auto merge of #19899 : japaric/rust/unops-by-value, r=nikomatsakis

- The following operator traits now take their argument by value: `Neg`, `Not`. This breaks all existing implementations of these traits.

- The unary operation `OP a` now "desugars" to `OpTrait::op_method(a)` and consumes its argument.

[breaking-change]

---

r? @nikomatsakis This PR is very similar to the binops-by-value PR
cc @aturon 

1 files changed, 9 insertions, 1 deletions

diff --git a/src/libsyntax/ast_util.rs b/src/libsyntax/ast_util.rs
index aaa172633be..5243f07f327 100644
--- a/src/libsyntax/ast_util.rs
+++ b/src/libsyntax/ast_util.rs
@@ -85,7 +85,7 @@ pub fn is_shift_binop(b: BinOp) -> bool {
     }
 }
 
-/// Returns `true` is the binary operator takes its arguments by value
+/// Returns `true` if the binary operator takes its arguments by value
 pub fn is_by_value_binop(b: BinOp) -> bool {
     match b {
         BiAdd | BiSub | BiMul | BiDiv | BiRem | BiBitXor | BiBitAnd | BiBitOr | BiShl | BiShr => {
@@ -95,6 +95,14 @@ pub fn is_by_value_binop(b: BinOp) -> bool {
     }
 }
 
+/// Returns `true` if the unary operator takes its argument by value
+pub fn is_by_value_unop(u: UnOp) -> bool {
+    match u {
+        UnNeg | UnNot => true,
+        _ => false,
+    }
+}
+
 pub fn unop_to_string(op: UnOp) -> &'static str {
     match op {
       UnUniq => "box() ",