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//! Trait solving using Chalk.
use std::env::var;
use base_db::CrateId;
use chalk_ir::cast::Cast;
use chalk_solve::{logging_db::LoggingRustIrDatabase, Solver};
use hir_def::{lang_item::LangItemTarget, TraitId};
use stdx::panic_context;
use crate::{
db::HirDatabase, AliasEq, AliasTy, Canonical, DomainGoal, Guidance, HirDisplay, InEnvironment,
Solution, Ty, TyKind, WhereClause,
};
use self::chalk::{from_chalk, Interner, ToChalk};
pub(crate) mod chalk;
/// This controls how much 'time' we give the Chalk solver before giving up.
const CHALK_SOLVER_FUEL: i32 = 100;
#[derive(Debug, Copy, Clone)]
struct ChalkContext<'a> {
db: &'a dyn HirDatabase,
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 {
// 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(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
}
})
}
}
impl Default for TraitEnvironment {
fn default() -> Self {
TraitEnvironment {
traits_from_clauses: Vec::new(),
env: chalk_ir::Environment::new(&Interner),
}
}
}
/// Solve a trait goal using Chalk.
pub(crate) fn trait_solve_query(
db: &dyn HirDatabase,
krate: CrateId,
goal: Canonical<InEnvironment<DomainGoal>>,
) -> Option<Solution> {
let _p = profile::span("trait_solve_query").detail(|| match &goal.value.goal {
DomainGoal::Holds(WhereClause::Implemented(it)) => {
db.trait_data(it.hir_trait_id()).name.to_string()
}
DomainGoal::Holds(WhereClause::AliasEq(_)) => "alias_eq".to_string(),
});
log::info!("trait_solve_query({})", goal.value.goal.display(db));
if let DomainGoal::Holds(WhereClause::AliasEq(AliasEq {
alias: AliasTy::Projection(projection_ty),
..
})) = &goal.value.goal
{
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));
}
}
let canonical = goal.to_chalk(db).cast(&Interner);
// 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, universes: 1 };
let solution = solve(db, krate, &u_canonical);
solution.map(|solution| solution_from_chalk(db, solution))
}
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() { chalk::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()
}
fn solution_from_chalk(
db: &dyn HirDatabase,
solution: chalk_solve::Solution<Interner>,
) -> Solution {
match solution {
chalk_solve::Solution::Unique(constr_subst) => {
Solution::Unique(from_chalk(db, constr_subst))
}
chalk_solve::Solution::Ambig(chalk_solve::Guidance::Definite(subst)) => {
Solution::Ambig(Guidance::Definite(from_chalk(db, subst)))
}
chalk_solve::Solution::Ambig(chalk_solve::Guidance::Suggested(subst)) => {
Solution::Ambig(Guidance::Suggested(from_chalk(db, subst)))
}
chalk_solve::Solution::Ambig(chalk_solve::Guidance::Unknown) => {
Solution::Ambig(Guidance::Unknown)
}
}
}
#[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,
}
}
}
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