New miniphase: ExpandSAMs

The phase replaces SAM closures with anonymous classes when necessary.

4 files changed, 103 insertions, 0 deletions

diff --git a/src/dotty/tools/dotc/Compiler.scala b/src/dotty/tools/dotc/Compiler.scala
index 44e7ac450..a9aa65201 100644
--- a/src/dotty/tools/dotc/Compiler.scala
+++ b/src/dotty/tools/dotc/Compiler.scala
@@ -45,6 +45,7 @@ class Compiler {
            new ElimRepeated,
            new NormalizeFlags,
            new ExtensionMethods,
+           new ExpandSAMs,
            new TailRec),
       List(new PatternMatcher,
            new ExplicitOuter,
diff --git a/src/dotty/tools/dotc/core/StdNames.scala b/src/dotty/tools/dotc/core/StdNames.scala
index 74a121b47..826cbe2c6 100644
--- a/src/dotty/tools/dotc/core/StdNames.scala
+++ b/src/dotty/tools/dotc/core/StdNames.scala
@@ -418,6 +418,7 @@ object StdNames {
     val isArray: N              = "isArray"
     val isDefined: N            = "isDefined"
     val isDefinedAt: N          = "isDefinedAt"
+    val isDefinedAtImpl: N      = "$isDefinedAt"
     val isEmpty: N              = "isEmpty"
     val isInstanceOf_ : N       = "isInstanceOf"
     val java: N                 = "java"
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 595732b37..80cceed38 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -545,6 +545,11 @@ object Types {
         (name, buf) => buf ++= member(name).altsWith(x => x.isClass))
     }
 
+    final def fields(implicit ctx: Context): Seq[SingleDenotation] = track("fields") {
+      memberDenots(fieldFilter,
+        (name, buf) => buf ++= member(name).altsWith(x => !x.is(Method)))
+    }
+
     /** The set of members  of this type  having at least one of `requiredFlags` but none of  `excludedFlags` set */
     final def membersBasedOnFlags(requiredFlags: FlagSet, excludedFlags: FlagSet)(implicit ctx: Context): Seq[SingleDenotation] = track("implicitMembers") {
       memberDenots(takeAllFilter,
@@ -3049,6 +3054,11 @@ object Types {
     def apply(pre: Type, name: Name)(implicit ctx: Context): Boolean = name.isTypeName
   }
 
+  object fieldFilter extends NameFilter {
+    def apply(pre: Type, name: Name)(implicit ctx: Context): Boolean =
+      name.isTermName && (pre member name).hasAltWith(!_.symbol.is(Method))
+  }
+
   object takeAllFilter extends NameFilter {
     def apply(pre: Type, name: Name)(implicit ctx: Context): Boolean = true
   }
diff --git a/src/dotty/tools/dotc/transform/ExpandSAMs.scala b/src/dotty/tools/dotc/transform/ExpandSAMs.scala
new file mode 100644
index 000000000..1340a2067
--- /dev/null
+++ b/src/dotty/tools/dotc/transform/ExpandSAMs.scala
@@ -0,0 +1,91 @@
+package dotty.tools.dotc
+package transform
+
+import core._
+import Contexts._, Symbols._, Types._, Flags._, Decorators._, StdNames._, Constants._
+import SymDenotations.SymDenotation
+import TreeTransforms._
+import ast.untpd
+import ast.Trees._
+
+/** Expand SAM closures that cannot be represented by the JVM to anonymous classes.
+ *  These fall into three categories
+ *
+ *   1. Partial function closures, we need to generate a isDefinedAt method for these.
+ *   2. Closures implementaing non-trait classes.
+ *   3. Closures that get synthesized abstract methods in the transformation pipeline. These methods can be
+ *      (1) superaccessors, (2) outer references, (3) accessors for fields.
+ */
+class ExpandSAMs extends MiniPhaseTransform { thisTransformer =>
+  override def phaseName = "expandSAMs"
+
+  import ast.tpd._
+
+  def noJvmSam(cls: ClassSymbol)(implicit ctx: Context): Boolean =
+    !cls.is(Trait) || ExplicitOuter.needsOuterIfReferenced(cls) || cls.typeRef.fields.nonEmpty
+
+  override def transformBlock(tree: Block)(implicit ctx: Context, info: TransformerInfo): Tree = tree match {
+    case Block(stats @ (fn: DefDef) :: Nil, Closure(_, fnRef, tpt)) if fnRef.symbol == fn.symbol =>
+      tpt.tpe match {
+        case NoType => tree // it's a plain function
+        case tpe @ SAMType(_) if !noJvmSam(tpe.classSymbol.asClass) =>
+          if (tpe isRef defn.PartialFunctionClass) toPartialFunction(tree)
+          else tree
+        case tpe =>
+          cpy.Block(tree)(stats,
+              AnonClass(tpe, fn.symbol.asTerm :: Nil, nme.apply :: Nil))
+      }
+    case _ =>
+      tree
+  }
+
+  private def toPartialFunction(tree: Block)(implicit ctx: Context, info: TransformerInfo): Tree = {
+    val Block(
+          (applyDef @ DefDef(nme.ANON_FUN, Nil, List(params), _, _)) :: Nil,
+          Closure(_, _, tpt)) = tree
+    val List(param) = params
+    // Dotty problem: If we match instead List(List(param)) directly,
+    // we get:
+    // Exception in thread "main" java.lang.AssertionError: assertion failed: self instantiation of (A?
+    // ...
+    //  at scala.Predef$.assert(Predef.scala:165)
+    //  at dotty.tools.dotc.core.Types$TypeVar.instantiateWith(Types.scala:2308)
+    //  at dotty.tools.dotc.core.Types$TypeVar.instantiate(Types.scala:2363)
+    //  at dotty.tools.dotc.typer.Inferencing$$anonfun$interpolate$1$1$$anonfun$apply$mcV$sp$4.apply(Inferencing.scala:198)
+    // at dotty.tools.dotc.typer.Inferencing$$anonfun$interpolate$1$1$$anonfun$apply$mcV$sp$4.apply(Inferencing.scala:195)
+    //
+    // I think it has to do with the double :: (or List) pattern to extract `param`.
+
+    val applyRhs: Tree = applyDef.rhs
+    val applyFn = applyDef.symbol.asTerm
+
+    val MethodType(paramNames, paramTypes) = applyFn.info
+    val isDefinedAtFn = applyFn.copy(
+        name  = nme.isDefinedAtImpl,
+        flags = Synthetic | Method,
+        info = MethodType(paramNames, paramTypes, defn.BooleanType)).asTerm
+    val tru = Literal(Constant(true))
+    def isDefinedAtRhs(paramRefss: List[List[Tree]]) = applyRhs match {
+      case Match(selector, cases) =>
+        assert(selector.symbol == param.symbol)
+        val paramRef = paramRefss.head.head
+        // Again, the alternative
+        //     val List(List(paramRef)) = paramRefs
+        // fails with a similar self instantiation error
+        def translateCase(cdef: CaseDef): CaseDef =
+          cpy.CaseDef(cdef)(body = tru).changeOwner(applyFn, isDefinedAtFn)
+        val defaultSym = ctx.newSymbol(isDefinedAtFn, nme.WILDCARD, Synthetic, selector.tpe.widen)
+        val defaultCase =
+          CaseDef(
+            Bind(defaultSym, untpd.Ident(nme.WILDCARD).withType(selector.tpe.widen)),
+            EmptyTree,
+            Literal(Constant(false)))
+        cpy.Match(applyRhs)(paramRef, cases.map(translateCase) :+ defaultCase)
+      case _ =>
+        tru
+    }
+    val isDefinedAtDef = transformFollowingDeep(DefDef(isDefinedAtFn, isDefinedAtRhs(_)))
+    val anonCls = AnonClass(tpt.tpe, List(applyFn, isDefinedAtFn), List(nme.apply, nme.isDefinedAt))
+    cpy.Block(tree)(List(applyDef, isDefinedAtDef), anonCls)
+  }
+}