crates/hir-ty/src/traits.rs

   1 //! Trait solving using Chalk.
   2
   3 use std::{env::var, sync::Arc};
   4
   5 use chalk_ir::GoalData;
   6 use chalk_recursive::Cache;
   7 use chalk_solve::{logging_db::LoggingRustIrDatabase, Solver};
   8
   9 use base_db::CrateId;
  10 use hir_def::{lang_item::LangItemTarget, TraitId};
  11 use stdx::panic_context;
  12 use syntax::SmolStr;
  13
  14 use crate::{
  15     db::HirDatabase, infer::unify::InferenceTable, AliasEq, AliasTy, Canonical, DomainGoal, Goal,
  16     Guidance, InEnvironment, Interner, ProjectionTy, Solution, TraitRefExt, Ty, TyKind,
  17     WhereClause,
  18 };
  19
  20 /// This controls how much 'time' we give the Chalk solver before giving up.
  21 const CHALK_SOLVER_FUEL: i32 = 100;
  22
  23 #[derive(Debug, Copy, Clone)]
  24 pub(crate) struct ChalkContext<'a> {
  25     pub(crate) db: &'a dyn HirDatabase,
  26     pub(crate) krate: CrateId,
  27 }
  28
  29 fn create_chalk_solver() -> chalk_recursive::RecursiveSolver<Interner> {
  30     let overflow_depth =
  31         var("CHALK_OVERFLOW_DEPTH").ok().and_then(|s| s.parse().ok()).unwrap_or(500);
  32     let max_size = var("CHALK_SOLVER_MAX_SIZE").ok().and_then(|s| s.parse().ok()).unwrap_or(150);
  33     chalk_recursive::RecursiveSolver::new(overflow_depth, max_size, Some(Cache::new()))
  34 }
  35
  36 /// A set of clauses that we assume to be true. E.g. if we are inside this function:
  37 /// ```rust
  38 /// fn foo<T: Default>(t: T) {}
  39 /// ```
  40 /// we assume that `T: Default`.
  41 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
  42 pub struct TraitEnvironment {
  43     pub krate: CrateId,
  44     // FIXME make this a BTreeMap
  45     pub(crate) traits_from_clauses: Vec<(Ty, TraitId)>,
  46     pub env: chalk_ir::Environment<Interner>,
  47 }
  48
  49 impl TraitEnvironment {
  50     pub fn empty(krate: CrateId) -> Self {
  51         TraitEnvironment {
  52             krate,
  53             traits_from_clauses: Vec::new(),
  54             env: chalk_ir::Environment::new(Interner),
  55         }
  56     }
  57
  58     pub fn traits_in_scope_from_clauses<'a>(
  59         &'a self,
  60         ty: Ty,
  61     ) -> impl Iterator<Item = TraitId> + 'a {
  62         self.traits_from_clauses
  63             .iter()
  64             .filter_map(move |(self_ty, trait_id)| (*self_ty == ty).then(|| *trait_id))
  65     }
  66 }
  67
  68 pub(crate) fn normalize_projection_query(
  69     db: &dyn HirDatabase,
  70     projection: ProjectionTy,
  71     env: Arc<TraitEnvironment>,
  72 ) -> Option<Ty> {
  73     let mut table = InferenceTable::new(db, env.clone());
  74     let ty = table.normalize_projection_ty(projection);
  75     Some(table.resolve_completely(ty))
  76 }
  77
  78 /// Solve a trait goal using Chalk.
  79 pub(crate) fn trait_solve_query(
  80     db: &dyn HirDatabase,
  81     krate: CrateId,
  82     goal: Canonical<InEnvironment<Goal>>,
  83 ) -> Option<Solution> {
  84     let _p = profile::span("trait_solve_query").detail(|| match &goal.value.goal.data(Interner) {
  85         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::Implemented(it))) => {
  86             db.trait_data(it.hir_trait_id()).name.to_string()
  87         }
  88         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(_))) => "alias_eq".to_string(),
  89         _ => "??".to_string(),
  90     });
  91     tracing::info!("trait_solve_query({:?})", goal.value.goal);
  92
  93     if let GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(AliasEq {
  94         alias: AliasTy::Projection(projection_ty),
  95         ..
  96     }))) = &goal.value.goal.data(Interner)
  97     {
  98         if let TyKind::BoundVar(_) = projection_ty.self_type_parameter(Interner).kind(Interner) {
  99             // Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
 100             return Some(Solution::Ambig(Guidance::Unknown));
 101         }
 102     }
 103
 104     // We currently don't deal with universes (I think / hope they're not yet
 105     // relevant for our use cases?)
 106     let u_canonical = chalk_ir::UCanonical { canonical: goal, universes: 1 };
 107     solve(db, krate, &u_canonical)
 108 }
 109
 110 fn solve(
 111     db: &dyn HirDatabase,
 112     krate: CrateId,
 113     goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
 114 ) -> Option<chalk_solve::Solution<Interner>> {
 115     let context = ChalkContext { db, krate };
 116     tracing::debug!("solve goal: {:?}", goal);
 117     let mut solver = create_chalk_solver();
 118
 119     let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
 120
 121     let should_continue = || {
 122         db.unwind_if_cancelled();
 123         let remaining = fuel.get();
 124         fuel.set(remaining - 1);
 125         if remaining == 0 {
 126             tracing::debug!("fuel exhausted");
 127         }
 128         remaining > 0
 129     };
 130
 131     let mut solve = || {
 132         let _ctx = if is_chalk_debug() || is_chalk_print() {
 133             Some(panic_context::enter(format!("solving {:?}", goal)))
 134         } else {
 135             None
 136         };
 137         let solution = if is_chalk_print() {
 138             let logging_db =
 139                 LoggingRustIrDatabaseLoggingOnDrop(LoggingRustIrDatabase::new(context));
 140             solver.solve_limited(&logging_db.0, goal, &should_continue)
 141         } else {
 142             solver.solve_limited(&context, goal, &should_continue)
 143         };
 144
 145         tracing::debug!("solve({:?}) => {:?}", goal, solution);
 146
 147         solution
 148     };
 149
 150     // don't set the TLS for Chalk unless Chalk debugging is active, to make
 151     // extra sure we only use it for debugging
 152     if is_chalk_debug() {
 153         crate::tls::set_current_program(db, solve)
 154     } else {
 155         solve()
 156     }
 157 }
 158
 159 struct LoggingRustIrDatabaseLoggingOnDrop<'a>(LoggingRustIrDatabase<Interner, ChalkContext<'a>>);
 160
 161 impl<'a> Drop for LoggingRustIrDatabaseLoggingOnDrop<'a> {
 162     fn drop(&mut self) {
 163         eprintln!("chalk program:\n{}", self.0);
 164     }
 165 }
 166
 167 fn is_chalk_debug() -> bool {
 168     std::env::var("CHALK_DEBUG").is_ok()
 169 }
 170
 171 fn is_chalk_print() -> bool {
 172     std::env::var("CHALK_PRINT").is_ok()
 173 }
 174
 175 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 176 pub enum FnTrait {
 177     FnOnce,
 178     FnMut,
 179     Fn,
 180 }
 181
 182 impl FnTrait {
 183     const fn lang_item_name(self) -> &'static str {
 184         match self {
 185             FnTrait::FnOnce => "fn_once",
 186             FnTrait::FnMut => "fn_mut",
 187             FnTrait::Fn => "fn",
 188         }
 189     }
 190
 191     pub fn get_id(&self, db: &dyn HirDatabase, krate: CrateId) -> Option<TraitId> {
 192         let target = db.lang_item(krate, SmolStr::new_inline(self.lang_item_name()))?;
 193         match target {
 194             LangItemTarget::TraitId(t) => Some(t),
 195             _ => None,
 196         }
 197     }
 198 }