Constant fold all the number conversion methods (#17446)

Co-authored-by: Eugene Flesselle <eugenefle@users.noreply.github.com>
Co-authored-by: Martin Kucera <github@mkucera.cz>

Fixes #13990. Made during the Scala Spree :)

Author: TheElectronWill

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

@@ -23,7 +23,11 @@ object ConstFold:
     nme.ADD, nme.SUB, nme.MUL, nme.DIV, nme.MOD)
 
   val foldedUnops = Set[Name](
-    nme.UNARY_!, nme.UNARY_~, nme.UNARY_+, nme.UNARY_-)
+    nme.UNARY_!, nme.UNARY_~, nme.UNARY_+, nme.UNARY_-,
+    nme.toChar, nme.toInt, nme.toFloat, nme.toLong, nme.toDouble,
+    // toByte and toShort are NOT included because we cannot write
+    // the type of a constant byte or short
+  )
 
   def Apply[T <: Apply](tree: T)(using Context): T =
     tree.fun match
@@ -89,6 +93,12 @@ object ConstFold:
     case (nme.UNARY_- , FloatTag  ) => Constant(-x.floatValue)
     case (nme.UNARY_- , DoubleTag ) => Constant(-x.doubleValue)
 
+    case (nme.toChar  , _ ) if x.isNumeric => Constant(x.charValue)
+    case (nme.toInt   , _ ) if x.isNumeric => Constant(x.intValue)
+    case (nme.toLong  , _ ) if x.isNumeric => Constant(x.longValue)
+    case (nme.toFloat , _ ) if x.isNumeric => Constant(x.floatValue)
+    case (nme.toDouble, _ ) if x.isNumeric => Constant(x.doubleValue)
+
     case _ => null
   }
 

tests/neg/serialversionuid-not-const.scala

@@ -1,4 +1,4 @@
-@SerialVersionUID(13l.toLong) class C1 extends Serializable // error
+@SerialVersionUID(13l.toLong) class C1 extends Serializable // OK because toLong is constant-folded
 @SerialVersionUID(13l) class C2 extends Serializable // OK
 @SerialVersionUID(13.asInstanceOf[Long]) class C3 extends Serializable // error
 @SerialVersionUID(Test.bippy) class C4 extends Serializable // error

tests/pos/i13990.scala

@@ -0,0 +1,26 @@
+
+object Test:
+
+  inline val myInt = 1 << 6
+
+  // toLong
+  inline val char2Long: 99L = 'c'.toLong
+  inline val int2Long: 0L = 0.toLong
+  inline val long2Long: 0L = 0L.toLong
+  inline val int2LongPropagated: 64L = myInt.toLong
+
+  // toInt
+  inline val char2Int: 99 = 'c'.toInt
+  inline val int2Int: 0 = 0.toInt
+  inline val long2Int: 0 = 0L.toInt
+  inline val long2IntWrapped: -2147483648 = 2147483648L.toInt
+  inline val int2IntPropagated: 64 = myInt.toInt
+
+  // toChar
+  inline val char2Char: 'c' = 'c'.toChar
+  inline val int2Char: 'c' = 99.toChar
+  inline val long2Char: 'c' = 99L.toChar
+  inline val int2CharPropagated: '@' = myInt.toChar
+
+  // chain everything
+  inline val wow: 1.0 = 1.toChar.toInt.toLong.toFloat.toDouble