Break fold's circular reference during unwinding

This converts the AST fold into a resource that breaks it's own circular
reference (just a temporary workaround until GC), so that failure during fold
will unwind correctly.

Issue #936

src/comp/front/config.rs

@@ -17,8 +17,6 @@ fn strip_unconfigured_items(crate: @ast::crate) -> @ast::crate {
 
     let fold = fold::make_fold(precursor);
     let res = @fold.fold_crate(*crate);
-    // FIXME: This is necessary to break a circular reference
-    fold::dummy_out(fold);
     ret res;
 }
 

src/comp/front/test.rs

@@ -47,8 +47,6 @@ fn modify_for_testing(crate: @ast::crate) -> @ast::crate {
 
     let fold = fold::make_fold(precursor);
     let res = @fold.fold_crate(*crate);
-    // FIXME: This is necessary to break a circular reference
-    fold::dummy_out(fold);
     ret res;
 }
 

src/comp/syntax/ext/expand.rs

@@ -56,7 +56,6 @@ fn expand_crate(sess: session::session, c: @crate) -> @crate {
             with *afp};
     let f = make_fold(f_pre);
     let res = @f.fold_crate(*c);
-    dummy_out(f); //temporary: kill circular reference
     ret res;
 
 }

src/comp/syntax/ext/simplext.rs

@@ -206,7 +206,6 @@ fn transcribe(cx: ext_ctxt, b: bindings, body: @expr) -> @expr {
          new_span: bind new_span(cx, _) with *afp};
     let f = make_fold(f_pre);
     let result = f.fold_expr(body);
-    dummy_out(f); //temporary: kill circular reference
     ret result;
 }
 
@@ -258,7 +257,6 @@ iter free_vars(b: bindings, e: @expr) -> ident {
             with *default_ast_fold()};
     let f = make_fold(f_pre);
     f.fold_expr(e); // ignore result
-    dummy_out(f);
     for each id: ident in idents.keys() { put id; }
 }
 

src/comp/syntax/fold.rs

@@ -563,8 +563,13 @@ fn dummy_out(a: ast_fold) {
          new_span: noop_span};
 }
 
+// FIXME: Fold has a circular reference that has to be broken. With GC this
+// can go away
+resource foldres(f: ast_fold) {
+    dummy_out(f);
+}
 
-fn make_fold(afp: ast_fold_precursor) -> ast_fold {
+fn make_fold(afp: ast_fold_precursor) -> @foldres {
     let result: ast_fold =
         @mutable {fold_crate: nf_crate_dummy,
                   fold_crate_directive: nf_crate_directive_dummy,
@@ -699,7 +704,7 @@ fn make_fold(afp: ast_fold_precursor) -> ast_fold {
          map_exprs: afp.map_exprs,
          new_id: afp.new_id,
          new_span: afp.new_span};
-    ret result;
+    ret @foldres(result);
 }
 
 

src/fuzzer/fuzzer.rs

@@ -149,7 +149,6 @@ fn replace_expr_in_crate(crate: ast::crate, i: uint, newexpr: ast::expr) ->
             with *fold::default_ast_fold()};
     let af = fold::make_fold(afp);
     let crate2: @ast::crate = @af.fold_crate(crate);
-    fold::dummy_out(af); // work around a leak (https://github.com/graydon/rust/issues/651)
     *crate2
 }
 
@@ -170,7 +169,6 @@ fn replace_ty_in_crate(crate: ast::crate, i: uint, newty: ast::ty) ->
             with *fold::default_ast_fold()};
     let af = fold::make_fold(afp);
     let crate2: @ast::crate = @af.fold_crate(crate);
-    fold::dummy_out(af); // work around a leak (https://github.com/graydon/rust/issues/651)
     *crate2
 }