1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
use crate::ty::{self, Binder, Ty, TyCtxt, TypeFlags};

use rustc_data_structures::fx::FxHashSet;
use rustc_data_structures::sso::SsoHashSet;
use rustc_type_ir::fold::TypeFoldable;
use std::ops::ControlFlow;

pub use rustc_type_ir::visit::{TypeSuperVisitable, TypeVisitable, TypeVisitableExt, TypeVisitor};

///////////////////////////////////////////////////////////////////////////
// Region folder

impl<'tcx> TyCtxt<'tcx> {
    /// Invoke `callback` on every region appearing free in `value`.
    pub fn for_each_free_region(
        self,
        value: &impl TypeVisitable<TyCtxt<'tcx>>,
        mut callback: impl FnMut(ty::Region<'tcx>),
    ) {
        self.any_free_region_meets(value, |r| {
            callback(r);
            false
        });
    }

    /// Returns `true` if `callback` returns true for every region appearing free in `value`.
    pub fn all_free_regions_meet(
        self,
        value: &impl TypeVisitable<TyCtxt<'tcx>>,
        mut callback: impl FnMut(ty::Region<'tcx>) -> bool,
    ) -> bool {
        !self.any_free_region_meets(value, |r| !callback(r))
    }

    /// Returns `true` if `callback` returns true for some region appearing free in `value`.
    pub fn any_free_region_meets(
        self,
        value: &impl TypeVisitable<TyCtxt<'tcx>>,
        callback: impl FnMut(ty::Region<'tcx>) -> bool,
    ) -> bool {
        struct RegionVisitor<F> {
            /// The index of a binder *just outside* the things we have
            /// traversed. If we encounter a bound region bound by this
            /// binder or one outer to it, it appears free. Example:
            ///
            /// ```ignore (illustrative)
            ///       for<'a> fn(for<'b> fn(), T)
            /// // ^          ^          ^     ^
            /// // |          |          |     | here, would be shifted in 1
            /// // |          |          | here, would be shifted in 2
            /// // |          | here, would be `INNERMOST` shifted in by 1
            /// // | here, initially, binder would be `INNERMOST`
            /// ```
            ///
            /// You see that, initially, *any* bound value is free,
            /// because we've not traversed any binders. As we pass
            /// through a binder, we shift the `outer_index` by 1 to
            /// account for the new binder that encloses us.
            outer_index: ty::DebruijnIndex,
            callback: F,
        }

        impl<'tcx, F> TypeVisitor<TyCtxt<'tcx>> for RegionVisitor<F>
        where
            F: FnMut(ty::Region<'tcx>) -> bool,
        {
            type BreakTy = ();

            fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
                &mut self,
                t: &Binder<'tcx, T>,
            ) -> ControlFlow<Self::BreakTy> {
                self.outer_index.shift_in(1);
                let result = t.super_visit_with(self);
                self.outer_index.shift_out(1);
                result
            }

            fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
                match *r {
                    ty::ReBound(debruijn, _) if debruijn < self.outer_index => {
                        ControlFlow::Continue(())
                    }
                    _ => {
                        if (self.callback)(r) {
                            ControlFlow::Break(())
                        } else {
                            ControlFlow::Continue(())
                        }
                    }
                }
            }

            fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
                // We're only interested in types involving regions
                if ty.flags().intersects(TypeFlags::HAS_FREE_REGIONS) {
                    ty.super_visit_with(self)
                } else {
                    ControlFlow::Continue(())
                }
            }
        }

        value.visit_with(&mut RegionVisitor { outer_index: ty::INNERMOST, callback }).is_break()
    }

    /// Returns a set of all late-bound regions that are constrained
    /// by `value`, meaning that if we instantiate those LBR with
    /// variables and equate `value` with something else, those
    /// variables will also be equated.
    pub fn collect_constrained_late_bound_regions<T>(
        self,
        value: Binder<'tcx, T>,
    ) -> FxHashSet<ty::BoundRegionKind>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        self.collect_late_bound_regions(value, true)
    }

    /// Returns a set of all late-bound regions that appear in `value` anywhere.
    pub fn collect_referenced_late_bound_regions<T>(
        self,
        value: Binder<'tcx, T>,
    ) -> FxHashSet<ty::BoundRegionKind>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        self.collect_late_bound_regions(value, false)
    }

    fn collect_late_bound_regions<T>(
        self,
        value: Binder<'tcx, T>,
        just_constrained: bool,
    ) -> FxHashSet<ty::BoundRegionKind>
    where
        T: TypeFoldable<TyCtxt<'tcx>>,
    {
        let mut collector = LateBoundRegionsCollector::new(just_constrained);
        let value = value.skip_binder();
        let value = if just_constrained { self.expand_weak_alias_tys(value) } else { value };
        let result = value.visit_with(&mut collector);
        assert!(result.is_continue()); // should never have stopped early
        collector.regions
    }
}

pub struct ValidateBoundVars<'tcx> {
    bound_vars: &'tcx ty::List<ty::BoundVariableKind>,
    binder_index: ty::DebruijnIndex,
    // We may encounter the same variable at different levels of binding, so
    // this can't just be `Ty`
    visited: SsoHashSet<(ty::DebruijnIndex, Ty<'tcx>)>,
}

impl<'tcx> ValidateBoundVars<'tcx> {
    pub fn new(bound_vars: &'tcx ty::List<ty::BoundVariableKind>) -> Self {
        ValidateBoundVars {
            bound_vars,
            binder_index: ty::INNERMOST,
            visited: SsoHashSet::default(),
        }
    }
}

impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ValidateBoundVars<'tcx> {
    type BreakTy = ();

    fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
        &mut self,
        t: &Binder<'tcx, T>,
    ) -> ControlFlow<Self::BreakTy> {
        self.binder_index.shift_in(1);
        let result = t.super_visit_with(self);
        self.binder_index.shift_out(1);
        result
    }

    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
        if t.outer_exclusive_binder() < self.binder_index
            || !self.visited.insert((self.binder_index, t))
        {
            return ControlFlow::Break(());
        }
        match *t.kind() {
            ty::Bound(debruijn, bound_ty) if debruijn == self.binder_index => {
                if self.bound_vars.len() <= bound_ty.var.as_usize() {
                    bug!("Not enough bound vars: {:?} not found in {:?}", t, self.bound_vars);
                }
                let list_var = self.bound_vars[bound_ty.var.as_usize()];
                match list_var {
                    ty::BoundVariableKind::Ty(kind) => {
                        if kind != bound_ty.kind {
                            bug!(
                                "Mismatched type kinds: {:?} doesn't var in list {:?}",
                                bound_ty.kind,
                                list_var
                            );
                        }
                    }
                    _ => {
                        bug!("Mismatched bound variable kinds! Expected type, found {:?}", list_var)
                    }
                }
            }

            _ => (),
        };

        t.super_visit_with(self)
    }

    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
        match *r {
            ty::ReBound(index, br) if index == self.binder_index => {
                if self.bound_vars.len() <= br.var.as_usize() {
                    bug!("Not enough bound vars: {:?} not found in {:?}", br, self.bound_vars);
                }
                let list_var = self.bound_vars[br.var.as_usize()];
                match list_var {
                    ty::BoundVariableKind::Region(kind) => {
                        if kind != br.kind {
                            bug!(
                                "Mismatched region kinds: {:?} doesn't match var ({:?}) in list ({:?})",
                                br.kind,
                                list_var,
                                self.bound_vars
                            );
                        }
                    }
                    _ => bug!(
                        "Mismatched bound variable kinds! Expected region, found {:?}",
                        list_var
                    ),
                }
            }

            _ => (),
        };

        ControlFlow::Continue(())
    }
}

/// Collects all the late-bound regions at the innermost binding level
/// into a hash set.
struct LateBoundRegionsCollector {
    current_index: ty::DebruijnIndex,
    regions: FxHashSet<ty::BoundRegionKind>,

    /// `true` if we only want regions that are known to be
    /// "constrained" when you equate this type with another type. In
    /// particular, if you have e.g., `&'a u32` and `&'b u32`, equating
    /// them constraints `'a == 'b`. But if you have `<&'a u32 as
    /// Trait>::Foo` and `<&'b u32 as Trait>::Foo`, normalizing those
    /// types may mean that `'a` and `'b` don't appear in the results,
    /// so they are not considered *constrained*.
    just_constrained: bool,
}

impl LateBoundRegionsCollector {
    fn new(just_constrained: bool) -> Self {
        Self { current_index: ty::INNERMOST, regions: Default::default(), just_constrained }
    }
}

impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for LateBoundRegionsCollector {
    fn visit_binder<T: TypeVisitable<TyCtxt<'tcx>>>(
        &mut self,
        t: &Binder<'tcx, T>,
    ) -> ControlFlow<Self::BreakTy> {
        self.current_index.shift_in(1);
        let result = t.super_visit_with(self);
        self.current_index.shift_out(1);
        result
    }

    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
        if self.just_constrained {
            match t.kind() {
                // If we are only looking for "constrained" regions, we have to ignore the
                // inputs to a projection as they may not appear in the normalized form.
                ty::Alias(ty::Projection | ty::Inherent | ty::Opaque, _) => {
                    return ControlFlow::Continue(());
                }
                // All weak alias types should've been expanded beforehand.
                ty::Alias(ty::Weak, _) => bug!("unexpected weak alias type"),
                _ => {}
            }
        }

        t.super_visit_with(self)
    }

    fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
        // if we are only looking for "constrained" region, we have to
        // ignore the inputs of an unevaluated const, as they may not appear
        // in the normalized form
        if self.just_constrained {
            if let ty::ConstKind::Unevaluated(..) = c.kind() {
                return ControlFlow::Continue(());
            }
        }

        c.super_visit_with(self)
    }

    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
        if let ty::ReBound(debruijn, br) = *r {
            if debruijn == self.current_index {
                self.regions.insert(br.kind);
            }
        }
        ControlFlow::Continue(())
    }
}

/// Finds the max universe present
pub struct MaxUniverse {
    max_universe: ty::UniverseIndex,
}

impl MaxUniverse {
    pub fn new() -> Self {
        MaxUniverse { max_universe: ty::UniverseIndex::ROOT }
    }

    pub fn max_universe(self) -> ty::UniverseIndex {
        self.max_universe
    }
}

impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for MaxUniverse {
    fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
        if let ty::Placeholder(placeholder) = t.kind() {
            self.max_universe = ty::UniverseIndex::from_u32(
                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
            );
        }

        t.super_visit_with(self)
    }

    fn visit_const(&mut self, c: ty::consts::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
        if let ty::ConstKind::Placeholder(placeholder) = c.kind() {
            self.max_universe = ty::UniverseIndex::from_u32(
                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
            );
        }

        c.super_visit_with(self)
    }

    fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
        if let ty::RePlaceholder(placeholder) = *r {
            self.max_universe = ty::UniverseIndex::from_u32(
                self.max_universe.as_u32().max(placeholder.universe.as_u32()),
            );
        }

        ControlFlow::Continue(())
    }
}