistent_bug2/src/main/scala

[FabioPinheiro]

I updated the documentation above
There is also the issue #13028 about incremental-compilation that I open. From what I could see is similar to this but I wasn't able to minimize the code.

The error as being changing:
1'- first was java.lang.NoClassDefFoundError
2'- later was java.lang.NoSuchMethodError: app.fmgp.File1$package$.extensionMethod(I)Ljava/lang/String;
3'- now is Not Found Error