auto merge of #6260 : alexcrichton/rust/issue-3466-no-swap, r=pcwalton

There may be a more efficient implementation of `core::util::swap_ptr`. The issue mentioned using `move_val_init`, but I couldn't figure out what that did, so I just used `copy_memory` a few times instead.

I'm not exactly the best at reading LLVM generated by rust, but this does appear to be optimized away just as expected (when possible).

2 files changed, 11 insertions, 4 deletions

diff --git a/src/libsyntax/parse/obsolete.rs b/src/libsyntax/parse/obsolete.rs
index a4ac038cf46..e9e5bdfe13d 100644
--- a/src/libsyntax/parse/obsolete.rs
+++ b/src/libsyntax/parse/obsolete.rs
@@ -40,6 +40,7 @@ pub enum ObsoleteSyntax {
     ObsoleteModeInFnType,
     ObsoleteMoveInit,
     ObsoleteBinaryMove,
+    ObsoleteSwap,
     ObsoleteUnsafeBlock,
     ObsoleteUnenforcedBound,
     ObsoleteImplSyntax,
@@ -129,6 +130,10 @@ pub impl Parser {
                 "binary move",
                 "Write `foo = move bar` instead"
             ),
+            ObsoleteSwap => (
+                "swap",
+                "Use core::util::{swap, replace} instead"
+            ),
             ObsoleteUnsafeBlock => (
                 "non-standalone unsafe block",
                 "use an inner `unsafe { ... }` block instead"
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index 3ddc7a87924..5aa45ab3c9b 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -26,7 +26,7 @@ use ast::{expr_break, expr_call, expr_cast, expr_copy, expr_do_body};
 use ast::{expr_field, expr_fn_block, expr_if, expr_index};
 use ast::{expr_lit, expr_log, expr_loop, expr_loop_body, expr_mac};
 use ast::{expr_method_call, expr_paren, expr_path, expr_repeat};
-use ast::{expr_ret, expr_swap, expr_struct, expr_tup, expr_unary};
+use ast::{expr_ret, expr_struct, expr_tup, expr_unary};
 use ast::{expr_vec, expr_vstore, expr_vstore_mut_box};
 use ast::{expr_vstore_slice, expr_vstore_box};
 use ast::{expr_vstore_mut_slice, expr_while, extern_fn, field, fn_decl};
@@ -70,7 +70,7 @@ use parse::lexer::reader;
 use parse::lexer::TokenAndSpan;
 use parse::obsolete::{ObsoleteClassTraits};
 use parse::obsolete::{ObsoleteLet, ObsoleteFieldTerminator};
-use parse::obsolete::{ObsoleteMoveInit, ObsoleteBinaryMove};
+use parse::obsolete::{ObsoleteMoveInit, ObsoleteBinaryMove, ObsoleteSwap};
 use parse::obsolete::{ObsoleteSyntax, ObsoleteLowerCaseKindBounds};
 use parse::obsolete::{ObsoleteUnsafeBlock, ObsoleteImplSyntax};
 use parse::obsolete::{ObsoleteTraitBoundSeparator, ObsoleteMutOwnedPointer};
@@ -1849,9 +1849,11 @@ pub impl Parser {
                            expr_break(None))
           }
           token::DARROW => {
+            self.obsolete(*self.span, ObsoleteSwap);
             self.bump();
-            let rhs = self.parse_expr();
-            self.mk_expr(lo, rhs.span.hi, expr_swap(lhs, rhs))
+            // Ignore what we get, this is an error anyway
+            self.parse_expr();
+            self.mk_expr(lo, self.span.hi, expr_break(None))
           }
           _ => {
               lhs