crates/hir_ty/src/traits.rs

   1 //! Trait solving using Chalk.
   2
   3 use std::env::var;
   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, AliasEq, AliasTy, Canonical, DomainGoal, Goal, Guidance, InEnvironment,
  16     Interner, Solution, TraitRefExt, Ty, TyKind, WhereClause,
  17 };
  18
  19 /// This controls how much 'time' we give the Chalk solver before giving up.
  20 const CHALK_SOLVER_FUEL: i32 = 100;
  21
  22 #[derive(Debug, Copy, Clone)]
  23 pub(crate) struct ChalkContext<'a> {
  24     pub(crate) db: &'a dyn HirDatabase,
  25     pub(crate) krate: CrateId,
  26 }
  27
  28 fn create_chalk_solver() -> chalk_recursive::RecursiveSolver<Interner> {
  29     let overflow_depth =
  30         var("CHALK_OVERFLOW_DEPTH").ok().and_then(|s| s.parse().ok()).unwrap_or(300);
  31     let max_size = var("CHALK_SOLVER_MAX_SIZE").ok().and_then(|s| s.parse().ok()).unwrap_or(150);
  32     chalk_recursive::RecursiveSolver::new(overflow_depth, max_size, Some(Cache::new()))
  33 }
  34
  35 /// A set of clauses that we assume to be true. E.g. if we are inside this function:
  36 /// ```rust
  37 /// fn foo<T: Default>(t: T) {}
  38 /// ```
  39 /// we assume that `T: Default`.
  40 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
  41 pub struct TraitEnvironment {
  42     pub krate: CrateId,
  43     // When we're using Chalk's Ty we can make this a BTreeMap since it's Ord,
  44     // but for now it's too annoying...
  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 /// Solve a trait goal using Chalk.
  69 pub(crate) fn trait_solve_query(
  70     db: &dyn HirDatabase,
  71     krate: CrateId,
  72     goal: Canonical<InEnvironment<Goal>>,
  73 ) -> Option<Solution> {
  74     let _p = profile::span("trait_solve_query").detail(|| match &goal.value.goal.data(Interner) {
  75         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::Implemented(it))) => {
  76             db.trait_data(it.hir_trait_id()).name.to_string()
  77         }
  78         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(_))) => "alias_eq".to_string(),
  79         _ => "??".to_string(),
  80     });
  81     tracing::info!("trait_solve_query({:?})", goal.value.goal);
  82
  83     if let GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(AliasEq {
  84         alias: AliasTy::Projection(projection_ty),
  85         ..
  86     }))) = &goal.value.goal.data(Interner)
  87     {
  88         if let TyKind::BoundVar(_) = projection_ty.self_type_parameter(Interner).kind(Interner) {
  89             // Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
  90             return Some(Solution::Ambig(Guidance::Unknown));
  91         }
  92     }
  93
  94     // We currently don't deal with universes (I think / hope they're not yet
  95     // relevant for our use cases?)
  96     let u_canonical = chalk_ir::UCanonical { canonical: goal, universes: 1 };
  97     solve(db, krate, &u_canonical)
  98 }
  99
 100 fn solve(
 101     db: &dyn HirDatabase,
 102     krate: CrateId,
 103     goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
 104 ) -> Option<chalk_solve::Solution<Interner>> {
 105     let context = ChalkContext { db, krate };
 106     tracing::debug!("solve goal: {:?}", goal);
 107     let mut solver = create_chalk_solver();
 108
 109     let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
 110
 111     let should_continue = || {
 112         db.unwind_if_cancelled();
 113         let remaining = fuel.get();
 114         fuel.set(remaining - 1);
 115         if remaining == 0 {
 116             tracing::debug!("fuel exhausted");
 117         }
 118         remaining > 0
 119     };
 120
 121     let mut solve = || {
 122         let _ctx = if is_chalk_debug() || is_chalk_print() {
 123             Some(panic_context::enter(format!("solving {:?}", goal)))
 124         } else {
 125             None
 126         };
 127         let solution = if is_chalk_print() {
 128             let logging_db =
 129                 LoggingRustIrDatabaseLoggingOnDrop(LoggingRustIrDatabase::new(context));
 130             solver.solve_limited(&logging_db.0, goal, &should_continue)
 131         } else {
 132             solver.solve_limited(&context, goal, &should_continue)
 133         };
 134
 135         tracing::debug!("solve({:?}) => {:?}", goal, solution);
 136
 137         solution
 138     };
 139
 140     // don't set the TLS for Chalk unless Chalk debugging is active, to make
 141     // extra sure we only use it for debugging
 142     if is_chalk_debug() {
 143         crate::tls::set_current_program(db, solve)
 144     } else {
 145         solve()
 146     }
 147 }
 148
 149 struct LoggingRustIrDatabaseLoggingOnDrop<'a>(LoggingRustIrDatabase<Interner, ChalkContext<'a>>);
 150
 151 impl<'a> Drop for LoggingRustIrDatabaseLoggingOnDrop<'a> {
 152     fn drop(&mut self) {
 153         eprintln!("chalk program:\n{}", self.0);
 154     }
 155 }
 156
 157 fn is_chalk_debug() -> bool {
 158     std::env::var("CHALK_DEBUG").is_ok()
 159 }
 160
 161 fn is_chalk_print() -> bool {
 162     std::env::var("CHALK_PRINT").is_ok()
 163 }
 164
 165 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 166 pub enum FnTrait {
 167     FnOnce,
 168     FnMut,
 169     Fn,
 170 }
 171
 172 impl FnTrait {
 173     const fn lang_item_name(self) -> &'static str {
 174         match self {
 175             FnTrait::FnOnce => "fn_once",
 176             FnTrait::FnMut => "fn_mut",
 177             FnTrait::Fn => "fn",
 178         }
 179     }
 180
 181     pub fn get_id(&self, db: &dyn HirDatabase, krate: CrateId) -> Option<TraitId> {
 182         let target = db.lang_item(krate, SmolStr::new_inline(self.lang_item_name()))?;
 183         match target {
 184             LangItemTarget::TraitId(t) => Some(t),
 185             _ => None,
 186         }
 187     }
 188 }