RuntimeError in backend when with implicit conversions on super

[sir-wabbit]

class I0 {
  super.+("")
}

Unexpected tree in genLoad: Super(This(Ident()),Ident())/class dotty.tools.dotc.ast.Trees$Super at: [11..16]
exception occurred while compiling RE-341cc574ffab7ad1cca7c0683c727f4cd8ca9f68.scala
Exception in thread "main" java.lang.RuntimeException: Unexpected tree in genLoad: Super(This(Ident()),Ident())/class dotty.tools.dotc.ast.Trees$Super at: [11..16]
	at dotty.tools.backend.jvm.DottyBackendInterface.abort(DottyBackendInterface.scala:394)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:430)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadArguments$$anonfun$1(BCodeBodyBuilder.scala:1018)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoadArguments(BCodeBodyBuilder.scala:1018)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genNormalMethodCall$1(BCodeBodyBuilder.scala:725)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genApply(BCodeBodyBuilder.scala:754)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:337)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:290)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:89)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genNormalBlock$2$$anonfun$1(BCodeBodyBuilder.scala:860)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:18)
	at scala.compat.java8.JProcedure1.apply(JProcedure1.java:10)
	at scala.collection.immutable.List.foreach(List.scala:389)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genNormalBlock$1(BCodeBodyBuilder.scala:860)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genBlock(BCodeBodyBuilder.scala:892)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genLoad(BCodeBodyBuilder.scala:408)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genStat(BCodeBodyBuilder.scala:89)
	at scala.tools.nsc.backend.jvm.BCodeBodyBuilder$PlainBodyBuilder.genNormalBlock$2$$anonfun$1(BCodeBodyBuilder.scala:860)

RE-341cc574ffab7ad1cca7c0683c727f4cd8ca9f68

[nicolasstucki]

The issue is that we try to find an implicit conversion for the tree of super to have the method +. Placing super as argument which is not a correct tree.

class I0 {
  implicit def foo(any: Any): String = ()
  super.+("")
}

result of Foo.scala after frontend:
package <empty> {
  class I0() extends Object() { 
    implicit def foo(any: Any): String = this.foo(())
    this.foo(super).+("")
  }
}

I imagine that we simply should not try to do implicit conversions on Super trees.

[sir-wabbit]

https://github.com/lampepfl/dotty/blob/master/tests/untried/neg/t5063.scala
It looks like the same snippet was imported from scala/tests back in 2014 but was never tried.

[Blaisorblade]

@alexknvl Thanks for the pointer!

I imagine that we simply should not try to do implicit conversions on Super trees.

That's indeed the scalac fix to scala/bug#5063 (comment).

[Blaisorblade]

And if we try the same thing:

diff --git a/compiler/src/dotty/tools/dotc/typer/Implicits.scala b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
index feb6bc391..546cce74a 100644
--- a/compiler/src/dotty/tools/dotc/typer/Implicits.scala
+++ b/compiler/src/dotty/tools/dotc/typer/Implicits.scala
@@ -552,6 +552,7 @@ trait Implicits { self: Typer =>
         || (from.tpe isRef defn.NothingClass)
         || (from.tpe isRef defn.NullClass)
         || !(ctx.mode is Mode.ImplicitsEnabled)
+        || from.isInstanceOf[Super]
         || (from.tpe eq NoPrefix)) NoMatchingImplicitsFailure
     else {
       def adjust(to: Type) = to.stripTypeVar.widenExpr match {

we get:

scala> class I0 {
     |   super.+("")
     | }
2 |  super.+("")
  |  ^^^^^^^
  | value `+` is not a member of Object - did you mean `Object(I0.super).eq`?