mv compiler to compiler/

3 files changed, 1106 insertions, 0 deletions

diff --git a/compiler/rustc_graphviz/Cargo.toml b/compiler/rustc_graphviz/Cargo.toml
new file mode 100644
index 00000000000..d07b75a5c8f
--- /dev/null
+++ b/compiler/rustc_graphviz/Cargo.toml
@@ -0,0 +1,5 @@
+[package]
+authors = ["The Rust Project Developers"]
+name = "rustc_graphviz"
+version = "0.0.0"
+edition = "2018"
diff --git a/compiler/rustc_graphviz/src/lib.rs b/compiler/rustc_graphviz/src/lib.rs
new file mode 100644
index 00000000000..4339092b63e
--- /dev/null
+++ b/compiler/rustc_graphviz/src/lib.rs
@@ -0,0 +1,693 @@
+//! Generate files suitable for use with [Graphviz](http://www.graphviz.org/)
+//!
+//! The `render` function generates output (e.g., an `output.dot` file) for
+//! use with [Graphviz](http://www.graphviz.org/) by walking a labeled
+//! graph. (Graphviz can then automatically lay out the nodes and edges
+//! of the graph, and also optionally render the graph as an image or
+//! other [output formats](
+//! http://www.graphviz.org/content/output-formats), such as SVG.)
+//!
+//! Rather than impose some particular graph data structure on clients,
+//! this library exposes two traits that clients can implement on their
+//! own structs before handing them over to the rendering function.
+//!
+//! Note: This library does not yet provide access to the full
+//! expressiveness of the [DOT language](
+//! http://www.graphviz.org/doc/info/lang.html). For example, there are
+//! many [attributes](http://www.graphviz.org/content/attrs) related to
+//! providing layout hints (e.g., left-to-right versus top-down, which
+//! algorithm to use, etc). The current intention of this library is to
+//! emit a human-readable .dot file with very regular structure suitable
+//! for easy post-processing.
+//!
+//! # Examples
+//!
+//! The first example uses a very simple graph representation: a list of
+//! pairs of ints, representing the edges (the node set is implicit).
+//! Each node label is derived directly from the int representing the node,
+//! while the edge labels are all empty strings.
+//!
+//! This example also illustrates how to use `Cow<[T]>` to return
+//! an owned vector or a borrowed slice as appropriate: we construct the
+//! node vector from scratch, but borrow the edge list (rather than
+//! constructing a copy of all the edges from scratch).
+//!
+//! The output from this example renders five nodes, with the first four
+//! forming a diamond-shaped acyclic graph and then pointing to the fifth
+//! which is cyclic.
+//!
+//! ```rust
+//! #![feature(rustc_private)]
+//!
+//! use std::io::Write;
+//! use rustc_graphviz as dot;
+//!
+//! type Nd = isize;
+//! type Ed = (isize,isize);
+//! struct Edges(Vec<Ed>);
+//!
+//! pub fn render_to<W: Write>(output: &mut W) {
+//!     let edges = Edges(vec![(0,1), (0,2), (1,3), (2,3), (3,4), (4,4)]);
+//!     dot::render(&edges, output).unwrap()
+//! }
+//!
+//! impl<'a> dot::Labeller<'a> for Edges {
+//!     type Node = Nd;
+//!     type Edge = Ed;
+//!     fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example1").unwrap() }
+//!
+//!     fn node_id(&'a self, n: &Nd) -> dot::Id<'a> {
+//!         dot::Id::new(format!("N{}", *n)).unwrap()
+//!     }
+//! }
+//!
+//! impl<'a> dot::GraphWalk<'a> for Edges {
+//!     type Node = Nd;
+//!     type Edge = Ed;
+//!     fn nodes(&self) -> dot::Nodes<'a,Nd> {
+//!         // (assumes that |N| \approxeq |E|)
+//!         let &Edges(ref v) = self;
+//!         let mut nodes = Vec::with_capacity(v.len());
+//!         for &(s,t) in v {
+//!             nodes.push(s); nodes.push(t);
+//!         }
+//!         nodes.sort();
+//!         nodes.dedup();
+//!         nodes.into()
+//!     }
+//!
+//!     fn edges(&'a self) -> dot::Edges<'a,Ed> {
+//!         let &Edges(ref edges) = self;
+//!         (&edges[..]).into()
+//!     }
+//!
+//!     fn source(&self, e: &Ed) -> Nd { let &(s,_) = e; s }
+//!
+//!     fn target(&self, e: &Ed) -> Nd { let &(_,t) = e; t }
+//! }
+//!
+//! # pub fn main() { render_to(&mut Vec::new()) }
+//! ```
+//!
+//! ```no_run
+//! # pub fn render_to<W:std::io::Write>(output: &mut W) { unimplemented!() }
+//! pub fn main() {
+//!     use std::fs::File;
+//!     let mut f = File::create("example1.dot").unwrap();
+//!     render_to(&mut f)
+//! }
+//! ```
+//!
+//! Output from first example (in `example1.dot`):
+//!
+//! ```dot
+//! digraph example1 {
+//!     N0[label="N0"];
+//!     N1[label="N1"];
+//!     N2[label="N2"];
+//!     N3[label="N3"];
+//!     N4[label="N4"];
+//!     N0 -> N1[label=""];
+//!     N0 -> N2[label=""];
+//!     N1 -> N3[label=""];
+//!     N2 -> N3[label=""];
+//!     N3 -> N4[label=""];
+//!     N4 -> N4[label=""];
+//! }
+//! ```
+//!
+//! The second example illustrates using `node_label` and `edge_label` to
+//! add labels to the nodes and edges in the rendered graph. The graph
+//! here carries both `nodes` (the label text to use for rendering a
+//! particular node), and `edges` (again a list of `(source,target)`
+//! indices).
+//!
+//! This example also illustrates how to use a type (in this case the edge
+//! type) that shares substructure with the graph: the edge type here is a
+//! direct reference to the `(source,target)` pair stored in the graph's
+//! internal vector (rather than passing around a copy of the pair
+//! itself). Note that this implies that `fn edges(&'a self)` must
+//! construct a fresh `Vec<&'a (usize,usize)>` from the `Vec<(usize,usize)>`
+//! edges stored in `self`.
+//!
+//! Since both the set of nodes and the set of edges are always
+//! constructed from scratch via iterators, we use the `collect()` method
+//! from the `Iterator` trait to collect the nodes and edges into freshly
+//! constructed growable `Vec` values (rather than using `Cow` as in the
+//! first example above).
+//!
+//! The output from this example renders four nodes that make up the
+//! Hasse-diagram for the subsets of the set `{x, y}`. Each edge is
+//! labeled with the &sube; character (specified using the HTML character
+//! entity `&sube`).
+//!
+//! ```rust
+//! #![feature(rustc_private)]
+//!
+//! use std::io::Write;
+//! use rustc_graphviz as dot;
+//!
+//! type Nd = usize;
+//! type Ed<'a> = &'a (usize, usize);
+//! struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }
+//!
+//! pub fn render_to<W: Write>(output: &mut W) {
+//!     let nodes = vec!["{x,y}","{x}","{y}","{}"];
+//!     let edges = vec![(0,1), (0,2), (1,3), (2,3)];
+//!     let graph = Graph { nodes: nodes, edges: edges };
+//!
+//!     dot::render(&graph, output).unwrap()
+//! }
+//!
+//! impl<'a> dot::Labeller<'a> for Graph {
+//!     type Node = Nd;
+//!     type Edge = Ed<'a>;
+//!     fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example2").unwrap() }
+//!     fn node_id(&'a self, n: &Nd) -> dot::Id<'a> {
+//!         dot::Id::new(format!("N{}", n)).unwrap()
+//!     }
+//!     fn node_label<'b>(&'b self, n: &Nd) -> dot::LabelText<'b> {
+//!         dot::LabelText::LabelStr(self.nodes[*n].into())
+//!     }
+//!     fn edge_label<'b>(&'b self, _: &Ed) -> dot::LabelText<'b> {
+//!         dot::LabelText::LabelStr("&sube;".into())
+//!     }
+//! }
+//!
+//! impl<'a> dot::GraphWalk<'a> for Graph {
+//!     type Node = Nd;
+//!     type Edge = Ed<'a>;
+//!     fn nodes(&self) -> dot::Nodes<'a,Nd> { (0..self.nodes.len()).collect() }
+//!     fn edges(&'a self) -> dot::Edges<'a,Ed<'a>> { self.edges.iter().collect() }
+//!     fn source(&self, e: &Ed) -> Nd { let & &(s,_) = e; s }
+//!     fn target(&self, e: &Ed) -> Nd { let & &(_,t) = e; t }
+//! }
+//!
+//! # pub fn main() { render_to(&mut Vec::new()) }
+//! ```
+//!
+//! ```no_run
+//! # pub fn render_to<W:std::io::Write>(output: &mut W) { unimplemented!() }
+//! pub fn main() {
+//!     use std::fs::File;
+//!     let mut f = File::create("example2.dot").unwrap();
+//!     render_to(&mut f)
+//! }
+//! ```
+//!
+//! The third example is similar to the second, except now each node and
+//! edge now carries a reference to the string label for each node as well
+//! as that node's index. (This is another illustration of how to share
+//! structure with the graph itself, and why one might want to do so.)
+//!
+//! The output from this example is the same as the second example: the
+//! Hasse-diagram for the subsets of the set `{x, y}`.
+//!
+//! ```rust
+//! #![feature(rustc_private)]
+//!
+//! use std::io::Write;
+//! use rustc_graphviz as dot;
+//!
+//! type Nd<'a> = (usize, &'a str);
+//! type Ed<'a> = (Nd<'a>, Nd<'a>);
+//! struct Graph { nodes: Vec<&'static str>, edges: Vec<(usize,usize)> }
+//!
+//! pub fn render_to<W: Write>(output: &mut W) {
+//!     let nodes = vec!["{x,y}","{x}","{y}","{}"];
+//!     let edges = vec![(0,1), (0,2), (1,3), (2,3)];
+//!     let graph = Graph { nodes: nodes, edges: edges };
+//!
+//!     dot::render(&graph, output).unwrap()
+//! }
+//!
+//! impl<'a> dot::Labeller<'a> for Graph {
+//!     type Node = Nd<'a>;
+//!     type Edge = Ed<'a>;
+//!     fn graph_id(&'a self) -> dot::Id<'a> { dot::Id::new("example3").unwrap() }
+//!     fn node_id(&'a self, n: &Nd<'a>) -> dot::Id<'a> {
+//!         dot::Id::new(format!("N{}", n.0)).unwrap()
+//!     }
+//!     fn node_label<'b>(&'b self, n: &Nd<'b>) -> dot::LabelText<'b> {
+//!         let &(i, _) = n;
+//!         dot::LabelText::LabelStr(self.nodes[i].into())
+//!     }
+//!     fn edge_label<'b>(&'b self, _: &Ed<'b>) -> dot::LabelText<'b> {
+//!         dot::LabelText::LabelStr("&sube;".into())
+//!     }
+//! }
+//!
+//! impl<'a> dot::GraphWalk<'a> for Graph {
+//!     type Node = Nd<'a>;
+//!     type Edge = Ed<'a>;
+//!     fn nodes(&'a self) -> dot::Nodes<'a,Nd<'a>> {
+//!         self.nodes.iter().map(|s| &s[..]).enumerate().collect()
+//!     }
+//!     fn edges(&'a self) -> dot::Edges<'a,Ed<'a>> {
+//!         self.edges.iter()
+//!             .map(|&(i,j)|((i, &self.nodes[i][..]),
+//!                           (j, &self.nodes[j][..])))
+//!             .collect()
+//!     }
+//!     fn source(&self, e: &Ed<'a>) -> Nd<'a> { let &(s,_) = e; s }
+//!     fn target(&self, e: &Ed<'a>) -> Nd<'a> { let &(_,t) = e; t }
+//! }
+//!
+//! # pub fn main() { render_to(&mut Vec::new()) }
+//! ```
+//!
+//! ```no_run
+//! # pub fn render_to<W:std::io::Write>(output: &mut W) { unimplemented!() }
+//! pub fn main() {
+//!     use std::fs::File;
+//!     let mut f = File::create("example3.dot").unwrap();
+//!     render_to(&mut f)
+//! }
+//! ```
+//!
+//! # References
+//!
+//! * [Graphviz](http://www.graphviz.org/)
+//!
+//! * [DOT language](http://www.graphviz.org/doc/info/lang.html)
+
+#![doc(
+    html_root_url = "https://doc.rust-lang.org/nightly/",
+    test(attr(allow(unused_variables), deny(warnings)))
+)]
+#![feature(nll)]
+
+use LabelText::*;
+
+use std::borrow::Cow;
+use std::io;
+use std::io::prelude::*;
+
+/// The text for a graphviz label on a node or edge.
+pub enum LabelText<'a> {
+    /// This kind of label preserves the text directly as is.
+    ///
+    /// Occurrences of backslashes (`\`) are escaped, and thus appear
+    /// as backslashes in the rendered label.
+    LabelStr(Cow<'a, str>),
+
+    /// This kind of label uses the graphviz label escString type:
+    /// <http://www.graphviz.org/content/attrs#kescString>
+    ///
+    /// Occurrences of backslashes (`\`) are not escaped; instead they
+    /// are interpreted as initiating an escString escape sequence.
+    ///
+    /// Escape sequences of particular interest: in addition to `\n`
+    /// to break a line (centering the line preceding the `\n`), there
+    /// are also the escape sequences `\l` which left-justifies the
+    /// preceding line and `\r` which right-justifies it.
+    EscStr(Cow<'a, str>),
+
+    /// This uses a graphviz [HTML string label][html]. The string is
+    /// printed exactly as given, but between `<` and `>`. **No
+    /// escaping is performed.**
+    ///
+    /// [html]: http://www.graphviz.org/content/node-shapes#html
+    HtmlStr(Cow<'a, str>),
+}
+
+/// The style for a node or edge.
+/// See <http://www.graphviz.org/doc/info/attrs.html#k:style> for descriptions.
+/// Note that some of these are not valid for edges.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum Style {
+    None,
+    Solid,
+    Dashed,
+    Dotted,
+    Bold,
+    Rounded,
+    Diagonals,
+    Filled,
+    Striped,
+    Wedged,
+}
+
+impl Style {
+    pub fn as_slice(self) -> &'static str {
+        match self {
+            Style::None => "",
+            Style::Solid => "solid",
+            Style::Dashed => "dashed",
+            Style::Dotted => "dotted",
+            Style::Bold => "bold",
+            Style::Rounded => "rounded",
+            Style::Diagonals => "diagonals",
+            Style::Filled => "filled",
+            Style::Striped => "striped",
+            Style::Wedged => "wedged",
+        }
+    }
+}
+
+// There is a tension in the design of the labelling API.
+//
+// For example, I considered making a `Labeller<T>` trait that
+// provides labels for `T`, and then making the graph type `G`
+// implement `Labeller<Node>` and `Labeller<Edge>`. However, this is
+// not possible without functional dependencies. (One could work
+// around that, but I did not explore that avenue heavily.)
+//
+// Another approach that I actually used for a while was to make a
+// `Label<Context>` trait that is implemented by the client-specific
+// Node and Edge types (as well as an implementation on Graph itself
+// for the overall name for the graph). The main disadvantage of this
+// second approach (compared to having the `G` type parameter
+// implement a Labelling service) that I have encountered is that it
+// makes it impossible to use types outside of the current crate
+// directly as Nodes/Edges; you need to wrap them in newtype'd
+// structs. See e.g., the `No` and `Ed` structs in the examples. (In
+// practice clients using a graph in some other crate would need to
+// provide some sort of adapter shim over the graph anyway to
+// interface with this library).
+//
+// Another approach would be to make a single `Labeller<N,E>` trait
+// that provides three methods (graph_label, node_label, edge_label),
+// and then make `G` implement `Labeller<N,E>`. At first this did not
+// appeal to me, since I had thought I would need separate methods on
+// each data variant for dot-internal identifiers versus user-visible
+// labels. However, the identifier/label distinction only arises for
+// nodes; graphs themselves only have identifiers, and edges only have
+// labels.
+//
+// So in the end I decided to use the third approach described above.
+
+/// `Id` is a Graphviz `ID`.
+pub struct Id<'a> {
+    name: Cow<'a, str>,
+}
+
+impl<'a> Id<'a> {
+    /// Creates an `Id` named `name`.
+    ///
+    /// The caller must ensure that the input conforms to an
+    /// identifier format: it must be a non-empty string made up of
+    /// alphanumeric or underscore characters, not beginning with a
+    /// digit (i.e., the regular expression `[a-zA-Z_][a-zA-Z_0-9]*`).
+    ///
+    /// (Note: this format is a strict subset of the `ID` format
+    /// defined by the DOT language. This function may change in the
+    /// future to accept a broader subset, or the entirety, of DOT's
+    /// `ID` format.)
+    ///
+    /// Passing an invalid string (containing spaces, brackets,
+    /// quotes, ...) will return an empty `Err` value.
+    pub fn new<Name: Into<Cow<'a, str>>>(name: Name) -> Result<Id<'a>, ()> {
+        let name = name.into();
+        match name.chars().next() {
+            Some(c) if c.is_ascii_alphabetic() || c == '_' => {}
+            _ => return Err(()),
+        }
+        if !name.chars().all(|c| c.is_ascii_alphanumeric() || c == '_') {
+            return Err(());
+        }
+
+        Ok(Id { name })
+    }
+
+    pub fn as_slice(&'a self) -> &'a str {
+        &*self.name
+    }
+
+    pub fn name(self) -> Cow<'a, str> {
+        self.name
+    }
+}
+
+/// Each instance of a type that implements `Label<C>` maps to a
+/// unique identifier with respect to `C`, which is used to identify
+/// it in the generated .dot file. They can also provide more
+/// elaborate (and non-unique) label text that is used in the graphviz
+/// rendered output.
+
+/// The graph instance is responsible for providing the DOT compatible
+/// identifiers for the nodes and (optionally) rendered labels for the nodes and
+/// edges, as well as an identifier for the graph itself.
+pub trait Labeller<'a> {
+    type Node;
+    type Edge;
+
+    /// Must return a DOT compatible identifier naming the graph.
+    fn graph_id(&'a self) -> Id<'a>;
+
+    /// Maps `n` to a unique identifier with respect to `self`. The
+    /// implementor is responsible for ensuring that the returned name
+    /// is a valid DOT identifier.
+    fn node_id(&'a self, n: &Self::Node) -> Id<'a>;
+
+    /// Maps `n` to one of the [graphviz `shape` names][1]. If `None`
+    /// is returned, no `shape` attribute is specified.
+    ///
+    /// [1]: http://www.graphviz.org/content/node-shapes
+    fn node_shape(&'a self, _node: &Self::Node) -> Option<LabelText<'a>> {
+        None
+    }
+
+    /// Maps `n` to a label that will be used in the rendered output.
+    /// The label need not be unique, and may be the empty string; the
+    /// default is just the output from `node_id`.
+    fn node_label(&'a self, n: &Self::Node) -> LabelText<'a> {
+        LabelStr(self.node_id(n).name)
+    }
+
+    /// Maps `e` to a label that will be used in the rendered output.
+    /// The label need not be unique, and may be the empty string; the
+    /// default is in fact the empty string.
+    fn edge_label(&'a self, _e: &Self::Edge) -> LabelText<'a> {
+        LabelStr("".into())
+    }
+
+    /// Maps `n` to a style that will be used in the rendered output.
+    fn node_style(&'a self, _n: &Self::Node) -> Style {
+        Style::None
+    }
+
+    /// Maps `e` to a style that will be used in the rendered output.
+    fn edge_style(&'a self, _e: &Self::Edge) -> Style {
+        Style::None
+    }
+}
+
+/// Escape tags in such a way that it is suitable for inclusion in a
+/// Graphviz HTML label.
+pub fn escape_html(s: &str) -> String {
+    s.replace("&", "&amp;").replace("\"", "&quot;").replace("<", "&lt;").replace(">", "&gt;")
+}
+
+impl<'a> LabelText<'a> {
+    pub fn label<S: Into<Cow<'a, str>>>(s: S) -> LabelText<'a> {
+        LabelStr(s.into())
+    }
+
+    pub fn escaped<S: Into<Cow<'a, str>>>(s: S) -> LabelText<'a> {
+        EscStr(s.into())
+    }
+
+    pub fn html<S: Into<Cow<'a, str>>>(s: S) -> LabelText<'a> {
+        HtmlStr(s.into())
+    }
+
+    fn escape_char<F>(c: char, mut f: F)
+    where
+        F: FnMut(char),
+    {
+        match c {
+            // not escaping \\, since Graphviz escString needs to
+            // interpret backslashes; see EscStr above.
+            '\\' => f(c),
+            _ => {
+                for c in c.escape_default() {
+                    f(c)
+                }
+            }
+        }
+    }
+    fn escape_str(s: &str) -> String {
+        let mut out = String::with_capacity(s.len());
+        for c in s.chars() {
+            LabelText::escape_char(c, |c| out.push(c));
+        }
+        out
+    }
+
+    /// Renders text as string suitable for a label in a .dot file.
+    /// This includes quotes or suitable delimiters.
+    pub fn to_dot_string(&self) -> String {
+        match *self {
+            LabelStr(ref s) => format!("\"{}\"", s.escape_default()),
+            EscStr(ref s) => format!("\"{}\"", LabelText::escape_str(&s)),
+            HtmlStr(ref s) => format!("<{}>", s),
+        }
+    }
+
+    /// Decomposes content into string suitable for making EscStr that
+    /// yields same content as self. The result obeys the law
+    /// render(`lt`) == render(`EscStr(lt.pre_escaped_content())`) for
+    /// all `lt: LabelText`.
+    fn pre_escaped_content(self) -> Cow<'a, str> {
+        match self {
+            EscStr(s) => s,
+            LabelStr(s) => {
+                if s.contains('\\') {
+                    (&*s).escape_default().to_string().into()
+                } else {
+                    s
+                }
+            }
+            HtmlStr(s) => s,
+        }
+    }
+
+    /// Puts `prefix` on a line above this label, with a blank line separator.
+    pub fn prefix_line(self, prefix: LabelText<'_>) -> LabelText<'static> {
+        prefix.suffix_line(self)
+    }
+
+    /// Puts `suffix` on a line below this label, with a blank line separator.
+    pub fn suffix_line(self, suffix: LabelText<'_>) -> LabelText<'static> {
+        let mut prefix = self.pre_escaped_content().into_owned();
+        let suffix = suffix.pre_escaped_content();
+        prefix.push_str(r"\n\n");
+        prefix.push_str(&suffix);
+        EscStr(prefix.into())
+    }
+}
+
+pub type Nodes<'a, N> = Cow<'a, [N]>;
+pub type Edges<'a, E> = Cow<'a, [E]>;
+
+// (The type parameters in GraphWalk should be associated items,
+// when/if Rust supports such.)
+
+/// GraphWalk is an abstraction over a directed graph = (nodes,edges)
+/// made up of node handles `N` and edge handles `E`, where each `E`
+/// can be mapped to its source and target nodes.
+///
+/// The lifetime parameter `'a` is exposed in this trait (rather than
+/// introduced as a generic parameter on each method declaration) so
+/// that a client impl can choose `N` and `E` that have substructure
+/// that is bound by the self lifetime `'a`.
+///
+/// The `nodes` and `edges` method each return instantiations of
+/// `Cow<[T]>` to leave implementors the freedom to create
+/// entirely new vectors or to pass back slices into internally owned
+/// vectors.
+pub trait GraphWalk<'a> {
+    type Node: Clone;
+    type Edge: Clone;
+
+    /// Returns all the nodes in this graph.
+    fn nodes(&'a self) -> Nodes<'a, Self::Node>;
+    /// Returns all of the edges in this graph.
+    fn edges(&'a self) -> Edges<'a, Self::Edge>;
+    /// The source node for `edge`.
+    fn source(&'a self, edge: &Self::Edge) -> Self::Node;
+    /// The target node for `edge`.
+    fn target(&'a self, edge: &Self::Edge) -> Self::Node;
+}
+
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum RenderOption {
+    NoEdgeLabels,
+    NoNodeLabels,
+    NoEdgeStyles,
+    NoNodeStyles,
+
+    Monospace,
+}
+
+/// Returns vec holding all the default render options.
+pub fn default_options() -> Vec<RenderOption> {
+    vec![]
+}
+
+/// Renders directed graph `g` into the writer `w` in DOT syntax.
+/// (Simple wrapper around `render_opts` that passes a default set of options.)
+pub fn render<'a, N, E, G, W>(g: &'a G, w: &mut W) -> io::Result<()>
+where
+    N: Clone + 'a,
+    E: Clone + 'a,
+    G: Labeller<'a, Node = N, Edge = E> + GraphWalk<'a, Node = N, Edge = E>,
+    W: Write,
+{
+    render_opts(g, w, &[])
+}
+
+/// Renders directed graph `g` into the writer `w` in DOT syntax.
+/// (Main entry point for the library.)
+pub fn render_opts<'a, N, E, G, W>(g: &'a G, w: &mut W, options: &[RenderOption]) -> io::Result<()>
+where
+    N: Clone + 'a,
+    E: Clone + 'a,
+    G: Labeller<'a, Node = N, Edge = E> + GraphWalk<'a, Node = N, Edge = E>,
+    W: Write,
+{
+    writeln!(w, "digraph {} {{", g.graph_id().as_slice())?;
+
+    // Global graph properties
+    if options.contains(&RenderOption::Monospace) {
+        writeln!(w, r#"    graph[fontname="monospace"];"#)?;
+        writeln!(w, r#"    node[fontname="monospace"];"#)?;
+        writeln!(w, r#"    edge[fontname="monospace"];"#)?;
+    }
+
+    for n in g.nodes().iter() {
+        write!(w, "    ")?;
+        let id = g.node_id(n);
+
+        let escaped = &g.node_label(n).to_dot_string();
+
+        let mut text = Vec::new();
+        write!(text, "{}", id.as_slice()).unwrap();
+
+        if !options.contains(&RenderOption::NoNodeLabels) {
+            write!(text, "[label={}]", escaped).unwrap();
+        }
+
+        let style = g.node_style(n);
+        if !options.contains(&RenderOption::NoNodeStyles) && style != Style::None {
+            write!(text, "[style=\"{}\"]", style.as_slice()).unwrap();
+        }
+
+        if let Some(s) = g.node_shape(n) {
+            write!(text, "[shape={}]", &s.to_dot_string()).unwrap();
+        }
+
+        writeln!(text, ";").unwrap();
+        w.write_all(&text[..])?;
+    }
+
+    for e in g.edges().iter() {
+        let escaped_label = &g.edge_label(e).to_dot_string();
+        write!(w, "    ")?;
+        let source = g.source(e);
+        let target = g.target(e);
+        let source_id = g.node_id(&source);
+        let target_id = g.node_id(&target);
+
+        let mut text = Vec::new();
+        write!(text, "{} -> {}", source_id.as_slice(), target_id.as_slice()).unwrap();
+
+        if !options.contains(&RenderOption::NoEdgeLabels) {
+            write!(text, "[label={}]", escaped_label).unwrap();
+        }
+
+        let style = g.edge_style(e);
+        if !options.contains(&RenderOption::NoEdgeStyles) && style != Style::None {
+            write!(text, "[style=\"{}\"]", style.as_slice()).unwrap();
+        }
+
+        writeln!(text, ";").unwrap();
+        w.write_all(&text[..])?;
+    }
+
+    writeln!(w, "}}")
+}
+
+#[cfg(test)]
+mod tests;
diff --git a/compiler/rustc_graphviz/src/tests.rs b/compiler/rustc_graphviz/src/tests.rs
new file mode 100644
index 00000000000..055e13156ae
--- /dev/null
+++ b/compiler/rustc_graphviz/src/tests.rs
@@ -0,0 +1,408 @@
+use super::LabelText::{self, EscStr, HtmlStr, LabelStr};
+use super::{render, Edges, GraphWalk, Id, Labeller, Nodes, Style};
+use std::io;
+use std::io::prelude::*;
+use NodeLabels::*;
+
+/// each node is an index in a vector in the graph.
+type Node = usize;
+struct Edge {
+    from: usize,
+    to: usize,
+    label: &'static str,
+    style: Style,
+}
+
+fn edge(from: usize, to: usize, label: &'static str, style: Style) -> Edge {
+    Edge { from, to, label, style }
+}
+
+struct LabelledGraph {
+    /// The name for this graph. Used for labeling generated `digraph`.
+    name: &'static str,
+
+    /// Each node is an index into `node_labels`; these labels are
+    /// used as the label text for each node. (The node *names*,
+    /// which are unique identifiers, are derived from their index
+    /// in this array.)
+    ///
+    /// If a node maps to None here, then just use its name as its
+    /// text.
+    node_labels: Vec<Option<&'static str>>,
+
+    node_styles: Vec<Style>,
+
+    /// Each edge relates a from-index to a to-index along with a
+    /// label; `edges` collects them.
+    edges: Vec<Edge>,
+}
+
+// A simple wrapper around LabelledGraph that forces the labels to
+// be emitted as EscStr.
+struct LabelledGraphWithEscStrs {
+    graph: LabelledGraph,
+}
+
+enum NodeLabels<L> {
+    AllNodesLabelled(Vec<L>),
+    UnlabelledNodes(usize),
+    SomeNodesLabelled(Vec<Option<L>>),
+}
+
+type Trivial = NodeLabels<&'static str>;
+
+impl NodeLabels<&'static str> {
+    fn to_opt_strs(self) -> Vec<Option<&'static str>> {
+        match self {
+            UnlabelledNodes(len) => vec![None; len],
+            AllNodesLabelled(lbls) => lbls.into_iter().map(|l| Some(l)).collect(),
+            SomeNodesLabelled(lbls) => lbls.into_iter().collect(),
+        }
+    }
+
+    fn len(&self) -> usize {
+        match self {
+            &UnlabelledNodes(len) => len,
+            &AllNodesLabelled(ref lbls) => lbls.len(),
+            &SomeNodesLabelled(ref lbls) => lbls.len(),
+        }
+    }
+}
+
+impl LabelledGraph {
+    fn new(
+        name: &'static str,
+        node_labels: Trivial,
+        edges: Vec<Edge>,
+        node_styles: Option<Vec<Style>>,
+    ) -> LabelledGraph {
+        let count = node_labels.len();
+        LabelledGraph {
+            name,
+            node_labels: node_labels.to_opt_strs(),
+            edges,
+            node_styles: match node_styles {
+                Some(nodes) => nodes,
+                None => vec![Style::None; count],
+            },
+        }
+    }
+}
+
+impl LabelledGraphWithEscStrs {
+    fn new(name: &'static str, node_labels: Trivial, edges: Vec<Edge>) -> LabelledGraphWithEscStrs {
+        LabelledGraphWithEscStrs { graph: LabelledGraph::new(name, node_labels, edges, None) }
+    }
+}
+
+fn id_name<'a>(n: &Node) -> Id<'a> {
+    Id::new(format!("N{}", *n)).unwrap()
+}
+
+impl<'a> Labeller<'a> for LabelledGraph {
+    type Node = Node;
+    type Edge = &'a Edge;
+    fn graph_id(&'a self) -> Id<'a> {
+        Id::new(self.name).unwrap()
+    }
+    fn node_id(&'a self, n: &Node) -> Id<'a> {
+        id_name(n)
+    }
+    fn node_label(&'a self, n: &Node) -> LabelText<'a> {
+        match self.node_labels[*n] {
+            Some(l) => LabelStr(l.into()),
+            None => LabelStr(id_name(n).name()),
+        }
+    }
+    fn edge_label(&'a self, e: &&'a Edge) -> LabelText<'a> {
+        LabelStr(e.label.into())
+    }
+    fn node_style(&'a self, n: &Node) -> Style {
+        self.node_styles[*n]
+    }
+    fn edge_style(&'a self, e: &&'a Edge) -> Style {
+        e.style
+    }
+}
+
+impl<'a> Labeller<'a> for LabelledGraphWithEscStrs {
+    type Node = Node;
+    type Edge = &'a Edge;
+    fn graph_id(&'a self) -> Id<'a> {
+        self.graph.graph_id()
+    }
+    fn node_id(&'a self, n: &Node) -> Id<'a> {
+        self.graph.node_id(n)
+    }
+    fn node_label(&'a self, n: &Node) -> LabelText<'a> {
+        match self.graph.node_label(n) {
+            LabelStr(s) | EscStr(s) | HtmlStr(s) => EscStr(s),
+        }
+    }
+    fn edge_label(&'a self, e: &&'a Edge) -> LabelText<'a> {
+        match self.graph.edge_label(e) {
+            LabelStr(s) | EscStr(s) | HtmlStr(s) => EscStr(s),
+        }
+    }
+}
+
+impl<'a> GraphWalk<'a> for LabelledGraph {
+    type Node = Node;
+    type Edge = &'a Edge;
+    fn nodes(&'a self) -> Nodes<'a, Node> {
+        (0..self.node_labels.len()).collect()
+    }
+    fn edges(&'a self) -> Edges<'a, &'a Edge> {
+        self.edges.iter().collect()
+    }
+    fn source(&'a self, edge: &&'a Edge) -> Node {
+        edge.from
+    }
+    fn target(&'a self, edge: &&'a Edge) -> Node {
+        edge.to
+    }
+}
+
+impl<'a> GraphWalk<'a> for LabelledGraphWithEscStrs {
+    type Node = Node;
+    type Edge = &'a Edge;
+    fn nodes(&'a self) -> Nodes<'a, Node> {
+        self.graph.nodes()
+    }
+    fn edges(&'a self) -> Edges<'a, &'a Edge> {
+        self.graph.edges()
+    }
+    fn source(&'a self, edge: &&'a Edge) -> Node {
+        edge.from
+    }
+    fn target(&'a self, edge: &&'a Edge) -> Node {
+        edge.to
+    }
+}
+
+fn test_input(g: LabelledGraph) -> io::Result<String> {
+    let mut writer = Vec::new();
+    render(&g, &mut writer).unwrap();
+    let mut s = String::new();
+    Read::read_to_string(&mut &*writer, &mut s)?;
+    Ok(s)
+}
+
+// All of the tests use raw-strings as the format for the expected outputs,
+// so that you can cut-and-paste the content into a .dot file yourself to
+// see what the graphviz visualizer would produce.
+
+#[test]
+fn empty_graph() {
+    let labels: Trivial = UnlabelledNodes(0);
+    let r = test_input(LabelledGraph::new("empty_graph", labels, vec![], None));
+    assert_eq!(
+        r.unwrap(),
+        r#"digraph empty_graph {
+}
+"#
+    );
+}
+
+#[test]
+fn single_node() {
+    let labels: Trivial = UnlabelledNodes(1);
+    let r = test_input(LabelledGraph::new("single_node", labels, vec![], None));
+    assert_eq!(
+        r.unwrap(),
+        r#"digraph single_node {
+    N0[label="N0"];
+}
+"#
+    );
+}
+
+#[test]
+fn single_node_with_style() {
+    let labels: Trivial = UnlabelledNodes(1);
+    let styles = Some(vec![Style::Dashed]);
+    let r = test_input(LabelledGraph::new("single_node", labels, vec![], styles));
+    assert_eq!(
+        r.unwrap(),
+        r#"digraph single_node {
+    N0[label="N0"][style="dashed"];
+}
+"#
+    );
+}
+
+#[test]
+fn single_edge() {
+    let labels: Trivial = UnlabelledNodes(2);
+    let result = test_input(LabelledGraph::new(
+        "single_edge",
+        labels,
+        vec![edge(0, 1, "E", Style::None)],
+        None,
+    ));
+    assert_eq!(
+        result.unwrap(),
+        r#"digraph single_edge {
+    N0[label="N0"];
+    N1[label="N1"];
+    N0 -> N1[label="E"];
+}
+"#
+    );
+}
+
+#[test]
+fn single_edge_with_style() {
+    let labels: Trivial = UnlabelledNodes(2);
+    let result = test_input(LabelledGraph::new(
+        "single_edge",
+        labels,
+        vec![edge(0, 1, "E", Style::Bold)],
+        None,
+    ));
+    assert_eq!(
+        result.unwrap(),
+        r#"digraph single_edge {
+    N0[label="N0"];
+    N1[label="N1"];
+    N0 -> N1[label="E"][style="bold"];
+}
+"#
+    );
+}
+
+#[test]
+fn test_some_labelled() {
+    let labels: Trivial = SomeNodesLabelled(vec![Some("A"), None]);
+    let styles = Some(vec![Style::None, Style::Dotted]);
+    let result = test_input(LabelledGraph::new(
+        "test_some_labelled",
+        labels,
+        vec![edge(0, 1, "A-1", Style::None)],
+        styles,
+    ));
+    assert_eq!(
+        result.unwrap(),
+        r#"digraph test_some_labelled {
+    N0[label="A"];
+    N1[label="N1"][style="dotted"];
+    N0 -> N1[label="A-1"];
+}
+"#
+    );
+}
+
+#[test]
+fn single_cyclic_node() {
+    let labels: Trivial = UnlabelledNodes(1);
+    let r = test_input(LabelledGraph::new(
+        "single_cyclic_node",
+        labels,
+        vec![edge(0, 0, "E", Style::None)],
+        None,
+    ));
+    assert_eq!(
+        r.unwrap(),
+        r#"digraph single_cyclic_node {
+    N0[label="N0"];
+    N0 -> N0[label="E"];
+}
+"#
+    );
+}
+
+#[test]
+fn hasse_diagram() {
+    let labels = AllNodesLabelled(vec!["{x,y}", "{x}", "{y}", "{}"]);
+    let r = test_input(LabelledGraph::new(
+        "hasse_diagram",
+        labels,
+        vec![
+            edge(0, 1, "", Style::None),
+            edge(0, 2, "", Style::None),
+            edge(1, 3, "", Style::None),
+            edge(2, 3, "", Style::None),
+        ],
+        None,
+    ));
+    assert_eq!(
+        r.unwrap(),
+        r#"digraph hasse_diagram {
+    N0[label="{x,y}"];
+    N1[label="{x}"];
+    N2[label="{y}"];
+    N3[label="{}"];
+    N0 -> N1[label=""];
+    N0 -> N2[label=""];
+    N1 -> N3[label=""];
+    N2 -> N3[label=""];
+}
+"#
+    );
+}
+
+#[test]
+fn left_aligned_text() {
+    let labels = AllNodesLabelled(vec![
+        "if test {\
+       \\l    branch1\
+       \\l} else {\
+       \\l    branch2\
+       \\l}\
+       \\lafterward\
+       \\l",
+        "branch1",
+        "branch2",
+        "afterward",
+    ]);
+
+    let mut writer = Vec::new();
+
+    let g = LabelledGraphWithEscStrs::new(
+        "syntax_tree",
+        labels,
+        vec![
+            edge(0, 1, "then", Style::None),
+            edge(0, 2, "else", Style::None),
+            edge(1, 3, ";", Style::None),
+            edge(2, 3, ";", Style::None),
+        ],
+    );
+
+    render(&g, &mut writer).unwrap();
+    let mut r = String::new();
+    Read::read_to_string(&mut &*writer, &mut r).unwrap();
+
+    assert_eq!(
+        r,
+        r#"digraph syntax_tree {
+    N0[label="if test {\l    branch1\l} else {\l    branch2\l}\lafterward\l"];
+    N1[label="branch1"];
+    N2[label="branch2"];
+    N3[label="afterward"];
+    N0 -> N1[label="then"];
+    N0 -> N2[label="else"];
+    N1 -> N3[label=";"];
+    N2 -> N3[label=";"];
+}
+"#
+    );
+}
+
+#[test]
+fn simple_id_construction() {
+    let id1 = Id::new("hello");
+    match id1 {
+        Ok(_) => {}
+        Err(..) => panic!("'hello' is not a valid value for id anymore"),
+    }
+}
+
+#[test]
+fn badly_formatted_id() {
+    let id2 = Id::new("Weird { struct : ure } !!!");
+    match id2 {
+        Ok(_) => panic!("graphviz id suddenly allows spaces, brackets and stuff"),
+        Err(..) => {}
+    }
+}