Refactor from distribute{And,Or} to {meet,join}Info

The refactored logic only applies to infos of denotations, not
general types. The reactoring avoids special cases down the road
then PolyTypes and MethodTypes can be used for terms as well as
type(bounds).

Author: odersky

src/dotty/tools/dotc/core/Denotations.scala

@@ -6,6 +6,7 @@ import SymDenotations.{ SymDenotation, ClassDenotation, NoDenotation, NotDefined
 import Contexts.{Context, ContextBase}
 import Names.{Name, PreName}
 import Names.TypeName
+import StdNames._
 import Symbols.NoSymbol
 import Symbols._
 import Types._
@@ -247,6 +248,25 @@ object Denotations {
       else asSingleDenotation
     }
 
+    /** Handle merge conflict by throwing a `MergeError` exception */
+    private def mergeConflict(tp1: Type, tp2: Type)(implicit ctx: Context): Type = {
+      def showType(tp: Type) = tp match {
+        case ClassInfo(_, cls, _, _, _) => cls.showLocated
+        case bounds: TypeBounds => i"type bounds $bounds"
+        case _ => tp.show
+      }
+      if (true) throw new MergeError(s"cannot merge ${showType(tp1)} with ${showType(tp2)}", tp1, tp2)
+      else throw new Error(s"cannot merge ${showType(tp1)} with ${showType(tp2)}") // flip condition for debugging
+    }
+
+    /** Merge two lists of names. If names in corresponding positions match, keep them,
+     *  otherwise generate new synthetic names.
+     */
+    def mergeNames[N <: Name](names1: List[N], names2: List[N], syntheticName: Int => N): List[N] = {
+      for ((name1, name2, idx) <- (names1, names2, 0 until names1.length).zipped)
+        yield if (name1 == name2) name1 else syntheticName(idx)
+    }.toList
+
     /** Form a denotation by conjoining with denotation `that`.
      *
      *  NoDenotations are dropped. MultiDenotations are handled by merging
@@ -277,6 +297,50 @@ object Denotations {
      */
     def & (that: Denotation, pre: Type, safeIntersection: Boolean = false)(implicit ctx: Context): Denotation = {
 
+      /** Normally, `tp1 & tp2`. Special cases for matching methods and classes, with
+       *  the possibility of raising a merge error.
+       */
+      def infoMeet(tp1: Type, tp2: Type): Type = {
+        if (tp1 eq tp2) tp1
+        else tp1 match {
+          case tp1: TypeBounds =>
+            tp2 match {
+              case tp2: TypeBounds => if (safeIntersection) tp1 safe_& tp2 else tp1 & tp2
+              case tp2: ClassInfo if tp1 contains tp2 => tp2
+              case _ => mergeConflict(tp1, tp2)
+            }
+          case tp1: ClassInfo =>
+            tp2 match {
+              case tp2: ClassInfo if tp1.cls eq tp2.cls => tp1.derivedClassInfo(tp1.prefix & tp2.prefix)
+              case tp2: TypeBounds if tp2 contains tp1 => tp1
+              case _ => mergeConflict(tp1, tp2)
+            }
+          case tp1 @ MethodType(names1, formals1) if isTerm =>
+            tp2 match {
+              case tp2 @ MethodType(names2, formals2) if ctx.typeComparer.matchingParams(formals1, formals2, tp1.isJava, tp2.isJava) &&
+                tp1.isImplicit == tp2.isImplicit =>
+                tp1.derivedMethodType(
+                  mergeNames(names1, names2, nme.syntheticParamName),
+                  formals1,
+                  infoMeet(tp1.resultType, tp2.resultType.subst(tp2, tp1)))
+              case _ =>
+                mergeConflict(tp1, tp2)
+            }
+          case tp1: PolyType if isTerm =>
+            tp2 match {
+              case tp2: PolyType if ctx.typeComparer.matchingTypeParams(tp1, tp2) =>
+                tp1.derivedPolyType(
+                  mergeNames(tp1.paramNames, tp2.paramNames, tpnme.syntheticTypeParamName),
+                  tp1.paramBounds,
+                  infoMeet(tp1.resultType, tp2.resultType.subst(tp2, tp1)))
+              case _: MethodicType =>
+                mergeConflict(tp1, tp2)
+            }
+          case _ =>
+            tp1 & tp2
+        }
+      }
+
       /** Try to merge denot1 and denot2 without adding a new signature. */
       def mergeDenot(denot1: Denotation, denot2: SingleDenotation): Denotation = denot1 match {
         case denot1 @ MultiDenotation(denot11, denot12) =>
@@ -289,95 +353,94 @@ object Denotations {
           }
         case denot1: SingleDenotation =>
           if (denot1 eq denot2) denot1
-          else if (denot1.matches(denot2)) {
-            val info1 = denot1.info
-            val info2 = denot2.info
-            val sym1 = denot1.symbol
-            val sym2 = denot2.symbol
-
-            val sym2Accessible = sym2.isAccessibleFrom(pre)
-
-            /** Does `sym1` come before `sym2` in the linearization of `pre`? */
-            def precedes(sym1: Symbol, sym2: Symbol) = {
-              def precedesIn(bcs: List[ClassSymbol]): Boolean = bcs match {
-                case bc :: bcs1 => (sym1 eq bc) || !(sym2 eq bc) && precedesIn(bcs1)
-                case Nil => true
-              }
-              (sym1 ne sym2) &&
-              (sym1.derivesFrom(sym2) ||
-                !sym2.derivesFrom(sym1) && precedesIn(pre.baseClasses))
-            }
+          else if (denot1.matches(denot2)) mergeSingleDenot(denot1, denot2)
+          else NoDenotation
+      }
 
-            /** Similar to SymDenotation#accessBoundary, but without the special cases. */
-            def accessBoundary(sym: Symbol) =
-              if (sym.is(Private)) sym.owner
-              else sym.privateWithin.orElse(
-                if (sym.is(Protected)) sym.owner.enclosingPackageClass
-                else defn.RootClass
-              )
-
-            /** Establish a partial order "preference" order between symbols.
-             *  Give preference to `sym1` over `sym2` if one of the following
-             *  conditions holds, in decreasing order of weight:
-             *   1. sym1 is concrete and sym2 is abstract
-             *   2. The owner of sym1 comes before the owner of sym2 in the linearization
-             *      of the type of the prefix `pre`.
-             *   3. The access boundary of sym2 is properly contained in the access
-             *      boundary of sym1. For protected access, we count the enclosing
-             *      package as access boundary.
-             *   4. sym1 a method but sym2 is not.
-             *  The aim of these criteria is to give some disambiguation on access which
-             *   - does not depend on textual order or other arbitrary choices
-             *   - minimizes raising of doubleDef errors
-             */
-            def preferSym(sym1: Symbol, sym2: Symbol) =
-              sym1.eq(sym2) ||
-                sym1.isAsConcrete(sym2) &&
-                (!sym2.isAsConcrete(sym1) ||
-                 precedes(sym1.owner, sym2.owner) ||
-                 accessBoundary(sym2).isProperlyContainedIn(accessBoundary(sym1)) ||
-                 sym1.is(Method) && !sym2.is(Method))
-
-            /** Sym preference provided types also override */
-            def prefer(sym1: Symbol, sym2: Symbol, info1: Type, info2: Type) =
-              preferSym(sym1, sym2) && info1.overrides(info2)
-
-            def handleDoubleDef =
-              if (preferSym(sym1, sym2)) denot1
-              else if (preferSym(sym2, sym1)) denot2
-              else doubleDefError(denot1, denot2, pre)
-
-            if (sym2Accessible && prefer(sym2, sym1, info2, info1)) denot2
-            else {
-              val sym1Accessible = sym1.isAccessibleFrom(pre)
-              if (sym1Accessible && prefer(sym1, sym2, info1, info2)) denot1
-              else if (sym1Accessible && sym2.exists && !sym2Accessible) denot1
-              else if (sym2Accessible && sym1.exists && !sym1Accessible) denot2
-              else if (isDoubleDef(sym1, sym2)) handleDoubleDef
-              else {
-                val sym =
-                  if (!sym1.exists) sym2
-                  else if (!sym2.exists) sym1
-                  else if (preferSym(sym2, sym1)) sym2
-                  else sym1
-                val jointInfo =
-                  try
-                    if (safeIntersection)
-                      info1 safe_& info2
-                    else
-                      info1 & info2
-                  catch {
-                    case ex: MergeError =>
-                      if (pre.widen.classSymbol.is(Scala2x) || ctx.scala2Mode)
-                        info1 // follow Scala2 linearization -
-                              // compare with way merge is performed in SymDenotation#computeMembersNamed
-                      else
-                        throw new MergeError(s"${ex.getMessage} as members of type ${pre.show}", ex.tp1, ex.tp2)
-                  }
-                new JointRefDenotation(sym, jointInfo, denot1.validFor & denot2.validFor)
+      /** Try to merge single-denotations. */
+      def mergeSingleDenot(denot1: SingleDenotation, denot2: SingleDenotation): SingleDenotation = {
+        val info1 = denot1.info
+        val info2 = denot2.info
+        val sym1 = denot1.symbol
+        val sym2 = denot2.symbol
+
+        val sym2Accessible = sym2.isAccessibleFrom(pre)
+
+        /** Does `sym1` come before `sym2` in the linearization of `pre`? */
+        def precedes(sym1: Symbol, sym2: Symbol) = {
+          def precedesIn(bcs: List[ClassSymbol]): Boolean = bcs match {
+            case bc :: bcs1 => (sym1 eq bc) || !(sym2 eq bc) && precedesIn(bcs1)
+            case Nil => true
+          }
+          (sym1 ne sym2) &&
+            (sym1.derivesFrom(sym2) ||
+              !sym2.derivesFrom(sym1) && precedesIn(pre.baseClasses))
+        }
+
+        /** Similar to SymDenotation#accessBoundary, but without the special cases. */
+        def accessBoundary(sym: Symbol) =
+          if (sym.is(Private)) sym.owner
+          else sym.privateWithin.orElse(
+            if (sym.is(Protected)) sym.owner.enclosingPackageClass
+            else defn.RootClass)
+
+        /** Establish a partial order "preference" order between symbols.
+         *  Give preference to `sym1` over `sym2` if one of the following
+         *  conditions holds, in decreasing order of weight:
+         *   1. sym1 is concrete and sym2 is abstract
+         *   2. The owner of sym1 comes before the owner of sym2 in the linearization
+         *      of the type of the prefix `pre`.
+         *   3. The access boundary of sym2 is properly contained in the access
+         *      boundary of sym1. For protected access, we count the enclosing
+         *      package as access boundary.
+         *   4. sym1 a method but sym2 is not.
+         *  The aim of these criteria is to give some disambiguation on access which
+         *   - does not depend on textual order or other arbitrary choices
+         *   - minimizes raising of doubleDef errors
+         */
+        def preferSym(sym1: Symbol, sym2: Symbol) =
+          sym1.eq(sym2) ||
+            sym1.isAsConcrete(sym2) &&
+            (!sym2.isAsConcrete(sym1) ||
+              precedes(sym1.owner, sym2.owner) ||
+              accessBoundary(sym2).isProperlyContainedIn(accessBoundary(sym1)) ||
+              sym1.is(Method) && !sym2.is(Method))
+
+        /** Sym preference provided types also override */
+        def prefer(sym1: Symbol, sym2: Symbol, info1: Type, info2: Type) =
+          preferSym(sym1, sym2) && info1.overrides(info2)
+
+        def handleDoubleDef =
+          if (preferSym(sym1, sym2)) denot1
+          else if (preferSym(sym2, sym1)) denot2
+          else doubleDefError(denot1, denot2, pre)
+
+        if (sym2Accessible && prefer(sym2, sym1, info2, info1)) denot2
+        else {
+          val sym1Accessible = sym1.isAccessibleFrom(pre)
+          if (sym1Accessible && prefer(sym1, sym2, info1, info2)) denot1
+          else if (sym1Accessible && sym2.exists && !sym2Accessible) denot1
+          else if (sym2Accessible && sym1.exists && !sym1Accessible) denot2
+          else if (isDoubleDef(sym1, sym2)) handleDoubleDef
+          else {
+            val sym =
+              if (!sym1.exists) sym2
+              else if (!sym2.exists) sym1
+              else if (preferSym(sym2, sym1)) sym2
+              else sym1
+            val jointInfo =
+              try infoMeet(info1, info2)
+              catch {
+                case ex: MergeError =>
+                  if (pre.widen.classSymbol.is(Scala2x) || ctx.scala2Mode)
+                    info1 // follow Scala2 linearization -
+                  // compare with way merge is performed in SymDenotation#computeMembersNamed
+                  else
+                    throw new MergeError(s"${ex.getMessage} as members of type ${pre.show}", ex.tp1, ex.tp2)
               }
-            }
-          } else NoDenotation
+            new JointRefDenotation(sym, jointInfo, denot1.validFor & denot2.validFor)
+          }
+        }
       }
 
       if (this eq that) this
@@ -398,6 +461,46 @@ object Denotations {
      */
     def | (that: Denotation, pre: Type)(implicit ctx: Context): Denotation = {
 
+      /** Normally, `tp1 | tp2`. Special cases for matching methods and classes, with
+       *  the possibility of raising a merge error.
+       */
+      def infoJoin(tp1: Type, tp2: Type): Type = tp1 match {
+        case tp1: TypeBounds =>
+          tp2 match {
+            case tp2: TypeBounds => tp1 | tp2
+            case tp2: ClassInfo if tp1 contains tp2 => tp1
+            case _ => mergeConflict(tp1, tp2)
+          }
+        case tp1: ClassInfo =>
+          tp2 match {
+            case tp2: ClassInfo if tp1.cls eq tp2.cls => tp1.derivedClassInfo(tp1.prefix | tp2.prefix)
+            case tp2: TypeBounds if tp2 contains tp1 => tp2
+            case _ => mergeConflict(tp1, tp2)
+          }
+        case tp1 @ MethodType(names1, formals1) =>
+          tp2 match {
+            case tp2 @ MethodType(names2, formals2)
+            if ctx.typeComparer.matchingParams(formals1, formals2, tp1.isJava, tp2.isJava) &&
+              tp1.isImplicit == tp2.isImplicit =>
+              tp1.derivedMethodType(
+                mergeNames(names1, names2, nme.syntheticParamName),
+                formals1, tp1.resultType | tp2.resultType.subst(tp2, tp1))
+            case _ =>
+              mergeConflict(tp1, tp2)
+          }
+        case tp1: PolyType =>
+          tp2 match {
+            case tp2: PolyType if ctx.typeComparer.matchingTypeParams(tp1, tp2) =>
+              tp1.derivedPolyType(
+                mergeNames(tp1.paramNames, tp2.paramNames, tpnme.syntheticTypeParamName),
+                tp1.paramBounds, tp1.resultType | tp2.resultType.subst(tp2, tp1))
+            case _ =>
+              mergeConflict(tp1, tp2)
+          }
+        case _ =>
+          tp1 | tp2
+      }
+
       def unionDenot(denot1: SingleDenotation, denot2: SingleDenotation): Denotation =
         if (denot1.matches(denot2)) {
           val sym1 = denot1.symbol
@@ -427,7 +530,8 @@ object Denotations {
                   }
                 lubSym(sym1.allOverriddenSymbols, NoSymbol)
               }
-            new JointRefDenotation(jointSym, info1 | info2, denot1.validFor & denot2.validFor)
+            new JointRefDenotation(
+                jointSym, infoJoin(info1, info2), denot1.validFor & denot2.validFor)
           }
         }
         else NoDenotation
@@ -1133,5 +1237,4 @@ object Denotations {
     util.Stats.record("not defined here")
     override def getMessage() = msg
   }
-}
-
+}