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use indexmap::IndexMap;
use petgraph::prelude::*;
use rustc_hash::FxHashMap;
use crate::solve::Solver;
use crate::RustIrDatabase;
use chalk_ir::interner::Interner;
use chalk_ir::{self, ImplId, TraitId};
use std::fmt;
use std::sync::Arc;
pub mod orphan;
mod solve;
pub struct CoherenceSolver<'a, I: Interner> {
db: &'a dyn RustIrDatabase<I>,
solver_builder: &'a dyn Fn() -> Box<dyn Solver<I>>,
trait_id: TraitId<I>,
}
#[derive(Debug)]
pub enum CoherenceError<I: Interner> {
OverlappingImpls(TraitId<I>),
FailedOrphanCheck(TraitId<I>),
}
impl<I: Interner> fmt::Display for CoherenceError<I> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
match self {
CoherenceError::OverlappingImpls(id) => {
write!(f, "overlapping impls of trait `{:?}`", id)
}
CoherenceError::FailedOrphanCheck(id) => {
write!(f, "impl for trait `{:?}` violates the orphan rules", id)
}
}
}
}
impl<I: Interner> std::error::Error for CoherenceError<I> {}
/// Stores the specialization priorities for a set of impls.
/// This basically encodes which impls specialize one another.
#[derive(Clone, Debug, Default, PartialEq, Eq)]
pub struct SpecializationPriorities<I: Interner> {
map: IndexMap<ImplId<I>, SpecializationPriority>,
}
impl<I: Interner> SpecializationPriorities<I> {
pub fn new() -> Self {
Self {
map: IndexMap::new(),
}
}
/// Lookup the priority of an impl in the set (panics if impl is not in set).
pub fn priority(&self, impl_id: ImplId<I>) -> SpecializationPriority {
self.map[&impl_id]
}
/// Store the priority of an impl (used during construction).
/// Panics if we have already stored the priority for this impl.
fn insert(&mut self, impl_id: ImplId<I>, p: SpecializationPriority) {
let old_value = self.map.insert(impl_id, p);
assert!(old_value.is_none());
}
}
/// Impls with higher priority take precedence over impls with lower
/// priority (if both apply to the same types). Impls with equal
/// priority should never apply to the same set of input types.
#[derive(Copy, Clone, Default, PartialOrd, Ord, PartialEq, Eq, Debug)]
pub struct SpecializationPriority(usize);
impl<'a, I> CoherenceSolver<'a, I>
where
I: Interner,
{
/// Constructs a new `CoherenceSolver`.
pub fn new(
db: &'a dyn RustIrDatabase<I>,
solver_builder: &'a dyn Fn() -> Box<dyn Solver<I>>,
trait_id: TraitId<I>,
) -> Self {
Self {
db,
solver_builder,
trait_id,
}
}
pub fn specialization_priorities(
&self,
) -> Result<Arc<SpecializationPriorities<I>>, CoherenceError<I>> {
let mut result = SpecializationPriorities::<I>::new();
let forest = self.build_specialization_forest()?;
// Visit every root in the forest & set specialization
// priority for the tree that is the root of.
for root_idx in forest.externals(Direction::Incoming) {
self.set_priorities(root_idx, &forest, 0, &mut result);
}
Ok(Arc::new(result))
}
// Build the forest of specialization relationships.
fn build_specialization_forest(&self) -> Result<Graph<ImplId<I>, ()>, CoherenceError<I>> {
let mut forest = DiGraph::new();
let mut node_map = FxHashMap::default();
// Find all specializations. Record them in the forest
// by adding an edge from the less special to the more special.
self.visit_specializations_of_trait(|less_special, more_special| {
let less_special_node = *node_map
.entry(less_special)
.or_insert_with(|| forest.add_node(less_special));
let more_special_node = *node_map
.entry(more_special)
.or_insert_with(|| forest.add_node(more_special));
forest.update_edge(less_special_node, more_special_node, ());
})?;
Ok(forest)
}
// Recursively set priorities for those node and all of its children.
fn set_priorities(
&self,
idx: NodeIndex,
forest: &Graph<ImplId<I>, ()>,
p: usize,
map: &mut SpecializationPriorities<I>,
) {
// Get the impl datum recorded at this node and reset its priority
{
let impl_id = forest
.node_weight(idx)
.expect("index should be a valid index into graph");
map.insert(*impl_id, SpecializationPriority(p));
}
// Visit all children of this node, setting their priority to this + 1
for child_idx in forest.neighbors(idx) {
self.set_priorities(child_idx, forest, p + 1, map);
}
}
}
|
