Whitespace-sensitive AssertionError somewhere in the typer (parser stability)

[sir-wabbit]

// The bug is whitespace sensitive!!!
object i0 {
1 match {
def this(): Int
  def this()
}
}

Exception in thread "main" java.lang.AssertionError: assertion failed
	at dotty.DottyPredef$.assertFail(DottyPredef.scala:37)
	at dotty.tools.dotc.core.Types$MethodType.<init>(Types.scala:2941)
	at dotty.tools.dotc.core.Types$CachedMethodType.<init>(Types.scala:2958)
	at dotty.tools.dotc.core.Types$MethodTypeCompanion.apply(Types.scala:3026)
	at dotty.tools.dotc.core.Types$MethodTypeCompanion.fromSymbols(Types.scala:3022)
	at dotty.tools.dotc.typer.NamerContextOps.$anonfun$1(Namer.scala:144)
	at scala.collection.immutable.List.$anonfun$foldRight$1(List.scala:405)
	at scala.collection.immutable.List.foldRight(List.scala:86)
	at scala.collection.TraversableOnce.$colon$bslash(TraversableOnce.scala:153)
	at scala.collection.TraversableOnce.$colon$bslash$(TraversableOnce.scala:153)
	at scala.collection.AbstractTraversable.$colon$bslash(Traversable.scala:104)
	at dotty.tools.dotc.typer.NamerContextOps.methodType(Namer.scala:144)
	at dotty.tools.dotc.typer.Namer.wrapMethType$1(Namer.scala:1196)
	at dotty.tools.dotc.typer.Namer.defDefSig(Namer.scala:1210)
	at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:721)
	at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:801)
	at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:746)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:237)
	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:184)
	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:186)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:343)
	at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:1771)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1796)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1868)

AE-4f7e66f7ee706c59e8d8ba100db9d2bf0152b119

[Blaisorblade]

This is less whitespace-sensitive:

object i0 {
  1 match {
    case null =>
      def this(): Int
      def this()
  }
}

package <empty> {
  module object i0 {
    1 match
      {
        case null =>
          def <init>(): Unit =
            {
              <init>(null)
              ()
            }
          def <init>() =
            {
              <init>(null)
              ()
            }
          <empty>
      }
  }
}

and when naming the second <init> in Namer.defDefSig, the ddef.name is <init> while sym.name is $init$$1 — apparently, it's <init>.freshened created by checkNoConflict because of the name-conflict. The code assumes they're the same and produces NoType otherwise. However, fixing that via this one-liner leads to another crash:

diff --git a/compiler/src/dotty/tools/dotc/typer/Namer.scala b/compiler/src/dotty/tools/dotc/typer/Namer.scala
index f8d83964e..5281f7a0d 100644
--- a/compiler/src/dotty/tools/dotc/typer/Namer.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Namer.scala
@@ -1158,8 +1158,8 @@ class Namer { typer: Typer =>

   /** The type signature of a DefDef with given symbol */
   def defDefSig(ddef: DefDef, sym: Symbol)(implicit ctx: Context) = {
-    val DefDef(name, tparams, vparamss, _, _) = ddef
-    val isConstructor = name == nme.CONSTRUCTOR
+    val DefDef(_, tparams, vparamss, _, _) = ddef
+    val isConstructor = sym.name == nme.CONSTRUCTOR

     // The following 3 lines replace what was previously just completeParams(tparams).
     // But that can cause bad bounds being computed, as witnessed by

new crash:

-- [E040] Syntax Error: tests/neg/i5004.scala:5:16 -----------------------------
5 |      def this(): Int
  |                ^
  |                '=' expected, but ':' found
-- [E040] Syntax Error: tests/neg/i5004.scala:7:2 ------------------------------
7 |  }
  |  ^
  |  '=' expected, but '}' found
8 |}
-- Error: tests/neg/i5004.scala:6:10 -------------------------------------------
6 |      def this()
  |      ^^^^^^^^^^
  |      <init> is already defined as constructor <local i0$>
-- Error: tests/neg/i5004.scala:5:6 --------------------------------------------
5 |      def this(): Int
  |      ^
  |      too many arguments for constructor <local i0$>: (): i0.<local i0$>
exception occurred while typechecking tests/neg/i5004.scala
exception occurred while compiling tests/neg/i5004.scala
Exception in thread "main" java.lang.AssertionError: assertion failed
	at scala.Predef$.assert(Predef.scala:204)
	at dotty.tools.dotc.core.Contexts$Context.thisCallArgContext(Contexts.scala:354)
	at dotty.tools.dotc.typer.Applications.argCtx(Applications.scala:685)
	at dotty.tools.dotc.typer.Applications.argCtx$(Applications.scala:684)
	at dotty.tools.dotc.typer.Typer.argCtx(Typer.scala:82)
	at dotty.tools.dotc.typer.Applications.$anonfun$typedApply$1(Applications.scala:694)
	at dotty.tools.dotc.util.Stats$.track(Stats.scala:37)
	at dotty.tools.dotc.typer.Applications.realApply$1(Applications.scala:693)
	at dotty.tools.dotc.typer.Applications.typedApply(Applications.scala:794)
	at dotty.tools.dotc.typer.Applications.typedApply$(Applications.scala:691)
	at dotty.tools.dotc.typer.Typer.typedApply(Typer.scala:82)
	at dotty.tools.dotc.typer.Typer.typedUnnamed$1(Typer.scala:1828)
	at dotty.tools.dotc.typer.Typer.typedUnadapted(Typer.scala:1879)

[sir-wabbit]

This might be the same bug:

object i0 {
  {
    def this
    def this
  }
}

Exception in thread "main" java.lang.AssertionError: assertion failed
	at dotty.DottyPredef$.assertFail(DottyPredef.scala:37)
	at dotty.tools.dotc.core.Types$MethodType.<init>(Types.scala:2941)
	at dotty.tools.dotc.core.Types$CachedMethodType.<init>(Types.scala:2958)
	at dotty.tools.dotc.core.Types$MethodTypeCompanion.apply(Types.scala:3026)
	at dotty.tools.dotc.core.Types$MethodTypeCompanion.fromSymbols(Types.scala:3022)
	at dotty.tools.dotc.typer.NamerContextOps.$anonfun$1(Namer.scala:144)
	at scala.collection.immutable.List.$anonfun$foldRight$1(List.scala:405)
	at scala.collection.immutable.List.foldRight(List.scala:86)
	at scala.collection.TraversableOnce.$colon$bslash(TraversableOnce.scala:153)
	at scala.collection.TraversableOnce.$colon$bslash$(TraversableOnce.scala:153)
	at scala.collection.AbstractTraversable.$colon$bslash(Traversable.scala:104)
	at dotty.tools.dotc.typer.NamerContextOps.methodType(Namer.scala:144)
	at dotty.tools.dotc.typer.Namer.wrapMethType$1(Namer.scala:1196)
	at dotty.tools.dotc.typer.Namer.defDefSig(Namer.scala:1210)
	at dotty.tools.dotc.typer.Namer$Completer.typeSig(Namer.scala:721)
	at dotty.tools.dotc.typer.Namer$Completer.completeInCreationContext(Namer.scala:801)
	at dotty.tools.dotc.typer.Namer$Completer.complete(Namer.scala:746)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.completeFrom(SymDenotations.scala:237)
	at dotty.tools.dotc.core.Denotations$Denotation.completeInfo$1(Denotations.scala:184)
	at dotty.tools.dotc.core.Denotations$Denotation.info(Denotations.scala:186)
	at dotty.tools.dotc.core.SymDenotations$SymDenotation.ensureCompleted(SymDenotations.scala:343)
	at dotty.tools.dotc.typer.Typer.retrieveSym(Typer.scala:1771)
	at dotty.tools.dotc.typer.Typer.typedNamed$1(Typer.scala:1796)

AE-4f7e66f7ee706c59e8d8ba100db9d2bf0152b119

[Blaisorblade]

Yep, seems very likely the same from my analysis!

[Blaisorblade]

@odersky Can you take a look at this? This is the bug with freshened constructors (tho they're under a block!):

object i0 {
  {
    def this
    def this
  }
}