src/librustc_infer/infer/lexical_region_resolve/graphviz.rs

//! This module provides linkage between libgraphviz traits and
//! `rustc_trait_selection::infer::region_constraints`, generating a
//! rendering of the graph represented by the list of `Constraint`
//! instances (which make up the edges of the graph), as well as the
//! origin for each constraint (which are attached to the labels on
//! each edge).

/// For clarity, rename the graphviz crate locally to dot.
use graphviz as dot;

use super::Constraint;
use crate::infer::region_constraints::RegionConstraintData;
use crate::infer::SubregionOrigin;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir::def_id::DefIndex;
use rustc_middle::middle::free_region::RegionRelations;
use rustc_middle::middle::region;
use rustc_middle::ty;

use std::borrow::Cow;
use std::collections::btree_map::BTreeMap;
use std::collections::hash_map::Entry::Vacant;
use std::env;
use std::fs;
use std::io;
use std::sync::atomic::{AtomicBool, Ordering};

fn print_help_message() {
    println!(
        "\
-Z print-region-graph by default prints a region constraint graph for every \n\
function body, to the path `constraints.nodeXXX.dot`, where the XXX is \n\
replaced with the node id of the function under analysis.                   \n\
                                                                            \n\
To select one particular function body, set `RUST_REGION_GRAPH_NODE=XXX`,   \n\
where XXX is the node id desired.                                           \n\
                                                                            \n\
To generate output to some path other than the default                      \n\
`constraints.nodeXXX.dot`, set `RUST_REGION_GRAPH=/path/desired.dot`;  \n\
occurrences of the character `%` in the requested path will be replaced with\n\
the node id of the function under analysis.                                 \n\
                                                                            \n\
(Since you requested help via RUST_REGION_GRAPH=help, no region constraint  \n\
graphs will be printed.                                                     \n\
"
    );
}

pub fn maybe_print_constraints_for<'a, 'tcx>(
    region_data: &RegionConstraintData<'tcx>,
    region_rels: &RegionRelations<'a, 'tcx>,
) {
    let tcx = region_rels.tcx;
    let context = region_rels.context;

    if !tcx.sess.opts.debugging_opts.print_region_graph {
        return;
    }

    let requested_node = env::var("RUST_REGION_GRAPH_NODE")
        .ok()
        .and_then(|s| s.parse().map(DefIndex::from_u32).ok());

    if requested_node.is_some() && requested_node != Some(context.index) {
        return;
    }

    let requested_output = env::var("RUST_REGION_GRAPH");
    debug!("requested_output: {:?} requested_node: {:?}", requested_output, requested_node);

    let output_path = {
        let output_template = match requested_output {
            Ok(ref s) if s == "help" => {
                static PRINTED_YET: AtomicBool = AtomicBool::new(false);
                if !PRINTED_YET.load(Ordering::SeqCst) {
                    print_help_message();
                    PRINTED_YET.store(true, Ordering::SeqCst);
                }
                return;
            }

            Ok(other_path) => other_path,
            Err(_) => "constraints.node%.dot".to_string(),
        };

        if output_template.is_empty() {
            panic!("empty string provided as RUST_REGION_GRAPH");
        }

        if output_template.contains('%') {
            let mut new_str = String::new();
            for c in output_template.chars() {
                if c == '%' {
                    new_str.push_str(&context.index.as_u32().to_string());
                } else {
                    new_str.push(c);
                }
            }
            new_str
        } else {
            output_template
        }
    };

    if let Err(e) = dump_region_data_to(region_rels, &region_data.constraints, &output_path) {
        let msg = format!("io error dumping region constraints: {}", e);
        tcx.sess.err(&msg)
    }
}

struct ConstraintGraph<'a, 'tcx> {
    graph_name: String,
    region_rels: &'a RegionRelations<'a, 'tcx>,
    map: &'a BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>,
    node_ids: FxHashMap<Node, usize>,
}

#[derive(Clone, Hash, PartialEq, Eq, Debug, Copy)]
enum Node {
    RegionVid(ty::RegionVid),
    Region(ty::RegionKind),
}

#[derive(Clone, PartialEq, Eq, Debug, Copy)]
enum Edge<'tcx> {
    Constraint(Constraint<'tcx>),
    EnclScope(region::Scope, region::Scope),
}

impl<'a, 'tcx> ConstraintGraph<'a, 'tcx> {
    fn new(
        name: String,
        region_rels: &'a RegionRelations<'a, 'tcx>,
        map: &'a ConstraintMap<'tcx>,
    ) -> ConstraintGraph<'a, 'tcx> {
        let mut i = 0;
        let mut node_ids = FxHashMap::default();
        {
            let mut add_node = |node| {
                if let Vacant(e) = node_ids.entry(node) {
                    e.insert(i);
                    i += 1;
                }
            };

            for (n1, n2) in map.keys().map(|c| constraint_to_nodes(c)) {
                add_node(n1);
                add_node(n2);
            }

            region_rels.region_scope_tree.each_encl_scope(|sub, sup| {
                add_node(Node::Region(ty::ReScope(sub)));
                add_node(Node::Region(ty::ReScope(sup)));
            });
        }

        ConstraintGraph { map, node_ids, region_rels, graph_name: name }
    }
}

impl<'a, 'tcx> dot::Labeller<'a> for ConstraintGraph<'a, 'tcx> {
    type Node = Node;
    type Edge = Edge<'tcx>;
    fn graph_id(&self) -> dot::Id<'_> {
        dot::Id::new(&*self.graph_name).unwrap()
    }
    fn node_id(&self, n: &Node) -> dot::Id<'_> {
        let node_id = match self.node_ids.get(n) {
            Some(node_id) => node_id,
            None => bug!("no node_id found for node: {:?}", n),
        };
        let name = || format!("node_{}", node_id);

        dot::Id::new(name())
            .unwrap_or_else(|_| bug!("failed to create graphviz node identified by {}", name()))
    }
    fn node_label(&self, n: &Node) -> dot::LabelText<'_> {
        match *n {
            Node::RegionVid(n_vid) => dot::LabelText::label(format!("{:?}", n_vid)),
            Node::Region(n_rgn) => dot::LabelText::label(format!("{:?}", n_rgn)),
        }
    }
    fn edge_label(&self, e: &Edge<'_>) -> dot::LabelText<'_> {
        match *e {
            Edge::Constraint(ref c) => {
                dot::LabelText::label(format!("{:?}", self.map.get(c).unwrap()))
            }
            Edge::EnclScope(..) => dot::LabelText::label("(enclosed)".to_owned()),
        }
    }
}

fn constraint_to_nodes(c: &Constraint<'_>) -> (Node, Node) {
    match *c {
        Constraint::VarSubVar(rv_1, rv_2) => (Node::RegionVid(rv_1), Node::RegionVid(rv_2)),
        Constraint::RegSubVar(r_1, rv_2) => (Node::Region(*r_1), Node::RegionVid(rv_2)),
        Constraint::VarSubReg(rv_1, r_2) => (Node::RegionVid(rv_1), Node::Region(*r_2)),
        Constraint::RegSubReg(r_1, r_2) => (Node::Region(*r_1), Node::Region(*r_2)),
    }
}

fn edge_to_nodes(e: &Edge<'_>) -> (Node, Node) {
    match *e {
        Edge::Constraint(ref c) => constraint_to_nodes(c),
        Edge::EnclScope(sub, sup) => {
            (Node::Region(ty::ReScope(sub)), Node::Region(ty::ReScope(sup)))
        }
    }
}

impl<'a, 'tcx> dot::GraphWalk<'a> for ConstraintGraph<'a, 'tcx> {
    type Node = Node;
    type Edge = Edge<'tcx>;
    fn nodes(&self) -> dot::Nodes<'_, Node> {
        let set = self.node_ids.keys().cloned().collect::<FxHashSet<_>>();
        debug!("constraint graph has {} nodes", set.len());
        set.into_iter().collect()
    }
    fn edges(&self) -> dot::Edges<'_, Edge<'tcx>> {
        debug!("constraint graph has {} edges", self.map.len());
        let mut v: Vec<_> = self.map.keys().map(|e| Edge::Constraint(*e)).collect();
        self.region_rels
            .region_scope_tree
            .each_encl_scope(|sub, sup| v.push(Edge::EnclScope(sub, sup)));
        debug!("region graph has {} edges", v.len());
        Cow::Owned(v)
    }
    fn source(&self, edge: &Edge<'tcx>) -> Node {
        let (n1, _) = edge_to_nodes(edge);
        debug!("edge {:?} has source {:?}", edge, n1);
        n1
    }
    fn target(&self, edge: &Edge<'tcx>) -> Node {
        let (_, n2) = edge_to_nodes(edge);
        debug!("edge {:?} has target {:?}", edge, n2);
        n2
    }
}

pub type ConstraintMap<'tcx> = BTreeMap<Constraint<'tcx>, SubregionOrigin<'tcx>>;

fn dump_region_data_to<'a, 'tcx>(
    region_rels: &RegionRelations<'a, 'tcx>,
    map: &ConstraintMap<'tcx>,
    path: &str,
) -> io::Result<()> {
    debug!("dump_region_data map (len: {}) path: {}", map.len(), path);
    let g = ConstraintGraph::new("region_data".to_string(), region_rels, map);
    debug!("dump_region_data calling render");
    let mut v = Vec::new();
    dot::render(&g, &mut v).unwrap();
    fs::write(path, &v)
}