auto merge of #15929 : pcwalton/rust/by-ref-closures, r=alexcrichton

by-reference upvars.

This partially implements RFC 38. A snapshot will be needed to turn this
on, because stage0 cannot yet parse the keyword.

Part of #12831.

r? @alexcrichton

2 files changed, 6 insertions, 4 deletions

diff --git a/src/libsyntax/ext/build.rs b/src/libsyntax/ext/build.rs
index 0e687c02c1d..f7eddca4b7a 100644
--- a/src/libsyntax/ext/build.rs
+++ b/src/libsyntax/ext/build.rs
@@ -876,14 +876,14 @@ impl<'a> AstBuilder for ExtCtxt<'a> {
 
     fn lambda_fn_decl(&self, span: Span,
                       fn_decl: P<ast::FnDecl>, blk: P<ast::Block>) -> Gc<ast::Expr> {
-        self.expr(span, ast::ExprFnBlock(fn_decl, blk))
+        self.expr(span, ast::ExprFnBlock(ast::CaptureByRef, fn_decl, blk))
     }
     fn lambda(&self, span: Span, ids: Vec<ast::Ident> , blk: P<ast::Block>) -> Gc<ast::Expr> {
         let fn_decl = self.fn_decl(
             ids.iter().map(|id| self.arg(span, *id, self.ty_infer(span))).collect(),
             self.ty_infer(span));
 
-        self.expr(span, ast::ExprFnBlock(fn_decl, blk))
+        self.expr(span, ast::ExprFnBlock(ast::CaptureByRef, fn_decl, blk))
     }
     fn lambda0(&self, span: Span, blk: P<ast::Block>) -> Gc<ast::Expr> {
         self.lambda(span, Vec::new(), blk)
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 808532d55bb..d918b28d4dc 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -74,10 +74,12 @@ fn expand_expr(e: Gc<ast::Expr>, fld: &mut MacroExpander) -> Gc<ast::Expr> {
             fld.cx.expr(e.span, ast::ExprForLoop(pat, head, body, opt_ident))
         }
 
-        ast::ExprFnBlock(fn_decl, block) => {
+        ast::ExprFnBlock(capture_clause, fn_decl, block) => {
             let (rewritten_fn_decl, rewritten_block)
                 = expand_and_rename_fn_decl_and_block(&*fn_decl, block, fld);
-            let new_node = ast::ExprFnBlock(rewritten_fn_decl, rewritten_block);
+            let new_node = ast::ExprFnBlock(capture_clause,
+                                            rewritten_fn_decl,
+                                            rewritten_block);
             box(GC) ast::Expr{id:e.id, node: new_node, span: fld.new_span(e.span)}
         }