src/librustc/middle/reachable.rs - third_party/rust - Git at Google

 // Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.

 // Finds items that are externally reachable, to determine which items
 // need to have their metadata (and possibly their AST) serialized.
 // All items that can be referred to through an exported name are
 // reachable, and when a reachable thing is inline or generic, it
 // makes all other generics or inline functions that it references
 // reachable as well.

 use dep_graph::DepNode;
 use front::map as ast_map;
 use middle::def;
 use middle::def_id::DefId;
 use middle::ty;
 use middle::privacy;
 use session::config;
 use util::nodemap::NodeSet;

 use std::collections::HashSet;
 use syntax::abi;
 use syntax::ast;
 use syntax::attr;
 use rustc_front::hir;
 use rustc_front::intravisit::Visitor;
 use rustc_front::intravisit;

 // Returns true if the given set of generics implies that the item it's
 // associated with must be inlined.
 fn generics_require_inlining(generics: &hir::Generics) -> bool {
     !generics.ty_params.is_empty()
 }

 // Returns true if the given item must be inlined because it may be
 // monomorphized or it was marked with `#[inline]`. This will only return
 // true for functions.
 fn item_might_be_inlined(item: &hir::Item) -> bool {
     if attr::requests_inline(&item.attrs) {
         return true
     }

     match item.node {
         hir::ItemImpl(_, _, ref generics, _, _, _) |
         hir::ItemFn(_, _, _, _, ref generics, _) => {
             generics_require_inlining(generics)
         }
         _ => false,
     }
 }

 fn method_might_be_inlined(tcx: &ty::ctxt, sig: &hir::MethodSig,
                            impl_item: &hir::ImplItem,
                            impl_src: DefId) -> bool {
     if attr::requests_inline(&impl_item.attrs) ||
         generics_require_inlining(&sig.generics) {
         return true
     }
     if let Some(impl_node_id) = tcx.map.as_local_node_id(impl_src) {
         match tcx.map.find(impl_node_id) {
             Some(ast_map::NodeItem(item)) =>
                 item_might_be_inlined(&*item),
             Some(..) | None =>
                 tcx.sess.span_bug(impl_item.span, "impl did is not an item")
         }
     } else {
         tcx.sess.span_bug(impl_item.span, "found a foreign impl as a parent of a local method")
     }
 }

 // Information needed while computing reachability.
 struct ReachableContext<'a, 'tcx: 'a> {
     // The type context.
     tcx: &'a ty::ctxt<'tcx>,
     // The set of items which must be exported in the linkage sense.
     reachable_symbols: NodeSet,
     // A worklist of item IDs. Each item ID in this worklist will be inlined
     // and will be scanned for further references.
     worklist: Vec<ast::NodeId>,
     // Whether any output of this compilation is a library
     any_library: bool,
 }

 impl<'a, 'tcx, 'v> Visitor<'v> for ReachableContext<'a, 'tcx> {
     fn visit_expr(&mut self, expr: &hir::Expr) {
         match expr.node {
             hir::ExprPath(..) => {
                 let def = match self.tcx.def_map.borrow().get(&expr.id) {
                     Some(d) => d.full_def(),
                     None => {
                         self.tcx.sess.span_bug(expr.span,
                                                "def ID not in def map?!")
                     }
                 };

                 let def_id = def.def_id();
                 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
                     if self.def_id_represents_local_inlined_item(def_id) {
                         self.worklist.push(node_id);
                     } else {
                         match def {
                             // If this path leads to a constant, then we need to
                             // recurse into the constant to continue finding
                             // items that are reachable.
                             def::DefConst(..) | def::DefAssociatedConst(..) => {
                                 self.worklist.push(node_id);
                             }

                             // If this wasn't a static, then the destination is
                             // surely reachable.
                             _ => {
                                 self.reachable_symbols.insert(node_id);
                             }
                         }
                     }
                 }
             }
             hir::ExprMethodCall(..) => {
                 let method_call = ty::MethodCall::expr(expr.id);
                 let def_id = self.tcx.tables.borrow().method_map[&method_call].def_id;

                 // Mark the trait item (and, possibly, its default impl) as reachable
                 // Or mark inherent impl item as reachable
                 if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
                     if self.def_id_represents_local_inlined_item(def_id) {
                         self.worklist.push(node_id)
                     }
                     self.reachable_symbols.insert(node_id);
                 }
             }
             _ => {}
         }

         intravisit::walk_expr(self, expr)
     }
 }

 impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
     // Creates a new reachability computation context.
     fn new(tcx: &'a ty::ctxt<'tcx>) -> ReachableContext<'a, 'tcx> {
         let any_library = tcx.sess.crate_types.borrow().iter().any(|ty| {
             *ty != config::CrateTypeExecutable
         });
         ReachableContext {
             tcx: tcx,
             reachable_symbols: NodeSet(),
             worklist: Vec::new(),
             any_library: any_library,
         }
     }

     // Returns true if the given def ID represents a local item that is
     // eligible for inlining and false otherwise.
     fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
         let node_id = match self.tcx.map.as_local_node_id(def_id) {
             Some(node_id) => node_id,
             None => { return false; }
         };

         match self.tcx.map.find(node_id) {
             Some(ast_map::NodeItem(item)) => {
                 match item.node {
                     hir::ItemFn(..) => item_might_be_inlined(&*item),
                     _ => false,
                 }
             }
             Some(ast_map::NodeTraitItem(trait_method)) => {
                 match trait_method.node {
                     hir::ConstTraitItem(_, ref default) => default.is_some(),
                     hir::MethodTraitItem(_, ref body) => body.is_some(),
                     hir::TypeTraitItem(..) => false,
                 }
             }
             Some(ast_map::NodeImplItem(impl_item)) => {
                 match impl_item.node {
                     hir::ImplItemKind::Const(..) => true,
                     hir::ImplItemKind::Method(ref sig, _) => {
                         if generics_require_inlining(&sig.generics) ||
                                 attr::requests_inline(&impl_item.attrs) {
                             true
                         } else {
                             let impl_did = self.tcx
                                                .map
                                                .get_parent_did(node_id);
                             // Check the impl. If the generics on the self
                             // type of the impl require inlining, this method
                             // does too.
                             let impl_node_id = self.tcx.map.as_local_node_id(impl_did).unwrap();
                             match self.tcx.map.expect_item(impl_node_id).node {
                                 hir::ItemImpl(_, _, ref generics, _, _, _) => {
                                     generics_require_inlining(generics)
                                 }
                                 _ => false
                             }
                         }
                     }
                     hir::ImplItemKind::Type(_) => false,
                 }
             }
             Some(_) => false,
             None => false   // This will happen for default methods.
         }
     }

     // Step 2: Mark all symbols that the symbols on the worklist touch.
     fn propagate(&mut self) {
         let mut scanned = HashSet::new();
         loop {
             let search_item = match self.worklist.pop() {
                 Some(item) => item,
                 None => break,
             };
             if !scanned.insert(search_item) {
                 continue
             }

             if let Some(ref item) = self.tcx.map.find(search_item) {
                 self.propagate_node(item, search_item);
             }
         }
     }

     fn propagate_node(&mut self, node: &ast_map::Node,
                       search_item: ast::NodeId) {
         if !self.any_library {
             // If we are building an executable, then there's no need to flag
             // anything as external except for `extern fn` types. These
             // functions may still participate in some form of native interface,
             // but all other rust-only interfaces can be private (they will not
             // participate in linkage after this product is produced)
             if let ast_map::NodeItem(item) = *node {
                 if let hir::ItemFn(_, _, _, abi, _, _) = item.node {
                     if abi != abi::Rust {
                         self.reachable_symbols.insert(search_item);
                     }
                 }
             }
         } else {
             // If we are building a library, then reachable symbols will
             // continue to participate in linkage after this product is
             // produced. In this case, we traverse the ast node, recursing on
             // all reachable nodes from this one.
             self.reachable_symbols.insert(search_item);
         }

         match *node {
             ast_map::NodeItem(item) => {
                 match item.node {
                     hir::ItemFn(_, _, _, _, _, ref search_block) => {
                         if item_might_be_inlined(&*item) {
                             intravisit::walk_block(self, &**search_block)
                         }
                     }

                     // Reachable constants will be inlined into other crates
                     // unconditionally, so we need to make sure that their
                     // contents are also reachable.
                     hir::ItemConst(_, ref init) => {
                         self.visit_expr(&**init);
                     }

                     // These are normal, nothing reachable about these
                     // inherently and their children are already in the
                     // worklist, as determined by the privacy pass
                     hir::ItemExternCrate(_) | hir::ItemUse(_) |
                     hir::ItemTy(..) | hir::ItemStatic(_, _, _) |
                     hir::ItemMod(..) | hir::ItemForeignMod(..) |
                     hir::ItemImpl(..) | hir::ItemTrait(..) |
                     hir::ItemStruct(..) | hir::ItemEnum(..) |
                     hir::ItemDefaultImpl(..) => {}
                 }
             }
             ast_map::NodeTraitItem(trait_method) => {
                 match trait_method.node {
                     hir::ConstTraitItem(_, None) |
                     hir::MethodTraitItem(_, None) => {
                         // Keep going, nothing to get exported
                     }
                     hir::ConstTraitItem(_, Some(ref expr)) => {
                         self.visit_expr(&*expr);
                     }
                     hir::MethodTraitItem(_, Some(ref body)) => {
                         intravisit::walk_block(self, body);
                     }
                     hir::TypeTraitItem(..) => {}
                 }
             }
             ast_map::NodeImplItem(impl_item) => {
                 match impl_item.node {
                     hir::ImplItemKind::Const(_, ref expr) => {
                         self.visit_expr(&*expr);
                     }
                     hir::ImplItemKind::Method(ref sig, ref body) => {
                         let did = self.tcx.map.get_parent_did(search_item);
                         if method_might_be_inlined(self.tcx, sig, impl_item, did) {
                             intravisit::walk_block(self, body)
                         }
                     }
                     hir::ImplItemKind::Type(_) => {}
                 }
             }
             // Nothing to recurse on for these
             ast_map::NodeForeignItem(_) |
             ast_map::NodeVariant(_) |
             ast_map::NodeStructCtor(_) => {}
             _ => {
                 self.tcx
                     .sess
                     .bug(&format!("found unexpected thingy in worklist: {}",
                                  self.tcx
                                      .map
                                      .node_to_string(search_item)))
             }
         }
     }
 }

 // Some methods from non-exported (completely private) trait impls still have to be
 // reachable if they are called from inlinable code. Generally, it's not known until
 // monomorphization if a specific trait impl item can be reachable or not. So, we
 // conservatively mark all of them as reachable.
 // FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
 // items of non-exported traits (or maybe all local traits?) unless their respective
 // trait items are used from inlinable code through method call syntax or UFCS, or their
 // trait is a lang item.
 struct CollectPrivateImplItemsVisitor<'a> {
     access_levels: &'a privacy::AccessLevels,
     worklist: &'a mut Vec<ast::NodeId>,
 }

 impl<'a, 'v> Visitor<'v> for CollectPrivateImplItemsVisitor<'a> {
     fn visit_item(&mut self, item: &hir::Item) {
         // We need only trait impls here, not inherent impls, and only non-exported ones
         if let hir::ItemImpl(_, _, _, Some(_), _, ref impl_items) = item.node {
             if !self.access_levels.is_reachable(item.id) {
                 for impl_item in impl_items {
                     self.worklist.push(impl_item.id);
                 }
             }
         }
     }
 }

 pub fn find_reachable(tcx: &ty::ctxt,
                       access_levels: &privacy::AccessLevels)
                       -> NodeSet {
     let _task = tcx.dep_graph.in_task(DepNode::Reachability);

     let mut reachable_context = ReachableContext::new(tcx);

     // Step 1: Seed the worklist with all nodes which were found to be public as
     //         a result of the privacy pass along with all local lang items and impl items.
     //         If other crates link to us, they're going to expect to be able to
     //         use the lang items, so we need to be sure to mark them as
     //         exported.
     for (id, _) in &access_levels.map {
         reachable_context.worklist.push(*id);
     }
     for (_, item) in tcx.lang_items.items() {
         if let Some(did) = *item {
             if let Some(node_id) = tcx.map.as_local_node_id(did) {
                 reachable_context.worklist.push(node_id);
             }
         }
     }
     {
         let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
             access_levels: access_levels,
             worklist: &mut reachable_context.worklist,
         };
         tcx.map.krate().visit_all_items(&mut collect_private_impl_items);
     }

     // Step 2: Mark all symbols that the symbols on the worklist touch.
     reachable_context.propagate();

     // Return the set of reachable symbols.
     reachable_context.reachable_symbols
 }
	// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
	// file at the top-level directory of this distribution and at
	// http://rust-lang.org/COPYRIGHT.
	//
	// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
	// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
	// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
	// option. This file may not be copied, modified, or distributed
	// except according to those terms.

	// Finds items that are externally reachable, to determine which items
	// need to have their metadata (and possibly their AST) serialized.
	// All items that can be referred to through an exported name are
	// reachable, and when a reachable thing is inline or generic, it
	// makes all other generics or inline functions that it references
	// reachable as well.

	use dep_graph::DepNode;
	use front::map as ast_map;
	use middle::def;
	use middle::def_id::DefId;
	use middle::ty;
	use middle::privacy;
	use session::config;
	use util::nodemap::NodeSet;

	use std::collections::HashSet;
	use syntax::abi;
	use syntax::ast;
	use syntax::attr;
	use rustc_front::hir;
	use rustc_front::intravisit::Visitor;
	use rustc_front::intravisit;

	// Returns true if the given set of generics implies that the item it's
	// associated with must be inlined.
	fn generics_require_inlining(generics: &hir::Generics) -> bool {
	!generics.ty_params.is_empty()
	}

	// Returns true if the given item must be inlined because it may be
	// monomorphized or it was marked with `#[inline]`. This will only return
	// true for functions.
	fn item_might_be_inlined(item: &hir::Item) -> bool {
	if attr::requests_inline(&item.attrs) {
	return true
	}

	match item.node {
	hir::ItemImpl(_, _, ref generics, _, _, _) \|
	hir::ItemFn(_, _, _, _, ref generics, _) => {
	generics_require_inlining(generics)
	}
	_ => false,
	}
	}

	fn method_might_be_inlined(tcx: &ty::ctxt, sig: &hir::MethodSig,
	impl_item: &hir::ImplItem,
	impl_src: DefId) -> bool {
	if attr::requests_inline(&impl_item.attrs) \|\|
	generics_require_inlining(&sig.generics) {
	return true
	}
	if let Some(impl_node_id) = tcx.map.as_local_node_id(impl_src) {
	match tcx.map.find(impl_node_id) {
	Some(ast_map::NodeItem(item)) =>
	item_might_be_inlined(&*item),
	Some(..) \| None =>
	tcx.sess.span_bug(impl_item.span, "impl did is not an item")
	}
	} else {
	tcx.sess.span_bug(impl_item.span, "found a foreign impl as a parent of a local method")
	}
	}

	// Information needed while computing reachability.
	struct ReachableContext<'a, 'tcx: 'a> {
	// The type context.
	tcx: &'a ty::ctxt<'tcx>,
	// The set of items which must be exported in the linkage sense.
	reachable_symbols: NodeSet,
	// A worklist of item IDs. Each item ID in this worklist will be inlined
	// and will be scanned for further references.
	worklist: Vec<ast::NodeId>,
	// Whether any output of this compilation is a library
	any_library: bool,
	}

	impl<'a, 'tcx, 'v> Visitor<'v> for ReachableContext<'a, 'tcx> {
	fn visit_expr(&mut self, expr: &hir::Expr) {
	match expr.node {
	hir::ExprPath(..) => {
	let def = match self.tcx.def_map.borrow().get(&expr.id) {
	Some(d) => d.full_def(),
	None => {
	self.tcx.sess.span_bug(expr.span,
	"def ID not in def map?!")
	}
	};

	let def_id = def.def_id();
	if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
	if self.def_id_represents_local_inlined_item(def_id) {
	self.worklist.push(node_id);
	} else {
	match def {
	// If this path leads to a constant, then we need to
	// recurse into the constant to continue finding
	// items that are reachable.
	def::DefConst(..) \| def::DefAssociatedConst(..) => {
	self.worklist.push(node_id);
	}

	// If this wasn't a static, then the destination is
	// surely reachable.
	_ => {
	self.reachable_symbols.insert(node_id);
	}
	}
	}
	}
	}
	hir::ExprMethodCall(..) => {
	let method_call = ty::MethodCall::expr(expr.id);
	let def_id = self.tcx.tables.borrow().method_map[&method_call].def_id;

	// Mark the trait item (and, possibly, its default impl) as reachable
	// Or mark inherent impl item as reachable
	if let Some(node_id) = self.tcx.map.as_local_node_id(def_id) {
	if self.def_id_represents_local_inlined_item(def_id) {
	self.worklist.push(node_id)
	}
	self.reachable_symbols.insert(node_id);
	}
	}
	_ => {}
	}

	intravisit::walk_expr(self, expr)
	}
	}

	impl<'a, 'tcx> ReachableContext<'a, 'tcx> {
	// Creates a new reachability computation context.
	fn new(tcx: &'a ty::ctxt<'tcx>) -> ReachableContext<'a, 'tcx> {
	let any_library = tcx.sess.crate_types.borrow().iter().any(\|ty\| {
	*ty != config::CrateTypeExecutable
	});
	ReachableContext {
	tcx: tcx,
	reachable_symbols: NodeSet(),
	worklist: Vec::new(),
	any_library: any_library,
	}
	}

	// Returns true if the given def ID represents a local item that is
	// eligible for inlining and false otherwise.
	fn def_id_represents_local_inlined_item(&self, def_id: DefId) -> bool {
	let node_id = match self.tcx.map.as_local_node_id(def_id) {
	Some(node_id) => node_id,
	None => { return false; }
	};

	match self.tcx.map.find(node_id) {
	Some(ast_map::NodeItem(item)) => {
	match item.node {
	hir::ItemFn(..) => item_might_be_inlined(&*item),
	_ => false,
	}
	}
	Some(ast_map::NodeTraitItem(trait_method)) => {
	match trait_method.node {
	hir::ConstTraitItem(_, ref default) => default.is_some(),
	hir::MethodTraitItem(_, ref body) => body.is_some(),
	hir::TypeTraitItem(..) => false,
	}
	}
	Some(ast_map::NodeImplItem(impl_item)) => {
	match impl_item.node {
	hir::ImplItemKind::Const(..) => true,
	hir::ImplItemKind::Method(ref sig, _) => {
	if generics_require_inlining(&sig.generics) \|\|
	attr::requests_inline(&impl_item.attrs) {
	true
	} else {
	let impl_did = self.tcx
	.map
	.get_parent_did(node_id);
	// Check the impl. If the generics on the self
	// type of the impl require inlining, this method
	// does too.
	let impl_node_id = self.tcx.map.as_local_node_id(impl_did).unwrap();
	match self.tcx.map.expect_item(impl_node_id).node {
	hir::ItemImpl(_, _, ref generics, _, _, _) => {
	generics_require_inlining(generics)
	}
	_ => false
	}
	}
	}
	hir::ImplItemKind::Type(_) => false,
	}
	}
	Some(_) => false,
	None => false // This will happen for default methods.
	}
	}

	// Step 2: Mark all symbols that the symbols on the worklist touch.
	fn propagate(&mut self) {
	let mut scanned = HashSet::new();
	loop {
	let search_item = match self.worklist.pop() {
	Some(item) => item,
	None => break,
	};
	if !scanned.insert(search_item) {
	continue
	}

	if let Some(ref item) = self.tcx.map.find(search_item) {
	self.propagate_node(item, search_item);
	}
	}
	}

	fn propagate_node(&mut self, node: &ast_map::Node,
	search_item: ast::NodeId) {
	if !self.any_library {
	// If we are building an executable, then there's no need to flag
	// anything as external except for `extern fn` types. These
	// functions may still participate in some form of native interface,
	// but all other rust-only interfaces can be private (they will not
	// participate in linkage after this product is produced)
	if let ast_map::NodeItem(item) = *node {
	if let hir::ItemFn(_, _, _, abi, _, _) = item.node {
	if abi != abi::Rust {
	self.reachable_symbols.insert(search_item);
	}
	}
	}
	} else {
	// If we are building a library, then reachable symbols will
	// continue to participate in linkage after this product is
	// produced. In this case, we traverse the ast node, recursing on
	// all reachable nodes from this one.
	self.reachable_symbols.insert(search_item);
	}

	match *node {
	ast_map::NodeItem(item) => {
	match item.node {
	hir::ItemFn(_, _, _, _, _, ref search_block) => {
	if item_might_be_inlined(&*item) {
	intravisit::walk_block(self, &**search_block)
	}
	}

	// Reachable constants will be inlined into other crates
	// unconditionally, so we need to make sure that their
	// contents are also reachable.
	hir::ItemConst(_, ref init) => {
	self.visit_expr(&**init);
	}

	// These are normal, nothing reachable about these
	// inherently and their children are already in the
	// worklist, as determined by the privacy pass
	hir::ItemExternCrate(_) \| hir::ItemUse(_) \|
	hir::ItemTy(..) \| hir::ItemStatic(_, _, _) \|
	hir::ItemMod(..) \| hir::ItemForeignMod(..) \|
	hir::ItemImpl(..) \| hir::ItemTrait(..) \|
	hir::ItemStruct(..) \| hir::ItemEnum(..) \|
	hir::ItemDefaultImpl(..) => {}
	}
	}
	ast_map::NodeTraitItem(trait_method) => {
	match trait_method.node {
	hir::ConstTraitItem(_, None) \|
	hir::MethodTraitItem(_, None) => {
	// Keep going, nothing to get exported
	}
	hir::ConstTraitItem(_, Some(ref expr)) => {
	self.visit_expr(&*expr);
	}
	hir::MethodTraitItem(_, Some(ref body)) => {
	intravisit::walk_block(self, body);
	}
	hir::TypeTraitItem(..) => {}
	}
	}
	ast_map::NodeImplItem(impl_item) => {
	match impl_item.node {
	hir::ImplItemKind::Const(_, ref expr) => {
	self.visit_expr(&*expr);
	}
	hir::ImplItemKind::Method(ref sig, ref body) => {
	let did = self.tcx.map.get_parent_did(search_item);
	if method_might_be_inlined(self.tcx, sig, impl_item, did) {
	intravisit::walk_block(self, body)
	}
	}
	hir::ImplItemKind::Type(_) => {}
	}
	}
	// Nothing to recurse on for these
	ast_map::NodeForeignItem(_) \|
	ast_map::NodeVariant(_) \|
	ast_map::NodeStructCtor(_) => {}
	_ => {
	self.tcx
	.sess
	.bug(&format!("found unexpected thingy in worklist: {}",
	self.tcx
	.map
	.node_to_string(search_item)))
	}
	}
	}
	}

	// Some methods from non-exported (completely private) trait impls still have to be
	// reachable if they are called from inlinable code. Generally, it's not known until
	// monomorphization if a specific trait impl item can be reachable or not. So, we
	// conservatively mark all of them as reachable.
	// FIXME: One possible strategy for pruning the reachable set is to avoid marking impl
	// items of non-exported traits (or maybe all local traits?) unless their respective
	// trait items are used from inlinable code through method call syntax or UFCS, or their
	// trait is a lang item.
	struct CollectPrivateImplItemsVisitor<'a> {
	access_levels: &'a privacy::AccessLevels,
	worklist: &'a mut Vec<ast::NodeId>,
	}

	impl<'a, 'v> Visitor<'v> for CollectPrivateImplItemsVisitor<'a> {
	fn visit_item(&mut self, item: &hir::Item) {
	// We need only trait impls here, not inherent impls, and only non-exported ones
	if let hir::ItemImpl(_, _, _, Some(_), _, ref impl_items) = item.node {
	if !self.access_levels.is_reachable(item.id) {
	for impl_item in impl_items {
	self.worklist.push(impl_item.id);
	}
	}
	}
	}
	}

	pub fn find_reachable(tcx: &ty::ctxt,
	access_levels: &privacy::AccessLevels)
	-> NodeSet {
	let _task = tcx.dep_graph.in_task(DepNode::Reachability);

	let mut reachable_context = ReachableContext::new(tcx);

	// Step 1: Seed the worklist with all nodes which were found to be public as
	// a result of the privacy pass along with all local lang items and impl items.
	// If other crates link to us, they're going to expect to be able to
	// use the lang items, so we need to be sure to mark them as
	// exported.
	for (id, _) in &access_levels.map {
	reachable_context.worklist.push(*id);
	}
	for (_, item) in tcx.lang_items.items() {
	if let Some(did) = *item {
	if let Some(node_id) = tcx.map.as_local_node_id(did) {
	reachable_context.worklist.push(node_id);
	}
	}
	}
	{
	let mut collect_private_impl_items = CollectPrivateImplItemsVisitor {
	access_levels: access_levels,
	worklist: &mut reachable_context.worklist,
	};
	tcx.map.krate().visit_all_items(&mut collect_private_impl_items);
	}

	// Step 2: Mark all symbols that the symbols on the worklist touch.
	reachable_context.propagate();

	// Return the set of reachable symbols.
	reachable_context.reachable_symbols
	}