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
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
//! Visitor for a run-time value with a given layout: Traverse enums, structs and other compound
//! types until we arrive at the leaves, with custom handling for primitive types.

use rustc_middle::mir::interpret::InterpResult;
use rustc_middle::ty;
use rustc_middle::ty::layout::TyAndLayout;
use rustc_target::abi::{FieldsShape, VariantIdx, Variants};

use std::num::NonZeroUsize;

use super::{InterpCx, MPlaceTy, Machine, OpTy, PlaceTy};

/// A thing that we can project into, and that has a layout.
/// This wouldn't have to depend on `Machine` but with the current type inference,
/// that's just more convenient to work with (avoids repeating all the `Machine` bounds).
pub trait Value<'mir, 'tcx, M: Machine<'mir, 'tcx>>: Sized {
    /// Gets this value's layout.
    fn layout(&self) -> TyAndLayout<'tcx>;

    /// Makes this into an `OpTy`, in a cheap way that is good for reading.
    fn to_op_for_read(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;

    /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections.
    fn to_op_for_proj(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        self.to_op_for_read(ecx)
    }

    /// Creates this from an `OpTy`.
    ///
    /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`.
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self;

    /// Projects to the given enum variant.
    fn project_downcast(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self>;

    /// Projects to the n-th field.
    fn project_field(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self>;
}

/// A thing that we can project into given *mutable* access to `ecx`, and that has a layout.
/// This wouldn't have to depend on `Machine` but with the current type inference,
/// that's just more convenient to work with (avoids repeating all the `Machine` bounds).
pub trait ValueMut<'mir, 'tcx, M: Machine<'mir, 'tcx>>: Sized {
    /// Gets this value's layout.
    fn layout(&self) -> TyAndLayout<'tcx>;

    /// Makes this into an `OpTy`, in a cheap way that is good for reading.
    fn to_op_for_read(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;

    /// Makes this into an `OpTy`, in a potentially more expensive way that is good for projections.
    fn to_op_for_proj(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>>;

    /// Creates this from an `OpTy`.
    ///
    /// If `to_op_for_proj` only ever produces `Indirect` operands, then this one is definitely `Indirect`.
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self;

    /// Projects to the given enum variant.
    fn project_downcast(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self>;

    /// Projects to the n-th field.
    fn project_field(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self>;
}

// We cannot have a general impl which shows that Value implies ValueMut. (When we do, it says we
// cannot `impl ValueMut for PlaceTy` because some downstream crate could `impl Value for PlaceTy`.)
// So we have some copy-paste here. (We could have a macro but since we only have 2 types with this
// double-impl, that would barely make the code shorter, if at all.)

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M> for OpTy<'tcx, M::Provenance> {
    #[inline(always)]
    fn layout(&self) -> TyAndLayout<'tcx> {
        self.layout
    }

    #[inline(always)]
    fn to_op_for_read(
        &self,
        _ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.clone())
    }

    #[inline(always)]
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
        op.clone()
    }

    #[inline(always)]
    fn project_downcast(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self> {
        ecx.operand_downcast(self, variant)
    }

    #[inline(always)]
    fn project_field(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self> {
        ecx.operand_field(self, field)
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
    for OpTy<'tcx, M::Provenance>
{
    #[inline(always)]
    fn layout(&self) -> TyAndLayout<'tcx> {
        self.layout
    }

    #[inline(always)]
    fn to_op_for_read(
        &self,
        _ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.clone())
    }

    #[inline(always)]
    fn to_op_for_proj(
        &self,
        _ecx: &mut InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.clone())
    }

    #[inline(always)]
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
        op.clone()
    }

    #[inline(always)]
    fn project_downcast(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self> {
        ecx.operand_downcast(self, variant)
    }

    #[inline(always)]
    fn project_field(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self> {
        ecx.operand_field(self, field)
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> Value<'mir, 'tcx, M>
    for MPlaceTy<'tcx, M::Provenance>
{
    #[inline(always)]
    fn layout(&self) -> TyAndLayout<'tcx> {
        self.layout
    }

    #[inline(always)]
    fn to_op_for_read(
        &self,
        _ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.into())
    }

    #[inline(always)]
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
        // assert is justified because our `to_op_for_read` only ever produces `Indirect` operands.
        op.assert_mem_place()
    }

    #[inline(always)]
    fn project_downcast(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self> {
        ecx.mplace_downcast(self, variant)
    }

    #[inline(always)]
    fn project_field(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self> {
        ecx.mplace_field(self, field)
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
    for MPlaceTy<'tcx, M::Provenance>
{
    #[inline(always)]
    fn layout(&self) -> TyAndLayout<'tcx> {
        self.layout
    }

    #[inline(always)]
    fn to_op_for_read(
        &self,
        _ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.into())
    }

    #[inline(always)]
    fn to_op_for_proj(
        &self,
        _ecx: &mut InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        Ok(self.into())
    }

    #[inline(always)]
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
        // assert is justified because our `to_op_for_proj` only ever produces `Indirect` operands.
        op.assert_mem_place()
    }

    #[inline(always)]
    fn project_downcast(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self> {
        ecx.mplace_downcast(self, variant)
    }

    #[inline(always)]
    fn project_field(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self> {
        ecx.mplace_field(self, field)
    }
}

impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> ValueMut<'mir, 'tcx, M>
    for PlaceTy<'tcx, M::Provenance>
{
    #[inline(always)]
    fn layout(&self) -> TyAndLayout<'tcx> {
        self.layout
    }

    #[inline(always)]
    fn to_op_for_read(
        &self,
        ecx: &InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        // We `force_allocation` here so that `from_op` below can work.
        ecx.place_to_op(self)
    }

    #[inline(always)]
    fn to_op_for_proj(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
    ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
        // We `force_allocation` here so that `from_op` below can work.
        Ok(ecx.force_allocation(self)?.into())
    }

    #[inline(always)]
    fn from_op(op: &OpTy<'tcx, M::Provenance>) -> Self {
        // assert is justified because our `to_op` only ever produces `Indirect` operands.
        op.assert_mem_place().into()
    }

    #[inline(always)]
    fn project_downcast(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        variant: VariantIdx,
    ) -> InterpResult<'tcx, Self> {
        ecx.place_downcast(self, variant)
    }

    #[inline(always)]
    fn project_field(
        &self,
        ecx: &mut InterpCx<'mir, 'tcx, M>,
        field: usize,
    ) -> InterpResult<'tcx, Self> {
        ecx.place_field(self, field)
    }
}

macro_rules! make_value_visitor {
    ($visitor_trait:ident, $value_trait:ident, $($mutability:ident)?) => {
        // How to traverse a value and what to do when we are at the leaves.
        pub trait $visitor_trait<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>>: Sized {
            type V: $value_trait<'mir, 'tcx, M>;

            /// The visitor must have an `InterpCx` in it.
            fn ecx(&$($mutability)? self)
                -> &$($mutability)? InterpCx<'mir, 'tcx, M>;

            /// `read_discriminant` can be hooked for better error messages.
            #[inline(always)]
            fn read_discriminant(
                &mut self,
                op: &OpTy<'tcx, M::Provenance>,
            ) -> InterpResult<'tcx, VariantIdx> {
                Ok(self.ecx().read_discriminant(op)?.1)
            }

            // Recursive actions, ready to be overloaded.
            /// Visits the given value, dispatching as appropriate to more specialized visitors.
            #[inline(always)]
            fn visit_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
            {
                self.walk_value(v)
            }
            /// Visits the given value as a union. No automatic recursion can happen here.
            #[inline(always)]
            fn visit_union(&mut self, _v: &Self::V, _fields: NonZeroUsize) -> InterpResult<'tcx>
            {
                Ok(())
            }
            /// Visits the given value as the pointer of a `Box`. There is nothing to recurse into.
            /// The type of `v` will be a raw pointer, but this is a field of `Box<T>` and the
            /// pointee type is the actual `T`.
            #[inline(always)]
            fn visit_box(&mut self, _v: &Self::V) -> InterpResult<'tcx>
            {
                Ok(())
            }
            /// Visits this value as an aggregate, you are getting an iterator yielding
            /// all the fields (still in an `InterpResult`, you have to do error handling yourself).
            /// Recurses into the fields.
            #[inline(always)]
            fn visit_aggregate(
                &mut self,
                v: &Self::V,
                fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
            ) -> InterpResult<'tcx> {
                self.walk_aggregate(v, fields)
            }

            /// Called each time we recurse down to a field of a "product-like" aggregate
            /// (structs, tuples, arrays and the like, but not enums), passing in old (outer)
            /// and new (inner) value.
            /// This gives the visitor the chance to track the stack of nested fields that
            /// we are descending through.
            #[inline(always)]
            fn visit_field(
                &mut self,
                _old_val: &Self::V,
                _field: usize,
                new_val: &Self::V,
            ) -> InterpResult<'tcx> {
                self.visit_value(new_val)
            }
            /// Called when recursing into an enum variant.
            /// This gives the visitor the chance to track the stack of nested fields that
            /// we are descending through.
            #[inline(always)]
            fn visit_variant(
                &mut self,
                _old_val: &Self::V,
                _variant: VariantIdx,
                new_val: &Self::V,
            ) -> InterpResult<'tcx> {
                self.visit_value(new_val)
            }

            // Default recursors. Not meant to be overloaded.
            fn walk_aggregate(
                &mut self,
                v: &Self::V,
                fields: impl Iterator<Item=InterpResult<'tcx, Self::V>>,
            ) -> InterpResult<'tcx> {
                // Now iterate over it.
                for (idx, field_val) in fields.enumerate() {
                    self.visit_field(v, idx, &field_val?)?;
                }
                Ok(())
            }
            fn walk_value(&mut self, v: &Self::V) -> InterpResult<'tcx>
            {
                let ty = v.layout().ty;
                trace!("walk_value: type: {ty}");

                // Special treatment for special types, where the (static) layout is not sufficient.
                match *ty.kind() {
                    // If it is a trait object, switch to the real type that was used to create it.
                    ty::Dynamic(..) => {
                        // unsized values are never immediate, so we can assert_mem_place
                        let op = v.to_op_for_read(self.ecx())?;
                        let dest = op.assert_mem_place();
                        let inner_mplace = self.ecx().unpack_dyn_trait(&dest)?;
                        trace!("walk_value: dyn object layout: {:#?}", inner_mplace.layout);
                        // recurse with the inner type
                        return self.visit_field(&v, 0, &$value_trait::from_op(&inner_mplace.into()));
                    },
                    // Slices do not need special handling here: they have `Array` field
                    // placement with length 0, so we enter the `Array` case below which
                    // indirectly uses the metadata to determine the actual length.

                    // However, `Box`... let's talk about `Box`.
                    ty::Adt(def, ..) if def.is_box() => {
                        // `Box` is a hybrid primitive-library-defined type that one the one hand is
                        // a dereferenceable pointer, on the other hand has *basically arbitrary
                        // user-defined layout* since the user controls the 'allocator' field. So it
                        // cannot be treated like a normal pointer, since it does not fit into an
                        // `Immediate`. Yeah, it is quite terrible. But many visitors want to do
                        // something with "all boxed pointers", so we handle this mess for them.
                        //
                        // When we hit a `Box`, we do not do the usual `visit_aggregate`; instead,
                        // we (a) call `visit_box` on the pointer value, and (b) recurse on the
                        // allocator field. We also assert tons of things to ensure we do not miss
                        // any other fields.

                        // `Box` has two fields: the pointer we care about, and the allocator.
                        assert_eq!(v.layout().fields.count(), 2, "`Box` must have exactly 2 fields");
                        let (unique_ptr, alloc) =
                            (v.project_field(self.ecx(), 0)?, v.project_field(self.ecx(), 1)?);
                        // Unfortunately there is some type junk in the way here: `unique_ptr` is a `Unique`...
                        // (which means another 2 fields, the second of which is a `PhantomData`)
                        assert_eq!(unique_ptr.layout().fields.count(), 2);
                        let (nonnull_ptr, phantom) = (
                            unique_ptr.project_field(self.ecx(), 0)?,
                            unique_ptr.project_field(self.ecx(), 1)?,
                        );
                        assert!(
                            phantom.layout().ty.ty_adt_def().is_some_and(|adt| adt.is_phantom_data()),
                            "2nd field of `Unique` should be PhantomData but is {:?}",
                            phantom.layout().ty,
                        );
                        // ... that contains a `NonNull`... (gladly, only a single field here)
                        assert_eq!(nonnull_ptr.layout().fields.count(), 1);
                        let raw_ptr = nonnull_ptr.project_field(self.ecx(), 0)?; // the actual raw ptr
                        // ... whose only field finally is a raw ptr we can dereference.
                        self.visit_box(&raw_ptr)?;

                        // The second `Box` field is the allocator, which we recursively check for validity
                        // like in regular structs.
                        self.visit_field(v, 1, &alloc)?;

                        // We visited all parts of this one.
                        return Ok(());
                    }
                    _ => {},
                };

                // Visit the fields of this value.
                match v.layout().fields {
                    FieldsShape::Primitive => {}
                    FieldsShape::Union(fields) => {
                        self.visit_union(v, fields)?;
                    }
                    FieldsShape::Arbitrary { ref offsets, .. } => {
                        // FIXME: We collect in a vec because otherwise there are lifetime
                        // errors: Projecting to a field needs access to `ecx`.
                        let fields: Vec<InterpResult<'tcx, Self::V>> =
                            (0..offsets.len()).map(|i| {
                                v.project_field(self.ecx(), i)
                            })
                            .collect();
                        self.visit_aggregate(v, fields.into_iter())?;
                    }
                    FieldsShape::Array { .. } => {
                        // Let's get an mplace (or immediate) first.
                        // This might `force_allocate` if `v` is a `PlaceTy`, but `place_index` does that anyway.
                        let op = v.to_op_for_proj(self.ecx())?;
                        // Now we can go over all the fields.
                        // This uses the *run-time length*, i.e., if we are a slice,
                        // the dynamic info from the metadata is used.
                        let iter = self.ecx().operand_array_fields(&op)?
                            .map(|f| f.and_then(|f| {
                                Ok($value_trait::from_op(&f))
                            }));
                        self.visit_aggregate(v, iter)?;
                    }
                }

                match v.layout().variants {
                    // If this is a multi-variant layout, find the right variant and proceed
                    // with *its* fields.
                    Variants::Multiple { .. } => {
                        let op = v.to_op_for_read(self.ecx())?;
                        let idx = self.read_discriminant(&op)?;
                        let inner = v.project_downcast(self.ecx(), idx)?;
                        trace!("walk_value: variant layout: {:#?}", inner.layout());
                        // recurse with the inner type
                        self.visit_variant(v, idx, &inner)
                    }
                    // For single-variant layouts, we already did anything there is to do.
                    Variants::Single { .. } => Ok(())
                }
            }
        }
    }
}

make_value_visitor!(ValueVisitor, Value,);
make_value_visitor!(MutValueVisitor, ValueMut, mut);