Any info out there on migrating a Scala 2.9 compiler plugin to 2.10?

Question

I have a Scala 2.9 compiler plugin (source code) and works just fine in 2.9 but does not even compile with 2.10. There are dozens (maybe 100+) of errors all of the same kind such as:

    [scalac] C:\***.scala:31: error: illegal cyclic reference involving class Global
    [scalac]   val fileSeparator = System.getProperty("file.separator");
    [scalac]                       ^

... that eventually terminate with:

    [scalac] scala.reflect.internal.Types$TypeError: illegal cyclic reference involving class Global
    [scalac]     at scala.reflect.internal.Types$class.defineBaseClassesOfCompoundType(Types.scala:1731)
    [scalac]     at scala.reflect.internal.SymbolTable.defineBaseClassesOfCompoundType(SymbolTable.scala:12)
    [scalac]     at scala.reflect.internal.Types$CompoundType.baseClasses(Types.scala:1581)
    [scalac]     at scala.reflect.internal.Types$TypeRef.baseClasses(Types.scala:2369)
    [scalac]     at scala.reflect.internal.Types$SimpleTypeProxy$class.baseClasses(Types.scala:248)
    [scalac]     at scala.reflect.internal.Types$SingletonType.baseClasses(Types.scala:1292)
    [scalac]     at scala.reflect.internal.Types$Type.findMembers(Types.scala:1058)
    [scalac]     at scala.reflect.internal.Types$Type.membersBasedOnFlags(Types.scala:683)
    [scalac]     at scala.reflect.internal.Types$Type.implicitMembers(Types.scala:637)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.collect$1(Contexts.scala:630)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.collectImplicitImports(Contexts.scala:642)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:670)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Contexts$Context.implicitss(Contexts.scala:675)
    [scalac]     at scala.tools.nsc.typechecker.Implicits$ImplicitSearch.bestImplicit(Implicits.scala:1378)
    [scalac]     at scala.tools.nsc.typechecker.Implicits$class.inferImplicit(Implicits.scala:82)
    [scalac]     at scala.tools.nsc.Global$$anon$1.inferImplicit(Global.scala:490)
    [scalac]     at scala.tools.nsc.typechecker.Implicits$class.inferImplicit(Implicits.scala:37)
    [scalac]     at scala.tools.nsc.Global$$anon$1.inferImplicit(Global.scala:490)
    [scalac]     at scala.tools.nsc.typechecker.Typers$Typer.hasImport$1(Typers.scala:764)
    [scalac]     at scala.tools.nsc.typechecker.Typers$Typer.scala$tools$nsc$typechecker$Typers$Typer$$action$1(Typers.scala:766)
    [scalac]     at scala.tools.nsc.typechecker.Typers$Typer$$anonfun$checkFeature$1.apply$mcV$sp(Typers.scala:788)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$apply$1.apply(Analyzer.scala:100)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$apply$1.apply(Analyzer.scala:100)
    [scalac]     at scala.collection.immutable.List.foreach(List.scala:309)
    [scalac]     at scala.collection.generic.TraversableForwarder$class.foreach(TraversableForwarder.scala:32)
    [scalac]     at scala.collection.mutable.ListBuffer.foreach(ListBuffer.scala:45)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3.apply(Analyzer.scala:100)
    [scalac]     at scala.tools.nsc.Global$GlobalPhase.applyPhase(Global.scala:461)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$run$1.apply(Analyzer.scala:90)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3$$anonfun$run$1.apply(Analyzer.scala:90)
    [scalac]     at scala.collection.Iterator$class.foreach(Iterator.scala:727)
    [scalac]     at scala.collection.AbstractIterator.foreach(Iterator.scala:1156)
    [scalac]     at scala.tools.nsc.typechecker.Analyzer$typerFactory$$anon$3.run(Analyzer.scala:90)
    [scalac]     at scala.tools.nsc.Global$Run.compileUnitsInternal(Global.scala:1574)
    [scalac]     at scala.tools.nsc.Global$Run.compileUnits(Global.scala:1548)
    [scalac]     at scala.tools.nsc.Global$Run.compileSources(Global.scala:1544)
    [scalac]     at scala.tools.nsc.Global$Run.compile(Global.scala:1654)
    [scalac]     at scala.tools.ant.Scalac.executeInternal(Scalac.scala:699)
    [scalac]     at scala.tools.ant.Scalac.execute(Scalac.scala:647)
    ...

I need some info or help as to what has changed in 2.10 or how to otherwise deal with this... I tried Googling around and looking in forums but found very little information on this subject.

Will be grateful for any help!

EDIT: Additional info. This is obviously using ant task (see stack trace). That task has been defined:

    <taskdef resource="scala/tools/ant/antlib.xml">
        <classpath>
          <pathelement location=".../scala-library.jar"   />
          <pathelement location=".../scala-reflect.jar"   />
          <pathelement location=".../scala-compiler.jar"  />
        </classpath>
    </taskdef>

EDIT 2: More additional info: I managed to get this plugin to compile (did not run it yet as other things failed) using command-line 2.10 compiler (remember - all is fine in 2.9 world) - ant-based build continues to fail the same way (bug?). I had to make two changes. First deals with varargs. There is a method such as:

    def foo(arg: String*) { ... }

There is another method which is effectively a synonym for it ad was written in 2.9 Scala as:

    def bar = foo _;

I had to change this to the following to get it to work:

    def bar(arg: String*) = foo(arg: *);

Another dealt with 'hasAssignedAnnotations' not being present in ValOrDefDef.symbol any more (I just commented that out to get it to compile, not a real fix).

Again, does anyone know of a web site or a document out there that can help me with migration - i.e. what changed from 2.9 to 2.10 in terms that I need, including compiler plugins.

Thanks!

Answer 1

I do not think there is any usable documentation. If I remember correctly Martin Odersky said in this presentation that more than 1000 files were edited. For 2.10 they have rewritten large parts of the compiler to support better reflection. As a side effect macros popped into existence. The other side effect of course is that a lot of compiler plugins stopped working.

In theory you could browse / search the git history of the scala source code, in practice this will most likely be too time consuming. Some compiler plugins have been converted to macro's, as they are a bit easier to ship. I don't know if this is an option for you.

Your best bet might be to look at the changes made to plugins that are shipped with scala. I found this commit (The new reflection - Showing 190 changed files with 9,001 additions and 6,403 deletions) of the continuations plugin that contains a lot of information and changes. I hope this is of any help.