Refine equality of Constant types over floating point values.

The constant types for 0d and -0d should not be equal.

This is implemented by checking equality of the result of
doubleToRawLongBits / floatToRawIntBits, which also correctly
considers two NaNs of the same flavour to be equal.

Followup to SI-6331.

Author: retronym

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

@@ -83,8 +83,16 @@ trait Constants extends api.Constants {
      */
     override def equals(other: Any): Boolean = other match {
       case that: Constant =>
-        this.tag == that.tag &&
-        (this.value == that.value || this.isNaN && that.isNaN)
+        // Consider two NaNs to be identical, despite non-equality
+        // Consider -0d to be distinct from 0d, despite equality
+        import java.lang.Double.doubleToRawLongBits
+        import java.lang.Float.floatToRawIntBits
+
+        this.tag == that.tag && ((value, that.value) match {
+          case (f1: Float, f2: Float)   => floatToRawIntBits(f1) == floatToRawIntBits(f2)
+          case (d1: Double, d2: Double) => doubleToRawLongBits(d1) == doubleToRawLongBits(d2)
+          case (v1, v2)                 => v1 == v2
+        })
       case _ => false
     }
 

test/files/run/t6331.check

@@ -0,0 +1,23 @@
+          () == ()
+        true == true
+        true != false
+       false != true
+    0.toByte == 0.toByte
+    0.toByte != 1.toByte
+   0.toShort == 0.toShort
+   0.toShort != 1.toShort
+           0 == 0
+           0 != 1
+          0L == 0L
+          0L != 1L
+        0.0f == 0.0f
+        0.0f != -0.0f
+       -0.0f != 0.0f
+        NaNf == NaNf
+        0.0d == 0.0d
+        0.0d != -0.0d
+       -0.0d != 0.0d
+        NaNd == NaNd
+           0 != 0.0d
+           0 != 0L
+        0.0d != 0.0f

test/files/run/t6331.scala

@@ -0,0 +1,63 @@
+import scala.tools.partest._
+import java.io._
+import scala.tools.nsc._
+import scala.tools.nsc.util.CommandLineParser
+import scala.tools.nsc.{Global, Settings, CompilerCommand}
+import scala.tools.nsc.reporters.ConsoleReporter
+
+// Test of Constant#equals, which must must account for floating point intricacies.
+object Test extends DirectTest {
+
+  override def code = ""
+
+  override def show() {
+    val global = newCompiler()
+    import global._
+
+    def check(c1: Any, c2: Any): Unit = {
+      val equal = Constant(c1) == Constant(c2)
+      def show(a: Any) = "" + a + (a match {
+        case _: Byte   => ".toByte"
+        case _: Short  => ".toShort"
+        case _: Long   => "L"
+        case _: Float  => "f"
+        case _: Double => "d"
+        case _ => ""
+      })
+      val op = if (equal) "==" else "!="
+      println(f"${show(c1)}%12s $op ${show(c2)}")
+    }
+
+    check((), ())
+
+    check(true, true)
+    check(true, false)
+    check(false, true)
+
+    check(0.toByte, 0.toByte)
+    check(0.toByte, 1.toByte)
+
+    check(0.toShort, 0.toShort)
+    check(0.toShort, 1.toShort)
+
+    check(0, 0)
+    check(0, 1)
+
+    check(0L, 0L)
+    check(0L, 1L)
+
+    check(0f, 0f)
+    check(0f, -0f)
+    check(-0f, 0f)
+    check(Float.NaN, Float.NaN)
+
+    check(0d, 0d)
+    check(0d, -0d)
+    check(-0d, 0d)
+    check(Double.NaN, Double.NaN)
+
+    check(0, 0d)
+    check(0, 0L)
+    check(0d, 0f)
+  }
+}