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
  13 use crate::{
  14     db::HirDatabase, AliasEq, AliasTy, Canonical, DomainGoal, Goal, Guidance, InEnvironment,
  15     Interner, Solution, TraitRefExt, Ty, TyKind, WhereClause,
  16 };
  17
  18 /// This controls how much 'time' we give the Chalk solver before giving up.
  19 const CHALK_SOLVER_FUEL: i32 = 100;
  20
  21 #[derive(Debug, Copy, Clone)]
  22 pub(crate) struct ChalkContext<'a> {
  23     pub(crate) db: &'a dyn HirDatabase,
  24     pub(crate) krate: CrateId,
  25 }
  26
  27 fn create_chalk_solver() -> chalk_recursive::RecursiveSolver<Interner> {
  28     let overflow_depth =
  29         var("CHALK_OVERFLOW_DEPTH").ok().and_then(|s| s.parse().ok()).unwrap_or(300);
  30     let max_size = var("CHALK_SOLVER_MAX_SIZE").ok().and_then(|s| s.parse().ok()).unwrap_or(30);
  31     chalk_recursive::RecursiveSolver::new(overflow_depth, max_size, Some(Cache::new()))
  32 }
  33
  34 /// A set of clauses that we assume to be true. E.g. if we are inside this function:
  35 /// ```rust
  36 /// fn foo<T: Default>(t: T) {}
  37 /// ```
  38 /// we assume that `T: Default`.
  39 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
  40 pub struct TraitEnvironment {
  41     pub krate: CrateId,
  42     // When we're using Chalk's Ty we can make this a BTreeMap since it's Ord,
  43     // but for now it's too annoying...
  44     pub(crate) traits_from_clauses: Vec<(Ty, TraitId)>,
  45     pub env: chalk_ir::Environment<Interner>,
  46 }
  47
  48 impl TraitEnvironment {
  49     pub fn empty(krate: CrateId) -> Self {
  50         TraitEnvironment {
  51             krate,
  52             traits_from_clauses: Vec::new(),
  53             env: chalk_ir::Environment::new(&Interner),
  54         }
  55     }
  56
  57     pub(crate) fn traits_in_scope_from_clauses<'a>(
  58         &'a self,
  59         ty: &'a Ty,
  60     ) -> impl Iterator<Item = TraitId> + 'a {
  61         self.traits_from_clauses.iter().filter_map(move |(self_ty, trait_id)| {
  62             if self_ty == ty {
  63                 Some(*trait_id)
  64             } else {
  65                 None
  66             }
  67         })
  68     }
  69 }
  70
  71 /// Solve a trait goal using Chalk.
  72 pub(crate) fn trait_solve_query(
  73     db: &dyn HirDatabase,
  74     krate: CrateId,
  75     goal: Canonical<InEnvironment<Goal>>,
  76 ) -> Option<Solution> {
  77     let _p = profile::span("trait_solve_query").detail(|| match &goal.value.goal.data(&Interner) {
  78         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::Implemented(it))) => {
  79             db.trait_data(it.hir_trait_id()).name.to_string()
  80         }
  81         GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(_))) => "alias_eq".to_string(),
  82         _ => "??".to_string(),
  83     });
  84     tracing::info!("trait_solve_query({:?})", goal.value.goal);
  85
  86     if let GoalData::DomainGoal(DomainGoal::Holds(WhereClause::AliasEq(AliasEq {
  87         alias: AliasTy::Projection(projection_ty),
  88         ..
  89     }))) = &goal.value.goal.data(&Interner)
  90     {
  91         if let TyKind::BoundVar(_) = projection_ty.self_type_parameter(&Interner).kind(&Interner) {
  92             // Hack: don't ask Chalk to normalize with an unknown self type, it'll say that's impossible
  93             return Some(Solution::Ambig(Guidance::Unknown));
  94         }
  95     }
  96
  97     // We currently don't deal with universes (I think / hope they're not yet
  98     // relevant for our use cases?)
  99     let u_canonical = chalk_ir::UCanonical { canonical: goal, universes: 1 };
 100     solve(db, krate, &u_canonical)
 101 }
 102
 103 fn solve(
 104     db: &dyn HirDatabase,
 105     krate: CrateId,
 106     goal: &chalk_ir::UCanonical<chalk_ir::InEnvironment<chalk_ir::Goal<Interner>>>,
 107 ) -> Option<chalk_solve::Solution<Interner>> {
 108     let context = ChalkContext { db, krate };
 109     tracing::debug!("solve goal: {:?}", goal);
 110     let mut solver = create_chalk_solver();
 111
 112     let fuel = std::cell::Cell::new(CHALK_SOLVER_FUEL);
 113
 114     let should_continue = || {
 115         db.unwind_if_cancelled();
 116         let remaining = fuel.get();
 117         fuel.set(remaining - 1);
 118         if remaining == 0 {
 119             tracing::debug!("fuel exhausted");
 120         }
 121         remaining > 0
 122     };
 123
 124     let mut solve = || {
 125         let _ctx = if is_chalk_debug() || is_chalk_print() {
 126             Some(panic_context::enter(format!("solving {:?}", goal)))
 127         } else {
 128             None
 129         };
 130         let solution = if is_chalk_print() {
 131             let logging_db =
 132                 LoggingRustIrDatabaseLoggingOnDrop(LoggingRustIrDatabase::new(context));
 133             solver.solve_limited(&logging_db.0, goal, &should_continue)
 134         } else {
 135             solver.solve_limited(&context, goal, &should_continue)
 136         };
 137
 138         tracing::debug!("solve({:?}) => {:?}", goal, solution);
 139
 140         solution
 141     };
 142
 143     // don't set the TLS for Chalk unless Chalk debugging is active, to make
 144     // extra sure we only use it for debugging
 145     if is_chalk_debug() {
 146         crate::tls::set_current_program(db, solve)
 147     } else {
 148         solve()
 149     }
 150 }
 151
 152 struct LoggingRustIrDatabaseLoggingOnDrop<'a>(LoggingRustIrDatabase<Interner, ChalkContext<'a>>);
 153
 154 impl<'a> Drop for LoggingRustIrDatabaseLoggingOnDrop<'a> {
 155     fn drop(&mut self) {
 156         eprintln!("chalk program:\n{}", self.0);
 157     }
 158 }
 159
 160 fn is_chalk_debug() -> bool {
 161     std::env::var("CHALK_DEBUG").is_ok()
 162 }
 163
 164 fn is_chalk_print() -> bool {
 165     std::env::var("CHALK_PRINT").is_ok()
 166 }
 167
 168 #[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
 169 pub enum FnTrait {
 170     FnOnce,
 171     FnMut,
 172     Fn,
 173 }
 174
 175 impl FnTrait {
 176     fn lang_item_name(self) -> &'static str {
 177         match self {
 178             FnTrait::FnOnce => "fn_once",
 179             FnTrait::FnMut => "fn_mut",
 180             FnTrait::Fn => "fn",
 181         }
 182     }
 183
 184     pub fn get_id(&self, db: &dyn HirDatabase, krate: CrateId) -> Option<TraitId> {
 185         let target = db.lang_item(krate, self.lang_item_name().into())?;
 186         match target {
 187             LangItemTarget::TraitId(t) => Some(t),
 188             _ => None,
 189         }
 190     }
 191 }