rust-analyzer/crates/hir_ty/src/traits.rs
Florian Diebold 1250ddc5cf Rework obligation handling
We can't do the easy hack that we did before anymore, where we kept
track of whether any inference variables changed since the last time we
rechecked obligations. Instead, we store the obligations in
canonicalized form; that way we can easily check the inference variables
to see whether they have changed since the goal was canonicalized.
2021-05-21 17:48:34 +02:00

191 lines
5.9 KiB
Rust

//! Trait solving using Chalk.
use std::env::var;
use chalk_ir::GoalData;
use chalk_solve::{logging_db::LoggingRustIrDatabase, Solver};
use base_db::CrateId;
use hir_def::{lang_item::LangItemTarget, TraitId};
use stdx::panic_context;
use crate::{
db::HirDatabase, AliasEq, AliasTy, Canonical, DomainGoal, Goal, Guidance, InEnvironment,
Interner, Solution, TraitRefExt, Ty, TyKind, WhereClause,
};
/// This controls how much 'time' we give the Chalk solver before giving up.
const CHALK_SOLVER_FUEL: i32 = 100;
#[derive(Debug, Copy, Clone)]
pub(crate) struct ChalkContext<'a> {
pub(crate) db: &'a dyn HirDatabase,
pub(crate) krate: CrateId,
}
fn create_chalk_solver() -> chalk_recursive::RecursiveSolver<Interner> {
let overflow_depth =
var("CHALK_OVERFLOW_DEPTH").ok().and_then(|s| s.parse().ok()).unwrap_or(100);
let caching_enabled = true;
let max_size = var("CHALK_SOLVER_MAX_SIZE").ok().and_then(|s| s.parse().ok()).unwrap_or(30);
chalk_recursive::RecursiveSolver::new(overflow_depth, max_size, caching_enabled)
}
/// A set of clauses that we assume to be true. E.g. if we are inside this function:
/// ```rust
/// fn foo<T: Default>(t: T) {}
/// ```
/// we assume that `T: Default`.
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
pub struct TraitEnvironment {
pub krate: CrateId,
// When we're using Chalk's Ty we can make this a BTreeMap since it's Ord,
// but for now it's too annoying...
pub(crate) traits_from_clauses: Vec<(Ty, TraitId)>,
pub env: chalk_ir::Environment<Interner>,
}
impl TraitEnvironment {
pub fn empty(krate: CrateId) -> Self {
TraitEnvironment {
krate,
traits_from_clauses: Vec::new(),
env: chalk_ir::Environment::new(&Interner),
}
}
pub(crate) fn traits_in_scope_from_clauses<'a>(
&'a self,
ty: &'a Ty,
) -> impl Iterator<Item = TraitId> + 'a {
self.traits_from_clauses.iter().filter_map(move |(self_ty, trait_id)| {
if self_ty == ty {
Some(*trait_id)
} else {
None
}
})
}
}
/// Solve a trait goal using Chalk.
pub(crate) fn trait_solve_query(
db: &dyn HirDatabase,
krate: CrateId,
goal: Canonical<InEnvironment<Goal>>,
) -> Option<Solution> {
let _p = profile::span("trait_solve_query").detail(|| match &goal.value.goal.data(&Interner) {
GoalData::DomainGoal(DomainGoal::Holds(WhereClause::Implemented(it))) => {
db.trait_data(it.hir_trait_id()).name.to_string()
}
GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(_))) => "alias_eq".to_string(),
_ => "??".to_string(),
});
log::info!("trait_solve_query({:?})", goal.value.goal);
if let GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(AliasEq {
alias: AliasTy::Projection(projection_ty),
..
}))) = &goal.value.goal.data(&Interner)
{
if let TyKind::BoundVar(_) = projection_ty.self_type_parameter(&Interner).kind(&Interner) {
// Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
return Some(Solution::Ambig(Guidance::Unknown));
}
}
// We currently don't deal with universes (I think / hope they're not yet
// relevant for our use cases?)
let u_canonical = chalk_ir::UCanonical { canonical: goal, universes: 1 };
solve(db, krate, &u_canonical)
}
fn solve(
db: &dyn HirDatabase,
krate: CrateId,
goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
) -> Option<chalk_solve::Solution<Interner>> {
let context = ChalkContext { db, krate };
log::debug!("solve goal: {:?}", goal);
let mut solver = create_chalk_solver();
let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
let should_continue = || {
context.db.check_canceled();
let remaining = fuel.get();
fuel.set(remaining - 1);
if remaining == 0 {
log::debug!("fuel exhausted");
}
remaining > 0
};
let mut solve = || {
let _ctx = if is_chalk_debug() || is_chalk_print() {
Some(panic_context::enter(format!("solving {:?}", goal)))
} else {
None
};
let solution = if is_chalk_print() {
let logging_db =
LoggingRustIrDatabaseLoggingOnDrop(LoggingRustIrDatabase::new(context));
let solution = solver.solve_limited(&logging_db.0, goal, &should_continue);
solution
} else {
solver.solve_limited(&context, goal, &should_continue)
};
log::debug!("solve({:?}) => {:?}", goal, solution);
solution
};
// don't set the TLS for Chalk unless Chalk debugging is active, to make
// extra sure we only use it for debugging
let solution =
if is_chalk_debug() { crate::tls::set_current_program(db, solve) } else { solve() };
solution
}
struct LoggingRustIrDatabaseLoggingOnDrop<'a>(LoggingRustIrDatabase<Interner, ChalkContext<'a>>);
impl<'a> Drop for LoggingRustIrDatabaseLoggingOnDrop<'a> {
fn drop(&mut self) {
eprintln!("chalk program:\n{}", self.0);
}
}
fn is_chalk_debug() -> bool {
std::env::var("CHALK_DEBUG").is_ok()
}
fn is_chalk_print() -> bool {
std::env::var("CHALK_PRINT").is_ok()
}
#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
pub enum FnTrait {
FnOnce,
FnMut,
Fn,
}
impl FnTrait {
fn lang_item_name(self) -> &'static str {
match self {
FnTrait::FnOnce => "fn_once",
FnTrait::FnMut => "fn_mut",
FnTrait::Fn => "fn",
}
}
pub fn get_id(&self, db: &dyn HirDatabase, krate: CrateId) -> Option<TraitId> {
let target = db.lang_item(krate, self.lang_item_name().into())?;
match target {
LangItemTarget::TraitId(t) => Some(t),
_ => None,
}
}
}