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| 1 | +//! Defining opaque types via inference. |
| 2 | +
|
| 3 | +use rustc_type_ir::TypeVisitableExt; |
| 4 | +use tracing::{debug, instrument}; |
| 5 | + |
| 6 | +use crate::{ |
| 7 | + infer::InferenceContext, |
| 8 | + next_solver::{ |
| 9 | + EarlyBinder, OpaqueTypeKey, SolverDefId, TypingMode, |
| 10 | + infer::{opaque_types::OpaqueHiddenType, traits::ObligationCause}, |
| 11 | + }, |
| 12 | +}; |
| 13 | + |
| 14 | +impl<'db> InferenceContext<'_, 'db> { |
| 15 | + /// This takes all the opaque type uses during HIR typeck. It first computes |
| 16 | + /// the concrete hidden type by iterating over all defining uses. |
| 17 | + /// |
| 18 | + /// A use during HIR typeck is defining if all non-lifetime arguments are |
| 19 | + /// unique generic parameters and the hidden type does not reference any |
| 20 | + /// inference variables. |
| 21 | + /// |
| 22 | + /// It then uses these defining uses to guide inference for all other uses. |
| 23 | + #[instrument(level = "debug", skip(self))] |
| 24 | + pub(super) fn handle_opaque_type_uses(&mut self) { |
| 25 | + // We clone the opaques instead of stealing them here as they are still used for |
| 26 | + // normalization in the next generation trait solver. |
| 27 | + let opaque_types: Vec<_> = self.table.infer_ctxt.clone_opaque_types(); |
| 28 | + |
| 29 | + self.compute_definition_site_hidden_types(opaque_types); |
| 30 | + } |
| 31 | +} |
| 32 | + |
| 33 | +#[expect(unused, reason = "rustc has this")] |
| 34 | +#[derive(Copy, Clone, Debug)] |
| 35 | +enum UsageKind<'db> { |
| 36 | + None, |
| 37 | + NonDefiningUse(OpaqueTypeKey<'db>, OpaqueHiddenType<'db>), |
| 38 | + UnconstrainedHiddenType(OpaqueHiddenType<'db>), |
| 39 | + HasDefiningUse(OpaqueHiddenType<'db>), |
| 40 | +} |
| 41 | + |
| 42 | +impl<'db> UsageKind<'db> { |
| 43 | + fn merge(&mut self, other: UsageKind<'db>) { |
| 44 | + match (&*self, &other) { |
| 45 | + (UsageKind::HasDefiningUse(_), _) | (_, UsageKind::None) => unreachable!(), |
| 46 | + (UsageKind::None, _) => *self = other, |
| 47 | + // When mergining non-defining uses, prefer earlier ones. This means |
| 48 | + // the error happens as early as possible. |
| 49 | + ( |
| 50 | + UsageKind::NonDefiningUse(..) | UsageKind::UnconstrainedHiddenType(..), |
| 51 | + UsageKind::NonDefiningUse(..), |
| 52 | + ) => {} |
| 53 | + // When merging unconstrained hidden types, we prefer later ones. This is |
| 54 | + // used as in most cases, the defining use is the final return statement |
| 55 | + // of our function, and other uses with defining arguments are likely not |
| 56 | + // intended to be defining. |
| 57 | + ( |
| 58 | + UsageKind::NonDefiningUse(..) | UsageKind::UnconstrainedHiddenType(..), |
| 59 | + UsageKind::UnconstrainedHiddenType(..) | UsageKind::HasDefiningUse(_), |
| 60 | + ) => *self = other, |
| 61 | + } |
| 62 | + } |
| 63 | +} |
| 64 | + |
| 65 | +impl<'db> InferenceContext<'_, 'db> { |
| 66 | + fn compute_definition_site_hidden_types( |
| 67 | + &mut self, |
| 68 | + mut opaque_types: Vec<(OpaqueTypeKey<'db>, OpaqueHiddenType<'db>)>, |
| 69 | + ) { |
| 70 | + for entry in opaque_types.iter_mut() { |
| 71 | + *entry = self.table.infer_ctxt.resolve_vars_if_possible(*entry); |
| 72 | + } |
| 73 | + debug!(?opaque_types); |
| 74 | + |
| 75 | + let interner = self.interner(); |
| 76 | + let TypingMode::Analysis { defining_opaque_types_and_generators } = |
| 77 | + self.table.infer_ctxt.typing_mode() |
| 78 | + else { |
| 79 | + unreachable!(); |
| 80 | + }; |
| 81 | + |
| 82 | + for def_id in defining_opaque_types_and_generators { |
| 83 | + let def_id = match def_id { |
| 84 | + SolverDefId::InternedOpaqueTyId(it) => it, |
| 85 | + _ => continue, |
| 86 | + }; |
| 87 | + |
| 88 | + // We do actually need to check this the second pass (we can't just |
| 89 | + // store this), because we can go from `UnconstrainedHiddenType` to |
| 90 | + // `HasDefiningUse` (because of fallback) |
| 91 | + let mut usage_kind = UsageKind::None; |
| 92 | + for &(opaque_type_key, hidden_type) in &opaque_types { |
| 93 | + if opaque_type_key.def_id != def_id.into() { |
| 94 | + continue; |
| 95 | + } |
| 96 | + |
| 97 | + usage_kind.merge(self.consider_opaque_type_use(opaque_type_key, hidden_type)); |
| 98 | + |
| 99 | + if let UsageKind::HasDefiningUse(..) = usage_kind { |
| 100 | + break; |
| 101 | + } |
| 102 | + } |
| 103 | + |
| 104 | + if let UsageKind::HasDefiningUse(ty) = usage_kind { |
| 105 | + for &(opaque_type_key, hidden_type) in &opaque_types { |
| 106 | + if opaque_type_key.def_id != def_id.into() { |
| 107 | + continue; |
| 108 | + } |
| 109 | + |
| 110 | + let expected = |
| 111 | + EarlyBinder::bind(ty.ty).instantiate(interner, opaque_type_key.args); |
| 112 | + self.demand_eqtype(expected, hidden_type.ty); |
| 113 | + } |
| 114 | + |
| 115 | + self.result.type_of_opaque.insert(def_id, ty.ty); |
| 116 | + |
| 117 | + continue; |
| 118 | + } |
| 119 | + |
| 120 | + self.result.type_of_opaque.insert(def_id, self.types.error); |
| 121 | + } |
| 122 | + } |
| 123 | + |
| 124 | + #[tracing::instrument(skip(self), ret)] |
| 125 | + fn consider_opaque_type_use( |
| 126 | + &self, |
| 127 | + opaque_type_key: OpaqueTypeKey<'db>, |
| 128 | + hidden_type: OpaqueHiddenType<'db>, |
| 129 | + ) -> UsageKind<'db> { |
| 130 | + // We ignore uses of the opaque if they have any inference variables |
| 131 | + // as this can frequently happen with recursive calls. |
| 132 | + // |
| 133 | + // See `tests/ui/traits/next-solver/opaques/universal-args-non-defining.rs`. |
| 134 | + if hidden_type.ty.has_non_region_infer() { |
| 135 | + return UsageKind::UnconstrainedHiddenType(hidden_type); |
| 136 | + } |
| 137 | + |
| 138 | + let cause = ObligationCause::new(); |
| 139 | + let at = self.table.infer_ctxt.at(&cause, self.table.trait_env.env); |
| 140 | + let hidden_type = match at.deeply_normalize(hidden_type) { |
| 141 | + Ok(hidden_type) => hidden_type, |
| 142 | + Err(_errors) => OpaqueHiddenType { ty: self.types.error }, |
| 143 | + }; |
| 144 | + UsageKind::HasDefiningUse(hidden_type) |
| 145 | + } |
| 146 | +} |
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