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stitching.rs
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// -*- coding: utf-8 -*-
// ------------------------------------------------------------------------------------------------
// Copyright © 2021, stack-graphs authors.
// Licensed under either of Apache License, Version 2.0, or MIT license, at your option.
// Please see the LICENSE-APACHE or LICENSE-MIT files in this distribution for license details.
// ------------------------------------------------------------------------------------------------
//! Partial paths can be "stitched together" to produce name-binding paths.
//!
//! The "path stitching" algorithm defined in this module is how we take a collection of [partial
//! paths][] and use them to build up name-binding paths. Our conjecture is that by building paths
//! this way, we can precompute a useful amount of work at _index time_ (when we construct the
//! partial paths), to reduce the amount of work that needs to be done at _query time_ (when those
//! partial paths are stitched together into paths).
//!
//! Complicating this story is that for large codebases (especially those with many upstream and
//! downstream dependencies), there is a _very_ large set of partial paths available to us. We
//! want to be able to load those in _lazily_, during the execution of the path-stitching
//! algorithm.
//!
//! The [`Database`][] and [`PathStitcher`][] types provide this functionality. `Database`
//! manages a collection of partial paths that have been loaded into this process from some
//! external data store. `PathStitcher` implements the path-stitching algorithm in _phases_.
//! During each phase, we will process a set of (possibly incomplete) paths, looking in the
//! `Database` for the set of partial paths that are compatible with those paths. It is your
//! responsibility to make sure that the database contains all of possible extensions of the paths
//! that we're going to process in that phase. For the first phase, you already know which
//! paths you're starting the search from, and must make sure that the database starts out
//! containing the possible extensions of those "seed" paths. For subsequent phases, you get to
//! see which paths will be processed in the _next_ phase as part of handling the _current_ phase.
//! This gives you the opporunity to load additional partial paths into the `Database` before
//! allowing the next phase to proceed.
//!
//! [partial paths]: ../partial/index.html
//! [`Database`]: struct.Database.html
//! [`PathStitcher`]: struct.PathStitcher.html
use std::cmp::Ordering;
use std::collections::HashMap;
use std::collections::VecDeque;
#[cfg(feature = "copious-debugging")]
use std::fmt::Display;
use itertools::izip;
use itertools::Itertools;
use crate::arena::Arena;
use crate::arena::Handle;
use crate::arena::HandleSet;
use crate::arena::List;
use crate::arena::ListArena;
use crate::arena::ListCell;
use crate::arena::SupplementalArena;
use crate::cycles::Appendables;
use crate::cycles::AppendingCycleDetector;
use crate::cycles::SimilarPathDetector;
use crate::cycles::SimilarPathStats;
use crate::graph::Degree;
use crate::graph::Edge;
use crate::graph::File;
use crate::graph::Node;
use crate::graph::StackGraph;
use crate::graph::Symbol;
use crate::partial::Cyclicity;
use crate::partial::PartialPath;
use crate::partial::PartialPaths;
use crate::partial::PartialSymbolStack;
use crate::paths::Extend;
use crate::paths::PathResolutionError;
use crate::stats::FrequencyDistribution;
use crate::CancellationError;
use crate::CancellationFlag;
//-------------------------------------------------------------------------------------------------
// Appendable
/// Something that can be appended to a partial path.
pub trait Appendable {
/// Append this appendable to the given path. Resolving jump nodes and renaming unused_variables
/// is part of the responsibility of this method.
fn append_to(
&self,
graph: &StackGraph,
partials: &mut PartialPaths,
path: &mut PartialPath,
) -> Result<(), PathResolutionError>;
/// Return the start node.
fn start_node(&self) -> Handle<Node>;
/// Return the end node.
fn end_node(&self) -> Handle<Node>;
/// Return a Display implementation.
fn display<'a>(
&'a self,
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
) -> Box<dyn std::fmt::Display + 'a>;
}
impl Appendable for Edge {
fn append_to(
&self,
graph: &StackGraph,
partials: &mut PartialPaths,
path: &mut PartialPath,
) -> Result<(), PathResolutionError> {
path.resolve_to_node(graph, partials, self.source)?;
path.append(graph, partials, *self)
}
fn start_node(&self) -> Handle<Node> {
self.source
}
fn end_node(&self) -> Handle<Node> {
self.sink
}
fn display<'a>(
&'a self,
graph: &'a StackGraph,
_partials: &'a mut PartialPaths,
) -> Box<dyn std::fmt::Display + 'a> {
Box::new(format!(
"{} -> {}",
self.source.display(graph),
self.sink.display(graph)
))
}
}
impl Appendable for PartialPath {
fn append_to(
&self,
graph: &StackGraph,
partials: &mut PartialPaths,
path: &mut PartialPath,
) -> Result<(), PathResolutionError> {
path.resolve_to_node(graph, partials, self.start_node)?;
path.ensure_no_overlapping_variables(partials, self);
path.concatenate(graph, partials, self)?;
Ok(())
}
fn start_node(&self) -> Handle<Node> {
self.start_node
}
fn end_node(&self) -> Handle<Node> {
self.end_node
}
fn display<'a>(
&'a self,
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
) -> Box<dyn std::fmt::Display + 'a> {
Box::new(self.display(graph, partials))
}
}
//-------------------------------------------------------------------------------------------------
// ToAppendable
/// A trait to be implemented on types such as [`Database`][] that allow converting handles
/// to appendables.
///
/// It is very similar to the [`std::ops::Index`] trait, but returns a reference instead
/// of a value, such that an efficient identifity implementation is possible, that doesn't
/// require cloning values.
pub trait ToAppendable<H, A>
where
A: Appendable,
{
fn get_appendable<'a>(&'a self, handle: &'a H) -> &'a A;
}
//-------------------------------------------------------------------------------------------------
// Candidates
/// A trait to support finding candidates for partial path extension. The candidates are represented
/// by handles `H`, which are mapped to appendables `A` using the database `Db`. Loading errors are
/// reported as values of the `Err` type.
pub trait ForwardCandidates<H, A, Db, Err>
where
A: Appendable,
Db: ToAppendable<H, A>,
{
/// Load possible forward candidates for the given partial path into this candidates instance.
/// Must be called before [`get_forward_candidates`] to allow lazy-loading implementations.
fn load_forward_candidates(
&mut self,
_path: &PartialPath,
_cancellation_flag: &dyn CancellationFlag,
) -> Result<(), Err> {
Ok(())
}
/// Get forward candidates for extending the given partial path and add them to the provided
/// result instance. If this instance loads data lazily, this only considers previously loaded
/// data.
fn get_forward_candidates<R>(&mut self, path: &PartialPath, result: &mut R)
where
R: std::iter::Extend<H>;
/// Get the number of available candidates that share the given path's end node.
fn get_joining_candidate_degree(&self, path: &PartialPath) -> Degree;
/// Get the graph, partial path arena, and database backing this candidates instance.
fn get_graph_partials_and_db(&mut self) -> (&StackGraph, &mut PartialPaths, &Db);
}
//-------------------------------------------------------------------------------------------------
// FileEdges
/// Acts as a database of the edges in the graph.
pub struct GraphEdgeCandidates<'a> {
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
file: Option<Handle<File>>,
edges: GraphEdges,
}
impl<'a> GraphEdgeCandidates<'a> {
pub fn new(
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
file: Option<Handle<File>>,
) -> Self {
Self {
graph,
partials,
file,
edges: GraphEdges,
}
}
}
impl ForwardCandidates<Edge, Edge, GraphEdges, CancellationError> for GraphEdgeCandidates<'_> {
fn get_forward_candidates<R>(&mut self, path: &PartialPath, result: &mut R)
where
R: std::iter::Extend<Edge>,
{
result.extend(self.graph.outgoing_edges(path.end_node).filter(|e| {
self.file
.map_or(true, |file| self.graph[e.sink].is_in_file(file))
}));
}
fn get_joining_candidate_degree(&self, path: &PartialPath) -> Degree {
self.graph.incoming_edge_degree(path.end_node)
}
fn get_graph_partials_and_db(&mut self) -> (&StackGraph, &mut PartialPaths, &GraphEdges) {
(self.graph, self.partials, &self.edges)
}
}
/// A dummy type to act as the "database" for graph edges. Its [`ToAppendable`] implementation
/// is the identity on edges.
pub struct GraphEdges;
impl ToAppendable<Edge, Edge> for GraphEdges {
fn get_appendable<'a>(&'a self, edge: &'a Edge) -> &'a Edge {
edge
}
}
//-------------------------------------------------------------------------------------------------
// Databases
/// Contains a "database" of partial paths.
///
/// This type is meant to be a lazily loaded "view" into a proper storage layer. During the
/// path-stitching algorithm, we repeatedly try to extend a currently incomplete path with any
/// partial paths that are compatible with it. For large codebases, or projects with a large
/// number of dependencies, it can be prohibitive to load in _all_ of the partial paths up-front.
/// We've written the path-stitching algorithm so that you have a chance to only load in the
/// partial paths that are actually needed, placing them into a `Database` instance as they're
/// needed.
pub struct Database {
pub(crate) partial_paths: Arena<PartialPath>,
pub(crate) local_nodes: HandleSet<Node>,
symbol_stack_keys: ListArena<Handle<Symbol>>,
symbol_stack_key_cache: HashMap<SymbolStackCacheKey, SymbolStackKeyHandle>,
paths_by_start_node: SupplementalArena<Node, Vec<Handle<PartialPath>>>,
root_paths_by_precondition_prefix:
SupplementalArena<SymbolStackKeyCell, Vec<Handle<PartialPath>>>,
root_paths_by_precondition_with_variable:
SupplementalArena<SymbolStackKeyCell, Vec<Handle<PartialPath>>>,
root_paths_by_precondition_without_variable:
SupplementalArena<SymbolStackKeyCell, Vec<Handle<PartialPath>>>,
incoming_paths: SupplementalArena<Node, Degree>,
}
impl Database {
/// Creates a new, empty database.
pub fn new() -> Database {
Database {
partial_paths: Arena::new(),
local_nodes: HandleSet::new(),
symbol_stack_keys: List::new_arena(),
symbol_stack_key_cache: HashMap::new(),
paths_by_start_node: SupplementalArena::new(),
root_paths_by_precondition_prefix: SupplementalArena::new(),
root_paths_by_precondition_with_variable: SupplementalArena::new(),
root_paths_by_precondition_without_variable: SupplementalArena::new(),
incoming_paths: SupplementalArena::new(),
}
}
/// Clear the database. After this, all previous handles into the database are
/// invalid.
#[cfg_attr(not(feature = "storage"), allow(dead_code))]
pub(crate) fn clear(&mut self) {
self.partial_paths.clear();
self.local_nodes.clear();
self.symbol_stack_keys.clear();
self.symbol_stack_key_cache.clear();
self.paths_by_start_node.clear();
self.root_paths_by_precondition_prefix.clear();
self.root_paths_by_precondition_with_variable.clear();
self.root_paths_by_precondition_without_variable.clear();
self.incoming_paths.clear();
}
/// Adds a partial path to this database. We do not deduplicate partial paths in any way; it's
/// your responsibility to only add each partial path once.
pub fn add_partial_path(
&mut self,
graph: &StackGraph,
partials: &mut PartialPaths,
path: PartialPath,
) -> Handle<PartialPath> {
let start_node = path.start_node;
let end_node = path.end_node;
copious_debugging!(
" Add {} path to database {}",
if graph[start_node].is_root() {
"root"
} else {
"node"
},
path.display(graph, partials)
);
let symbol_stack_precondition = path.symbol_stack_precondition;
let handle = self.partial_paths.add(path);
// If the partial path starts at the root node, index it by its symbol stack precondition.
if graph[start_node].is_root() {
// The join node is root, so there's no need to use half-open symbol stacks here, as we
// do for [`PartialPath::concatenate`][].
let mut key = SymbolStackKey::from_partial_symbol_stack(
partials,
self,
symbol_stack_precondition,
);
if !key.is_empty() {
match symbol_stack_precondition.has_variable() {
true => self.root_paths_by_precondition_with_variable[key.back_handle()]
.push(handle),
false => self.root_paths_by_precondition_without_variable[key.back_handle()]
.push(handle),
}
}
while key.pop_back(self).is_some() && !key.is_empty() {
self.root_paths_by_precondition_prefix[key.back_handle()].push(handle);
}
} else {
// Otherwise index it by its source node.
self.paths_by_start_node[start_node].push(handle);
}
self.incoming_paths[end_node] += Degree::One;
handle
}
/// Find all partial paths in this database that start at the given path's end node.
/// If the end node is the root node, returns paths with a symbol stack precondition
/// that are compatible with the path's symbol stack post condition.
pub fn find_candidate_partial_paths<R>(
&mut self,
graph: &StackGraph,
partials: &mut PartialPaths,
path: &PartialPath,
result: &mut R,
) where
R: std::iter::Extend<Handle<PartialPath>>,
{
if graph[path.end_node].is_root() {
// The join node is root, so there's no need to use half-open symbol stacks here, as we
// do for [`PartialPath::concatenate`][].
self.find_candidate_partial_paths_from_root(
graph,
partials,
Some(path.symbol_stack_postcondition),
result,
);
} else {
self.find_candidate_partial_paths_from_node(graph, partials, path.end_node, result);
}
}
/// Find all partial paths in this database that start at the root node, and have a symbol
/// stack precondition that is compatible with a given symbol stack.
#[cfg_attr(not(feature = "copious-debugging"), allow(unused_variables))]
pub fn find_candidate_partial_paths_from_root<R>(
&mut self,
graph: &StackGraph,
partials: &mut PartialPaths,
symbol_stack: Option<PartialSymbolStack>,
result: &mut R,
) where
R: std::iter::Extend<Handle<PartialPath>>,
{
// If the path currently ends at the root node, then we need to look up partial paths whose
// symbol stack precondition is compatible with the path.
match symbol_stack {
Some(symbol_stack) => {
let mut key =
SymbolStackKey::from_partial_symbol_stack(partials, self, symbol_stack);
copious_debugging!(
" Search for symbol stack <{}>",
key.display(graph, self)
);
// paths that have exactly this symbol stack
if let Some(paths) = self
.root_paths_by_precondition_without_variable
.get(key.back_handle())
{
#[cfg(feature = "copious-debugging")]
{
for path in paths {
copious_debugging!(
" Found path with exact stack {}",
self[*path].display(graph, partials)
);
}
}
result.extend(paths.iter().copied());
}
// paths that have an extension of this symbol stack
if symbol_stack.has_variable() {
if let Some(paths) = self
.root_paths_by_precondition_prefix
.get(key.back_handle())
{
#[cfg(feature = "copious-debugging")]
{
for path in paths {
copious_debugging!(
" Found path with smaller stack {}",
self[*path].display(graph, partials)
);
}
}
result.extend(paths.iter().copied());
}
}
loop {
// paths that have a prefix of this symbol stack
if let Some(paths) = self
.root_paths_by_precondition_with_variable
.get(key.back_handle())
{
#[cfg(feature = "copious-debugging")]
{
for path in paths {
copious_debugging!(
" Found path with smaller stack {}",
self[*path].display(graph, partials)
);
}
}
result.extend(paths.iter().copied());
}
if key.pop_back(self).is_none() {
break;
}
}
}
None => {
copious_debugging!(" Search for all root paths");
for (_, paths) in self
.root_paths_by_precondition_with_variable
.iter()
.chain(self.root_paths_by_precondition_without_variable.iter())
{
#[cfg(feature = "copious-debugging")]
{
for path in paths {
copious_debugging!(
" Found path {}",
self[*path].display(graph, partials)
);
}
}
result.extend(paths.iter().copied());
}
}
}
}
/// Find all partial paths in the database that start at the given node. We don't filter the
/// results any further than that, since we have to check each partial path for compatibility
/// as we try to append it to the current incomplete path anyway, and non-root nodes will
/// typically have a small number of outgoing edges.
#[cfg_attr(not(feature = "copious-debugging"), allow(unused_variables))]
pub fn find_candidate_partial_paths_from_node<R>(
&self,
graph: &StackGraph,
partials: &mut PartialPaths,
start_node: Handle<Node>,
result: &mut R,
) where
R: std::iter::Extend<Handle<PartialPath>>,
{
copious_debugging!(" Search for start node {}", start_node.display(graph));
// Return all of the partial paths that start at the requested node.
if let Some(paths) = self.paths_by_start_node.get(start_node) {
#[cfg(feature = "copious-debugging")]
{
for path in paths {
copious_debugging!(
" Found path {}",
self[*path].display(graph, partials)
);
}
}
result.extend(paths.iter().copied());
}
}
/// Returns the number of paths in this database that share the given end node.
pub fn get_incoming_path_degree(&self, end_node: Handle<Node>) -> Degree {
self.incoming_paths[end_node]
}
/// Determines which nodes in the stack graph are “local”, taking into account the partial
/// paths in this database.
///
/// A local node has no partial path that connects it to the root node in either direction.
/// That means that it cannot participate in any paths that leave the file.
///
/// This method is meant to be used at index time, to calculate the set of nodes that are local
/// after having just calculated the set of partial paths for the file.
pub fn find_local_nodes(&mut self) {
// Assume that any node that is the start or end of a partial path is local to this file
// until we see a path connecting the root node to it (in either direction).
self.local_nodes.clear();
for handle in self.iter_partial_paths() {
self.local_nodes.add(self[handle].start_node);
self.local_nodes.add(self[handle].end_node);
}
// The root node and jump-to-scope node are the most obvious non-local nodes.
let mut nonlocal_start_nodes = HandleSet::new();
let mut nonlocal_end_nodes = HandleSet::new();
self.local_nodes.remove(StackGraph::root_node());
nonlocal_start_nodes.add(StackGraph::root_node());
nonlocal_end_nodes.add(StackGraph::root_node());
self.local_nodes.remove(StackGraph::jump_to_node());
nonlocal_start_nodes.add(StackGraph::jump_to_node());
nonlocal_end_nodes.add(StackGraph::jump_to_node());
// Other nodes are non-local if we see any partial path that connects it to another
// non-local node. Repeat until we reach a fixed point.
let mut keep_checking = true;
while keep_checking {
keep_checking = false;
for handle in self.iter_partial_paths() {
let start_node = self[handle].start_node;
let end_node = self[handle].end_node;
// First check forwards paths, where non-localness propagates from the start node
// of each path.
let start_node_is_nonlocal = nonlocal_start_nodes.contains(start_node);
let end_node_is_nonlocal = nonlocal_start_nodes.contains(end_node);
if start_node_is_nonlocal && !end_node_is_nonlocal {
keep_checking = true;
nonlocal_start_nodes.add(end_node);
self.local_nodes.remove(end_node);
}
// Then check reverse paths, where non-localness propagates from the end node of
// each path.
let start_node_is_nonlocal = nonlocal_end_nodes.contains(start_node);
let end_node_is_nonlocal = nonlocal_end_nodes.contains(end_node);
if !start_node_is_nonlocal && end_node_is_nonlocal {
keep_checking = true;
nonlocal_end_nodes.add(start_node);
self.local_nodes.remove(start_node);
}
}
}
}
/// Marks that a stack graph node is local.
///
/// This method is meant to be used at query time. You will have precalculated the set of
/// local nodes for a file at index time; at query time, you will load this information from
/// your storage layer and use this method to update our internal view of which nodes are
/// local.
pub fn mark_local_node(&mut self, node: Handle<Node>) {
self.local_nodes.add(node);
}
/// Returns whether a node is local according to the partial paths in this database. You must
/// have already called [`find_local_nodes`][] or [`mark_local_node`][], depending on whether
/// it is index time or query time.
pub fn node_is_local(&self, node: Handle<Node>) -> bool {
self.local_nodes.contains(node)
}
/// Returns an iterator over all of the handles of all of the partial paths in this database.
/// (Note that because we're only returning _handles_, this iterator does not retain a
/// reference to the `Database`.)
pub fn iter_partial_paths(&self) -> impl Iterator<Item = Handle<PartialPath>> {
self.partial_paths.iter_handles()
}
pub fn ensure_both_directions(&mut self, partials: &mut PartialPaths) {
for path in self.partial_paths.iter_handles() {
self.partial_paths
.get_mut(path)
.ensure_both_directions(partials);
}
}
pub fn ensure_forwards(&mut self, partials: &mut PartialPaths) {
for path in self.partial_paths.iter_handles() {
self.partial_paths.get_mut(path).ensure_forwards(partials);
}
}
}
impl std::ops::Index<Handle<PartialPath>> for Database {
type Output = PartialPath;
#[inline(always)]
fn index(&self, handle: Handle<PartialPath>) -> &PartialPath {
self.partial_paths.get(handle)
}
}
impl ToAppendable<Handle<PartialPath>, PartialPath> for Database {
fn get_appendable<'a>(&'a self, handle: &'a Handle<PartialPath>) -> &'a PartialPath {
&self[*handle]
}
}
pub struct DatabaseCandidates<'a> {
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
database: &'a mut Database,
}
impl<'a> DatabaseCandidates<'a> {
pub fn new(
graph: &'a StackGraph,
partials: &'a mut PartialPaths,
database: &'a mut Database,
) -> Self {
Self {
graph,
partials,
database,
}
}
}
impl ForwardCandidates<Handle<PartialPath>, PartialPath, Database, CancellationError>
for DatabaseCandidates<'_>
{
fn get_forward_candidates<R>(&mut self, path: &PartialPath, result: &mut R)
where
R: std::iter::Extend<Handle<PartialPath>>,
{
self.database
.find_candidate_partial_paths(self.graph, self.partials, path, result);
}
fn get_joining_candidate_degree(&self, path: &PartialPath) -> Degree {
self.database.get_incoming_path_degree(path.end_node)
}
fn get_graph_partials_and_db(&mut self) -> (&StackGraph, &mut PartialPaths, &Database) {
(self.graph, self.partials, self.database)
}
}
/// The key type that we use to find partial paths that start from the root node and have a
/// particular symbol stack as their precondition.
#[derive(Clone, Copy)]
pub struct SymbolStackKey {
// Note: the symbols are stored in reverse order, with the "front" of the List being the "back"
// of the symbol stack. That lets us easily get a handle to the back of the symbol stack, and
// also lets us easily pops items off the back of key, which we need to do to search for all
// prefixes of a particular symbol stack down in `find_candidate_partial_paths_from_root`.
symbols: List<Handle<Symbol>>,
}
#[derive(Clone, Eq, Hash, PartialEq)]
struct SymbolStackCacheKey {
head: Handle<Symbol>,
tail: SymbolStackKeyHandle,
}
type SymbolStackKeyCell = ListCell<Handle<Symbol>>;
type SymbolStackKeyHandle = Handle<SymbolStackKeyCell>;
impl SymbolStackKey {
/// Returns an empty symbol stack key.
fn empty() -> SymbolStackKey {
SymbolStackKey {
symbols: List::empty(),
}
}
fn is_empty(&self) -> bool {
self.symbols.is_empty()
}
/// Pushes a new symbol onto the back of this symbol stack key.
fn push_back(&mut self, db: &mut Database, symbol: Handle<Symbol>) {
let cache_key = SymbolStackCacheKey {
head: symbol,
tail: self.back_handle(),
};
if let Some(handle) = db.symbol_stack_key_cache.get(&cache_key) {
self.symbols = List::from_handle(*handle);
return;
}
// push_front because we store the key's symbols in reverse order.
self.symbols.push_front(&mut db.symbol_stack_keys, symbol);
let handle = self.back_handle();
db.symbol_stack_key_cache.insert(cache_key, handle);
}
/// Pops a symbol from the back of this symbol stack key.
fn pop_back(&mut self, db: &Database) -> Option<Handle<Symbol>> {
// pop_front because we store the key's symbols in reverse order.
self.symbols.pop_front(&db.symbol_stack_keys).copied()
}
/// Extracts a new symbol stack key from a partial symbol stack.
pub fn from_partial_symbol_stack(
partials: &mut PartialPaths,
db: &mut Database,
mut stack: PartialSymbolStack,
) -> SymbolStackKey {
let mut result = SymbolStackKey::empty();
while let Some(symbol) = stack.pop_front(partials) {
result.push_back(db, symbol.symbol);
}
result
}
/// Returns a handle to the back of the symbol stack key.
fn back_handle(self) -> SymbolStackKeyHandle {
// Because the symbols are stored in reverse order, the handle to the "front" of the list
// is a handle to the "back" of the key.
self.symbols.handle()
}
#[cfg(feature = "copious-debugging")]
fn display<'a>(self, graph: &'a StackGraph, db: &'a Database) -> impl Display + 'a {
DisplaySymbolStackKey(self, graph, db)
}
}
#[cfg(feature = "copious-debugging")]
struct DisplaySymbolStackKey<'a>(SymbolStackKey, &'a StackGraph, &'a Database);
#[cfg(feature = "copious-debugging")]
impl<'a> Display for DisplaySymbolStackKey<'a> {
fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
// Use a recursive function to print the contents of the key out in reverse order.
fn display_one(
mut key: SymbolStackKey,
graph: &StackGraph,
db: &Database,
f: &mut std::fmt::Formatter,
) -> std::fmt::Result {
let last = match key.pop_back(db) {
Some(last) => last,
None => return Ok(()),
};
display_one(key, graph, db, f)?;
last.display(graph).fmt(f)
}
display_one(self.0, self.1, self.2, f)
}
}
//-------------------------------------------------------------------------------------------------
// Stitching partial paths together
/// Implements a phased forward partial path stitching algorithm.
///
/// Our overall goal is to start with a set of _seed_ partial paths, and to repeatedly extend each
/// partial path by concatenating another, compatible partial path onto the end of it. (If there
/// are multiple compatible partial paths, we concatenate each of them separately, resulting in
/// more than one extension for the current path.)
///
/// We perform this processing in _phases_. At the start of each phase, we have a _current set_ of
/// partial paths that need to be processed. As we extend those partial paths, we add the
/// extensions to the set of partial paths to process in the _next_ phase. Phases are processed
/// one at a time, each time you invoke the [`process_next_phase`][] method.
///
/// [`process_next_phase`]: #method.process_next_phase
///
/// After each phase has completed, you can use the [`previous_phase_partial_paths`][] method to
/// retrieve all of the partial paths that were discovered during that phase. That gives you a
/// chance to add to the `Database` all of the other partial paths that we might need to extend
/// those partial paths with before invoking the next phase.
///
/// [`previous_phase_partial_paths`]: #method.previous_phase_partial_paths
///
/// If you don't care about this phasing nonsense, you can instead preload your `Database` with all
/// possible partial paths, and run the forward partial path stitching algorithm all the way to
/// completion, using the [`find_all_complete_partial_paths`][] method.
///
/// [`find_all_complete_partial_paths`]: #method.find_all_complete_partial_paths
pub struct ForwardPartialPathStitcher<H> {
candidates: Vec<H>,
extensions: Vec<(PartialPath, AppendingCycleDetector<H>)>,
queue: VecDeque<(PartialPath, AppendingCycleDetector<H>, bool)>,
// tracks the number of initial paths in the queue because we do not want call
// extend_until on those
initial_paths_in_queue: usize,
// next_iteration is a tuple of queues instead of an queue of tuples so that the path queue
// can be cheaply exposed through the C API as a continuous memory block
next_iteration: (
VecDeque<PartialPath>,
VecDeque<AppendingCycleDetector<H>>,
VecDeque<bool>,
),
appended_paths: Appendables<H>,
similar_path_detector: Option<SimilarPathDetector<PartialPath>>,
check_only_join_nodes: bool,
max_work_per_phase: usize,
initial_paths: usize,
stats: Option<Stats>,
#[cfg(feature = "copious-debugging")]
phase_number: usize,
}
impl<H> ForwardPartialPathStitcher<H> {
/// Creates a new forward partial path stitcher that is "seeded" with a set of initial partial
/// paths. If the sticher is used to find complete paths, it is the responsibility of the caller
/// to ensure precondition variables are eliminated by calling [`PartialPath::eliminate_precondition_stack_variables`][].
pub fn from_partial_paths<I>(
_graph: &StackGraph,
_partials: &mut PartialPaths,
initial_partial_paths: I,
) -> Self
where
I: IntoIterator<Item = PartialPath>,
{
let mut appended_paths = Appendables::new();
let next_iteration: (VecDeque<_>, VecDeque<_>, VecDeque<_>) = initial_partial_paths
.into_iter()
.map(|p| {
let c = AppendingCycleDetector::from(&mut appended_paths, p.clone().into());
(p, c, false)
})
.multiunzip();
let initial_paths = next_iteration.0.len();
Self {
candidates: Vec::new(),
extensions: Vec::new(),
queue: VecDeque::new(),
initial_paths_in_queue: initial_paths,
next_iteration,
appended_paths,
// By default, all paths are checked for similarity
similar_path_detector: Some(SimilarPathDetector::new()),
// By default, all nodes are checked for cycles and (if enabled) similarity
check_only_join_nodes: false,
// By default, there's no artificial bound on the amount of work done per phase
max_work_per_phase: usize::MAX,
initial_paths,
stats: None,
#[cfg(feature = "copious-debugging")]
phase_number: 1,
}
}
/// Sets whether similar path detection should be enabled during path stitching. Paths are similar
/// if start and end node, and pre- and postconditions are the same. The presence of similar paths
/// can lead to exponential blow up during path stitching. Similar path detection is enabled by
/// default.
pub fn set_similar_path_detection(&mut self, detect_similar_paths: bool) {
if !detect_similar_paths {
self.similar_path_detector = None;
} else if self.similar_path_detector.is_none() {
let mut similar_path_detector = SimilarPathDetector::new();
similar_path_detector.set_collect_stats(self.stats.is_some());
self.similar_path_detector = Some(similar_path_detector);
}
}
/// Sets whether all nodes are checked for cycles and (if enabled) similar paths, or only nodes with multiple
/// incoming candidates. Checking only join nodes is **unsafe** unless the database of candidates is stable
/// between all stitching phases. If paths are added to the database from one phase to another, for example if
/// paths are dynamically loaded from storage, setting this to true is incorrect and might lead to non-termination!
pub fn set_check_only_join_nodes(&mut self, check_only_join_nodes: bool) {
self.check_only_join_nodes = check_only_join_nodes;
}
/// Sets the maximum amount of work that can be performed during each phase of the algorithm.
/// By bounding our work this way, you can ensure that it's not possible for our CPU-bound
/// algorithm to starve any worker threads or processes that you might be using. If you don't
/// call this method, then we allow ourselves to process all of the extensions of all of the
/// paths found in the previous phase, with no additional bound.
pub fn set_max_work_per_phase(&mut self, max_work_per_phase: usize) {
self.max_work_per_phase = max_work_per_phase;
}
/// Sets whether to collect statistics during stitching.
pub fn set_collect_stats(&mut self, collect_stats: bool) {
if !collect_stats {
self.stats = None;
} else if self.stats.is_none() {
let mut stats = Stats::default();
stats.initial_paths.record(self.initial_paths);
self.stats = Some(stats);
}
if let Some(similar_path_detector) = &mut self.similar_path_detector {
similar_path_detector.set_collect_stats(collect_stats);
}
}
pub fn into_stats(mut self) -> Stats {
if let (Some(stats), Some(similar_path_detector)) =
(&mut self.stats, self.similar_path_detector)
{
stats.similar_paths_stats = similar_path_detector.stats();
}
self.stats.unwrap_or_default()
}
}
impl<H: Clone> ForwardPartialPathStitcher<H> {
/// Returns an iterator of all of the (possibly incomplete) partial paths that were encountered
/// during the most recent phase of the algorithm.
pub fn previous_phase_partial_paths(&self) -> impl Iterator<Item = &PartialPath> + '_ {
self.next_iteration.0.iter()
}
/// Returns a slice of all of the (possibly incomplete) partial paths that were encountered
/// during the most recent phase of the algorithm.
pub fn previous_phase_partial_paths_slice(&mut self) -> &[PartialPath] {
self.next_iteration.0.make_contiguous();
self.next_iteration.0.as_slices().0
}
/// Returns a mutable slice of all of the (possibly incomplete) partial paths that were
/// encountered during the most recent phase of the algorithm.
pub fn previous_phase_partial_paths_slice_mut(&mut self) -> &mut [PartialPath] {
self.next_iteration.0.make_contiguous();
self.next_iteration.0.as_mut_slices().0
}
/// Attempts to extend one partial path as part of the algorithm. When calling this function,
/// you are responsible for ensuring that `db` already contains all of the possible appendables
/// that we might want to extend `partial_path` with.
fn extend<A, Db, C, Err>(
&mut self,
candidates: &mut C,
partial_path: &PartialPath,
cycle_detector: AppendingCycleDetector<H>,
has_split: bool,
) -> usize
where
A: Appendable,
Db: ToAppendable<H, A>,
C: ForwardCandidates<H, A, Db, Err>,
{
let check_cycle = !self.check_only_join_nodes
|| partial_path.start_node == partial_path.end_node
|| candidates.get_joining_candidate_degree(partial_path) == Degree::Multiple;
let (graph, partials, db) = candidates.get_graph_partials_and_db();
copious_debugging!(" Extend {}", partial_path.display(graph, partials));
if check_cycle {
// Check is path is cyclic, in which case we do not extend it. We only do this if the start and end nodes are the same,
// or the current end node has multiple incoming edges. If neither of these hold, the path cannot end in a cycle.
let has_precondition_variables = partial_path.symbol_stack_precondition.has_variable()
|| partial_path.scope_stack_precondition.has_variable();
let cycles = cycle_detector
.is_cyclic(graph, partials, db, &mut self.appended_paths)
.expect("cyclic test failed when stitching partial paths");
let cyclic = match has_precondition_variables {
// If the precondition has no variables, we allow cycles that strengthen the
// precondition, because we know they cannot strengthen the precondition of
// the overall path.