Merge branch 'master' into unblock-olaf

Author: OlivierBlanvillain

.drone.yml

@@ -1,8 +1,8 @@
 # After updating this file, you need to re-sign it:
 #
 # - Install [drone-cli](http://readme.drone.io/usage/getting-started-cli/)
-# - Copy your token from  http://dotty-ci.epfl.ch/account (Click SHOW TOKEN)
-# - (export DRONE_TOKEN=your-token; export DRONE_SERVER=http://dotty-ci.epfl.ch; drone sign lampepfl/dotty)
+# - Copy your token from http://dotty-ci.epfl.ch/account (Click SHOW TOKEN)
+# - DRONE_TOKEN=your-token DRONE_SERVER=http://dotty-ci.epfl.ch drone sign lampepfl/dotty
 #
 # Please note that the signing can only be done by collaborators.
 
@@ -76,3 +76,5 @@ matrix:
       CI_PUBLISH: false
     - CI_TEST: dotty-bootstrapped/test
       CI_PUBLISH: false
+    - CI_TEST: ;set bootstrapOptimised in ThisBuild := true ;dotty-bootstrapped/test
+      CI_PUBLISH: false

.drone.yml.sig

@@ -1 +1 @@
-eyJhbGciOiJIUzI1NiJ9.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.REtW8iikLellOXP5ex7tY4WJFc4aIFHXTFsbPi0qkiA
+eyJhbGciOiJIUzI1NiJ9.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.0COKo7FjFKxUxTYAwxWvpOHgRClgdi9A4M4Kb91h6HQ

README.md

@@ -14,6 +14,12 @@ Try it out
 ==========
 To try it in your project see also the [Getting Started User Guide](http://dotty.epfl.ch/#getting-started).
 
+Code of Conduct
+===============
+Dotty uses the [Scala Code of Conduct](https://www.scala-lang.org/conduct.html)
+for all communication and discussion. This includes both GitHub, Gitter chat and
+other more direct lines of communication such as email.
+
 How to Contribute
 =================
 * [Getting Started as Contributor](http://dotty.epfl.ch/docs/contributing/getting-started.html)

compiler/src/dotty/tools/dotc/ast/TreeInfo.scala

@@ -14,10 +14,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
   // Note: the <: Type constraint looks necessary (and is needed to make the file compile in dotc).
   // But Scalac accepts the program happily without it. Need to find out why.
 
-  def unsplice[T >: Untyped](tree: Trees.Tree[T]): Trees.Tree[T] = tree.asInstanceOf[untpd.Tree] match {
-    case untpd.TypedSplice(tree1) => tree1.asInstanceOf[Trees.Tree[T]]
-    case _ => tree
-  }
+  def unsplice(tree: Trees.Tree[T]): Trees.Tree[T] = tree
 
   def isDeclarationOrTypeDef(tree: Tree): Boolean = unsplice(tree) match {
     case DefDef(_, _, _, _, EmptyTree)
@@ -116,7 +113,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
     case _ => false
   }
 
-  def isSuperSelection(tree: untpd.Tree) = unsplice(tree) match {
+  def isSuperSelection(tree: Tree) = unsplice(tree) match {
     case Select(Super(_, _), _) => true
     case _ => false
   }
@@ -129,7 +126,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
   }
 
   /** Is tree a variable pattern? */
-  def isVarPattern(pat: untpd.Tree): Boolean = unsplice(pat) match {
+  def isVarPattern(pat: Tree): Boolean = unsplice(pat) match {
     case x: BackquotedIdent => false
     case x: Ident => x.name.isVariableName
     case _  => false
@@ -160,7 +157,7 @@ trait TreeInfo[T >: Untyped <: Type] { self: Trees.Instance[T] =>
   def isLeftAssoc(operator: Name) = !operator.isEmpty && (operator.toSimpleName.last != ':')
 
   /** can this type be a type pattern? */
-  def mayBeTypePat(tree: untpd.Tree): Boolean = unsplice(tree) match {
+  def mayBeTypePat(tree: Tree): Boolean = unsplice(tree) match {
     case AndTypeTree(tpt1, tpt2) => mayBeTypePat(tpt1) || mayBeTypePat(tpt2)
     case OrTypeTree(tpt1, tpt2) => mayBeTypePat(tpt1) || mayBeTypePat(tpt2)
     case RefinedTypeTree(tpt, refinements) => mayBeTypePat(tpt) || refinements.exists(_.isInstanceOf[Bind])
@@ -253,6 +250,13 @@ trait UntypedTreeInfo extends TreeInfo[Untyped] { self: Trees.Instance[Untyped]
   import TreeInfo._
   import untpd._
 
+  /** The underlying tree when stripping any TypedSplice or Parens nodes */
+  override def unsplice(tree: Tree): Tree = tree match {
+    case TypedSplice(tree1) => tree1
+    case Parens(tree1) => unsplice(tree1)
+    case _ => tree
+  }
+
   /** True iff definition is a val or def with no right-hand-side, or it
    *  is an abstract typoe declaration
    */

compiler/src/dotty/tools/dotc/ast/Trees.scala

@@ -1305,8 +1305,10 @@ object Trees {
             this(this(x, arg), annot)
           case Thicket(ts) =>
             this(x, ts)
-          case _ if ctx.reporter.errorsReported =>
-            // in case of errors it may be that typed trees point to untyped ones.
+          case _ if ctx.mode.is(Mode.Interactive) =>
+            // In case of errors it may be that typed trees point to untyped ones.
+            // The IDE can still traverse inside such trees, either in the run where errors
+            // are reported, or in subsequent ones.
             x
         }
       }

compiler/src/dotty/tools/dotc/core/SymDenotations.scala

@@ -1407,32 +1407,13 @@ object SymDenotations {
       baseData._2
 
     def computeBaseData(implicit onBehalf: BaseData, ctx: Context): (List[ClassSymbol], BaseClassSet) = {
-      val seen = new BaseClassSetBuilder
-      def addBaseClasses(bcs: List[ClassSymbol], to: List[ClassSymbol])
-          : List[ClassSymbol] = bcs match {
-        case bc :: bcs1 =>
-          val bcs1added = addBaseClasses(bcs1, to)
-          if (seen contains bc) bcs1added
-          else {
-            seen.add(bc)
-            bc :: bcs1added
-          }
-        case nil =>
-          to
-      }
-      def addParentBaseClasses(ps: List[TypeRef], to: List[ClassSymbol]): List[ClassSymbol] = ps match {
-        case p :: ps1 =>
-          addParentBaseClasses(ps1,
-              addBaseClasses(p.symbol.asClass.baseClasses, to))
-        case nil =>
-          to
-      }
       def emptyParentsExpected =
         is(Package) || (symbol == defn.AnyClass) || ctx.erasedTypes && (symbol == defn.ObjectClass)
       if (classParents.isEmpty && !emptyParentsExpected)
         onBehalf.signalProvisional()
-      (classSymbol :: addParentBaseClasses(classParents, Nil),
-       seen.result)
+      val builder = new BaseDataBuilder
+      for (p <- classParents) builder.addAll(p.symbol.asClass.baseClasses)
+      (classSymbol :: builder.baseClasses, builder.baseClassSet)
     }
 
     final override def derivesFrom(base: Symbol)(implicit ctx: Context): Boolean =
@@ -2096,7 +2077,14 @@ object SymDenotations {
     def contains(sym: Symbol): Boolean = contains(sym, classIds.length)
   }
 
-  private class BaseClassSetBuilder {
+  object BaseClassSet {
+    def apply(bcs: List[ClassSymbol]): BaseClassSet =
+      new BaseClassSet(bcs.toArray.map(_.id))
+  }
+
+  /** A class to combine base data from parent types */
+  class BaseDataBuilder {
+    private var classes: List[ClassSymbol] = Nil
     private var classIds = new Array[Int](32)
     private var length = 0
 
@@ -2106,19 +2094,32 @@ object SymDenotations {
       classIds = classIds1
     }
 
-    def contains(sym: Symbol): Boolean =
-      new BaseClassSet(classIds).contains(sym, length)
-
-    def add(sym: Symbol): Unit = {
+    private def add(sym: Symbol): Unit = {
       if (length == classIds.length) resize(length * 2)
       classIds(length) = sym.id
       length += 1
     }
 
-    def result = {
+    def addAll(bcs: List[ClassSymbol]): this.type = {
+      val len = length
+      bcs match {
+        case bc :: bcs1 =>
+          addAll(bcs1)
+          if (!new BaseClassSet(classIds).contains(bc, len)) {
+            add(bc)
+            classes = bc :: classes
+          }
+        case nil =>
+      }
+      this
+    }
+
+    def baseClassSet = {
       if (length != classIds.length) resize(length)
       new BaseClassSet(classIds)
     }
+
+    def baseClasses: List[ClassSymbol] = classes
   }
 
   @sharable private var indent = 0 // for completions printing

compiler/src/dotty/tools/dotc/core/Symbols.scala

@@ -556,9 +556,10 @@ object Symbols {
     type ThisName = TypeName
 
     /** If this is a top-level class, and if `-Yretain-trees` is set, return the TypeDef tree
-     *  for this class, otherwise EmptyTree.
+     *  for this class, otherwise EmptyTree. This will force the info of the class.
      */
     def tree(implicit ctx: Context): tpd.Tree /* tpd.TypeDef | tpd.EmptyTree */ = {
+      denot.info
       // TODO: Consider storing this tree like we store lazy trees for inline functions
       if (unpickler != null && !denot.isAbsent) {
         assert(myTree.isEmpty)

compiler/src/dotty/tools/dotc/core/TypeComparer.scala

@@ -1143,11 +1143,11 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
           case OrType(tp11, tp12) =>
             tp11 & tp2 | tp12 & tp2
           case _ =>
-            val t1 = mergeIfSub(tp1, tp2)
-            if (t1.exists) t1
+            val tp1a = dropIfSuper(tp1, tp2)
+            if (tp1a ne tp1) glb(tp1a, tp2)
             else {
-              val t2 = mergeIfSub(tp2, tp1)
-              if (t2.exists) t2
+              val tp2a = dropIfSuper(tp2, tp1)
+              if (tp2a ne tp2) glb(tp1, tp2a)
               else tp1 match {
                 case tp1: ConstantType =>
                   tp2 match {
@@ -1204,6 +1204,22 @@ class TypeComparer(initctx: Context) extends DotClass with ConstraintHandling {
   final def lub(tps: List[Type]): Type =
     ((defn.NothingType: Type) /: tps)(lub(_,_, canConstrain = false))
 
+  private def recombineAndOr(tp: AndOrType, tp1: Type, tp2: Type) =
+    if (!tp1.exists) tp2
+    else if (!tp2.exists) tp1
+    else tp.derivedAndOrType(tp1, tp2)
+
+  /** If some (&-operand of) this type is a supertype of `sub` replace it with `NoType`.
+   */
+  private def dropIfSuper(tp: Type, sub: Type): Type =
+    if (isSubTypeWhenFrozen(sub, tp)) NoType
+    else tp match {
+      case tp @ AndType(tp1, tp2) =>
+        recombineAndOr(tp, dropIfSuper(tp1, sub), dropIfSuper(tp2, sub))
+      case _ =>
+        tp
+    }
+
   /** Merge `t1` into `tp2` if t1 is a subtype of some &-summand of tp2.
    */
   private def mergeIfSub(tp1: Type, tp2: Type): Type =