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| 1 | +use std::{iter, mem::replace}; |
| 2 | + |
| 3 | +use chalk_engine::fallible::Fallible; |
| 4 | +use chalk_ir::{ |
| 5 | + cast::Cast, |
| 6 | + fold::{shift::Shift, Fold, Folder, SuperFold}, |
| 7 | + interner::Interner, |
| 8 | + AliasEq, AliasTy, Binders, BoundVar, DebruijnIndex, Goal, GoalData, Goals, ProgramClause, |
| 9 | + ProgramClauseData, ProgramClauseImplication, QuantifierKind, Ty, TyData, VariableKind, |
| 10 | + VariableKinds, |
| 11 | +}; |
| 12 | + |
| 13 | +pub fn syn_eq_lower<I: Interner, T: Fold<I>>(interner: &I, clause: &T) -> <T as Fold<I>>::Result { |
| 14 | + let mut folder = SynEqFolder { |
| 15 | + interner, |
| 16 | + new_params: vec![], |
| 17 | + new_goals: vec![], |
| 18 | + binders_len: 0, |
| 19 | + }; |
| 20 | + |
| 21 | + clause |
| 22 | + .fold_with(&mut folder, DebruijnIndex::INNERMOST) |
| 23 | + .unwrap() |
| 24 | +} |
| 25 | + |
| 26 | +struct SynEqFolder<'i, I: Interner> { |
| 27 | + interner: &'i I, |
| 28 | + new_params: Vec<VariableKind<I>>, |
| 29 | + new_goals: Vec<Goal<I>>, |
| 30 | + binders_len: usize, |
| 31 | +} |
| 32 | + |
| 33 | +impl<'i, I: Interner> Folder<'i, I> for SynEqFolder<'i, I> { |
| 34 | + fn as_dyn(&mut self) -> &mut dyn Folder<'i, I> { |
| 35 | + self |
| 36 | + } |
| 37 | + |
| 38 | + fn fold_ty(&mut self, ty: &Ty<I>, outer_binder: DebruijnIndex) -> Fallible<Ty<I>> { |
| 39 | + let interner = self.interner; |
| 40 | + let bound_var = BoundVar::new(DebruijnIndex::INNERMOST, self.binders_len); |
| 41 | + |
| 42 | + let new_ty = TyData::BoundVar(bound_var).intern(interner); |
| 43 | + match ty.data(interner) { |
| 44 | + TyData::Alias(alias @ AliasTy::Projection(_)) => { |
| 45 | + self.new_params.push(VariableKind::Ty); |
| 46 | + self.new_goals.push( |
| 47 | + AliasEq { |
| 48 | + alias: alias.clone(), |
| 49 | + ty: new_ty.clone(), |
| 50 | + } |
| 51 | + .cast(interner), |
| 52 | + ); |
| 53 | + self.binders_len += 1; |
| 54 | + ty.super_fold_with(self, outer_binder)?; |
| 55 | + Ok(new_ty) |
| 56 | + } |
| 57 | + TyData::Function(_) => Ok(ty.clone()), |
| 58 | + _ => Ok(ty.super_fold_with(self, outer_binder)?), |
| 59 | + } |
| 60 | + } |
| 61 | + |
| 62 | + fn fold_program_clause( |
| 63 | + &mut self, |
| 64 | + clause: &ProgramClause<I>, |
| 65 | + outer_binder: DebruijnIndex, |
| 66 | + ) -> Fallible<ProgramClause<I>> { |
| 67 | + let interner = self.interner; |
| 68 | + |
| 69 | + let ((binders, implication), in_binders) = match clause.data(interner) { |
| 70 | + ProgramClauseData::ForAll(for_all) => (for_all.clone().into(), true), |
| 71 | + // introduce a dummy binder and shift implication through it |
| 72 | + ProgramClauseData::Implies(implication) => ( |
| 73 | + ( |
| 74 | + VariableKinds::new(interner), |
| 75 | + implication.shifted_in(interner), |
| 76 | + ), |
| 77 | + false, |
| 78 | + ), |
| 79 | + }; |
| 80 | + let mut binders: Vec<_> = binders.as_slice(interner).clone().into(); |
| 81 | + |
| 82 | + let outer_binder = outer_binder.shifted_in(); |
| 83 | + |
| 84 | + self.binders_len = binders.len(); |
| 85 | + let consequence = implication.consequence.fold_with(self, outer_binder)?; |
| 86 | + // Immediately move `new_params` out of of the folder struct so it's safe |
| 87 | + // to call `.fold_with` again |
| 88 | + let new_params = replace(&mut self.new_params, vec![]); |
| 89 | + let new_goals = replace(&mut self.new_goals, vec![]); |
| 90 | + |
| 91 | + let mut conditions = implication.conditions.fold_with(self, outer_binder)?; |
| 92 | + if new_params.is_empty() && !in_binders { |
| 93 | + // shift the clause out since we didn't use the dummy binder |
| 94 | + return Ok(ProgramClauseData::Implies( |
| 95 | + ProgramClauseImplication { |
| 96 | + consequence, |
| 97 | + conditions, |
| 98 | + priority: implication.priority, |
| 99 | + } |
| 100 | + .shifted_out(interner)?, |
| 101 | + ) |
| 102 | + .intern(interner)); |
| 103 | + } |
| 104 | + |
| 105 | + binders.extend(new_params.into_iter()); |
| 106 | + |
| 107 | + conditions = Goals::from( |
| 108 | + interner, |
| 109 | + conditions.iter(interner).cloned().chain(new_goals), |
| 110 | + ); |
| 111 | + |
| 112 | + Ok(ProgramClauseData::ForAll(Binders::new( |
| 113 | + VariableKinds::from(interner, binders), |
| 114 | + ProgramClauseImplication { |
| 115 | + consequence, |
| 116 | + conditions, |
| 117 | + priority: implication.priority, |
| 118 | + }, |
| 119 | + )) |
| 120 | + .intern(interner)) |
| 121 | + } |
| 122 | + |
| 123 | + fn fold_goal(&mut self, goal: &Goal<I>, outer_binder: DebruijnIndex) -> Fallible<Goal<I>> { |
| 124 | + assert!(self.new_params.is_empty(), true); |
| 125 | + |
| 126 | + let interner = self.interner; |
| 127 | + match goal.data(interner) { |
| 128 | + GoalData::DomainGoal(_) | GoalData::EqGoal(_) => (), |
| 129 | + _ => return goal.super_fold_with(self, outer_binder), |
| 130 | + }; |
| 131 | + |
| 132 | + self.binders_len = 0; |
| 133 | + // shifted in because we introduce a new binder |
| 134 | + let outer_binder = outer_binder.shifted_in(); |
| 135 | + let syn_goal = goal |
| 136 | + .shifted_in(interner) |
| 137 | + .super_fold_with(self, outer_binder)?; |
| 138 | + let new_params = replace(&mut self.new_params, vec![]); |
| 139 | + let new_goals = replace(&mut self.new_goals, vec![]); |
| 140 | + |
| 141 | + if new_params.is_empty() { |
| 142 | + return Ok(goal.clone()); |
| 143 | + } |
| 144 | + |
| 145 | + let goal = GoalData::All(Goals::from( |
| 146 | + interner, |
| 147 | + iter::once(syn_goal).into_iter().chain(new_goals), |
| 148 | + )) |
| 149 | + .intern(interner); |
| 150 | + |
| 151 | + Ok(GoalData::Quantified( |
| 152 | + QuantifierKind::Exists, |
| 153 | + Binders::new(VariableKinds::from(interner, new_params), goal), |
| 154 | + ) |
| 155 | + .intern(interner)) |
| 156 | + } |
| 157 | + |
| 158 | + fn interner(&self) -> &'i I { |
| 159 | + self.interner |
| 160 | + } |
| 161 | + |
| 162 | + fn target_interner(&self) -> &'i I { |
| 163 | + self.interner |
| 164 | + } |
| 165 | +} |
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