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
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
//! Util methods for [`rustc_middle::ty`]

#![allow(clippy::module_name_repetitions)]

use core::ops::ControlFlow;
use rustc_ast::ast::Mutability;
use rustc_data_structures::fx::{FxHashMap, FxHashSet};
use rustc_hir as hir;
use rustc_hir::def::{CtorKind, CtorOf, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_hir::{Expr, FnDecl, LangItem, TyKind, Unsafety};
use rustc_infer::infer::TyCtxtInferExt;
use rustc_lint::LateContext;
use rustc_middle::mir::interpret::{ConstValue, Scalar};
use rustc_middle::ty::subst::{GenericArg, GenericArgKind, Subst};
use rustc_middle::ty::{
    self, AdtDef, Binder, BoundRegion, DefIdTree, FnSig, IntTy, ParamEnv, Predicate, PredicateKind, ProjectionTy,
    Region, RegionKind, Ty, TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor, UintTy, VariantDef, VariantDiscr,
};
use rustc_span::symbol::Ident;
use rustc_span::{sym, Span, Symbol, DUMMY_SP};
use rustc_target::abi::{Size, VariantIdx};
use rustc_trait_selection::infer::InferCtxtExt;
use rustc_trait_selection::traits::query::normalize::AtExt;
use std::iter;

use crate::{match_def_path, path_res, paths};

// Checks if the given type implements copy.
pub fn is_copy<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    ty.is_copy_modulo_regions(cx.tcx.at(DUMMY_SP), cx.param_env)
}

/// Checks whether a type can be partially moved.
pub fn can_partially_move_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    if has_drop(cx, ty) || is_copy(cx, ty) {
        return false;
    }
    match ty.kind() {
        ty::Param(_) => false,
        ty::Adt(def, subs) => def.all_fields().any(|f| !is_copy(cx, f.ty(cx.tcx, subs))),
        _ => true,
    }
}

/// Walks into `ty` and returns `true` if any inner type is an instance of the given adt
/// constructor.
pub fn contains_adt_constructor<'tcx>(ty: Ty<'tcx>, adt: AdtDef<'tcx>) -> bool {
    ty.walk().any(|inner| match inner.unpack() {
        GenericArgKind::Type(inner_ty) => inner_ty.ty_adt_def() == Some(adt),
        GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
    })
}

/// Resolves `<T as Iterator>::Item` for `T`
/// Do not invoke without first verifying that the type implements `Iterator`
pub fn get_iterator_item_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<Ty<'tcx>> {
    cx.tcx
        .get_diagnostic_item(sym::Iterator)
        .and_then(|iter_did| get_associated_type(cx, ty, iter_did, "Item"))
}

/// Returns the associated type `name` for `ty` as an implementation of `trait_id`.
/// Do not invoke without first verifying that the type implements the trait.
pub fn get_associated_type<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    name: &str,
) -> Option<Ty<'tcx>> {
    cx.tcx
        .associated_items(trait_id)
        .find_by_name_and_kind(cx.tcx, Ident::from_str(name), ty::AssocKind::Type, trait_id)
        .and_then(|assoc| {
            let proj = cx.tcx.mk_projection(assoc.def_id, cx.tcx.mk_substs_trait(ty, &[]));
            cx.tcx.try_normalize_erasing_regions(cx.param_env, proj).ok()
        })
}

/// Get the diagnostic name of a type, e.g. `sym::HashMap`. To check if a type
/// implements a trait marked with a diagnostic item use [`implements_trait`].
///
/// For a further exploitation what diagnostic items are see [diagnostic items] in
/// rustc-dev-guide.
///
/// [Diagnostic Items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
pub fn get_type_diagnostic_name(cx: &LateContext<'_>, ty: Ty<'_>) -> Option<Symbol> {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.get_diagnostic_name(adt.did()),
        _ => None,
    }
}

/// Returns true if ty has `iter` or `iter_mut` methods
pub fn has_iter_method(cx: &LateContext<'_>, probably_ref_ty: Ty<'_>) -> Option<Symbol> {
    // FIXME: instead of this hard-coded list, we should check if `<adt>::iter`
    // exists and has the desired signature. Unfortunately FnCtxt is not exported
    // so we can't use its `lookup_method` method.
    let into_iter_collections: &[Symbol] = &[
        sym::Vec,
        sym::Option,
        sym::Result,
        sym::BTreeMap,
        sym::BTreeSet,
        sym::VecDeque,
        sym::LinkedList,
        sym::BinaryHeap,
        sym::HashSet,
        sym::HashMap,
        sym::PathBuf,
        sym::Path,
        sym::Receiver,
    ];

    let ty_to_check = match probably_ref_ty.kind() {
        ty::Ref(_, ty_to_check, _) => *ty_to_check,
        _ => probably_ref_ty,
    };

    let def_id = match ty_to_check.kind() {
        ty::Array(..) => return Some(sym::array),
        ty::Slice(..) => return Some(sym::slice),
        ty::Adt(adt, _) => adt.did(),
        _ => return None,
    };

    for &name in into_iter_collections {
        if cx.tcx.is_diagnostic_item(name, def_id) {
            return Some(cx.tcx.item_name(def_id));
        }
    }
    None
}

/// Checks whether a type implements a trait.
/// The function returns false in case the type contains an inference variable.
///
/// See:
/// * [`get_trait_def_id`](super::get_trait_def_id) to get a trait [`DefId`].
/// * [Common tools for writing lints] for an example how to use this function and other options.
///
/// [Common tools for writing lints]: https://github.com/rust-lang/rust-clippy/blob/master/book/src/development/common_tools_writing_lints.md#checking-if-a-type-implements-a-specific-trait
pub fn implements_trait<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    ty_params: &[GenericArg<'tcx>],
) -> bool {
    implements_trait_with_env(cx.tcx, cx.param_env, ty, trait_id, ty_params)
}

/// Same as `implements_trait` but allows using a `ParamEnv` different from the lint context.
pub fn implements_trait_with_env<'tcx>(
    tcx: TyCtxt<'tcx>,
    param_env: ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    trait_id: DefId,
    ty_params: &[GenericArg<'tcx>],
) -> bool {
    // Clippy shouldn't have infer types
    assert!(!ty.needs_infer());

    let ty = tcx.erase_regions(ty);
    if ty.has_escaping_bound_vars() {
        return false;
    }
    let ty_params = tcx.mk_substs(ty_params.iter());
    tcx.infer_ctxt().enter(|infcx| {
        infcx
            .type_implements_trait(trait_id, ty, ty_params, param_env)
            .must_apply_modulo_regions()
    })
}

/// Checks whether this type implements `Drop`.
pub fn has_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.ty_adt_def() {
        Some(def) => def.has_dtor(cx.tcx),
        None => false,
    }
}

// Returns whether the type has #[must_use] attribute
pub fn is_must_use_ty<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.has_attr(adt.did(), sym::must_use),
        ty::Foreign(did) => cx.tcx.has_attr(*did, sym::must_use),
        ty::Slice(ty) | ty::Array(ty, _) | ty::RawPtr(ty::TypeAndMut { ty, .. }) | ty::Ref(_, ty, _) => {
            // for the Array case we don't need to care for the len == 0 case
            // because we don't want to lint functions returning empty arrays
            is_must_use_ty(cx, *ty)
        },
        ty::Tuple(substs) => substs.iter().any(|ty| is_must_use_ty(cx, ty)),
        ty::Opaque(def_id, _) => {
            for (predicate, _) in cx.tcx.explicit_item_bounds(*def_id) {
                if let ty::PredicateKind::Trait(trait_predicate) = predicate.kind().skip_binder() {
                    if cx.tcx.has_attr(trait_predicate.trait_ref.def_id, sym::must_use) {
                        return true;
                    }
                }
            }
            false
        },
        ty::Dynamic(binder, _, _) => {
            for predicate in binder.iter() {
                if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() {
                    if cx.tcx.has_attr(trait_ref.def_id, sym::must_use) {
                        return true;
                    }
                }
            }
            false
        },
        _ => false,
    }
}

// FIXME: Per https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/at/struct.At.html#method.normalize
// this function can be removed once the `normalize` method does not panic when normalization does
// not succeed
/// Checks if `Ty` is normalizable. This function is useful
/// to avoid crashes on `layout_of`.
pub fn is_normalizable<'tcx>(cx: &LateContext<'tcx>, param_env: ty::ParamEnv<'tcx>, ty: Ty<'tcx>) -> bool {
    is_normalizable_helper(cx, param_env, ty, &mut FxHashMap::default())
}

fn is_normalizable_helper<'tcx>(
    cx: &LateContext<'tcx>,
    param_env: ty::ParamEnv<'tcx>,
    ty: Ty<'tcx>,
    cache: &mut FxHashMap<Ty<'tcx>, bool>,
) -> bool {
    if let Some(&cached_result) = cache.get(&ty) {
        return cached_result;
    }
    // prevent recursive loops, false-negative is better than endless loop leading to stack overflow
    cache.insert(ty, false);
    let result = cx.tcx.infer_ctxt().enter(|infcx| {
        let cause = rustc_middle::traits::ObligationCause::dummy();
        if infcx.at(&cause, param_env).normalize(ty).is_ok() {
            match ty.kind() {
                ty::Adt(def, substs) => def.variants().iter().all(|variant| {
                    variant
                        .fields
                        .iter()
                        .all(|field| is_normalizable_helper(cx, param_env, field.ty(cx.tcx, substs), cache))
                }),
                _ => ty.walk().all(|generic_arg| match generic_arg.unpack() {
                    GenericArgKind::Type(inner_ty) if inner_ty != ty => {
                        is_normalizable_helper(cx, param_env, inner_ty, cache)
                    },
                    _ => true, // if inner_ty == ty, we've already checked it
                }),
            }
        } else {
            false
        }
    });
    cache.insert(ty, result);
    result
}

/// Returns `true` if the given type is a non aggregate primitive (a `bool` or `char`, any
/// integer or floating-point number type). For checking aggregation of primitive types (e.g.
/// tuples and slices of primitive type) see `is_recursively_primitive_type`
pub fn is_non_aggregate_primitive_type(ty: Ty<'_>) -> bool {
    matches!(ty.kind(), ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_))
}

/// Returns `true` if the given type is a primitive (a `bool` or `char`, any integer or
/// floating-point number type, a `str`, or an array, slice, or tuple of those types).
pub fn is_recursively_primitive_type(ty: Ty<'_>) -> bool {
    match *ty.kind() {
        ty::Bool | ty::Char | ty::Int(_) | ty::Uint(_) | ty::Float(_) | ty::Str => true,
        ty::Ref(_, inner, _) if *inner.kind() == ty::Str => true,
        ty::Array(inner_type, _) | ty::Slice(inner_type) => is_recursively_primitive_type(inner_type),
        ty::Tuple(inner_types) => inner_types.iter().all(is_recursively_primitive_type),
        _ => false,
    }
}

/// Checks if the type is a reference equals to a diagnostic item
pub fn is_type_ref_to_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
    match ty.kind() {
        ty::Ref(_, ref_ty, _) => match ref_ty.kind() {
            ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did()),
            _ => false,
        },
        _ => false,
    }
}

/// Checks if the type is equal to a diagnostic item. To check if a type implements a
/// trait marked with a diagnostic item use [`implements_trait`].
///
/// For a further exploitation what diagnostic items are see [diagnostic items] in
/// rustc-dev-guide.
///
/// ---
///
/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
///
/// [Diagnostic Items]: https://rustc-dev-guide.rust-lang.org/diagnostics/diagnostic-items.html
pub fn is_type_diagnostic_item(cx: &LateContext<'_>, ty: Ty<'_>, diag_item: Symbol) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx.tcx.is_diagnostic_item(diag_item, adt.did()),
        _ => false,
    }
}

/// Checks if the type is equal to a lang item.
///
/// Returns `false` if the `LangItem` is not defined.
pub fn is_type_lang_item(cx: &LateContext<'_>, ty: Ty<'_>, lang_item: hir::LangItem) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => cx
            .tcx
            .lang_items()
            .require(lang_item)
            .map_or(false, |li| li == adt.did()),
        _ => false,
    }
}

/// Return `true` if the passed `typ` is `isize` or `usize`.
pub fn is_isize_or_usize(typ: Ty<'_>) -> bool {
    matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
}

/// Checks if type is struct, enum or union type with the given def path.
///
/// If the type is a diagnostic item, use `is_type_diagnostic_item` instead.
/// If you change the signature, remember to update the internal lint `MatchTypeOnDiagItem`
pub fn match_type(cx: &LateContext<'_>, ty: Ty<'_>, path: &[&str]) -> bool {
    match ty.kind() {
        ty::Adt(adt, _) => match_def_path(cx, adt.did(), path),
        _ => false,
    }
}

/// Checks if the drop order for a type matters. Some std types implement drop solely to
/// deallocate memory. For these types, and composites containing them, changing the drop order
/// won't result in any observable side effects.
pub fn needs_ordered_drop<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    fn needs_ordered_drop_inner<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, seen: &mut FxHashSet<Ty<'tcx>>) -> bool {
        if !seen.insert(ty) {
            return false;
        }
        if !ty.has_significant_drop(cx.tcx, cx.param_env) {
            false
        }
        // Check for std types which implement drop, but only for memory allocation.
        else if is_type_lang_item(cx, ty, LangItem::OwnedBox)
            || matches!(
                get_type_diagnostic_name(cx, ty),
                Some(sym::HashSet | sym::Rc | sym::Arc | sym::cstring_type)
            )
            || match_type(cx, ty, &paths::WEAK_RC)
            || match_type(cx, ty, &paths::WEAK_ARC)
        {
            // Check all of the generic arguments.
            if let ty::Adt(_, subs) = ty.kind() {
                subs.types().any(|ty| needs_ordered_drop_inner(cx, ty, seen))
            } else {
                true
            }
        } else if !cx
            .tcx
            .lang_items()
            .drop_trait()
            .map_or(false, |id| implements_trait(cx, ty, id, &[]))
        {
            // This type doesn't implement drop, so no side effects here.
            // Check if any component type has any.
            match ty.kind() {
                ty::Tuple(fields) => fields.iter().any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                ty::Array(ty, _) => needs_ordered_drop_inner(cx, *ty, seen),
                ty::Adt(adt, subs) => adt
                    .all_fields()
                    .map(|f| f.ty(cx.tcx, subs))
                    .any(|ty| needs_ordered_drop_inner(cx, ty, seen)),
                _ => true,
            }
        } else {
            true
        }
    }

    needs_ordered_drop_inner(cx, ty, &mut FxHashSet::default())
}

/// Peels off all references on the type. Returns the underlying type and the number of references
/// removed.
pub fn peel_mid_ty_refs(ty: Ty<'_>) -> (Ty<'_>, usize) {
    fn peel(ty: Ty<'_>, count: usize) -> (Ty<'_>, usize) {
        if let ty::Ref(_, ty, _) = ty.kind() {
            peel(*ty, count + 1)
        } else {
            (ty, count)
        }
    }
    peel(ty, 0)
}

/// Peels off all references on the type. Returns the underlying type, the number of references
/// removed, and whether the pointer is ultimately mutable or not.
pub fn peel_mid_ty_refs_is_mutable(ty: Ty<'_>) -> (Ty<'_>, usize, Mutability) {
    fn f(ty: Ty<'_>, count: usize, mutability: Mutability) -> (Ty<'_>, usize, Mutability) {
        match ty.kind() {
            ty::Ref(_, ty, Mutability::Mut) => f(*ty, count + 1, mutability),
            ty::Ref(_, ty, Mutability::Not) => f(*ty, count + 1, Mutability::Not),
            _ => (ty, count, mutability),
        }
    }
    f(ty, 0, Mutability::Mut)
}

/// Returns `true` if the given type is an `unsafe` function.
pub fn type_is_unsafe_function<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> bool {
    match ty.kind() {
        ty::FnDef(..) | ty::FnPtr(_) => ty.fn_sig(cx.tcx).unsafety() == Unsafety::Unsafe,
        _ => false,
    }
}

/// Returns the base type for HIR references and pointers.
pub fn walk_ptrs_hir_ty<'tcx>(ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
    match ty.kind {
        TyKind::Ptr(ref mut_ty) | TyKind::Rptr(_, ref mut_ty) => walk_ptrs_hir_ty(mut_ty.ty),
        _ => ty,
    }
}

/// Returns the base type for references and raw pointers, and count reference
/// depth.
pub fn walk_ptrs_ty_depth(ty: Ty<'_>) -> (Ty<'_>, usize) {
    fn inner(ty: Ty<'_>, depth: usize) -> (Ty<'_>, usize) {
        match ty.kind() {
            ty::Ref(_, ty, _) => inner(*ty, depth + 1),
            _ => (ty, depth),
        }
    }
    inner(ty, 0)
}

/// Returns `true` if types `a` and `b` are same types having same `Const` generic args,
/// otherwise returns `false`
pub fn same_type_and_consts<'tcx>(a: Ty<'tcx>, b: Ty<'tcx>) -> bool {
    match (&a.kind(), &b.kind()) {
        (&ty::Adt(did_a, substs_a), &ty::Adt(did_b, substs_b)) => {
            if did_a != did_b {
                return false;
            }

            substs_a
                .iter()
                .zip(substs_b.iter())
                .all(|(arg_a, arg_b)| match (arg_a.unpack(), arg_b.unpack()) {
                    (GenericArgKind::Const(inner_a), GenericArgKind::Const(inner_b)) => inner_a == inner_b,
                    (GenericArgKind::Type(type_a), GenericArgKind::Type(type_b)) => {
                        same_type_and_consts(type_a, type_b)
                    },
                    _ => true,
                })
        },
        _ => a == b,
    }
}

/// Checks if a given type looks safe to be uninitialized.
pub fn is_uninit_value_valid_for_ty(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
    match *ty.kind() {
        ty::Array(component, _) => is_uninit_value_valid_for_ty(cx, component),
        ty::Tuple(types) => types.iter().all(|ty| is_uninit_value_valid_for_ty(cx, ty)),
        ty::Adt(adt, _) => cx.tcx.lang_items().maybe_uninit() == Some(adt.did()),
        _ => false,
    }
}

/// Gets an iterator over all predicates which apply to the given item.
pub fn all_predicates_of(tcx: TyCtxt<'_>, id: DefId) -> impl Iterator<Item = &(Predicate<'_>, Span)> {
    let mut next_id = Some(id);
    iter::from_fn(move || {
        next_id.take().map(|id| {
            let preds = tcx.predicates_of(id);
            next_id = preds.parent;
            preds.predicates.iter()
        })
    })
    .flatten()
}

/// A signature for a function like type.
#[derive(Clone, Copy)]
pub enum ExprFnSig<'tcx> {
    Sig(Binder<'tcx, FnSig<'tcx>>, Option<DefId>),
    Closure(Option<&'tcx FnDecl<'tcx>>, Binder<'tcx, FnSig<'tcx>>),
    Trait(Binder<'tcx, Ty<'tcx>>, Option<Binder<'tcx, Ty<'tcx>>>, Option<DefId>),
}
impl<'tcx> ExprFnSig<'tcx> {
    /// Gets the argument type at the given offset. This will return `None` when the index is out of
    /// bounds only for variadic functions, otherwise this will panic.
    pub fn input(self, i: usize) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs().map_bound(|inputs| inputs.get(i).copied()).transpose()
                } else {
                    Some(sig.input(i))
                }
            },
            Self::Closure(_, sig) => Some(sig.input(0).map_bound(|ty| ty.tuple_fields()[i])),
            Self::Trait(inputs, _, _) => Some(inputs.map_bound(|ty| ty.tuple_fields()[i])),
        }
    }

    /// Gets the argument type at the given offset. For closures this will also get the type as
    /// written. This will return `None` when the index is out of bounds only for variadic
    /// functions, otherwise this will panic.
    pub fn input_with_hir(self, i: usize) -> Option<(Option<&'tcx hir::Ty<'tcx>>, Binder<'tcx, Ty<'tcx>>)> {
        match self {
            Self::Sig(sig, _) => {
                if sig.c_variadic() {
                    sig.inputs()
                        .map_bound(|inputs| inputs.get(i).copied())
                        .transpose()
                        .map(|arg| (None, arg))
                } else {
                    Some((None, sig.input(i)))
                }
            },
            Self::Closure(decl, sig) => Some((
                decl.and_then(|decl| decl.inputs.get(i)),
                sig.input(0).map_bound(|ty| ty.tuple_fields()[i]),
            )),
            Self::Trait(inputs, _, _) => Some((None, inputs.map_bound(|ty| ty.tuple_fields()[i]))),
        }
    }

    /// Gets the result type, if one could be found. Note that the result type of a trait may not be
    /// specified.
    pub fn output(self) -> Option<Binder<'tcx, Ty<'tcx>>> {
        match self {
            Self::Sig(sig, _) | Self::Closure(_, sig) => Some(sig.output()),
            Self::Trait(_, output, _) => output,
        }
    }

    pub fn predicates_id(&self) -> Option<DefId> {
        if let ExprFnSig::Sig(_, id) | ExprFnSig::Trait(_, _, id) = *self {
            id
        } else {
            None
        }
    }
}

/// If the expression is function like, get the signature for it.
pub fn expr_sig<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>) -> Option<ExprFnSig<'tcx>> {
    if let Res::Def(DefKind::Fn | DefKind::Ctor(_, CtorKind::Fn) | DefKind::AssocFn, id) = path_res(cx, expr) {
        Some(ExprFnSig::Sig(cx.tcx.fn_sig(id), Some(id)))
    } else {
        ty_sig(cx, cx.typeck_results().expr_ty_adjusted(expr).peel_refs())
    }
}

/// If the type is function like, get the signature for it.
pub fn ty_sig<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> Option<ExprFnSig<'tcx>> {
    if ty.is_box() {
        return ty_sig(cx, ty.boxed_ty());
    }
    match *ty.kind() {
        ty::Closure(id, subs) => {
            let decl = id
                .as_local()
                .and_then(|id| cx.tcx.hir().fn_decl_by_hir_id(cx.tcx.hir().local_def_id_to_hir_id(id)));
            Some(ExprFnSig::Closure(decl, subs.as_closure().sig()))
        },
        ty::FnDef(id, subs) => Some(ExprFnSig::Sig(cx.tcx.bound_fn_sig(id).subst(cx.tcx, subs), Some(id))),
        ty::Opaque(id, _) => sig_from_bounds(cx, ty, cx.tcx.item_bounds(id), cx.tcx.opt_parent(id)),
        ty::FnPtr(sig) => Some(ExprFnSig::Sig(sig, None)),
        ty::Dynamic(bounds, _, _) => {
            let lang_items = cx.tcx.lang_items();
            match bounds.principal() {
                Some(bound)
                    if Some(bound.def_id()) == lang_items.fn_trait()
                        || Some(bound.def_id()) == lang_items.fn_once_trait()
                        || Some(bound.def_id()) == lang_items.fn_mut_trait() =>
                {
                    let output = bounds
                        .projection_bounds()
                        .find(|p| lang_items.fn_once_output().map_or(false, |id| id == p.item_def_id()))
                        .map(|p| p.map_bound(|p| p.term.ty().unwrap()));
                    Some(ExprFnSig::Trait(bound.map_bound(|b| b.substs.type_at(0)), output, None))
                },
                _ => None,
            }
        },
        ty::Projection(proj) => match cx.tcx.try_normalize_erasing_regions(cx.param_env, ty) {
            Ok(normalized_ty) if normalized_ty != ty => ty_sig(cx, normalized_ty),
            _ => sig_for_projection(cx, proj).or_else(|| sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None)),
        },
        ty::Param(_) => sig_from_bounds(cx, ty, cx.param_env.caller_bounds(), None),
        _ => None,
    }
}

fn sig_from_bounds<'tcx>(
    cx: &LateContext<'tcx>,
    ty: Ty<'tcx>,
    predicates: &'tcx [Predicate<'tcx>],
    predicates_id: Option<DefId>,
) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for pred in predicates {
        match pred.kind().skip_binder() {
            PredicateKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id()))
                    && p.self_ty() == ty =>
            {
                let i = pred.kind().rebind(p.trait_ref.substs.type_at(1));
                if inputs.map_or(false, |inputs| i != inputs) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            PredicateKind::Projection(p)
                if Some(p.projection_ty.item_def_id) == lang_items.fn_once_output()
                    && p.projection_ty.self_ty() == ty =>
            {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = Some(pred.kind().rebind(p.term.ty().unwrap()));
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, predicates_id))
}

fn sig_for_projection<'tcx>(cx: &LateContext<'tcx>, ty: ProjectionTy<'tcx>) -> Option<ExprFnSig<'tcx>> {
    let mut inputs = None;
    let mut output = None;
    let lang_items = cx.tcx.lang_items();

    for pred in cx
        .tcx
        .bound_explicit_item_bounds(ty.item_def_id)
        .transpose_iter()
        .map(|x| x.map_bound(|(p, _)| p))
    {
        match pred.0.kind().skip_binder() {
            PredicateKind::Trait(p)
                if (lang_items.fn_trait() == Some(p.def_id())
                    || lang_items.fn_mut_trait() == Some(p.def_id())
                    || lang_items.fn_once_trait() == Some(p.def_id())) =>
            {
                let i = pred
                    .map_bound(|pred| pred.kind().rebind(p.trait_ref.substs.type_at(1)))
                    .subst(cx.tcx, ty.substs);

                if inputs.map_or(false, |inputs| inputs != i) {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                inputs = Some(i);
            },
            PredicateKind::Projection(p) if Some(p.projection_ty.item_def_id) == lang_items.fn_once_output() => {
                if output.is_some() {
                    // Multiple different fn trait impls. Is this even allowed?
                    return None;
                }
                output = Some(
                    pred.map_bound(|pred| pred.kind().rebind(p.term.ty().unwrap()))
                        .subst(cx.tcx, ty.substs),
                );
            },
            _ => (),
        }
    }

    inputs.map(|ty| ExprFnSig::Trait(ty, output, None))
}

#[derive(Clone, Copy)]
pub enum EnumValue {
    Unsigned(u128),
    Signed(i128),
}
impl core::ops::Add<u32> for EnumValue {
    type Output = Self;
    fn add(self, n: u32) -> Self::Output {
        match self {
            Self::Unsigned(x) => Self::Unsigned(x + u128::from(n)),
            Self::Signed(x) => Self::Signed(x + i128::from(n)),
        }
    }
}

/// Attempts to read the given constant as though it were an an enum value.
#[expect(clippy::cast_possible_truncation, clippy::cast_possible_wrap)]
pub fn read_explicit_enum_value(tcx: TyCtxt<'_>, id: DefId) -> Option<EnumValue> {
    if let Ok(ConstValue::Scalar(Scalar::Int(value))) = tcx.const_eval_poly(id) {
        match tcx.type_of(id).kind() {
            ty::Int(_) => Some(EnumValue::Signed(match value.size().bytes() {
                1 => i128::from(value.assert_bits(Size::from_bytes(1)) as u8 as i8),
                2 => i128::from(value.assert_bits(Size::from_bytes(2)) as u16 as i16),
                4 => i128::from(value.assert_bits(Size::from_bytes(4)) as u32 as i32),
                8 => i128::from(value.assert_bits(Size::from_bytes(8)) as u64 as i64),
                16 => value.assert_bits(Size::from_bytes(16)) as i128,
                _ => return None,
            })),
            ty::Uint(_) => Some(EnumValue::Unsigned(match value.size().bytes() {
                1 => value.assert_bits(Size::from_bytes(1)),
                2 => value.assert_bits(Size::from_bytes(2)),
                4 => value.assert_bits(Size::from_bytes(4)),
                8 => value.assert_bits(Size::from_bytes(8)),
                16 => value.assert_bits(Size::from_bytes(16)),
                _ => return None,
            })),
            _ => None,
        }
    } else {
        None
    }
}

/// Gets the value of the given variant.
pub fn get_discriminant_value(tcx: TyCtxt<'_>, adt: AdtDef<'_>, i: VariantIdx) -> EnumValue {
    let variant = &adt.variant(i);
    match variant.discr {
        VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap(),
        VariantDiscr::Relative(x) => match adt.variant((i.as_usize() - x as usize).into()).discr {
            VariantDiscr::Explicit(id) => read_explicit_enum_value(tcx, id).unwrap() + x,
            VariantDiscr::Relative(_) => EnumValue::Unsigned(x.into()),
        },
    }
}

/// Check if the given type is either `core::ffi::c_void`, `std::os::raw::c_void`, or one of the
/// platform specific `libc::<platform>::c_void` types in libc.
pub fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
    if let ty::Adt(adt, _) = ty.kind()
        && let &[krate, .., name] = &*cx.get_def_path(adt.did())
        && let sym::libc | sym::core | sym::std = krate
        && name.as_str() == "c_void"
    {
        true
    } else {
        false
    }
}

pub fn for_each_top_level_late_bound_region<B>(
    ty: Ty<'_>,
    f: impl FnMut(BoundRegion) -> ControlFlow<B>,
) -> ControlFlow<B> {
    struct V<F> {
        index: u32,
        f: F,
    }
    impl<'tcx, B, F: FnMut(BoundRegion) -> ControlFlow<B>> TypeVisitor<'tcx> for V<F> {
        type BreakTy = B;
        fn visit_region(&mut self, r: Region<'tcx>) -> ControlFlow<Self::BreakTy> {
            if let RegionKind::ReLateBound(idx, bound) = r.kind() && idx.as_u32() == self.index {
                (self.f)(bound)
            } else {
                ControlFlow::Continue(())
            }
        }
        fn visit_binder<T: TypeVisitable<'tcx>>(&mut self, t: &Binder<'tcx, T>) -> ControlFlow<Self::BreakTy> {
            self.index += 1;
            let res = t.super_visit_with(self);
            self.index -= 1;
            res
        }
    }
    ty.visit_with(&mut V { index: 0, f })
}

/// Gets the struct or enum variant from the given `Res`
pub fn variant_of_res<'tcx>(cx: &LateContext<'tcx>, res: Res) -> Option<&'tcx VariantDef> {
    match res {
        Res::Def(DefKind::Struct, id) => Some(cx.tcx.adt_def(id).non_enum_variant()),
        Res::Def(DefKind::Variant, id) => Some(cx.tcx.adt_def(cx.tcx.parent(id)).variant_with_id(id)),
        Res::Def(DefKind::Ctor(CtorOf::Struct, _), id) => Some(cx.tcx.adt_def(cx.tcx.parent(id)).non_enum_variant()),
        Res::Def(DefKind::Ctor(CtorOf::Variant, _), id) => {
            let var_id = cx.tcx.parent(id);
            Some(cx.tcx.adt_def(cx.tcx.parent(var_id)).variant_with_id(var_id))
        },
        Res::SelfCtor(id) => Some(cx.tcx.type_of(id).ty_adt_def().unwrap().non_enum_variant()),
        _ => None,
    }
}

/// Checks if the type is a type parameter implementing `FnOnce`, but not `FnMut`.
pub fn ty_is_fn_once_param<'tcx>(tcx: TyCtxt<'_>, ty: Ty<'tcx>, predicates: &'tcx [Predicate<'_>]) -> bool {
    let ty::Param(ty) = *ty.kind() else {
        return false;
    };
    let lang = tcx.lang_items();
    let (Some(fn_once_id), Some(fn_mut_id), Some(fn_id))
        = (lang.fn_once_trait(), lang.fn_mut_trait(), lang.fn_trait())
    else {
        return false;
    };
    predicates
        .iter()
        .try_fold(false, |found, p| {
            if let PredicateKind::Trait(p) = p.kind().skip_binder()
            && let ty::Param(self_ty) = p.trait_ref.self_ty().kind()
            && ty.index == self_ty.index
        {
            // This should use `super_traits_of`, but that's a private function.
            if p.trait_ref.def_id == fn_once_id {
                return Some(true);
            } else if p.trait_ref.def_id == fn_mut_id || p.trait_ref.def_id == fn_id {
                return None;
            }
        }
            Some(found)
        })
        .unwrap_or(false)
}

/// Comes up with an "at least" guesstimate for the type's size, not taking into
/// account the layout of type parameters.
pub fn approx_ty_size<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>) -> u64 {
    use rustc_middle::ty::layout::LayoutOf;
    if !is_normalizable(cx, cx.param_env, ty) {
        return 0;
    }
    match (cx.layout_of(ty).map(|layout| layout.size.bytes()), ty.kind()) {
        (Ok(size), _) => size,
        (Err(_), ty::Tuple(list)) => list.as_substs().types().map(|t| approx_ty_size(cx, t)).sum(),
        (Err(_), ty::Array(t, n)) => {
            n.try_eval_usize(cx.tcx, cx.param_env).unwrap_or_default() * approx_ty_size(cx, *t)
        },
        (Err(_), ty::Adt(def, subst)) if def.is_struct() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .sum::<u64>()
            })
            .sum(),
        (Err(_), ty::Adt(def, subst)) if def.is_enum() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .sum::<u64>()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), ty::Adt(def, subst)) if def.is_union() => def
            .variants()
            .iter()
            .map(|v| {
                v.fields
                    .iter()
                    .map(|field| approx_ty_size(cx, field.ty(cx.tcx, subst)))
                    .max()
                    .unwrap_or_default()
            })
            .max()
            .unwrap_or_default(),
        (Err(_), _) => 0,
    }
}