Looks like there was a little baby in the parse...

Looks like there was a little baby in the parser bathwater, or at least
some bathwater still in the general shape of a baby. Apparently both
old forms weren't deprecated. The spec does not suggest that the 'val'
in for comprehension assignment is optional, but clearly it can't go
anywhere for a while yet regardless. Will seek clarification. No review.

src/compiler/scala/tools/nsc/ast/parser/Parsers.scala

@@ -1642,8 +1642,11 @@ self =>
 
       if (hasVal && !hasEq)
         syntaxError(in.offset, "val in for comprehension must be followed by assignment")
-      if (!hasVal && hasEq)
-        syntaxError(in.offset, "assignment in for comprehension must be preceded by `val`")
+      if (!hasVal && hasEq) {
+        deprecationWarning(in.lastOffset, "for comprehension assignment without a `val' declaration is deprecated.")
+        // not yet, deprecated in 2.10.0.
+        // syntaxError(in.offset, "assignment in for comprehension must be preceded by `val`")
+      }
 
       if (hasEq && eqOK) in.nextToken()
       else accept(LARROW)