Inlined non-eta-expanded trees message

[nicolasstucki]

Closes #11483

[nicolasstucki]

-- Error: tests/pos-macros/i11483/Test_2.scala:25:11 -------------------------------------------------------------------
25 |       Api.println(Api.doSomething())
   |       ^^^^^^^^^^^
   |       Cannot automaticaly eta-expand calls in macros: x.Api.println
   | This location contains code that was inlined from Test_2.scala:25

inlined at Test_2.scala:24:

[liufengyun]

Otherwise, LGTM

[liufengyun]

Can we do the check from the place where etaExpand is called?

[nicolasstucki]

Actually, we can catch it as soon as it is created by the macro and give the stack trace to the user.

[nicolasstucki]

Now it will fail under ycheck with

24 |    X.process[Future,Unit]{ // error
   |    ^
   |Exception occurred while executing macro expansion.
   |java.lang.AssertionError: assertion failed: Reference to a method must be eta-expanded before it is used as an expression: (
   |  {
   |    def $anonfun(x: concurrent.Future[String]): String = 
   |      {
   |        x.await[concurrent.Future, String](x)(x.FutureAsyncMonad)
   |      }
   |    closure($anonfun:Conversion[concurrent.Future[String], String])
   |  }
   |:Conversion[concurrent.Future[String], String]).apply
   |    at scala.runtime.Scala3RunTime$.assertFailed(Scala3RunTime.scala:8)
   |    at scala.quoted.runtime.impl.QuotesImpl$reflect$.scala$quoted$runtime$impl$QuotesImpl$reflect$$$yCheckValidExpr(QuotesImpl.scala:2884)
   |    at scala.quoted.runtime.impl.QuotesImpl$reflect$Apply$.yCheckArgs$$anonfun$1(QuotesImpl.scala:603)
   |    at scala.runtime.function.JProcedure1.apply(JProcedure1.java:15)
   |    at scala.runtime.function.JProcedure1.apply(JProcedure1.java:10)
   |    at scala.collection.immutable.List.foreach(List.scala:333)
   |    at scala.quoted.runtime.impl.QuotesImpl$reflect$Apply$.yCheckArgs(QuotesImpl.scala:603)
   |    at scala.quoted.runtime.impl.QuotesImpl$reflect$Apply$.apply(QuotesImpl.scala:595)
   |    at scala.quoted.runtime.impl.QuotesImpl$reflect$Apply$.apply(QuotesImpl.scala:594)
   |    at x.X$.processTree(Macro_1.scala:50)
   |    at x.X$.processTree(Macro_1.scala:45)
   |    at x.X$.processTree(Macro_1.scala:42)
   |    at x.X$.processTree(Macro_1.scala:39)
   |    at x.X$.processImpl(Macro_1.scala:32)

This lets the user know that he created the wrong tree at Macro_1.scala:50

Changed fix

[liufengyun]

For later: maybe provide a reflection API to perform eta-expansion?

[liufengyun]

It seems such well-formedness checks are very useful in macros development.

Is it possible to centralize the check for the expanded tree? I guess for debugging, the current approach is more helpful, as it shows the stacktrace.

[nicolasstucki]

For later: maybe provide a reflection API to perform eta-expansion?

We already have term.etaExpand

[nicolasstucki]

Is it possible to centralize the check for the expanded tree?

Centralize how? Like in normal yCheck?

[liufengyun]

Centralize how? Like in normal yCheck?

Yes, something like a TreeMap or ReTyper. But as I mentioned above, this might not be a good idea, as it cannot show the stacktrace how an ill-formed tree is created.

[nicolasstucki]

That did not work in this case because the crash happened before we finished the transformation in the Inlining phase.