4 files changed, 35 insertions, 31 deletions
diff --git a/src/libsyntax/ast_util.rs b/src/libsyntax/ast_util.rs
index 9196055267f..a8393ed9d39 100644
--- a/src/libsyntax/ast_util.rs
+++ b/src/libsyntax/ast_util.rs
@@ -618,34 +618,38 @@ pub fn compute_id_range_for_fn_body(fk: visit::FnKind,
     id_visitor.operation.result
 }
 
-// FIXME(#19596) unbox `it`
-pub fn walk_pat(pat: &Pat, it: |&Pat| -> bool) -> bool {
-    if !it(pat) {
-        return false;
-    }
-
-    match pat.node {
-        PatIdent(_, _, Some(ref p)) => walk_pat(&**p, it),
-        PatStruct(_, ref fields, _) => {
-            fields.iter().all(|field| walk_pat(&*field.node.pat, |p| it(p)))
-        }
-        PatEnum(_, Some(ref s)) | PatTup(ref s) => {
-            s.iter().all(|p| walk_pat(&**p, |p| it(p)))
+pub fn walk_pat<F>(pat: &Pat, mut it: F) -> bool where F: FnMut(&Pat) -> bool {
+    // FIXME(#19596) this is a workaround, but there should be a better way
+    fn walk_pat_<G>(pat: &Pat, it: &mut G) -> bool where G: FnMut(&Pat) -> bool {
+        if !(*it)(pat) {
+            return false;
         }
-        PatBox(ref s) | PatRegion(ref s) => {
-            walk_pat(&**s, it)
-        }
-        PatVec(ref before, ref slice, ref after) => {
-            before.iter().all(|p| walk_pat(&**p, |p| it(p))) &&
-            slice.iter().all(|p| walk_pat(&**p, |p| it(p))) &&
-            after.iter().all(|p| walk_pat(&**p, |p| it(p)))
-        }
-        PatMac(_) => panic!("attempted to analyze unexpanded pattern"),
-        PatWild(_) | PatLit(_) | PatRange(_, _) | PatIdent(_, _, _) |
-        PatEnum(_, _) => {
-            true
+
+        match pat.node {
+            PatIdent(_, _, Some(ref p)) => walk_pat_(&**p, it),
+            PatStruct(_, ref fields, _) => {
+                fields.iter().all(|field| walk_pat_(&*field.node.pat, it))
+            }
+            PatEnum(_, Some(ref s)) | PatTup(ref s) => {
+                s.iter().all(|p| walk_pat_(&**p, it))
+            }
+            PatBox(ref s) | PatRegion(ref s) => {
+                walk_pat_(&**s, it)
+            }
+            PatVec(ref before, ref slice, ref after) => {
+                before.iter().all(|p| walk_pat_(&**p, it)) &&
+                slice.iter().all(|p| walk_pat_(&**p, it)) &&
+                after.iter().all(|p| walk_pat_(&**p, it))
+            }
+            PatMac(_) => panic!("attempted to analyze unexpanded pattern"),
+            PatWild(_) | PatLit(_) | PatRange(_, _) | PatIdent(_, _, _) |
+            PatEnum(_, _) => {
+                true
+            }
         }
     }
+
+    walk_pat_(pat, &mut it)
 }
 
 pub trait EachViewItem {
diff --git a/src/libsyntax/ext/base.rs b/src/libsyntax/ext/base.rs
index 8e69076a2c5..5134897893f 100644
--- a/src/libsyntax/ext/base.rs
+++ b/src/libsyntax/ext/base.rs
@@ -47,18 +47,18 @@ pub trait ItemDecorator {
               sp: Span,
               meta_item: &ast::MetaItem,
               item: &ast::Item,
-              push: |P<ast::Item>|);
+              push: Box<FnMut(P<ast::Item>)>);
 }
 
 impl<F> ItemDecorator for F
-    where F : Fn(&mut ExtCtxt, Span, &ast::MetaItem, &ast::Item, |P<ast::Item>|)
+    where F : Fn(&mut ExtCtxt, Span, &ast::MetaItem, &ast::Item, Box<FnMut(P<ast::Item>)>)
 {
     fn expand(&self,
               ecx: &mut ExtCtxt,
               sp: Span,
               meta_item: &ast::MetaItem,
               item: &ast::Item,
-              push: |P<ast::Item>|) {
+              push: Box<FnMut(P<ast::Item>)>) {
         (*self)(ecx, sp, meta_item, item, push)
     }
 }
diff --git a/src/libsyntax/ext/deriving/mod.rs b/src/libsyntax/ext/deriving/mod.rs
index edf29e670eb..75f763b5c38 100644
--- a/src/libsyntax/ext/deriving/mod.rs
+++ b/src/libsyntax/ext/deriving/mod.rs
@@ -45,7 +45,7 @@ pub fn expand_meta_deriving(cx: &mut ExtCtxt,
                             _span: Span,
                             mitem: &MetaItem,
                             item: &Item,
-                            push: |P<Item>|) {
+                            mut push: Box<FnMut(P<Item>)>) {
     match mitem.node {
         MetaNameValue(_, ref l) => {
             cx.span_err(l.span, "unexpected value in `deriving`");
@@ -64,7 +64,7 @@ pub fn expand_meta_deriving(cx: &mut ExtCtxt,
                     MetaWord(ref tname) => {
                         macro_rules! expand(($func:path) => ($func(cx, titem.span,
                                                                    &**titem, item,
-                                                                   |i| push(i))));
+                                                                   |i| push.call_mut((i,)))));
                         match tname.get() {
                             "Clone" => expand!(clone::expand_deriving_clone),
 
diff --git a/src/libsyntax/ext/expand.rs b/src/libsyntax/ext/expand.rs
index 9fcaf2210c1..f9bffcc8974 100644
--- a/src/libsyntax/ext/expand.rs
+++ b/src/libsyntax/ext/expand.rs
@@ -424,7 +424,7 @@ pub fn expand_item(it: P<ast::Item>, fld: &mut MacroExpander)
                     // but that double-mut-borrows fld
                     let mut items: SmallVector<P<ast::Item>> = SmallVector::zero();
                     dec.expand(fld.cx, attr.span, &*attr.node.value, &*it,
-                               |item| items.push(item));
+                               box |&mut : item| items.push(item));
                     decorator_items.extend(items.into_iter()
                         .flat_map(|item| expand_item(item, fld).into_iter()));