src/librustc_trans/trans/assert_dep_graph.rs - third_party/rust - Git at Google

 // Copyright 2012-2015 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.

 //! This pass is only used for the UNIT TESTS and DEBUGGING NEEDS
 //! around dependency graph construction. It serves two purposes; it
 //! will dump graphs in graphviz form to disk, and it searches for
 //! `#[rustc_if_this_changed]` and `#[rustc_then_this_would_need]`
 //! annotations. These annotations can be used to test whether paths
 //! exist in the graph. We report errors on each
 //! `rustc_if_this_changed` annotation. If a path exists in all
 //! cases, then we would report "all path(s) exist". Otherwise, we
 //! report: "no path to `foo`" for each case where no path exists.
 //! `compile-fail` tests can then be used to check when paths exist or
 //! do not.
 //!
 //! The full form of the `rustc_if_this_changed` annotation is
 //! `#[rustc_if_this_changed(id)]`. The `"id"` is optional and
 //! defaults to `"id"` if omitted.
 //!
 //! Example:
 //!
 //! ```
 //! #[rustc_if_this_changed]
 //! fn foo() { }
 //!
 //! #[rustc_then_this_would_need("trans")] //~ ERROR no path from `foo`
 //! fn bar() { }
 //!
 //! #[rustc_then_this_would_need("trans")] //~ ERROR OK
 //! fn baz() { foo(); }
 //! ```

 use graphviz as dot;
 use rustc::dep_graph::{DepGraphQuery, DepNode};
 use rustc::middle::def_id::DefId;
 use rustc::middle::ty;
 use rustc_data_structures::fnv::{FnvHashMap, FnvHashSet};
 use rustc_data_structures::graph::{Direction, INCOMING, OUTGOING, NodeIndex};
 use rustc_front::hir;
 use rustc_front::intravisit::Visitor;
 use graphviz::IntoCow;
 use std::env;
 use std::fs::File;
 use std::io::Write;
 use syntax::ast;
 use syntax::attr::AttrMetaMethods;
 use syntax::codemap::Span;
 use syntax::parse::token::InternedString;

 const IF_THIS_CHANGED: &'static str = "rustc_if_this_changed";
 const THEN_THIS_WOULD_NEED: &'static str = "rustc_then_this_would_need";
 const ID: &'static str = "id";

 pub fn assert_dep_graph(tcx: &ty::ctxt) {
     let _ignore = tcx.dep_graph.in_ignore();

     if tcx.sess.opts.dump_dep_graph {
         dump_graph(tcx);
     }

     // Find annotations supplied by user (if any).
     let (if_this_changed, then_this_would_need) = {
         let mut visitor = IfThisChanged { tcx: tcx,
                                           if_this_changed: FnvHashMap(),
                                           then_this_would_need: FnvHashMap() };
         tcx.map.krate().visit_all_items(&mut visitor);
         (visitor.if_this_changed, visitor.then_this_would_need)
     };

     // Check paths.
     check_paths(tcx, &if_this_changed, &then_this_would_need);
 }

 type SourceHashMap = FnvHashMap<InternedString,
                                 FnvHashSet<(Span, DefId, DepNode)>>;
 type TargetHashMap = FnvHashMap<InternedString,
                                 FnvHashSet<(Span, InternedString, ast::NodeId, DepNode)>>;

 struct IfThisChanged<'a, 'tcx:'a> {
     tcx: &'a ty::ctxt<'tcx>,
     if_this_changed: SourceHashMap,
     then_this_would_need: TargetHashMap,
 }

 impl<'a, 'tcx> IfThisChanged<'a, 'tcx> {
     fn process_attrs(&mut self, node_id: ast::NodeId, def_id: DefId) {
         for attr in self.tcx.get_attrs(def_id).iter() {
             if attr.check_name(IF_THIS_CHANGED) {
                 let mut id = None;
                 for meta_item in attr.meta_item_list().unwrap_or_default() {
                     match meta_item.node {
                         ast::MetaWord(ref s) if id.is_none() => id = Some(s.clone()),
                         _ => {
                             self.tcx.sess.span_err(
                                 meta_item.span,
                                 &format!("unexpected meta-item {:?}", meta_item.node));
                         }
                     }
                 }
                 let id = id.unwrap_or(InternedString::new(ID));
                 self.if_this_changed.entry(id)
                                     .or_insert(FnvHashSet())
                                     .insert((attr.span, def_id, DepNode::Hir(def_id)));
             } else if attr.check_name(THEN_THIS_WOULD_NEED) {
                 let mut dep_node_interned = None;
                 let mut id = None;
                 for meta_item in attr.meta_item_list().unwrap_or_default() {
                     match meta_item.node {
                         ast::MetaWord(ref s) if dep_node_interned.is_none() =>
                             dep_node_interned = Some(s.clone()),
                         ast::MetaWord(ref s) if id.is_none() =>
                             id = Some(s.clone()),
                         _ => {
                             self.tcx.sess.span_err(
                                 meta_item.span,
                                 &format!("unexpected meta-item {:?}", meta_item.node));
                         }
                     }
                 }
                 let dep_node_str = dep_node_interned.as_ref().map(|s| &**s);
                 macro_rules! match_depnode_name {
                     ($input:expr, $def_id:expr, match { $($variant:ident,)* } else $y:expr) => {
                         match $input {
                             $(Some(stringify!($variant)) => DepNode::$variant($def_id),)*
                             _ => $y
                         }
                     }
                 }
                 let dep_node = match_depnode_name! {
                     dep_node_str, def_id, match {
                         CollectItem,
                         BorrowCheck,
                         TransCrateItem,
                         TypeckItemType,
                         TypeckItemBody,
                         ImplOrTraitItems,
                         ItemSignature,
                         FieldTy,
                         TraitItemDefIds,
                         InherentImpls,
                         ImplItems,
                         TraitImpls,
                         ReprHints,
                     } else {
                         self.tcx.sess.span_fatal(
                             attr.span,
                             &format!("unrecognized DepNode variant {:?}", dep_node_str));
                     }
                 };
                 let id = id.unwrap_or(InternedString::new(ID));
                 self.then_this_would_need
                     .entry(id)
                     .or_insert(FnvHashSet())
                     .insert((attr.span, dep_node_interned.clone().unwrap(), node_id, dep_node));
             }
         }
     }
 }

 impl<'a, 'tcx> Visitor<'tcx> for IfThisChanged<'a, 'tcx> {
     fn visit_item(&mut self, item: &'tcx hir::Item) {
         let def_id = self.tcx.map.local_def_id(item.id);
         self.process_attrs(item.id, def_id);
     }
 }

 fn check_paths(tcx: &ty::ctxt,
                if_this_changed: &SourceHashMap,
                then_this_would_need: &TargetHashMap)
 {
     // Return early here so as not to construct the query, which is not cheap.
     if if_this_changed.is_empty() {
         return;
     }
     let query = tcx.dep_graph.query();
     for (id, sources) in if_this_changed {
         let targets = match then_this_would_need.get(id) {
             Some(targets) => targets,
             None => {
                 for &(source_span, _, _) in sources.iter().take(1) {
                     tcx.sess.span_err(
                         source_span,
                         &format!("no targets for id `{}`", id));
                 }
                 continue;
             }
         };

         for &(_, source_def_id, source_dep_node) in sources {
             let dependents = query.dependents(source_dep_node);
             for &(target_span, ref target_pass, _, ref target_dep_node) in targets {
                 if !dependents.contains(&target_dep_node) {
                     tcx.sess.span_err(
                         target_span,
                         &format!("no path from `{}` to `{}`",
                                  tcx.item_path_str(source_def_id),
                                  target_pass));
                 } else {
                     tcx.sess.span_err(
                         target_span,
                         &format!("OK"));
                 }
             }
         }
     }
 }

 fn dump_graph(tcx: &ty::ctxt) {
     let path: String = env::var("RUST_DEP_GRAPH").unwrap_or_else(|_| format!("dep_graph"));
     let query = tcx.dep_graph.query();

     let nodes = match env::var("RUST_DEP_GRAPH_FILTER") {
         Ok(string) => {
             // Expect one of: "-> target", "source -> target", or "source ->".
             let parts: Vec<_> = string.split("->").collect();
             if parts.len() > 2 {
                 panic!("Invalid RUST_DEP_GRAPH_FILTER: expected '[source] -> [target]'");
             }
             let sources = node_set(&query, &parts[0]);
             let targets = node_set(&query, &parts[1]);
             filter_nodes(&query, &sources, &targets)
         }
         Err(_) => {
             query.nodes()
                  .into_iter()
                  .collect()
         }
     };
     let edges = filter_edges(&query, &nodes);

     { // dump a .txt file with just the edges:
         let txt_path = format!("{}.txt", path);
         let mut file = File::create(&txt_path).unwrap();
         for &(source, target) in &edges {
             write!(file, "{:?} -> {:?}\n", source, target).unwrap();
         }
     }

     { // dump a .dot file in graphviz format:
         let dot_path = format!("{}.dot", path);
         let mut v = Vec::new();
         dot::render(&GraphvizDepGraph(nodes, edges), &mut v).unwrap();
         File::create(&dot_path).and_then(|mut f| f.write_all(&v)).unwrap();
     }
 }

 pub struct GraphvizDepGraph(FnvHashSet<DepNode>, Vec<(DepNode, DepNode)>);

 impl<'a, 'tcx> dot::GraphWalk<'a, DepNode, (DepNode, DepNode)> for GraphvizDepGraph {
     fn nodes(&self) -> dot::Nodes<DepNode> {
         let nodes: Vec<_> = self.0.iter().cloned().collect();
         nodes.into_cow()
     }
     fn edges(&self) -> dot::Edges<(DepNode, DepNode)> {
         self.1[..].into_cow()
     }
     fn source(&self, edge: &(DepNode, DepNode)) -> DepNode {
         edge.0
     }
     fn target(&self, edge: &(DepNode, DepNode)) -> DepNode {
         edge.1
     }
 }

 impl<'a, 'tcx> dot::Labeller<'a, DepNode, (DepNode, DepNode)> for GraphvizDepGraph {
     fn graph_id(&self) -> dot::Id {
         dot::Id::new("DependencyGraph").unwrap()
     }
     fn node_id(&self, n: &DepNode) -> dot::Id {
         let s: String =
             format!("{:?}", n).chars()
                               .map(|c| if c == '_' || c.is_alphanumeric() { c } else { '_' })
                               .collect();
         debug!("n={:?} s={:?}", n, s);
         dot::Id::new(s).unwrap()
     }
     fn node_label(&self, n: &DepNode) -> dot::LabelText {
         dot::LabelText::label(format!("{:?}", n))
     }
 }

 // Given an optional filter like `"x,y,z"`, returns either `None` (no
 // filter) or the set of nodes whose labels contain all of those
 // substrings.
 fn node_set(query: &DepGraphQuery, filter: &str) -> Option<FnvHashSet<DepNode>> {
     debug!("node_set(filter={:?})", filter);

     if filter.trim().is_empty() {
         return None;
     }

     let filters: Vec<&str> = filter.split("&").map(|s| s.trim()).collect();

     debug!("node_set: filters={:?}", filters);

     Some(query.nodes()
          .into_iter()
          .filter(|n| {
              let s = format!("{:?}", n);
              filters.iter().all(|f| s.contains(f))
          })
         .collect())
 }

 fn filter_nodes(query: &DepGraphQuery,
                 sources: &Option<FnvHashSet<DepNode>>,
                 targets: &Option<FnvHashSet<DepNode>>)
                 -> FnvHashSet<DepNode>
 {
     if let &Some(ref sources) = sources {
         if let &Some(ref targets) = targets {
             walk_between(query, sources, targets)
         } else {
             walk_nodes(query, sources, OUTGOING)
         }
     } else if let &Some(ref targets) = targets {
         walk_nodes(query, targets, INCOMING)
     } else {
         query.nodes().into_iter().collect()
     }
 }

 fn walk_nodes(query: &DepGraphQuery,
               starts: &FnvHashSet<DepNode>,
               direction: Direction)
               -> FnvHashSet<DepNode>
 {
     let mut set = FnvHashSet();
     for start in starts {
         debug!("walk_nodes: start={:?} outgoing?={:?}", start, direction == OUTGOING);
         if set.insert(*start) {
             let mut stack = vec![query.indices[start]];
             while let Some(index) = stack.pop() {
                 for (_, edge) in query.graph.adjacent_edges(index, direction) {
                     let neighbor_index = edge.source_or_target(direction);
                     let neighbor = query.graph.node_data(neighbor_index);
                     if set.insert(*neighbor) {
                         stack.push(neighbor_index);
                     }
                 }
             }
         }
     }
     set
 }

 fn walk_between(query: &DepGraphQuery,
                 sources: &FnvHashSet<DepNode>,
                 targets: &FnvHashSet<DepNode>)
                 -> FnvHashSet<DepNode>
 {
     // This is a bit tricky. We want to include a node only if it is:
     // (a) reachable from a source and (b) will reach a target. And we
     // have to be careful about cycles etc.  Luckily efficiency is not
     // a big concern!

     #[derive(Copy, Clone, PartialEq)]
     enum State { Undecided, Deciding, Included, Excluded }

     let mut node_states = vec![State::Undecided; query.graph.len_nodes()];

     for &target in targets {
         node_states[query.indices[&target].0] = State::Included;
     }

     for source in sources.iter().map(|n| query.indices[n]) {
         recurse(query, &mut node_states, source);
     }

     return query.nodes()
                 .into_iter()
                 .filter(|n| {
                     let index = query.indices[n];
                     node_states[index.0] == State::Included
                 })
                 .collect();

     fn recurse(query: &DepGraphQuery,
                node_states: &mut [State],
                node: NodeIndex)
                -> bool
     {
         match node_states[node.0] {
             // known to reach a target
             State::Included => return true,

             // known not to reach a target
             State::Excluded => return false,

             // backedge, not yet known, say false
             State::Deciding => return false,

             State::Undecided => { }
         }

         node_states[node.0] = State::Deciding;

         for neighbor_index in query.graph.successor_nodes(node) {
             if recurse(query, node_states, neighbor_index) {
                 node_states[node.0] = State::Included;
             }
         }

         // if we didn't find a path to target, then set to excluded
         if node_states[node.0] == State::Deciding {
             node_states[node.0] = State::Excluded;
             false
         } else {
             assert!(node_states[node.0] == State::Included);
             true
         }
     }
 }

 fn filter_edges(query: &DepGraphQuery,
                 nodes: &FnvHashSet<DepNode>)
                 -> Vec<(DepNode, DepNode)>
 {
     query.edges()
          .into_iter()
          .filter(|&(source, target)| nodes.contains(&source) && nodes.contains(&target))
          .collect()
 }
	// Copyright 2012-2015 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.

	//! This pass is only used for the UNIT TESTS and DEBUGGING NEEDS
	//! around dependency graph construction. It serves two purposes; it
	//! will dump graphs in graphviz form to disk, and it searches for
	//! `#[rustc_if_this_changed]` and `#[rustc_then_this_would_need]`
	//! annotations. These annotations can be used to test whether paths
	//! exist in the graph. We report errors on each
	//! `rustc_if_this_changed` annotation. If a path exists in all
	//! cases, then we would report "all path(s) exist". Otherwise, we
	//! report: "no path to `foo`" for each case where no path exists.
	//! `compile-fail` tests can then be used to check when paths exist or
	//! do not.
	//!
	//! The full form of the `rustc_if_this_changed` annotation is
	//! `#[rustc_if_this_changed(id)]`. The `"id"` is optional and
	//! defaults to `"id"` if omitted.
	//!
	//! Example:
	//!
	//! ```
	//! #[rustc_if_this_changed]
	//! fn foo() { }
	//!
	//! #[rustc_then_this_would_need("trans")] //~ ERROR no path from `foo`
	//! fn bar() { }
	//!
	//! #[rustc_then_this_would_need("trans")] //~ ERROR OK
	//! fn baz() { foo(); }
	//! ```

	use graphviz as dot;
	use rustc::dep_graph::{DepGraphQuery, DepNode};
	use rustc::middle::def_id::DefId;
	use rustc::middle::ty;
	use rustc_data_structures::fnv::{FnvHashMap, FnvHashSet};
	use rustc_data_structures::graph::{Direction, INCOMING, OUTGOING, NodeIndex};
	use rustc_front::hir;
	use rustc_front::intravisit::Visitor;
	use graphviz::IntoCow;
	use std::env;
	use std::fs::File;
	use std::io::Write;
	use syntax::ast;
	use syntax::attr::AttrMetaMethods;
	use syntax::codemap::Span;
	use syntax::parse::token::InternedString;

	const IF_THIS_CHANGED: &'static str = "rustc_if_this_changed";
	const THEN_THIS_WOULD_NEED: &'static str = "rustc_then_this_would_need";
	const ID: &'static str = "id";

	pub fn assert_dep_graph(tcx: &ty::ctxt) {
	let _ignore = tcx.dep_graph.in_ignore();

	if tcx.sess.opts.dump_dep_graph {
	dump_graph(tcx);
	}

	// Find annotations supplied by user (if any).
	let (if_this_changed, then_this_would_need) = {
	let mut visitor = IfThisChanged { tcx: tcx,
	if_this_changed: FnvHashMap(),
	then_this_would_need: FnvHashMap() };
	tcx.map.krate().visit_all_items(&mut visitor);
	(visitor.if_this_changed, visitor.then_this_would_need)
	};

	// Check paths.
	check_paths(tcx, &if_this_changed, &then_this_would_need);
	}

	type SourceHashMap = FnvHashMap<InternedString,
	FnvHashSet<(Span, DefId, DepNode)>>;
	type TargetHashMap = FnvHashMap<InternedString,
	FnvHashSet<(Span, InternedString, ast::NodeId, DepNode)>>;

	struct IfThisChanged<'a, 'tcx:'a> {
	tcx: &'a ty::ctxt<'tcx>,
	if_this_changed: SourceHashMap,
	then_this_would_need: TargetHashMap,
	}

	impl<'a, 'tcx> IfThisChanged<'a, 'tcx> {
	fn process_attrs(&mut self, node_id: ast::NodeId, def_id: DefId) {
	for attr in self.tcx.get_attrs(def_id).iter() {
	if attr.check_name(IF_THIS_CHANGED) {
	let mut id = None;
	for meta_item in attr.meta_item_list().unwrap_or_default() {
	match meta_item.node {
	ast::MetaWord(ref s) if id.is_none() => id = Some(s.clone()),
	_ => {
	self.tcx.sess.span_err(
	meta_item.span,
	&format!("unexpected meta-item {:?}", meta_item.node));
	}
	}
	}
	let id = id.unwrap_or(InternedString::new(ID));
	self.if_this_changed.entry(id)
	.or_insert(FnvHashSet())
	.insert((attr.span, def_id, DepNode::Hir(def_id)));
	} else if attr.check_name(THEN_THIS_WOULD_NEED) {
	let mut dep_node_interned = None;
	let mut id = None;
	for meta_item in attr.meta_item_list().unwrap_or_default() {
	match meta_item.node {
	ast::MetaWord(ref s) if dep_node_interned.is_none() =>
	dep_node_interned = Some(s.clone()),
	ast::MetaWord(ref s) if id.is_none() =>
	id = Some(s.clone()),
	_ => {
	self.tcx.sess.span_err(
	meta_item.span,
	&format!("unexpected meta-item {:?}", meta_item.node));
	}
	}
	}
	let dep_node_str = dep_node_interned.as_ref().map(\|s\| &**s);
	macro_rules! match_depnode_name {
	($input:expr, $def_id:expr, match { $($variant:ident,)* } else $y:expr) => {
	match $input {
	$(Some(stringify!($variant)) => DepNode::$variant($def_id),)*
	_ => $y
	}
	}
	}
	let dep_node = match_depnode_name! {
	dep_node_str, def_id, match {
	CollectItem,
	BorrowCheck,
	TransCrateItem,
	TypeckItemType,
	TypeckItemBody,
	ImplOrTraitItems,
	ItemSignature,
	FieldTy,
	TraitItemDefIds,
	InherentImpls,
	ImplItems,
	TraitImpls,
	ReprHints,
	} else {
	self.tcx.sess.span_fatal(
	attr.span,
	&format!("unrecognized DepNode variant {:?}", dep_node_str));
	}
	};
	let id = id.unwrap_or(InternedString::new(ID));
	self.then_this_would_need
	.entry(id)
	.or_insert(FnvHashSet())
	.insert((attr.span, dep_node_interned.clone().unwrap(), node_id, dep_node));
	}
	}
	}
	}

	impl<'a, 'tcx> Visitor<'tcx> for IfThisChanged<'a, 'tcx> {
	fn visit_item(&mut self, item: &'tcx hir::Item) {
	let def_id = self.tcx.map.local_def_id(item.id);
	self.process_attrs(item.id, def_id);
	}
	}

	fn check_paths(tcx: &ty::ctxt,
	if_this_changed: &SourceHashMap,
	then_this_would_need: &TargetHashMap)
	{
	// Return early here so as not to construct the query, which is not cheap.
	if if_this_changed.is_empty() {
	return;
	}
	let query = tcx.dep_graph.query();
	for (id, sources) in if_this_changed {
	let targets = match then_this_would_need.get(id) {
	Some(targets) => targets,
	None => {
	for &(source_span, _, _) in sources.iter().take(1) {
	tcx.sess.span_err(
	source_span,
	&format!("no targets for id `{}`", id));
	}
	continue;
	}
	};

	for &(_, source_def_id, source_dep_node) in sources {
	let dependents = query.dependents(source_dep_node);
	for &(target_span, ref target_pass, _, ref target_dep_node) in targets {
	if !dependents.contains(&target_dep_node) {
	tcx.sess.span_err(
	target_span,
	&format!("no path from `{}` to `{}`",
	tcx.item_path_str(source_def_id),
	target_pass));
	} else {
	tcx.sess.span_err(
	target_span,
	&format!("OK"));
	}
	}
	}
	}
	}

	fn dump_graph(tcx: &ty::ctxt) {
	let path: String = env::var("RUST_DEP_GRAPH").unwrap_or_else(\|_\| format!("dep_graph"));
	let query = tcx.dep_graph.query();

	let nodes = match env::var("RUST_DEP_GRAPH_FILTER") {
	Ok(string) => {
	// Expect one of: "-> target", "source -> target", or "source ->".
	let parts: Vec<_> = string.split("->").collect();
	if parts.len() > 2 {
	panic!("Invalid RUST_DEP_GRAPH_FILTER: expected '[source] -> [target]'");
	}
	let sources = node_set(&query, &parts[0]);
	let targets = node_set(&query, &parts[1]);
	filter_nodes(&query, &sources, &targets)
	}
	Err(_) => {
	query.nodes()
	.into_iter()
	.collect()
	}
	};
	let edges = filter_edges(&query, &nodes);

	{ // dump a .txt file with just the edges:
	let txt_path = format!("{}.txt", path);
	let mut file = File::create(&txt_path).unwrap();
	for &(source, target) in &edges {
	write!(file, "{:?} -> {:?}\n", source, target).unwrap();
	}
	}

	{ // dump a .dot file in graphviz format:
	let dot_path = format!("{}.dot", path);
	let mut v = Vec::new();
	dot::render(&GraphvizDepGraph(nodes, edges), &mut v).unwrap();
	File::create(&dot_path).and_then(\|mut f\| f.write_all(&v)).unwrap();
	}
	}

	pub struct GraphvizDepGraph(FnvHashSet<DepNode>, Vec<(DepNode, DepNode)>);

	impl<'a, 'tcx> dot::GraphWalk<'a, DepNode, (DepNode, DepNode)> for GraphvizDepGraph {
	fn nodes(&self) -> dot::Nodes<DepNode> {
	let nodes: Vec<_> = self.0.iter().cloned().collect();
	nodes.into_cow()
	}
	fn edges(&self) -> dot::Edges<(DepNode, DepNode)> {
	self.1[..].into_cow()
	}
	fn source(&self, edge: &(DepNode, DepNode)) -> DepNode {
	edge.0
	}
	fn target(&self, edge: &(DepNode, DepNode)) -> DepNode {
	edge.1
	}
	}

	impl<'a, 'tcx> dot::Labeller<'a, DepNode, (DepNode, DepNode)> for GraphvizDepGraph {
	fn graph_id(&self) -> dot::Id {
	dot::Id::new("DependencyGraph").unwrap()
	}
	fn node_id(&self, n: &DepNode) -> dot::Id {
	let s: String =
	format!("{:?}", n).chars()
	.map(\|c\| if c == '_' \|\| c.is_alphanumeric() { c } else { '_' })
	.collect();
	debug!("n={:?} s={:?}", n, s);
	dot::Id::new(s).unwrap()
	}
	fn node_label(&self, n: &DepNode) -> dot::LabelText {
	dot::LabelText::label(format!("{:?}", n))
	}
	}

	// Given an optional filter like `"x,y,z"`, returns either `None` (no
	// filter) or the set of nodes whose labels contain all of those
	// substrings.
	fn node_set(query: &DepGraphQuery, filter: &str) -> Option<FnvHashSet<DepNode>> {
	debug!("node_set(filter={:?})", filter);

	if filter.trim().is_empty() {
	return None;
	}

	let filters: Vec<&str> = filter.split("&").map(\|s\| s.trim()).collect();

	debug!("node_set: filters={:?}", filters);

	Some(query.nodes()
	.into_iter()
	.filter(\|n\| {
	let s = format!("{:?}", n);
	filters.iter().all(\|f\| s.contains(f))
	})
	.collect())
	}

	fn filter_nodes(query: &DepGraphQuery,
	sources: &Option<FnvHashSet<DepNode>>,
	targets: &Option<FnvHashSet<DepNode>>)
	-> FnvHashSet<DepNode>
	{
	if let &Some(ref sources) = sources {
	if let &Some(ref targets) = targets {
	walk_between(query, sources, targets)
	} else {
	walk_nodes(query, sources, OUTGOING)
	}
	} else if let &Some(ref targets) = targets {
	walk_nodes(query, targets, INCOMING)
	} else {
	query.nodes().into_iter().collect()
	}
	}

	fn walk_nodes(query: &DepGraphQuery,
	starts: &FnvHashSet<DepNode>,
	direction: Direction)
	-> FnvHashSet<DepNode>
	{
	let mut set = FnvHashSet();
	for start in starts {
	debug!("walk_nodes: start={:?} outgoing?={:?}", start, direction == OUTGOING);
	if set.insert(*start) {
	let mut stack = vec![query.indices[start]];
	while let Some(index) = stack.pop() {
	for (_, edge) in query.graph.adjacent_edges(index, direction) {
	let neighbor_index = edge.source_or_target(direction);
	let neighbor = query.graph.node_data(neighbor_index);
	if set.insert(*neighbor) {
	stack.push(neighbor_index);
	}
	}
	}
	}
	}
	set
	}

	fn walk_between(query: &DepGraphQuery,
	sources: &FnvHashSet<DepNode>,
	targets: &FnvHashSet<DepNode>)
	-> FnvHashSet<DepNode>
	{
	// This is a bit tricky. We want to include a node only if it is:
	// (a) reachable from a source and (b) will reach a target. And we
	// have to be careful about cycles etc. Luckily efficiency is not
	// a big concern!

	#[derive(Copy, Clone, PartialEq)]
	enum State { Undecided, Deciding, Included, Excluded }

	let mut node_states = vec![State::Undecided; query.graph.len_nodes()];

	for &target in targets {
	node_states[query.indices[&target].0] = State::Included;
	}

	for source in sources.iter().map(\|n\| query.indices[n]) {
	recurse(query, &mut node_states, source);
	}

	return query.nodes()
	.into_iter()
	.filter(\|n\| {
	let index = query.indices[n];
	node_states[index.0] == State::Included
	})
	.collect();

	fn recurse(query: &DepGraphQuery,
	node_states: &mut [State],
	node: NodeIndex)
	-> bool
	{
	match node_states[node.0] {
	// known to reach a target
	State::Included => return true,

	// known not to reach a target
	State::Excluded => return false,

	// backedge, not yet known, say false
	State::Deciding => return false,

	State::Undecided => { }
	}

	node_states[node.0] = State::Deciding;

	for neighbor_index in query.graph.successor_nodes(node) {
	if recurse(query, node_states, neighbor_index) {
	node_states[node.0] = State::Included;
	}
	}

	// if we didn't find a path to target, then set to excluded
	if node_states[node.0] == State::Deciding {
	node_states[node.0] = State::Excluded;
	false
	} else {
	assert!(node_states[node.0] == State::Included);
	true
	}
	}
	}

	fn filter_edges(query: &DepGraphQuery,
	nodes: &FnvHashSet<DepNode>)
	-> Vec<(DepNode, DepNode)>
	{
	query.edges()
	.into_iter()
	.filter(\|&(source, target)\| nodes.contains(&source) && nodes.contains(&target))
	.collect()
	}