Weird macro recursive inline limit infinite loop bug/crash

Maximal number of successive inlines exceeds when using Scala 3 Macros across various dependent files.

Compiler version

3.0.0-RC1

Minimized code

Please see attached sample zipped project. This issue only appears to surface when having definitions across multiple files. I currently found 3 workaround so far, but the underlying issue remains.

1. If you either omit Transactions.scala and remove its reference, property in Chain.scala,
2. Change Transaction to use derive instead, like

   case class Transaction( sender: Address, 
                           recipient: Address, 
                           value: Long) derives Codec.AsObject
   

3. Group all the definitions in a single file as in here, it works too.

MacroBug.zip

To Reproduce:

1. Unzip the file.
2. Run sbt run in the directory.

Output

Without default flags

[error] -- Error: /Users/swoorup.joshi/IdeaProjects/temp/LBAbOJMVT1260OKUnBXuzw/src/main/scala/blockchain/Chain.scala:25:27
[error] 25 |given Encoder[ChainLink] = deriveEncoder[ChainLink]
[error]    |                           ^^^^^^^^^^^^^^^^^^^^^^^^
[error]    |                     Maximal number of successive inlines (32) exceeded,
[error]    |                     Maybe this is caused by a recursive inline method?
[error]    |                     You can use -Xmax-inlines to change the limit.
[error]    | This location contains code that was inlined from Chain.scala:25
[error]    | This location contains code that was inlined from Derivation.scala:47
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from Derivation.scala:16
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:38
[error]    | This location contains code that was inlined from Derivation.scala:12
[error]    | This location contains code that was inlined from Derivation.scala:50
[error]    | This location contains code that was inlined from semiauto.scala:27
[error] one error found
[error] one error found

Using max inlines -Xmax-inlines 10000000 flag does not do any justice either, it runs into stack overflow.

With max inlines

java.lang.StackOverflowError while compiling /Users/swoorup.joshi/IdeaProjects/temp/LBAbOJMVT1260OKUnBXuzw/src/main/scala/blockchain/Chain.scala, /Users/swoorup.joshi/IdeaProjects/temp/LBAbOJMVT1260OKUnBX
uzw/src/main/scala/blockchain/Transaction.scala, /Users/swoorup.joshi/IdeaProjects/temp/LBAbOJMVT1260OKUnBXuzw/src/main/scala/main.scala
[error] ## Exception when compiling 3 sources to /Users/swoorup.joshi/IdeaProjects/temp/LBAbOJMVT1260OKUnBXuzw/target/scala-3.0.0-RC1/classes
[error] java.lang.StackOverflowError
[error] dotty.tools.dotc.ast.Positioned.sourcePos(Positioned.scala:52)
[error] dotty.tools.dotc.report$.recur$1(report.scala:119)
[error] dotty.tools.dotc.report$.recur$1(report.scala:119)
[error] dotty.tools.dotc.report$.recur$1(report.scala:119)
[error] dotty.tools.dotc.report$.recur$1(report.scala:119)

Expectation

[info] running Main
{
  "index" : 1,
  "proof" : 2,
  "previousHash" : "",
  "values" : [
  ],
  "timestamp" : 1615684763839
}

The same example in scastie works however, when everything is lumped together in a single file. https://scastie.scala-lang.org/LBAbOJMVT1260OKUnBXuzw

[heksesang]

The zipped example works fine when:

• You put each given in their respective companion object.
• You declare given Encoder[Transaction] = blockchain.given_Encoder_Transaction in Chain.scala.
• You replace the List[Transaction] with just Transaction.

Also, the Scastie breaks if you use two different packages to separate the definitions: https://scastie.scala-lang.org/heksesang/Vr8kHxhURgWxQBmGcxB9ww/6

Based on the observations above, I think the problem is most likely the same as https://github.com/lampepfl/dotty/issues/11538 and thus fixed in RC2.

The thing that breaks the derivation is the fact that there is a List[Transaction] coupled with the bug mentioned above. The implicit circe uses for Encoder[List[A]] requires an implicit Encoder[A]. When it looks for a Encoder[List[Transaction]], it uses this implicit, but because of it does not find an implicit Encoder[Transaction], the summonFrom defaults to trying to derive an Encoder[List[Transaction]], and that causes some infinite recursion.

If you create case class A(val i: Int), do not derive an Encoder[A], but try to call deriveEncoder[List[A]] you will see the same problem.

If my deductions are correct, this is not a dotty bug, but a circe bug.

[smarter]

Sounds like we can close this then, thanks!