Restoring negative literal parsing behavior to ...

Restoring negative literal parsing behavior to what should be the least
surprising option. Thanks much to Johannes Rudolph for identifying the
bug in the bytecode generator which needed addressing for us to arrive
at proper -0.0 behavior, and for writing the majority of this patch.

A '-' followed immediately by either a number or a period should now
always be treated as a single numeric literal, which means the minus
binds more tightly than anything else. A specific example of how this
differs from 2.8 final is:

  -5.+(10) == 5.0   // and not -15.0

The full range of potentially ambiguous parses involving prefix
operators, numbers, and dots is quite large and still needs to be
completely and clearly specified.

Closes #2378 and #3657, review by odersky, jrudolph.

1 files changed, 14 insertions, 15 deletions

diff --git a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
index 61d45114a9..e44806139e 100644
--- a/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
+++ b/src/compiler/scala/tools/nsc/ast/parser/Parsers.scala
@@ -453,6 +453,15 @@ self =>
       case _ => false
     }
 
+    def isNumericLit: Boolean = in.token match {
+      case INTLIT | LONGLIT | FLOATLIT | DOUBLELIT => true
+      case _ => false
+    }
+    def isUnaryOp: Boolean = isIdent && (in.name match {
+      case MINUS | PLUS | TILDE | BANG  => true
+      case _                            => false
+    })
+
     def isIdent = in.token == IDENTIFIER || in.token == BACKQUOTED_IDENT
 
     def isExprIntroToken(token: Int): Boolean = token match {
@@ -1241,24 +1250,14 @@ self =>
     /** PrefixExpr   ::= [`-' | `+' | `~' | `!' | `&'] SimpleExpr
     */
     def prefixExpr(): Tree = {
-      def unaryOp(): Name = "unary_" + ident()
-      if (isIdent && in.name == MINUS) {
-        atPos(in.offset) {
-          val name = unaryOp()
-          in.token match {
-            // Don't include double and float here else we lose -0.0
-            case INTLIT | LONGLIT => literal(true)
-            case _ => Select(stripParens(simpleExpr()), name)
-          }
-        }
-      } else if (isIdent && (in.name == PLUS || in.name == TILDE || in.name == BANG)) {
+      if (isUnaryOp) {
         atPos(in.offset) {
-          val name = unaryOp()
-          Select(stripParens(simpleExpr()), name)
+          val name: Name = "unary_" + ident()
+          if (in.name == MINUS && isNumericLit) simpleExprRest(atPos(in.offset)(literal(true)), true)
+          else Select(stripParens(simpleExpr()), name)
         }
-      } else {
-        simpleExpr()
       }
+      else simpleExpr()
     }
     def xmlLiteral(): Tree