---

yaml
---
r: 83245
b: refs/heads/try
c: 2927ab1
h: refs/heads/master
i:
  83243: 74297a8
v: v3

Author: U-NOV2010\eugals

[refs]

@@ -2,7 +2,7 @@
 refs/heads/master: 0e4d1fc8cae42e15e00f71d9f439b01bb25a86ae
 refs/heads/snap-stage1: e33de59e47c5076a89eadeb38f4934f58a3618a6
 refs/heads/snap-stage3: 6c08cc2db4f98e9f07ae7d50338396c4123c2f0a
-refs/heads/try: da29a8e6be0af399ef8b350fa4b6d124d2610bf7
+refs/heads/try: 2927ab13df9436ae2042866885ea0b9d29cdcedc
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/heads/ndm: f3868061cd7988080c30d6d5bf352a5a5fe2460b
 refs/heads/try2: 147ecfdd8221e4a4d4e090486829a06da1e0ca3c

branches/try/src/librustc/middle/trans/expr.rs

@@ -313,6 +313,37 @@ pub fn trans_to_datum(bcx: @mut Block, expr: @ast::Expr) -> DatumBlock {
         let target_obj_ty = expr_ty_adjusted(bcx, expr);
         debug!("auto_borrow_obj(target=%s)",
                target_obj_ty.repr(tcx));
+
+        // Extract source store information
+        let (source_store, source_mutbl) = match ty::get(source_datum.ty).sty {
+            ty::ty_trait(_, _, s, m, _) => (s, m),
+            _ => {
+                bcx.sess().span_bug(
+                    expr.span,
+                    fmt!("auto_borrow_trait_obj expected a trait, found %s",
+                         source_datum.ty.repr(bcx.tcx())));
+            }
+        };
+
+        // check if any borrowing is really needed or we could reuse the source_datum instead
+        match ty::get(target_obj_ty).sty {
+            ty::ty_trait(_, _, ty::RegionTraitStore(target_scope), target_mutbl, _) => {
+                if target_mutbl == ast::MutImmutable && target_mutbl == source_mutbl {
+                    match source_store {
+                        ty::RegionTraitStore(source_scope) => {
+                            if tcx.region_maps.is_subregion_of(target_scope, source_scope) {
+                                return DatumBlock { bcx: bcx, datum: source_datum };
+                            }
+                        },
+                        _ => {}
+
+                    };
+                }
+            },
+            _ => {}
+        }
+
+        
         let scratch = scratch_datum(bcx, target_obj_ty,
                                     "__auto_borrow_obj", false);
 
@@ -331,15 +362,6 @@ pub fn trans_to_datum(bcx: @mut Block, expr: @ast::Expr) -> DatumBlock {
         // ~T, or &T, depending on source_obj_ty.
         let source_data_ptr = GEPi(bcx, source_llval, [0u, abi::trt_field_box]);
         let source_data = Load(bcx, source_data_ptr); // always a ptr
-        let (source_store, source_mutbl) = match ty::get(source_datum.ty).sty {
-            ty::ty_trait(_, _, s, m, _) => (s, m),
-            _ => {
-                bcx.sess().span_bug(
-                    expr.span,
-                    fmt!("auto_borrow_trait_obj expected a trait, found %s",
-                         source_datum.ty.repr(bcx.tcx())));
-            }
-        };
         let target_data = match source_store {
             ty::BoxTraitStore(*) => {
                 // For deref of @T or @mut T, create a dummy datum and

branches/try/src/libsyntax/ext/format.rs

@@ -76,7 +76,6 @@ impl Context {
                 self.ecx.span_err(sp, "expected token: `,`");
                 return (extra, None);
             }
-            if *p.token == token::EOF { break } // accept trailing commas
             if named || (token::is_ident(p.token) &&
                          p.look_ahead(1, |t| *t == token::EQ)) {
                 named = true;

branches/try/src/test/run-pass/ifmt.rs

@@ -243,10 +243,6 @@ pub fn main() {
     }
 
     test_format_args();
-
-    // test that trailing commas are acceptable
-    format!("{}", "test",);
-    format!("{foo}", foo="test",);
 }
 
 // Basic test to make sure that we can invoke the `write!` macro with an