Deprecate numeric widening of numeric literals which are not representable with Float/Double

spec/06-expressions.md

@@ -1344,7 +1344,12 @@ If $e$ has a primitive number type which [weakly conforms](03-types.html#weak-co
 to the expected type, it is widened to
 the expected type using one of the numeric conversion methods
 `toShort`, `toChar`, `toInt`, `toLong`,
-`toFloat`, `toDouble` defined [here](12-the-scala-standard-library.html#numeric-value-types).
+`toFloat`, `toDouble` defined [in the standard library](12-the-scala-standard-library.html#numeric-value-types).
+
+Since conversions from `Int` to `Float` and from `Long` to `Float` or `Double`
+may incur a loss of precision, those implicit conversions are deprecated.
+The conversion is permitted for literals if the original value can be recovered,
+that is, if conversion back to the original type produces the original value.
 
 ###### Numeric Literal Narrowing
 If the expected type is `Byte`, `Short` or `Char`, and

src/compiler/scala/tools/nsc/typechecker/ConstantFolder.scala

@@ -27,11 +27,12 @@ abstract class ConstantFolder {
 
   // We can fold side effect free terms and their types
   object FoldableTerm {
+    @inline private def effectless(sym: Symbol): Boolean = sym != null && !sym.isLazy && (sym.isVal || sym.isGetter && sym.accessed.isVal)
+
     def unapply(tree: Tree): Option[Constant] = tree match {
-      case Literal(x) => Some(x)
-      case term if term.symbol != null && !term.symbol.isLazy && (term.symbol.isVal || (term.symbol.isGetter && term.symbol.accessed.isVal)) =>
-        extractConstant(term.tpe)
-      case _ => None
+      case Literal(x)                      => Some(x)
+      case term if effectless(term.symbol) => extractConstant(term.tpe)
+      case _                               => None
     }
   }
 

src/compiler/scala/tools/nsc/typechecker/Typers.scala

@@ -1150,7 +1150,7 @@ trait Typers extends Adaptations with Tags with TypersTracking with PatternTyper
                 tpSym == LongClass && (ptSym == FloatClass || ptSym == DoubleClass)
               )
               if (isInharmonic)
-                context.warning(tree.pos, s"Automatic conversion from ${tpSym.name} to ${ptSym.name} is deprecated (since 2.13.1) because it loses precision. Write `.to${ptSym.name}` instead.")
+                context.warning(tree.pos, s"Widening conversion from ${tpSym.name} to ${ptSym.name} is deprecated because it loses precision. Write `.to${ptSym.name}` instead.")
               else if (settings.warnNumericWiden) context.warning(tree.pos, "implicit numeric widening")
             }
 

src/reflect/scala/reflect/internal/Constants.scala

@@ -63,7 +63,8 @@ trait Constants extends api.Constants {
     def isCharRange: Boolean  = isIntRange && Char.MinValue <= intValue && intValue <= Char.MaxValue
     def isIntRange: Boolean   = ByteTag <= tag && tag <= IntTag
     def isLongRange: Boolean  = ByteTag <= tag && tag <= LongTag
-    def isFloatRange: Boolean = ByteTag <= tag && tag <= FloatTag
+    def isFloatRepresentable: Boolean = ByteTag <= tag && tag <= FloatTag && (tag != IntTag || intValue == intValue.toFloat.toInt) && (tag != LongTag || longValue == longValue.toFloat.toLong)
+    def isDoubleRepresentable: Boolean = ByteTag <= tag && tag <= DoubleTag && (tag != LongTag || longValue == longValue.toDouble.toLong)
     def isNumeric: Boolean    = ByteTag <= tag && tag <= DoubleTag
     def isNonUnitAnyVal       = BooleanTag <= tag && tag <= DoubleTag
     def isSuitableLiteralType = BooleanTag <= tag && tag <= NullTag
@@ -218,9 +219,9 @@ trait Constants extends api.Constants {
         Constant(intValue)
       else if (target == LongClass && isLongRange)
         Constant(longValue)
-      else if (target == FloatClass && isFloatRange)
+      else if (target == FloatClass && isFloatRepresentable)
         Constant(floatValue)
-      else if (target == DoubleClass && isNumeric)
+      else if (target == DoubleClass && isDoubleRepresentable)
         Constant(doubleValue)
       else
         null

test/files/jvm/duration-tck.scala

@@ -3,10 +3,9 @@
  */
 
 import scala.concurrent.duration._
-import scala.reflect._
 import scala.tools.testkit.AssertUtil.assertThrows
 
-import scala.language.{ postfixOps }
+import scala.language.postfixOps
 
 object Test extends App {
 

test/files/neg/deprecated_widening.check

@@ -1,12 +1,57 @@
-deprecated_widening.scala:5: warning: Automatic conversion from Int to Float is deprecated (since 2.13.1) because it loses precision. Write `.toFloat` instead.
+deprecated_widening.scala:5: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
     val i_f: Float = i  // deprecated
                      ^
-deprecated_widening.scala:7: warning: Automatic conversion from Long to Float is deprecated (since 2.13.1) because it loses precision. Write `.toFloat` instead.
+deprecated_widening.scala:7: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
     val l_f: Float = l  // deprecated
                      ^
-deprecated_widening.scala:8: warning: Automatic conversion from Long to Double is deprecated (since 2.13.1) because it loses precision. Write `.toDouble` instead.
+deprecated_widening.scala:8: warning: Widening conversion from Long to Double is deprecated because it loses precision. Write `.toDouble` instead.
     val l_d: Double = l // deprecated
                       ^
+deprecated_widening.scala:23: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  val truncatedPosFloat:Float = 16777217L  // deprecated
+                                ^
+deprecated_widening.scala:26: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  val truncatedNegFloat: Float = - 16777217L // deprecated
+                                 ^
+deprecated_widening.scala:30: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  val truncatedPosFloatI:Float = 16777217  // deprecated
+                                 ^
+deprecated_widening.scala:33: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  val truncatedNegFloatI: Float = - 16777217 // deprecated
+                                  ^
+deprecated_widening.scala:37: warning: Widening conversion from Long to Double is deprecated because it loses precision. Write `.toDouble` instead.
+  val truncatedPosDouble:Double = 18014398509481985L // deprecated
+                                  ^
+deprecated_widening.scala:40: warning: Widening conversion from Long to Double is deprecated because it loses precision. Write `.toDouble` instead.
+  val truncatedNegDouble: Double = - 18014398509481985L // deprecated
+                                   ^
+deprecated_widening.scala:47: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def literals  = Set[Float](0x7fffffc0, 0x7ffffffd, 0x7ffffffe, 0x7fffffff)
+                             ^
+deprecated_widening.scala:47: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def literals  = Set[Float](0x7fffffc0, 0x7ffffffd, 0x7ffffffe, 0x7fffffff)
+                                         ^
+deprecated_widening.scala:47: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def literals  = Set[Float](0x7fffffc0, 0x7ffffffd, 0x7ffffffe, 0x7fffffff)
+                                                     ^
+deprecated_widening.scala:48: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def longingly = Set[Float](0x7fffffc0L, 0x7ffffffdL, 0x7ffffffeL, 0x7fffffffL)
+                             ^
+deprecated_widening.scala:48: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def longingly = Set[Float](0x7fffffc0L, 0x7ffffffdL, 0x7ffffffeL, 0x7fffffffL)
+                                          ^
+deprecated_widening.scala:48: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def longingly = Set[Float](0x7fffffc0L, 0x7ffffffdL, 0x7ffffffeL, 0x7fffffffL)
+                                                       ^
+deprecated_widening.scala:48: warning: Widening conversion from Long to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def longingly = Set[Float](0x7fffffc0L, 0x7ffffffdL, 0x7ffffffeL, 0x7fffffffL)
+                                                                    ^
+deprecated_widening.scala:50: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def `pick one` = Set[Float](0x1000003, 0x1000004, 0x1000005)
+                              ^
+deprecated_widening.scala:50: warning: Widening conversion from Int to Float is deprecated because it loses precision. Write `.toFloat` instead.
+  def `pick one` = Set[Float](0x1000003, 0x1000004, 0x1000005)
+                                                    ^
 deprecated_widening.scala:12: warning: method int2float in object Int is deprecated (since 2.13.1): Implicit conversion from Int to Float is dangerous because it loses precision. Write `.toFloat` instead.
     implicitly[Int => Float]   // deprecated
               ^
@@ -17,5 +62,5 @@ deprecated_widening.scala:15: warning: method long2double in object Long is depr
     implicitly[Long => Double] // deprecated
               ^
 error: No warnings can be incurred under -Werror.
-6 warnings
+21 warnings
 1 error

test/files/neg/deprecated_widening.scala

@@ -1,4 +1,4 @@
-// scalac: -deprecation -Werror
+// scalac: -Werror -Xlint:deprecation
 //
 object Test {
   def foo(i: Int, l: Long): Unit = {
@@ -18,4 +18,39 @@ object Test {
   // don't leak silent warning from float conversion
   val n = 42
   def clean = n max 27
+
+  val posFloat:Float = 16777216L  // OK
+  val truncatedPosFloat:Float = 16777217L  // deprecated
+  val losslessPosFloat:Float = 16777218L  // OK -- lossless
+  val negFloat: Float = - 16777216L // OK
+  val truncatedNegFloat: Float = - 16777217L // deprecated
+  val losslessNegFloat: Float = - 16777218L // OK -- lossless
+
+  val posFloatI:Float = 16777216  // OK
+  val truncatedPosFloatI:Float = 16777217  // deprecated
+  val losslessPosFloatI:Float = 16777218  // OK -- lossless
+  val negFloatI: Float = - 16777216 // OK
+  val truncatedNegFloatI: Float = - 16777217 // deprecated
+  val losslessNegFloatI: Float = - 16777218 // OK -- lossless
+
+  val posDouble:Double = 18014398509481984L// OK
+  val truncatedPosDouble:Double = 18014398509481985L // deprecated
+  val losslessPosDouble:Double = 18014398509481988L // OK -- lossless
+  val negDouble: Double = - 18014398509481984L // OK
+  val truncatedNegDouble: Double = - 18014398509481985L // deprecated
+  val losslessNegDouble: Double = - 18014398509481988L // OK -- lossless
+
+  // literals don't get a pass -- *especially* literals!
+
+  // 0x7ffffffc0 - 0x7fffffff
+  // Set[Float](2147483584, 2147483645, 2147483646, 2147483647)
+  def literals  = Set[Float](0x7fffffc0, 0x7ffffffd, 0x7ffffffe, 0x7fffffff)
+  def longingly = Set[Float](0x7fffffc0L, 0x7ffffffdL, 0x7ffffffeL, 0x7fffffffL)
+
+  def `pick one` = Set[Float](0x1000003, 0x1000004, 0x1000005)
+
+  def `no warn` = 1f + 2147483584
+  def `no warn either` = 2147483584 + 1f
+  def f = 1f
+  def `no warn sowieso` = f + 2147483584
 }