go/types: fix Eval to use correct file set when evaluating an expression

Change-Id: I221bd26cc90755de57c8f1941cabddd14d56584d
Reviewed-on: https://go-review.googlesource.com/10999
Reviewed-by: Alan Donovan <adonovan@google.com>

go/types/eval.go

@@ -65,11 +65,7 @@ func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (tv Typ
 	}
 
 	// parse expressions
-	// BUG(gri) In case of type-checking errors below, the type checker
-	//          doesn't have the correct file set for expr. The correct
-	//          solution requires a ParseExpr that uses the incoming
-	//          file set fset.
-	node, err := parser.ParseExpr(expr)
+	node, err := parser.ParseExprFrom(fset, "eval", expr, 0)
 	if err != nil {
 		return TypeAndValue{}, err
 	}