Tweak and implement weak conformance replacement

Author: odersky

compiler/src/dotty/tools/dotc/typer/Applications.scala

@@ -495,7 +495,8 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
                 addTyped(arg, formal)
               case _ =>
                 val elemFormal = formal.widenExpr.argTypesLo.head
-                val typedArgs = harmonic(harmonizeArgs)(args.map(typedArg(_, elemFormal)))
+                val typedArgs =
+                  harmonic(harmonizeArgs, elemFormal)(args.map(typedArg(_, elemFormal)))
                 typedArgs.foreach(addArg(_, elemFormal))
                 makeVarArg(args.length, elemFormal)
             }
@@ -1541,38 +1542,33 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
   }
 
   private def harmonizeWith[T <: AnyRef](ts: List[T])(tpe: T => Type, adapt: (T, Type) => T)(implicit ctx: Context): List[T] = {
-    def numericClasses(ts: List[T], acc: Set[Symbol]): Set[Symbol] = ts match {
+    def targetClass(ts: List[T], cls: Symbol, intLitSeen: Boolean): Symbol = ts match {
       case t :: ts1 =>
-        val sym = tpe(t).widen.classSymbol
-        if (sym.isNumericValueClass) numericClasses(ts1, acc + sym)
-        else Set()
+        tpe(t).widenTermRefExpr match {
+          case ConstantType(c: Constant) if c.tag == IntTag =>
+            targetClass(ts1, cls, true)
+          case t =>
+            val sym = t.widen.classSymbol
+            if (!sym.isNumericValueClass || cls.exists && cls != sym) NoSymbol
+            else targetClass(ts1, sym, intLitSeen)
+        }
       case Nil =>
-        acc
+        if (cls != defn.IntClass && intLitSeen) cls else NoSymbol
     }
-    val clss = numericClasses(ts, Set())
-    if (clss.size > 1) {
-      def isCompatible(cls: Symbol, sup: TypeRef) =
-        defn.isValueSubType(cls.typeRef, sup) &&
-        !(cls == defn.LongClass && sup.isRef(defn.FloatClass))
-          // exclude Long <: Float from list of allowable widenings
-          // TODO: should we do this everywhere we ask for isValueSubType?
-
-      val lub = defn.ScalaNumericValueTypeList.find(lubTpe =>
-        clss.forall(cls => isCompatible(cls, lubTpe))).get
-
-      def lossOfPrecision(ct: Constant): Boolean =
-        ct.tag == IntTag && lub.isRef(defn.FloatClass) &&
-          ct.intValue.toFloat.toInt != ct.intValue ||
-        ct.tag == LongTag && lub.isRef(defn.DoubleClass) &&
-          ct.longValue.toDouble.toLong != ct.longValue
-
+    val cls = targetClass(ts, NoSymbol, false)
+    if (cls.exists) {
+      def lossOfPrecision(n: Int): Boolean =
+        cls == defn.FloatClass && n.toFloat.toInt != n
+      var canAdapt = true
       val ts1 = ts.mapConserve { t =>
         tpe(t).widenTermRefExpr match {
-          case ct: ConstantType if !lossOfPrecision(ct.value) => adapt(t, lub)
+          case ConstantType(c: Constant) if c.tag == IntTag =>
+            canAdapt &= c.convertTo(cls.typeRef) != null && !lossOfPrecision(c.intValue)
+            if (canAdapt) adapt(t, cls.typeRef) else t
           case _ => t
         }
       }
-      if (numericClasses(ts1, Set()).size == 1) ts1 else ts
+      if (canAdapt) ts1 else ts
     }
     else ts
   }
@@ -1589,7 +1585,8 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
     if (ctx.isAfterTyper) trees else harmonizeWith(trees)(_.tpe, adaptDeep)
   }
 
-  /** Apply a transformation `harmonize` on the results of operation `op`.
+  /** Apply a transformation `harmonize` on the results of operation `op`,
+   *  unless the expected type `pt` is fully defined.
    *  If the result is different (wrt eq) from the original results of `op`,
    *  revert back to the constraint in force before computing `op`.
    *  This reset is needed because otherwise the original results might
@@ -1598,13 +1595,15 @@ trait Applications extends Compatibility { self: Typer with Dynamic =>
    *  the result of harmomization will be compared again with the expected type.
    *  Test cases where this matters are in pos/harmomize.scala.
    */
-  def harmonic[T](harmonize: List[T] => List[T])(op: => List[T])(implicit ctx: Context): List[T] = {
-    val origConstraint = ctx.typerState.constraint
-    val origElems = op
-    val harmonizedElems = harmonize(origElems)
-    if (harmonizedElems ne origElems) ctx.typerState.constraint = origConstraint
-    harmonizedElems
-  }
+  def harmonic[T](harmonize: List[T] => List[T], pt: Type)(op: => List[T])(implicit ctx: Context): List[T] =
+    if (!isFullyDefined(pt, ForceDegree.none)) {
+      val origConstraint = ctx.typerState.constraint
+      val origElems = op
+      val harmonizedElems = harmonize(origElems)
+      if (harmonizedElems ne origElems) ctx.typerState.constraint = origConstraint
+      harmonizedElems
+    }
+    else op
 
   /** If all `types` are numeric value types, and they are not all the same type,
    *  pick a common numeric supertype and widen any constant types in `tpes` to it.

compiler/src/dotty/tools/dotc/typer/Typer.scala

@@ -706,7 +706,7 @@ class Typer extends Namer
 
   def typedIf(tree: untpd.If, pt: Type)(implicit ctx: Context): Tree = track("typedIf") {
     val cond1 = typed(tree.cond, defn.BooleanType)
-    val thenp2 :: elsep2 :: Nil = harmonic(harmonize) {
+    val thenp2 :: elsep2 :: Nil = harmonic(harmonize, pt) {
       val thenp1 = typed(tree.thenp, pt.notApplied)
       val elsep1 = typed(tree.elsep orElse (untpd.unitLiteral withPos tree.pos), pt.notApplied)
       thenp1 :: elsep1 :: Nil
@@ -978,7 +978,7 @@ class Typer extends Namer
 
   // Overridden in InlineTyper for inline matches
   def typedMatchFinish(tree: untpd.Match, sel: Tree, selType: Type, pt: Type)(implicit ctx: Context): Tree = {
-    val cases1 = harmonic(harmonize)(typedCases(tree.cases, selType, pt.notApplied))
+    val cases1 = harmonic(harmonize, pt)(typedCases(tree.cases, selType, pt.notApplied))
       .asInstanceOf[List[CaseDef]]
     assignType(cpy.Match(tree)(sel, cases1), sel, cases1)
   }
@@ -1132,7 +1132,7 @@ class Typer extends Namer
   }
 
   def typedTry(tree: untpd.Try, pt: Type)(implicit ctx: Context): Try = track("typedTry") {
-    val expr2 :: cases2x = harmonic(harmonize) {
+    val expr2 :: cases2x = harmonic(harmonize, pt) {
       val expr1 = typed(tree.expr, pt.notApplied)
       val cases1 = typedCases(tree.cases, defn.ThrowableType, pt.notApplied)
       expr1 :: cases1

docs/docs/reference/dropped/weak-conformance-spec.md

@@ -16,16 +16,16 @@ assigning a type to a constant expression. The new rule is:
 
    and all expressions have primitive numeric types, but they do not
    all have the same type, then the following is attempted:
-   
-     - the expressions `Es` are partitioned into `Int` literals on the
-       one hand, and all other expressions on the other hand
+
+     - the expressions `Es` are partitioned into `Int` constants on the
+       one hand, and all other expressions on the other hand,
      - if all the other expressions have the same numeric type `T`
        (which can be one of `Byte`, `Short`, `Int`, `Long`, `Float`,
        `Double`), possibly after widening, and if none of the `Int`
        literals would incur a loss of precision when converted to `T`,
        then they are thus converted (the other expressions are left
-       unchanged regardless)
-     - otherwise, the expressions `Es` are used unchanged
+       unchanged regardless),
+     - otherwise, the expressions `Es` are used unchanged.
 
     A loss of precision occurs for an `Int -> Float` conversion of a constant
     `c` if `c.toFloat.toInt != c`. For an `Int -> Byte` conversion it occurs
@@ -36,11 +36,11 @@ __Examples:__
 
     inline val b = 33
     def f(): Int = b + 1
-    List(b, 33, 5.5)      : List[Double] // b is an inline val
-    List(f(), 33, 5.5)    : List[AnyVal] // f() is not a constant
-    List(5, 11L)          : List[Long]
-    List(5, 11L, 5.5)     : List[AnyVal] // Long and Double found
-    List(1.0f, 2)         : List[Float]
-    List(1.0f, 1234567890): List[AnyVal] // loss of precision
-    List(b, 33, 'a')      : List[AnyVal] // Char is not a numeric
-    List(5.toByte, 11)    : List[Byte]
+    Array(b, 33, 5.5)      : Array[Double] // b is an inline val
+    Array(f(), 33, 5.5)    : Array[AnyVal] // f() is not a constant
+    Array(5, 11L)          : Array[Long]
+    Array(5, 11L, 5.5)     : Array[AnyVal] // Long and Double found
+    Array(1.0f, 2)         : Array[Float]
+    Array(1.0f, 1234567890): Array[AnyVal] // loss of precision
+    Array(b, 33, 'a')      : Array[Char]
+    Array(5.toByte, 11)    : Array[Byte]

tests/pos/harmonize.scala renamed to tests/neg/harmonize.scala

@@ -5,7 +5,7 @@ object Test {
     val n = 1
     inline val nn = 2
     val y = if (x) 'A' else n
-    val z: Int = y
+    val z: Int = y // error: no widening
 
     val yy1 = n match {
       case 1 => 'A'
@@ -19,38 +19,47 @@ object Test {
       case 2 => nn
       case 3 => 1.0f
     }
-    val zz2: Float = yy2 // widening to Float
+    val zz2: Float = yy2 // error: no widening from Char to Float
 
     val yy3 = n match {
       case 1 => 'A'
       case 2 => 3L
       case 3 => 1.0f
     }
-    val zz3: Double = yy3 // widening to Double
+    val zz3: Double = yy3 // error: no widening from Char to Double
 
     val a = try {
       'A'
     } catch {
       case ex: Exception => nn
       case ex: Error => 3L
     }
-    val b: Long = a
+    val b: Long = a // error: no widening
+
+    val a_ok = try {
+        1
+      } catch {
+        case ex: Exception => nn
+        case ex: Error => 3L
+      }
+
+    val b_ok: Long = a_ok // ok
 
     val xs = List(1.0, nn, 'c')
-    val ys: List[Double] = xs
+    val ys: List[Double] = xs // error: no widening
 
   }
 
   inline val b = 33
   def f(): Int = b + 1
   val a1 = Array(b, 33, 'a')
-  val b1: Array[Int] = a1
+  val b1: Array[Int] = a1    // error: no widening
   val a2 = Array(b, 33, 'a', f())
-  val b2: Array[Int] = a2
+  val b2: Array[Int] = a2    // error: no widening
   val a3 = Array(1.0f, 'a', 0)
-  val b3: Array[Float] = a3
+  val b3: Array[Float] = a3  // error: no widening
   val a4 = Array(1.0f, 1L)
-  val b4: Array[Double] = a4
+  val b4: Array[Double] = a4 // error: no widening
   val a5 = Array(1.0f, 1L, f())
   val b5: Array[AnyVal] = a5
   val a6 = Array(1.0f, 1234567890)

tests/run/puzzle.check

@@ -1,2 +1,2 @@
-53.0
-53.0
+5
+5

tests/run/puzzle.scala

@@ -1,3 +1,4 @@
+// no longer a puzzler, now prints 5, 5
 object Test {
 
   def main(args: Array[String]): Unit = {

tests/run/weak-conformance.scala

@@ -0,0 +1,53 @@
+object Test extends App {
+  inline val b = 33
+
+  locally {
+    def f(): Int = b + 1
+    val x1 = List(b, 33, 5.5)      ; x1: List[Double] // b is an inline val
+    val x2 = List(f(), 33, 5.5)    ; x2: List[AnyVal] // f() is not a constant
+    val x3 = List(5, 11L)          ; x3: List[Long]
+    val x4 = List(5, 11L, 5.5)     ; x4: List[AnyVal] // Long and Double found
+    val x5 = List(1.0f, 2)         ; x5: List[Float]
+    val x6 = List(1.0f, 1234567890); x6: List[AnyVal] // loss of precision
+    val x7 = List(b, 33, 'a')      ; x7: List[Char]
+    val x8 = List(5.toByte, 11)    ; x8: List[Byte]
+
+    val x9: List[AnyVal] = List(1.0f, 0)
+    assert(x9(0).getClass == classOf[java.lang.Float])
+    assert(x9(1).getClass == classOf[java.lang.Float]) // expected type not fully defined, since `List` is covariant
+    val x10 = List[Any](1.0f, 0)
+    assert(x10(0).getClass == classOf[java.lang.Float])
+    assert(x10(1).getClass == classOf[java.lang.Integer])
+  }
+
+  locally {
+    def f(): Int = b + 1
+    val x1 = Array(b, 33, 5.5)      ; x1: Array[Double] // b is an inline val
+    val x2 = Array(f(), 33, 5.5)    ; x2: Array[AnyVal] // f() is not a constant
+    val x3 = Array(5, 11L)          ; x3: Array[Long]
+    val x4 = Array(5, 11L, 5.5)     ; x4: Array[AnyVal] // Long and Double found
+    val x5 = Array(1.0f, 2)         ; x5: Array[Float]
+    val x6 = Array(1.0f, 1234567890); x6: Array[AnyVal] // loss of precision
+    val x7 = Array(b, 33, 'a')      ; x7: Array[Char]
+    val x8 = Array(5.toByte, 11)    ; x8: Array[Byte]
+
+    val x9: Array[AnyVal] = Array(1.0f, 0)
+    assert(x9(0).getClass == classOf[java.lang.Float])
+    assert(x9(1).getClass == classOf[java.lang.Integer]) // expected type fully defined since Array is nonvariant
+    val x10 = Array[Any](1.0f, 0)
+    assert(x10(0).getClass == classOf[java.lang.Float])
+    assert(x10(1).getClass == classOf[java.lang.Integer])
+  }
+
+  locally {
+    def f(): Int = b + 1
+    val x1 = if (true) b else if (true) 33 else 5.5    ; x1: Double // b is an inline val
+    val x2 = if (true) f() else if (true) 33 else 5.5) ; x2: AnyVal // f() is not a constant
+    val x3 = if (true) 5 else 11L)                     ; x3: Long
+    val x4 = if (true) 5 else if (true) 11L else 5.5)  ; x4: AnyVal // Long and Double found
+    val x5 = if (true) 1.0f else 2)                    ; x5: Float
+    val x6 = if (true) 1.0f else 1234567890)           ; x6: AnyVal // loss of precision
+    val x7 = if (true) b else if (true) 33 else 'a')   ; x7: Char
+    val x8 = if (true) 5.toByte else 11)               ; x8: Byte
+  }
+}