Incremental Compilation inconsistent

[FabioPinheiro]

Compiler version

ScalaVersion: 3.0.0 but also on 3.0.2-RC1-bin-20210706-6011847-NIGHTLY
dependency: io.circe:circe-generic_3:0.14.1

Minimized code

File1.scala

object DDD
case class AAA(a: DDD.type)
//case class AAA(a: Int)

File2.scala

import io.circe.generic.auto._
val test = summon[io.circe.Decoder[AAA]]

First compile with case class AAA(a: Int) on File1.
Then compile File1.scala as above.
The recompilation should fail and it did not fail!

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

Output

sbt:fmgp-geometry> clean
[success] Total time: 0 s, completed Jul 7, 2021 3:33:49 PM
sbt:fmgp-geometry> compile
[info] compiling 2 Scala sources to /home/fabio/workspace/fmgp-threejs/target/scala-3.0.0/classes ...

Change code back to case class AAA(a: DDD.type)

[success] Total time: 1 s, completed Jul 7, 2021 3:33:52 PM
sbt:fmgp-geometry> compile
[info] compiling 1 Scala source to /home/fabio/workspace/fmgp-threejs/target/scala-3.0.0/classes ...
[success] Total time: 0 s, completed Jul 7, 2021 3:34:02 PM
sbt:fmgp-geometry> clean
[success] Total time: 0 s, completed Jul 7, 2021 3:34:05 PM
sbt:fmgp-geometry> compile
[info] compiling 2 Scala sources to /home/fabio/workspace/fmgp-threejs/target/scala-3.0.0/classes ...
[error] -- Error: /home/fabio/workspace/fmgp-threejs/src/main/scala/File2.scala:3:40 ---
[error] 3 |val test = summon[io.circe.Decoder[AAA]]
[error]   |                                        ^
[error]   |       cannot reduce summonFrom with
[error]   |        patterns :  case given decodeA @ _:io.circe.Decoder[DDD.type]
[error]   |                    case given evidence$2 @ _:deriving.Mirror.Of[DDD.type]
[error]   | This location contains code that was inlined from Derivation.scala:19
[error]   | This location contains code that was inlined from Derivation.scala:32
[error]   | This location contains code that was inlined from Derivation.scala:11
[error]   | This location contains code that was inlined from Derivation.scala:70
[error]   | This location contains code that was inlined from auto.scala:16
[error] one error found
[error] one error found
[error] (Compile / compileIncremental) Compilation failed
[error] Total time: 0 s, completed Jul 7, 2021 3:34:07 PM

Note: Just File1 was recompiled.
The expectation was for File2 to be recompiled also

Expectation

The recompilation should fail and it did not fail!
It needed a clean compilation to show the error.

[FabioPinheiro]

@smarter I minimized the code but it still depends on circe-generic.
I removed the cross versions. As far as I know everything is in Scala 3

[griggt]

A self-contained example:

Foo.scala

case class Foo(x: Int)                // (1) first compile with this definition of Foo
//case class Foo(x: Int, y: String)   // (2) ...then incrementally compile with this one

Test.scala

import scala.deriving.Mirror
import scala.compiletime.{erasedValue, summonInline}

trait Decoder[A]

object Decoder:
  given Decoder[Int] = ???

  inline def derived[A](using m: Mirror.Of[A]): Decoder[A] =
    val elemDecoders = summonDecodersRec[m.MirroredElemTypes]
    new Decoder[A] {}

  inline def summonDecodersRec[T <: Tuple]: List[Decoder[_]] =
    inline erasedValue[T] match
      case _: EmptyTuple => Nil
      case _: (t *: ts) => summonInline[Decoder[t]] :: summonDecodersRec[ts]
end Decoder

object Test:
  val d: Decoder[Foo] = Decoder.derived[Foo]

// clean compilation with definition (1) of Foo
sbt:i13028> clean; compile
[info] compiling 2 Scala sources to /tmp/i13028/target/scala-3.0.3-RC1-bin-20210716-cc47c56-NIGHTLY/classes ...
[info] done compiling
[success] Total time: 5 s, completed Jul 20, 2021 8:18:30 PM

// replace definition (1) with (2) in Foo.scala and incrementally compile... expected to fail
sbt:i13028> compile
[info] compiling 1 Scala source to /tmp/i13028/target/scala-3.0.3-RC1-bin-20210716-cc47c56-NIGHTLY/classes ...
[info] done compiling
[success] Total time: 1 s, completed Jul 20, 2021 8:18:40 PM

// clean compile with definition (2)
sbt:i13028> clean; compile
[info] compiling 2 Scala sources to /tmp/i13028/target/scala-3.0.3-RC1-bin-20210716-cc47c56-NIGHTLY/classes ...
[error] -- Error: /tmp/i13028/Test.scala:20:24 -----------------------------------------
[error] 20 |  val d: Decoder[Foo] = Decoder.derived[Foo]
[error]    |                        ^^^^^^^^^^^^^^^^^^^^
[error]    |                  no implicit argument of type Decoder[String] was found
[error]    | This location contains code that was inlined from Test.scala:16
[error]    | This location contains code that was inlined from Test.scala:16
[error]    | This location contains code that was inlined from Test.scala:10
[error] one error found
[error] one error found
[error] (Compile / compileIncremental) Compilation failed