Reworked TermRef handling

The main problem with TermRef handling was that signatures were not always tracked correctly.

New invariant: A TermRef that points to a symbol is always a TermRefWithSig, and the signature
is the one of the corresponding member.

We achieve this by sometimes generating a new TermRefWithSig if a TermRef gets a denotation.

One possible simplification would be to always store a signature in a TermRef.

There's still a problem in TermRefWithSig#newLikeThis, which currently works only if the previously stored
denotation references a symbol. We will need to generalize JointRefDenotation to contain multiple symbols for
a complete fix.

5 files changed, 126 insertions, 25 deletions

diff --git a/src/dotty/tools/dotc/core/Denotations.scala b/src/dotty/tools/dotc/core/Denotations.scala
index 0622829c5..63b94efbd 100644
--- a/src/dotty/tools/dotc/core/Denotations.scala
+++ b/src/dotty/tools/dotc/core/Denotations.scala
@@ -334,7 +334,7 @@ object Denotations {
     final def info(implicit ctx: Context) = infoOrCompleter
     final def validFor = denot1.validFor & denot2.validFor
     final def isType = false
-    def signature(implicit ctx: Context) = multiHasNot("signature")
+    final def signature(implicit ctx: Context) = Signature.OverloadedSignature
     def atSignature(sig: Signature)(implicit ctx: Context): SingleDenotation =
       denot1.atSignature(sig) orElse denot2.atSignature(sig)
     def current(implicit ctx: Context): Denotation =
diff --git a/src/dotty/tools/dotc/core/Signature.scala b/src/dotty/tools/dotc/core/Signature.scala
index 02b91b18e..eb85fbb99 100644
--- a/src/dotty/tools/dotc/core/Signature.scala
+++ b/src/dotty/tools/dotc/core/Signature.scala
@@ -1,7 +1,7 @@
 package dotty.tools.dotc
 package core
 
-import Names._, Types._, Contexts._
+import Names._, Types._, Contexts._, StdNames._
 import transform.Erasure.sigName
 
 /** The signature of a denotation.
@@ -49,6 +49,10 @@ object Signature {
    *  a type different from PolyType, MethodType, or ExprType.
    */
   val NotAMethod = Signature(List(), EmptyTypeName)
+  
+  /** The signature of an overloaded denotation.
+   */
+  val OverloadedSignature = Signature(List(tpnme.OVERLOADED), EmptyTypeName)
 
   /** The signature of a method with no parameters and result type `resultType`. */
   def apply(resultType: Type, isJava: Boolean)(implicit ctx: Context): Signature =
diff --git a/src/dotty/tools/dotc/core/StdNames.scala b/src/dotty/tools/dotc/core/StdNames.scala
index 3982c51f0..d01971982 100644
--- a/src/dotty/tools/dotc/core/StdNames.scala
+++ b/src/dotty/tools/dotc/core/StdNames.scala
@@ -109,6 +109,7 @@ object StdNames {
     val MODULE_VAR_SUFFIX: N          = "$module"
     val NAME_JOIN: N                  = NameTransformer.NAME_JOIN_STRING
     val USCORE_PARAM_PREFIX: N        = "_$"
+    val OVERLOADED: N                 = "<overloaded>"
     val PACKAGE: N                    = "package"
     val PACKAGE_CLS: N                = "package$"
     val PROTECTED_PREFIX: N           = "protected$"
diff --git a/src/dotty/tools/dotc/core/Symbols.scala b/src/dotty/tools/dotc/core/Symbols.scala
index b4db26ae6..8f66830e8 100644
--- a/src/dotty/tools/dotc/core/Symbols.scala
+++ b/src/dotty/tools/dotc/core/Symbols.scala
@@ -245,7 +245,7 @@ trait Symbols { this: Context =>
     for (name <- names) {
       val tparam = newNakedSymbol[TypeName](NoCoord)
       tparamBuf += tparam
-      trefBuf += TypeRef(owner.thisType, name) withSym tparam
+      trefBuf += TypeRef(owner.thisType, name).withSym(tparam, Signature.NotAMethod)
     }
     val tparams = tparamBuf.toList
     val bounds = boundsFn(trefBuf.toList)
@@ -319,7 +319,7 @@ object Symbols {
     type ThisName <: Name
 
     private[this] var _id: Int = nextId
-    //assert(_id != 5859)
+    //assert(_id != 12325)
 
     /** The unique id of this symbol */
     def id = _id
diff --git a/src/dotty/tools/dotc/core/Types.scala b/src/dotty/tools/dotc/core/Types.scala
index 8799f9fd0..7561abb10 100644
--- a/src/dotty/tools/dotc/core/Types.scala
+++ b/src/dotty/tools/dotc/core/Types.scala
@@ -656,6 +656,15 @@ object Types {
         if (res.exists) res else TypeRef(this, name, denot)
     }
 
+    /** The type <this . name> , reduced if possible, with given denotation if unreduced */
+    def selectNonMember(name: Name, denot: Denotation)(implicit ctx: Context): Type = name match {
+      case name: TermName =>
+        TermRef(this, name, denot)
+      case name: TypeName =>
+        val res = lookupRefined(name)
+        if (res.exists) res else TypeRef(this, name, denot)
+    }
+
     /** The type <this . name> with given symbol, reduced if possible */
     def select(sym: Symbol)(implicit ctx: Context): Type =
       if (sym.isTerm) TermRef(this, sym.asTerm)
@@ -991,6 +1000,8 @@ object Types {
     val prefix: Type
     val name: Name
 
+    type ThisType >: this.type <: NamedType
+
     assert(prefix.isValueType || (prefix eq NoPrefix), s"invalid prefix $prefix")
 
     private[this] var lastDenotation: Denotation = _
@@ -1049,19 +1060,48 @@ object Types {
       if (owner.isTerm) d else d.asSeenFrom(prefix)
     }
 
-    private[dotc] final def withDenot(denot: Denotation): this.type = {
+    private def checkSymAssign(sym: Symbol) =
+      assert(
+        (lastSymbol eq sym) ||
+        (lastSymbol eq null) ||
+        (lastSymbol.defRunId != sym.defRunId) ||
+        (lastSymbol.defRunId == NoRunId),
+        s"data race? overwriting symbol of $this / ${this.getClass} / ${lastSymbol.id} / ${sym.id}")
+
+    protected def sig: Signature = Signature.NotAMethod
+
+    private[dotc] def withDenot(denot: Denotation)(implicit ctx: Context): ThisType =
+      if (sig != denot.signature)
+        withSig(denot.signature).withDenot(denot).asInstanceOf[ThisType]
+      else {
+        setDenot(denot)
+        this
+      }
+
+    private[dotc] final def setDenot(denot: Denotation): Unit = {
+      if (Config.checkTermRefs) checkSymAssign(denot.symbol)
       lastDenotation = denot
       lastSymbol = denot.symbol
-      this
     }
 
-    private[dotc] final def withSym(sym: Symbol): this.type = {
+    private[dotc] def withSym(sym: Symbol, signature: Signature)(implicit ctx: Context): ThisType =
+      if (sig != signature)
+        withSig(signature).withSym(sym, signature).asInstanceOf[ThisType]
+      else {
+        setSym(sym)
+        this
+      }
+
+    private[dotc] final def setSym(sym: Symbol): Unit = {
+      if (Config.checkTermRefs) checkSymAssign(sym)
       lastDenotation = null
       lastSymbol = sym
       checkedPeriod = Nowhere
-      this
     }
 
+    private def withSig(sig: Signature)(implicit ctx: Context): NamedType =
+      TermRef.withSig(prefix, name.asTermName, sig)
+
     protected def loadDenot(implicit ctx: Context) = {
       val d = prefix.member(name)
       if (d.exists || ctx.phaseId == FirstPhaseId)
@@ -1136,6 +1176,9 @@ object Types {
 
   abstract case class TermRef(override val prefix: Type, name: TermName) extends NamedType with SingletonType {
 
+    type ThisType = TermRef
+
+    //assert(name.toString != "<local Coder>")
     override def underlying(implicit ctx: Context): Type = {
       val d = denot
       if (d.isOverloaded) NoType else d.info
@@ -1156,16 +1199,31 @@ object Types {
   }
 
   abstract case class TypeRef(override val prefix: Type, name: TypeName) extends NamedType {
+
+    type ThisType = TypeRef
+
     override def underlying(implicit ctx: Context): Type = info
   }
 
-  final class TermRefWithSignature(prefix: Type, name: TermName, val sig: Signature) extends TermRef(prefix, name) {
+  final class TermRefWithSignature(prefix: Type, name: TermName, override val sig: Signature) extends TermRef(prefix, name) {
     assert(prefix ne NoPrefix)
     override def signature(implicit ctx: Context) = sig
-    override def loadDenot(implicit ctx: Context): Denotation =
-      super.loadDenot.atSignature(sig)
-    override def newLikeThis(prefix: Type)(implicit ctx: Context): TermRef =
-      TermRef.withSig(prefix, name, sig)
+    override def loadDenot(implicit ctx: Context): Denotation = {
+      val d = super.loadDenot
+      if (sig eq Signature.OverloadedSignature) d
+      else d.atSignature(sig)
+    }
+
+    override def newLikeThis(prefix: Type)(implicit ctx: Context): TermRef = {
+      if (sig != Signature.NotAMethod &&
+          sig != Signature.OverloadedSignature &&
+          symbol.exists) {
+        val ownSym = symbol
+        TermRef(prefix, name).withDenot(prefix.member(name).disambiguate(_ eq ownSym))
+      }
+      else TermRef.withSig(prefix, name, sig)
+    }
+
     override def equals(that: Any) = that match {
       case that: TermRefWithSignature =>
         this.prefix == that.prefix &&
@@ -1177,15 +1235,25 @@ object Types {
     override def computeHash = doHash((name, sig), prefix)
   }
 
-  trait WithNoPrefix extends NamedType {
+  trait WithNonMemberSym extends NamedType {
     def fixedSym: Symbol
     assert(fixedSym ne NoSymbol)
-    withSym(fixedSym)
+    setSym(fixedSym)
+
+    override def withDenot(denot: Denotation)(implicit ctx: Context): ThisType = {
+      assert(denot.symbol eq fixedSym)
+      setDenot(denot)
+      this
+    }
+
+    override def withSym(sym: Symbol, signature: Signature)(implicit ctx: Context): ThisType =
+      unsupported("withSym")
+
     override def equals(that: Any) = that match {
-      case that: WithNoPrefix => this.fixedSym eq that.fixedSym
+      case that: WithNonMemberSym => this.prefix == that.prefix && (this.fixedSym eq that.fixedSym)
       case _ => false
     }
-    override def computeHash = doHash(fixedSym)
+    override def computeHash = doHash(fixedSym, prefix)
   }
 
   final class CachedTermRef(prefix: Type, name: TermName, hc: Int) extends TermRef(prefix, name) {
@@ -1200,8 +1268,8 @@ object Types {
     override def computeHash = unsupported("computeHash")
   }
 
-  final class NoPrefixTermRef(name: TermName, val fixedSym: TermSymbol) extends TermRef(NoPrefix, name) with WithNoPrefix
-  final class NoPrefixTypeRef(name: TypeName, val fixedSym: TypeSymbol) extends TypeRef(NoPrefix, name) with WithNoPrefix
+  final class NonMemberTermRef(prefix: Type, name: TermName, val fixedSym: TermSymbol) extends TermRef(prefix, name) with WithNonMemberSym
+  final class NonMemberTypeRef(prefix: Type, name: TypeName, val fixedSym: TypeSymbol) extends TypeRef(prefix, name) with WithNonMemberSym
 
   object NamedType {
     def apply(prefix: Type, name: Name)(implicit ctx: Context) =
@@ -1210,20 +1278,42 @@ object Types {
     def apply(prefix: Type, name: Name, denot: Denotation)(implicit ctx: Context) =
       if (name.isTermName) TermRef(prefix, name.asTermName, denot)
       else TypeRef(prefix, name.asTypeName, denot)
+    def withNonMemberSym(prefix: Type, sym: Symbol)(implicit ctx: Context) =
+      if (sym.isType) TypeRef.withNonMemberSym(prefix, sym.name.asTypeName, sym.asType)
+      else TermRef.withNonMemberSym(prefix, sym.name.asTermName, sym.asTerm)
   }
 
   object TermRef {
     def apply(prefix: Type, name: TermName)(implicit ctx: Context): TermRef =
       ctx.uniqueNamedTypes.enterIfNew(prefix, name).asInstanceOf[TermRef]
+
     def apply(prefix: Type, sym: TermSymbol)(implicit ctx: Context): TermRef =
       withSymAndName(prefix, sym, sym.name)
+
+    def apply(prefix: Type, name: TermName, denot: Denotation)(implicit ctx: Context): TermRef = {
+      if (prefix eq NoPrefix) apply(prefix, denot.symbol.asTerm)
+      else denot match {
+        case denot: SymDenotation if denot.isCompleted => withSig(prefix, name, denot.signature)
+        case _ => apply(prefix, name)
+      }
+    } withDenot denot
+
+    def withNonMemberSym(prefix: Type, name: TermName, sym: TermSymbol)(implicit ctx: Context): TermRef =
+      unique(new NonMemberTermRef(prefix, name, sym))
+
     def withSymAndName(prefix: Type, sym: TermSymbol, name: TermName)(implicit ctx: Context): TermRef =
-      if (prefix eq NoPrefix) unique(new NoPrefixTermRef(name, sym))
-      else apply(prefix, name) withSym sym
-    def apply(prefix: Type, name: TermName, denot: Denotation)(implicit ctx: Context): TermRef =
-      (if (prefix eq NoPrefix) apply(prefix, denot.symbol.asTerm) else apply(prefix, name)) withDenot denot
+      if (prefix eq NoPrefix) withNonMemberSym(prefix, name, sym)
+      else {
+        if (sym.defRunId != NoRunId && sym.isCompleted) withSig(prefix, name, sym.signature)
+        else  apply(prefix, name)
+      } withSym (sym, Signature.NotAMethod)
+
+    def withSig(prefix: Type, sym: TermSymbol)(implicit ctx: Context): TermRef =
+      unique(withSig(prefix, sym.name, sym.signature).withSym(sym, sym.signature))
+
     def withSig(prefix: Type, name: TermName, sig: Signature)(implicit ctx: Context): TermRef =
       unique(new TermRefWithSignature(prefix, name, sig))
+
     def withSig(prefix: Type, name: TermName, sig: Signature, denot: Denotation)(implicit ctx: Context): TermRef =
       (if (prefix eq NoPrefix) apply(prefix, denot.symbol.asTerm)
        else withSig(prefix, name, sig)) withDenot denot
@@ -1232,11 +1322,17 @@ object Types {
   object TypeRef {
     def apply(prefix: Type, name: TypeName)(implicit ctx: Context): TypeRef =
       ctx.uniqueNamedTypes.enterIfNew(prefix, name).asInstanceOf[TypeRef]
+
     def apply(prefix: Type, sym: TypeSymbol)(implicit ctx: Context): TypeRef =
       withSymAndName(prefix, sym, sym.name)
+
+    def withNonMemberSym(prefix: Type, name: TypeName, sym: TypeSymbol)(implicit ctx: Context): TypeRef =
+      unique(new NonMemberTypeRef(prefix, name, sym))
+
     def withSymAndName(prefix: Type, sym: TypeSymbol, name: TypeName)(implicit ctx: Context): TypeRef =
-      if (prefix eq NoPrefix) unique(new NoPrefixTypeRef(name, sym))
-      else apply(prefix, name) withSym sym
+      if (prefix eq NoPrefix) withNonMemberSym(prefix, name, sym)
+      else apply(prefix, name).withSym(sym, Signature.NotAMethod)
+
     def apply(prefix: Type, name: TypeName, denot: Denotation)(implicit ctx: Context): TypeRef =
       (if (prefix eq NoPrefix) apply(prefix, denot.symbol.asType) else apply(prefix, name)) withDenot denot
   }