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
use crate::definitions::DefPathData;
use crate::hir;

use rustc_ast as ast;
use rustc_ast::NodeId;
use rustc_data_structures::stable_hasher::ToStableHashKey;
use rustc_data_structures::unord::UnordMap;
use rustc_macros::HashStable_Generic;
use rustc_span::def_id::{DefId, LocalDefId};
use rustc_span::hygiene::MacroKind;
use rustc_span::symbol::kw;
use rustc_span::Symbol;

use std::array::IntoIter;
use std::fmt::Debug;

/// Encodes if a `DefKind::Ctor` is the constructor of an enum variant or a struct.
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
pub enum CtorOf {
    /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit struct.
    Struct,
    /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit variant.
    Variant,
}

/// What kind of constructor something is.
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
pub enum CtorKind {
    /// Constructor function automatically created by a tuple struct/variant.
    Fn,
    /// Constructor constant automatically created by a unit struct/variant.
    Const,
}

/// An attribute that is not a macro; e.g., `#[inline]` or `#[rustfmt::skip]`.
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
pub enum NonMacroAttrKind {
    /// Single-segment attribute defined by the language (`#[inline]`)
    Builtin(Symbol),
    /// Multi-segment custom attribute living in a "tool module" (`#[rustfmt::skip]`).
    Tool,
    /// Single-segment custom attribute registered by a derive macro (`#[serde(default)]`).
    DeriveHelper,
    /// Single-segment custom attribute registered by a derive macro
    /// but used before that derive macro was expanded (deprecated).
    DeriveHelperCompat,
}

/// What kind of definition something is; e.g., `mod` vs `struct`.
/// `enum DefPathData` may need to be updated if a new variant is added here.
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
pub enum DefKind {
    // Type namespace
    Mod,
    /// Refers to the struct itself, [`DefKind::Ctor`] refers to its constructor if it exists.
    Struct,
    Union,
    Enum,
    /// Refers to the variant itself, [`DefKind::Ctor`] refers to its constructor if it exists.
    Variant,
    Trait,
    /// Type alias: `type Foo = Bar;`
    TyAlias,
    /// Type from an `extern` block.
    ForeignTy,
    /// Trait alias: `trait IntIterator = Iterator<Item = i32>;`
    TraitAlias,
    /// Associated type: `trait MyTrait { type Assoc; }`
    AssocTy,
    /// Type parameter: the `T` in `struct Vec<T> { ... }`
    TyParam,

    // Value namespace
    Fn,
    Const,
    /// Constant generic parameter: `struct Foo<const N: usize> { ... }`
    ConstParam,
    Static {
        /// Whether it's a `static mut` or just a `static`.
        mutability: ast::Mutability,
        /// Whether it's an anonymous static generated for nested allocations.
        nested: bool,
    },
    /// Refers to the struct or enum variant's constructor.
    ///
    /// The reason `Ctor` exists in addition to [`DefKind::Struct`] and
    /// [`DefKind::Variant`] is because structs and enum variants exist
    /// in the *type* namespace, whereas struct and enum variant *constructors*
    /// exist in the *value* namespace.
    ///
    /// You may wonder why enum variants exist in the type namespace as opposed
    /// to the value namespace. Check out [RFC 2593] for intuition on why that is.
    ///
    /// [RFC 2593]: https://github.com/rust-lang/rfcs/pull/2593
    Ctor(CtorOf, CtorKind),
    /// Associated function: `impl MyStruct { fn associated() {} }`
    /// or `trait Foo { fn associated() {} }`
    AssocFn,
    /// Associated constant: `trait MyTrait { const ASSOC: usize; }`
    AssocConst,

    // Macro namespace
    Macro(MacroKind),

    // Not namespaced (or they are, but we don't treat them so)
    ExternCrate,
    Use,
    /// An `extern` block.
    ForeignMod,
    /// Anonymous constant, e.g. the `1 + 2` in `[u8; 1 + 2]`
    AnonConst,
    /// An inline constant, e.g. `const { 1 + 2 }`
    InlineConst,
    /// Opaque type, aka `impl Trait`.
    OpaqueTy,
    Field,
    /// Lifetime parameter: the `'a` in `struct Foo<'a> { ... }`
    LifetimeParam,
    /// A use of `global_asm!`.
    GlobalAsm,
    Impl {
        of_trait: bool,
    },
    /// A closure, coroutine, or coroutine-closure.
    ///
    /// These are all represented with the same `ExprKind::Closure` in the AST and HIR,
    /// which makes it difficult to distinguish these during def collection. Therefore,
    /// we treat them all the same, and code which needs to distinguish them can match
    /// or `hir::ClosureKind` or `type_of`.
    Closure,
}

impl DefKind {
    /// Get an English description for the item's kind.
    ///
    /// If you have access to `TyCtxt`, use `TyCtxt::def_descr` or
    /// `TyCtxt::def_kind_descr` instead, because they give better
    /// information for coroutines and associated functions.
    pub fn descr(self, def_id: DefId) -> &'static str {
        match self {
            DefKind::Fn => "function",
            DefKind::Mod if def_id.is_crate_root() && !def_id.is_local() => "crate",
            DefKind::Mod => "module",
            DefKind::Static { .. } => "static",
            DefKind::Enum => "enum",
            DefKind::Variant => "variant",
            DefKind::Ctor(CtorOf::Variant, CtorKind::Fn) => "tuple variant",
            DefKind::Ctor(CtorOf::Variant, CtorKind::Const) => "unit variant",
            DefKind::Struct => "struct",
            DefKind::Ctor(CtorOf::Struct, CtorKind::Fn) => "tuple struct",
            DefKind::Ctor(CtorOf::Struct, CtorKind::Const) => "unit struct",
            DefKind::OpaqueTy => "opaque type",
            DefKind::TyAlias => "type alias",
            DefKind::TraitAlias => "trait alias",
            DefKind::AssocTy => "associated type",
            DefKind::Union => "union",
            DefKind::Trait => "trait",
            DefKind::ForeignTy => "foreign type",
            DefKind::AssocFn => "associated function",
            DefKind::Const => "constant",
            DefKind::AssocConst => "associated constant",
            DefKind::TyParam => "type parameter",
            DefKind::ConstParam => "const parameter",
            DefKind::Macro(macro_kind) => macro_kind.descr(),
            DefKind::LifetimeParam => "lifetime parameter",
            DefKind::Use => "import",
            DefKind::ForeignMod => "foreign module",
            DefKind::AnonConst => "constant expression",
            DefKind::InlineConst => "inline constant",
            DefKind::Field => "field",
            DefKind::Impl { .. } => "implementation",
            DefKind::Closure => "closure",
            DefKind::ExternCrate => "extern crate",
            DefKind::GlobalAsm => "global assembly block",
        }
    }

    /// Gets an English article for the definition.
    ///
    /// If you have access to `TyCtxt`, use `TyCtxt::def_descr_article` or
    /// `TyCtxt::def_kind_descr_article` instead, because they give better
    /// information for coroutines and associated functions.
    pub fn article(&self) -> &'static str {
        match *self {
            DefKind::AssocTy
            | DefKind::AssocConst
            | DefKind::AssocFn
            | DefKind::Enum
            | DefKind::OpaqueTy
            | DefKind::Impl { .. }
            | DefKind::Use
            | DefKind::InlineConst
            | DefKind::ExternCrate => "an",
            DefKind::Macro(macro_kind) => macro_kind.article(),
            _ => "a",
        }
    }

    pub fn ns(&self) -> Option<Namespace> {
        match self {
            DefKind::Mod
            | DefKind::Struct
            | DefKind::Union
            | DefKind::Enum
            | DefKind::Variant
            | DefKind::Trait
            | DefKind::OpaqueTy
            | DefKind::TyAlias
            | DefKind::ForeignTy
            | DefKind::TraitAlias
            | DefKind::AssocTy
            | DefKind::TyParam => Some(Namespace::TypeNS),

            DefKind::Fn
            | DefKind::Const
            | DefKind::ConstParam
            | DefKind::Static { .. }
            | DefKind::Ctor(..)
            | DefKind::AssocFn
            | DefKind::AssocConst => Some(Namespace::ValueNS),

            DefKind::Macro(..) => Some(Namespace::MacroNS),

            // Not namespaced.
            DefKind::AnonConst
            | DefKind::InlineConst
            | DefKind::Field
            | DefKind::LifetimeParam
            | DefKind::ExternCrate
            | DefKind::Closure
            | DefKind::Use
            | DefKind::ForeignMod
            | DefKind::GlobalAsm
            | DefKind::Impl { .. } => None,
        }
    }

    pub fn def_path_data(self, name: Symbol) -> DefPathData {
        match self {
            DefKind::Struct | DefKind::Union if name == kw::Empty => DefPathData::AnonAdt,
            DefKind::Mod
            | DefKind::Struct
            | DefKind::Union
            | DefKind::Enum
            | DefKind::Variant
            | DefKind::Trait
            | DefKind::TyAlias
            | DefKind::ForeignTy
            | DefKind::TraitAlias
            | DefKind::AssocTy
            | DefKind::TyParam
            | DefKind::ExternCrate => DefPathData::TypeNs(name),
            // It's not exactly an anon const, but wrt DefPathData, there
            // is no difference.
            DefKind::Static { nested: true, .. } => DefPathData::AnonConst,
            DefKind::Fn
            | DefKind::Const
            | DefKind::ConstParam
            | DefKind::Static { .. }
            | DefKind::AssocFn
            | DefKind::AssocConst
            | DefKind::Field => DefPathData::ValueNs(name),
            DefKind::Macro(..) => DefPathData::MacroNs(name),
            DefKind::LifetimeParam => DefPathData::LifetimeNs(name),
            DefKind::Ctor(..) => DefPathData::Ctor,
            DefKind::Use => DefPathData::Use,
            DefKind::ForeignMod => DefPathData::ForeignMod,
            DefKind::AnonConst => DefPathData::AnonConst,
            DefKind::InlineConst => DefPathData::AnonConst,
            DefKind::OpaqueTy => DefPathData::OpaqueTy,
            DefKind::GlobalAsm => DefPathData::GlobalAsm,
            DefKind::Impl { .. } => DefPathData::Impl,
            DefKind::Closure => DefPathData::Closure,
        }
    }

    #[inline]
    pub fn is_fn_like(self) -> bool {
        matches!(self, DefKind::Fn | DefKind::AssocFn | DefKind::Closure)
    }

    /// Whether `query get_codegen_attrs` should be used with this definition.
    pub fn has_codegen_attrs(self) -> bool {
        match self {
            DefKind::Fn
            | DefKind::AssocFn
            | DefKind::Ctor(..)
            | DefKind::Closure
            | DefKind::Static { .. } => true,
            DefKind::Mod
            | DefKind::Struct
            | DefKind::Union
            | DefKind::Enum
            | DefKind::Variant
            | DefKind::Trait
            | DefKind::TyAlias
            | DefKind::ForeignTy
            | DefKind::TraitAlias
            | DefKind::AssocTy
            | DefKind::Const
            | DefKind::AssocConst
            | DefKind::Macro(..)
            | DefKind::Use
            | DefKind::ForeignMod
            | DefKind::OpaqueTy
            | DefKind::Impl { .. }
            | DefKind::Field
            | DefKind::TyParam
            | DefKind::ConstParam
            | DefKind::LifetimeParam
            | DefKind::AnonConst
            | DefKind::InlineConst
            | DefKind::GlobalAsm
            | DefKind::ExternCrate => false,
        }
    }
}

/// The resolution of a path or export.
///
/// For every path or identifier in Rust, the compiler must determine
/// what the path refers to. This process is called name resolution,
/// and `Res` is the primary result of name resolution.
///
/// For example, everything prefixed with `/* Res */` in this example has
/// an associated `Res`:
///
/// ```
/// fn str_to_string(s: & /* Res */ str) -> /* Res */ String {
///     /* Res */ String::from(/* Res */ s)
/// }
///
/// /* Res */ str_to_string("hello");
/// ```
///
/// The associated `Res`s will be:
///
/// - `str` will resolve to [`Res::PrimTy`];
/// - `String` will resolve to [`Res::Def`], and the `Res` will include the [`DefId`]
///   for `String` as defined in the standard library;
/// - `String::from` will also resolve to [`Res::Def`], with the [`DefId`]
///   pointing to `String::from`;
/// - `s` will resolve to [`Res::Local`];
/// - the call to `str_to_string` will resolve to [`Res::Def`], with the [`DefId`]
///   pointing to the definition of `str_to_string` in the current crate.
//
#[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug, HashStable_Generic)]
pub enum Res<Id = hir::HirId> {
    /// Definition having a unique ID (`DefId`), corresponds to something defined in user code.
    ///
    /// **Not bound to a specific namespace.**
    Def(DefKind, DefId),

    // Type namespace
    /// A primitive type such as `i32` or `str`.
    ///
    /// **Belongs to the type namespace.**
    PrimTy(hir::PrimTy),

    /// The `Self` type, as used within a trait.
    ///
    /// **Belongs to the type namespace.**
    ///
    /// See the examples on [`Res::SelfTyAlias`] for details.
    SelfTyParam {
        /// The trait this `Self` is a generic parameter for.
        trait_: DefId,
    },

    /// The `Self` type, as used somewhere other than within a trait.
    ///
    /// **Belongs to the type namespace.**
    ///
    /// Examples:
    /// ```
    /// struct Bar(Box<Self>); // SelfTyAlias
    ///
    /// trait Foo {
    ///     fn foo() -> Box<Self>; // SelfTyParam
    /// }
    ///
    /// impl Bar {
    ///     fn blah() {
    ///         let _: Self; // SelfTyAlias
    ///     }
    /// }
    ///
    /// impl Foo for Bar {
    ///     fn foo() -> Box<Self> { // SelfTyAlias
    ///         let _: Self;        // SelfTyAlias
    ///
    ///         todo!()
    ///     }
    /// }
    /// ```
    /// *See also [`Res::SelfCtor`].*
    ///
    SelfTyAlias {
        /// The item introducing the `Self` type alias. Can be used in the `type_of` query
        /// to get the underlying type.
        alias_to: DefId,

        /// Whether the `Self` type is disallowed from mentioning generics (i.e. when used in an
        /// anonymous constant).
        ///
        /// HACK(min_const_generics): self types also have an optional requirement to **not**
        /// mention any generic parameters to allow the following with `min_const_generics`:
        /// ```
        /// # struct Foo;
        /// impl Foo { fn test() -> [u8; std::mem::size_of::<Self>()] { todo!() } }
        ///
        /// struct Bar([u8; baz::<Self>()]);
        /// const fn baz<T>() -> usize { 10 }
        /// ```
        /// We do however allow `Self` in repeat expression even if it is generic to not break code
        /// which already works on stable while causing the `const_evaluatable_unchecked` future
        /// compat lint:
        /// ```
        /// fn foo<T>() {
        ///     let _bar = [1_u8; std::mem::size_of::<*mut T>()];
        /// }
        /// ```
        // FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
        forbid_generic: bool,

        /// Is this within an `impl Foo for bar`?
        is_trait_impl: bool,
    },

    // Value namespace
    /// The `Self` constructor, along with the [`DefId`]
    /// of the impl it is associated with.
    ///
    /// **Belongs to the value namespace.**
    ///
    /// *See also [`Res::SelfTyParam`] and [`Res::SelfTyAlias`].*
    SelfCtor(DefId),

    /// A local variable or function parameter.
    ///
    /// **Belongs to the value namespace.**
    Local(Id),

    /// A tool attribute module; e.g., the `rustfmt` in `#[rustfmt::skip]`.
    ///
    /// **Belongs to the type namespace.**
    ToolMod,

    // Macro namespace
    /// An attribute that is *not* implemented via macro.
    /// E.g., `#[inline]` and `#[rustfmt::skip]`, which are essentially directives,
    /// as opposed to `#[test]`, which is a builtin macro.
    ///
    /// **Belongs to the macro namespace.**
    NonMacroAttr(NonMacroAttrKind), // e.g., `#[inline]` or `#[rustfmt::skip]`

    // All namespaces
    /// Name resolution failed. We use a dummy `Res` variant so later phases
    /// of the compiler won't crash and can instead report more errors.
    ///
    /// **Not bound to a specific namespace.**
    Err,
}

/// The result of resolving a path before lowering to HIR,
/// with "module" segments resolved and associated item
/// segments deferred to type checking.
/// `base_res` is the resolution of the resolved part of the
/// path, `unresolved_segments` is the number of unresolved
/// segments.
///
/// ```text
/// module::Type::AssocX::AssocY::MethodOrAssocType
/// ^~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/// base_res      unresolved_segments = 3
///
/// <T as Trait>::AssocX::AssocY::MethodOrAssocType
///       ^~~~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~
///       base_res        unresolved_segments = 2
/// ```
#[derive(Copy, Clone, Debug)]
pub struct PartialRes {
    base_res: Res<NodeId>,
    unresolved_segments: usize,
}

impl PartialRes {
    #[inline]
    pub fn new(base_res: Res<NodeId>) -> Self {
        PartialRes { base_res, unresolved_segments: 0 }
    }

    #[inline]
    pub fn with_unresolved_segments(base_res: Res<NodeId>, mut unresolved_segments: usize) -> Self {
        if base_res == Res::Err {
            unresolved_segments = 0
        }
        PartialRes { base_res, unresolved_segments }
    }

    #[inline]
    pub fn base_res(&self) -> Res<NodeId> {
        self.base_res
    }

    #[inline]
    pub fn unresolved_segments(&self) -> usize {
        self.unresolved_segments
    }

    #[inline]
    pub fn full_res(&self) -> Option<Res<NodeId>> {
        (self.unresolved_segments == 0).then_some(self.base_res)
    }

    #[inline]
    pub fn expect_full_res(&self) -> Res<NodeId> {
        self.full_res().expect("unexpected unresolved segments")
    }
}

/// Different kinds of symbols can coexist even if they share the same textual name.
/// Therefore, they each have a separate universe (known as a "namespace").
#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug, Encodable, Decodable)]
#[derive(HashStable_Generic)]
pub enum Namespace {
    /// The type namespace includes `struct`s, `enum`s, `union`s, `trait`s, and `mod`s
    /// (and, by extension, crates).
    ///
    /// Note that the type namespace includes other items; this is not an
    /// exhaustive list.
    TypeNS,
    /// The value namespace includes `fn`s, `const`s, `static`s, and local variables (including function arguments).
    ValueNS,
    /// The macro namespace includes `macro_rules!` macros, declarative `macro`s,
    /// procedural macros, attribute macros, `derive` macros, and non-macro attributes
    /// like `#[inline]` and `#[rustfmt::skip]`.
    MacroNS,
}

impl Namespace {
    /// The English description of the namespace.
    pub fn descr(self) -> &'static str {
        match self {
            Self::TypeNS => "type",
            Self::ValueNS => "value",
            Self::MacroNS => "macro",
        }
    }
}

impl<CTX: crate::HashStableContext> ToStableHashKey<CTX> for Namespace {
    type KeyType = Namespace;

    #[inline]
    fn to_stable_hash_key(&self, _: &CTX) -> Namespace {
        *self
    }
}

/// Just a helper ‒ separate structure for each namespace.
#[derive(Copy, Clone, Default, Debug)]
pub struct PerNS<T> {
    pub value_ns: T,
    pub type_ns: T,
    pub macro_ns: T,
}

impl<T> PerNS<T> {
    pub fn map<U, F: FnMut(T) -> U>(self, mut f: F) -> PerNS<U> {
        PerNS { value_ns: f(self.value_ns), type_ns: f(self.type_ns), macro_ns: f(self.macro_ns) }
    }

    pub fn into_iter(self) -> IntoIter<T, 3> {
        [self.value_ns, self.type_ns, self.macro_ns].into_iter()
    }

    pub fn iter(&self) -> IntoIter<&T, 3> {
        [&self.value_ns, &self.type_ns, &self.macro_ns].into_iter()
    }
}

impl<T> ::std::ops::Index<Namespace> for PerNS<T> {
    type Output = T;

    fn index(&self, ns: Namespace) -> &T {
        match ns {
            Namespace::ValueNS => &self.value_ns,
            Namespace::TypeNS => &self.type_ns,
            Namespace::MacroNS => &self.macro_ns,
        }
    }
}

impl<T> ::std::ops::IndexMut<Namespace> for PerNS<T> {
    fn index_mut(&mut self, ns: Namespace) -> &mut T {
        match ns {
            Namespace::ValueNS => &mut self.value_ns,
            Namespace::TypeNS => &mut self.type_ns,
            Namespace::MacroNS => &mut self.macro_ns,
        }
    }
}

impl<T> PerNS<Option<T>> {
    /// Returns `true` if all the items in this collection are `None`.
    pub fn is_empty(&self) -> bool {
        self.type_ns.is_none() && self.value_ns.is_none() && self.macro_ns.is_none()
    }

    /// Returns an iterator over the items which are `Some`.
    pub fn present_items(self) -> impl Iterator<Item = T> {
        [self.type_ns, self.value_ns, self.macro_ns].into_iter().flatten()
    }
}

impl CtorKind {
    pub fn from_ast(vdata: &ast::VariantData) -> Option<(CtorKind, NodeId)> {
        match *vdata {
            ast::VariantData::Tuple(_, node_id) => Some((CtorKind::Fn, node_id)),
            ast::VariantData::Unit(node_id) => Some((CtorKind::Const, node_id)),
            ast::VariantData::Struct { .. } => None,
        }
    }
}

impl NonMacroAttrKind {
    pub fn descr(self) -> &'static str {
        match self {
            NonMacroAttrKind::Builtin(..) => "built-in attribute",
            NonMacroAttrKind::Tool => "tool attribute",
            NonMacroAttrKind::DeriveHelper | NonMacroAttrKind::DeriveHelperCompat => {
                "derive helper attribute"
            }
        }
    }

    // Currently trivial, but exists in case a new kind is added in the future whose name starts
    // with a vowel.
    pub fn article(self) -> &'static str {
        "a"
    }

    /// Users of some attributes cannot mark them as used, so they are considered always used.
    pub fn is_used(self) -> bool {
        match self {
            NonMacroAttrKind::Tool
            | NonMacroAttrKind::DeriveHelper
            | NonMacroAttrKind::DeriveHelperCompat => true,
            NonMacroAttrKind::Builtin(..) => false,
        }
    }
}

impl<Id> Res<Id> {
    /// Return the `DefId` of this `Def` if it has an ID, else panic.
    pub fn def_id(&self) -> DefId
    where
        Id: Debug,
    {
        self.opt_def_id().unwrap_or_else(|| panic!("attempted .def_id() on invalid res: {self:?}"))
    }

    /// Return `Some(..)` with the `DefId` of this `Res` if it has a ID, else `None`.
    pub fn opt_def_id(&self) -> Option<DefId> {
        match *self {
            Res::Def(_, id) => Some(id),

            Res::Local(..)
            | Res::PrimTy(..)
            | Res::SelfTyParam { .. }
            | Res::SelfTyAlias { .. }
            | Res::SelfCtor(..)
            | Res::ToolMod
            | Res::NonMacroAttr(..)
            | Res::Err => None,
        }
    }

    /// Return the `DefId` of this `Res` if it represents a module.
    pub fn mod_def_id(&self) -> Option<DefId> {
        match *self {
            Res::Def(DefKind::Mod, id) => Some(id),
            _ => None,
        }
    }

    /// A human readable name for the res kind ("function", "module", etc.).
    pub fn descr(&self) -> &'static str {
        match *self {
            Res::Def(kind, def_id) => kind.descr(def_id),
            Res::SelfCtor(..) => "self constructor",
            Res::PrimTy(..) => "builtin type",
            Res::Local(..) => "local variable",
            Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } => "self type",
            Res::ToolMod => "tool module",
            Res::NonMacroAttr(attr_kind) => attr_kind.descr(),
            Res::Err => "unresolved item",
        }
    }

    /// Gets an English article for the `Res`.
    pub fn article(&self) -> &'static str {
        match *self {
            Res::Def(kind, _) => kind.article(),
            Res::NonMacroAttr(kind) => kind.article(),
            Res::Err => "an",
            _ => "a",
        }
    }

    pub fn map_id<R>(self, mut map: impl FnMut(Id) -> R) -> Res<R> {
        match self {
            Res::Def(kind, id) => Res::Def(kind, id),
            Res::SelfCtor(id) => Res::SelfCtor(id),
            Res::PrimTy(id) => Res::PrimTy(id),
            Res::Local(id) => Res::Local(map(id)),
            Res::SelfTyParam { trait_ } => Res::SelfTyParam { trait_ },
            Res::SelfTyAlias { alias_to, forbid_generic, is_trait_impl } => {
                Res::SelfTyAlias { alias_to, forbid_generic, is_trait_impl }
            }
            Res::ToolMod => Res::ToolMod,
            Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
            Res::Err => Res::Err,
        }
    }

    pub fn apply_id<R, E>(self, mut map: impl FnMut(Id) -> Result<R, E>) -> Result<Res<R>, E> {
        Ok(match self {
            Res::Def(kind, id) => Res::Def(kind, id),
            Res::SelfCtor(id) => Res::SelfCtor(id),
            Res::PrimTy(id) => Res::PrimTy(id),
            Res::Local(id) => Res::Local(map(id)?),
            Res::SelfTyParam { trait_ } => Res::SelfTyParam { trait_ },
            Res::SelfTyAlias { alias_to, forbid_generic, is_trait_impl } => {
                Res::SelfTyAlias { alias_to, forbid_generic, is_trait_impl }
            }
            Res::ToolMod => Res::ToolMod,
            Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
            Res::Err => Res::Err,
        })
    }

    #[track_caller]
    pub fn expect_non_local<OtherId>(self) -> Res<OtherId> {
        self.map_id(
            #[track_caller]
            |_| panic!("unexpected `Res::Local`"),
        )
    }

    pub fn macro_kind(self) -> Option<MacroKind> {
        match self {
            Res::Def(DefKind::Macro(kind), _) => Some(kind),
            Res::NonMacroAttr(..) => Some(MacroKind::Attr),
            _ => None,
        }
    }

    /// Returns `None` if this is `Res::Err`
    pub fn ns(&self) -> Option<Namespace> {
        match self {
            Res::Def(kind, ..) => kind.ns(),
            Res::PrimTy(..) | Res::SelfTyParam { .. } | Res::SelfTyAlias { .. } | Res::ToolMod => {
                Some(Namespace::TypeNS)
            }
            Res::SelfCtor(..) | Res::Local(..) => Some(Namespace::ValueNS),
            Res::NonMacroAttr(..) => Some(Namespace::MacroNS),
            Res::Err => None,
        }
    }

    /// Always returns `true` if `self` is `Res::Err`
    pub fn matches_ns(&self, ns: Namespace) -> bool {
        self.ns().map_or(true, |actual_ns| actual_ns == ns)
    }

    /// Returns whether such a resolved path can occur in a tuple struct/variant pattern
    pub fn expected_in_tuple_struct_pat(&self) -> bool {
        matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) | Res::SelfCtor(..))
    }

    /// Returns whether such a resolved path can occur in a unit struct/variant pattern
    pub fn expected_in_unit_struct_pat(&self) -> bool {
        matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Const), _) | Res::SelfCtor(..))
    }
}

/// Resolution for a lifetime appearing in a type.
#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
pub enum LifetimeRes {
    /// Successfully linked the lifetime to a generic parameter.
    Param {
        /// Id of the generic parameter that introduced it.
        param: LocalDefId,
        /// Id of the introducing place. That can be:
        /// - an item's id, for the item's generic parameters;
        /// - a TraitRef's ref_id, identifying the `for<...>` binder;
        /// - a BareFn type's id.
        ///
        /// This information is used for impl-trait lifetime captures, to know when to or not to
        /// capture any given lifetime.
        binder: NodeId,
    },
    /// Created a generic parameter for an anonymous lifetime.
    Fresh {
        /// Id of the generic parameter that introduced it.
        ///
        /// Creating the associated `LocalDefId` is the responsibility of lowering.
        param: NodeId,
        /// Id of the introducing place. See `Param`.
        binder: NodeId,
    },
    /// This variant is used for anonymous lifetimes that we did not resolve during
    /// late resolution. Those lifetimes will be inferred by typechecking.
    Infer,
    /// Explicit `'static` lifetime.
    Static,
    /// Resolution failure.
    Error,
    /// HACK: This is used to recover the NodeId of an elided lifetime.
    ElidedAnchor { start: NodeId, end: NodeId },
}

pub type DocLinkResMap = UnordMap<(Symbol, Namespace), Option<Res<NodeId>>>;