Testing dotty on the Scala Standard Library

[samuelgruetter]

I ran the rewriting tool with the ExplicitUnitReturn and ExplicitImplicitTypes transformations on the Scala Library 2.10.
Then I fed the result to dotty. FYI here's a list of the errors that I got (with links to the source position on github). I think most of them arise because the rewrite tool does not yet do all the rewritings that it should do, so I'll see how to improve it.

• early definitions are not supported; use trait parameters instead IndexedSeqView.scala#L79
• early definitions are not supported; use trait parameters instead IndexedSeqView.scala#L80
• early definitions are not supported; use trait parameters instead IndexedSeqView.scala#L81
• early definitions are not supported; use trait parameters instead IndexedSeqView.scala#L82
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L76
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L81
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L82
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L83
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L84
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L85
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L86
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L87
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L88
• early definitions are not supported; use trait parameters instead IterableViewLike.scala#L89
• early definitions are not supported; use trait parameters instead ParIterableViewLike.scala#L147
• early definitions are not supported; use trait parameters instead ParSeqViewLike.scala#L109
• early definitions are not supported; use trait parameters instead ParSeqViewLike.scala#L131
• early definitions are not supported; use trait parameters instead ResizableParArrayCombiner.scala#L90
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L76
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L77
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L78
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L79
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L80
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L81
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L82
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L83
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L84
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L89
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L95
• early definitions are not supported; use trait parameters instead SeqViewLike.scala#L96
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L53
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L54
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L55
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L56
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L57
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L58
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L59
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L60
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L61
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L63
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L67
• early definitions are not supported; use trait parameters instead StreamViewLike.scala#L69
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L172
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L173
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L174
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L175
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L176
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L177
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L178
• early definitions are not supported; use trait parameters instead TraversableViewLike.scala#L179
• early definitions are not supported; use trait parameters instead TrieIterator.scala#L67

• existential types no longer supported; use a wildcard type or dependent type instead IndexedSeqView.scala#L108
• existential types no longer supported; use a wildcard type or dependent type instead IterableView.scala#L25
• existential types no longer supported; use a wildcard type or dependent type instead ParIterableView.scala#L39
• existential types no longer supported; use a wildcard type or dependent type instead ParSeqView.scala#L39
• existential types no longer supported; use a wildcard type or dependent type instead SeqView.scala#L25
• existential types no longer supported; use a wildcard type or dependent type instead TraversableView.scala#L30

• '=' expected but 'end of statement' found. Benchmark.scala#L49
• '=' expected but 'end of statement' found. BufferLike.scala#L105
• '=' expected but 'end of statement' found. BufferLike.scala#L74
• '=' expected but 'end of statement' found. BufferLike.scala#L87
• '=' expected but 'end of statement' found. Builder.scala#L43
• '=' expected but 'end of statement' found. DefaultMapModel.scala#L27
• '=' expected but 'end of statement' found. IndexedSeqLike.scala#L54
• '=' expected but 'end of statement' found. RedBlack.scala#L42
• '=' expected but 'end of statement' found. SeqLike.scala#L43
• '=' expected but 'end of statement' found. Signalling.scala#L80
• '=' expected but 'end of statement' found. Signalling.scala#L89
• '=' expected but 'end of statement' found. Signalling.scala#L95
• '=' expected but 'end of statement' found. Tasks.scala#L115
• '=' expected but 'end of statement' found. Tasks.scala#L117
• '=' expected but 'end of statement' found. Tasks.scala#L121
• '=' expected but 'end of statement' found. Tasks.scala#L35

• identifier expected but '_' found. RedBlackTree.scala#L89
• identifier expected but '_' found. RedBlackTree.scala#L90

• illegal start of simple pattern ContentModel.scala#L109
• illegal start of simple pattern ContentModel.scala#L39
• illegal start of simple pattern ContentModel.scala#L40
• illegal start of simple pattern ContentModel.scala#L68
• illegal start of simple pattern ContentModel.scala#L70
• illegal start of simple pattern ElementValidator.scala#L102
• illegal start of simple pattern Utility.scala#L46
• illegal start of simple pattern Utility.scala#L54
• illegal start of simple pattern Utility.scala#L73

[samuelgruetter]

Here's my analysis of the errors, plus questions:

1. Might be tricky to rewrite this automatically so that the generated code looks nice, but I'll give it a try.
   

2. Missing feature of the rewriting tool
   

3. Missing feature of the rewriting tool, already reported: https://github.com/lampepfl/dotty/issues/129
   

4. [Fixed](https://github.com/scala/scala/blob/2.11.x/src/library/scala/collection/immutable/RedBlackTree.scala#L114) in Scala 2.11, but do I still have to do something for this?
   

5. Looks like https://github.com/lampepfl/dotty/pull/168 was not sufficient
   

[smarter]

4 has been reported as #235

[samuelgruetter]

So I addressed all these problems and made the following changes to the rewrite tool:

1. make early initializers normal late initializers + emit warning
2. rewrite types using forSome with bounded wildcards
3. also treat procedure syntax for abstract methods
4. replace unnamed type parameters by fresh type variables
5. varargs patterns: replace @ by :

For reference, in addition to the above features, the rewrite tool also does the following:

• add explict types for implicit defs/vals
• no procedure syntax for defs and constructors
• [desactivated] undo autotupling

Then I ran the rewrite tool on the scala library of 2.10.x. You can find the changes that it performed in this commit.

When I run dotty on this rewritten code base, I get the following error:

exception occured while indexing /home/sam/Documents/git/scala/src/library/scala/Tuple9.scala
Exception in thread "main" java.lang.AssertionError: assertion failed: asTerm called on not-a-Term val <none>
    at scala.Predef$.assert(Predef.scala:165)
    at dotty.tools.dotc.core.Symbols$Symbol.asTerm(Symbols.scala:369)
    at dotty.tools.dotc.ast.tpd$.New(tpd.scala:305)
    at dotty.tools.dotc.ast.desugar$.makeAnnotated(Desugar.scala:550)
    at dotty.tools.dotc.ast.desugar$.dotty$tools$dotc$ast$desugar$$copyDefault$1(Desugar.scala:297)
    at dotty.tools.dotc.ast.desugar$$anonfun$12.apply(Desugar.scala:299)
    at dotty.tools.dotc.ast.desugar$$anonfun$12.apply(Desugar.scala:298)
    at scala.collection.immutable.List.map(List.scala:274)
    at dotty.tools.dotc.ast.desugar$.classDef(Desugar.scala:298)
    at dotty.tools.dotc.ast.desugar$.defTree(Desugar.scala:497)
    at dotty.tools.dotc.typer.Namer.expand(Namer.scala:288)
    at dotty.tools.dotc.typer.Namer$$anonfun$index$1.apply(Namer.scala:385)
    at dotty.tools.dotc.typer.Namer$$anonfun$index$1.apply(Namer.scala:385)
    at scala.collection.immutable.List.foreach(List.scala:383)
    at dotty.tools.dotc.typer.Namer.index(Namer.scala:385)
    at dotty.tools.dotc.typer.Namer.indexExpanded(Namer.scala:344)
    at dotty.tools.dotc.typer.Namer.index(Namer.scala:335)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$enterSyms$1.apply$mcV$sp(FrontEnd.scala:34)
    at dotty.tools.dotc.typer.FrontEnd.monitor(FrontEnd.scala:17)
    at dotty.tools.dotc.typer.FrontEnd.enterSyms(FrontEnd.scala:32)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$2.apply(FrontEnd.scala:50)
    at dotty.tools.dotc.typer.FrontEnd$$anonfun$runOn$2.apply(FrontEnd.scala:50)
    at scala.collection.immutable.List.foreach(List.scala:383)
    at dotty.tools.dotc.typer.FrontEnd.runOn(FrontEnd.scala:50)
    at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:49)
    at dotty.tools.dotc.Run$$anonfun$compileSources$1$$anonfun$apply$mcV$sp$3.apply(Run.scala:47)
    at scala.collection.IndexedSeqOptimized$class.foreach(IndexedSeqOptimized.scala:33)
    at scala.collection.mutable.ArrayOps$ofRef.foreach(ArrayOps.scala:186)
    at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply$mcV$sp(Run.scala:47)
    at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:39)
    at dotty.tools.dotc.Run$$anonfun$compileSources$1.apply(Run.scala:39)
    at dotty.tools.dotc.util.Stats$.monitorHeartBeat(Stats.scala:68)
    at dotty.tools.dotc.Run.compileSources(Run.scala:38)
    at dotty.tools.dotc.Run.compile(Run.scala:29)
    at dotty.tools.dotc.Driver.doCompile(Driver.scala:19)
    at dotty.tools.dotc.Main$.doCompile(Main.scala:26)
    at dotty.tools.dotc.Driver.process(Driver.scala:30)
    at dotty.tools.dotc.Driver.main(Driver.scala:44)
    at dotty.tools.dotc.Main.main(Main.scala)

It's not (yet) clear to me why this happens, because I've not yet studied this error in detail.

[smarter]

Work is under way to get the standard library to compile, both by changing it and making the dotty compiler deal with more Scala2 stuff, so I'll close this issue.