compiler/rustc_hir/src/def.rs

   1 use crate::def_id::DefId;
   2 use crate::hir;
   3
   4 use rustc_ast as ast;
   5 use rustc_ast::NodeId;
   6 use rustc_macros::HashStable_Generic;
   7 use rustc_span::hygiene::MacroKind;
   8 use rustc_span::Symbol;
   9
  10 use std::array::IntoIter;
  11 use std::fmt::Debug;
  12
  13 /// Encodes if a `DefKind::Ctor` is the constructor of an enum variant or a struct.
  14 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
  15 #[derive(HashStable_Generic)]
  16 pub enum CtorOf {
  17     /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit struct.
  18     Struct,
  19     /// This `DefKind::Ctor` is a synthesized constructor of a tuple or unit variant.
  20     Variant,
  21 }
  22
  23 /// What kind of constructor something is.
  24 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
  25 #[derive(HashStable_Generic)]
  26 pub enum CtorKind {
  27     /// Constructor function automatically created by a tuple struct/variant.
  28     Fn,
  29     /// Constructor constant automatically created by a unit struct/variant.
  30     Const,
  31     /// Unusable name in value namespace created by a struct variant.
  32     Fictive,
  33 }
  34
  35 /// An attribute that is not a macro; e.g., `#[inline]` or `#[rustfmt::skip]`.
  36 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
  37 #[derive(HashStable_Generic)]
  38 pub enum NonMacroAttrKind {
  39     /// Single-segment attribute defined by the language (`#[inline]`)
  40     Builtin(Symbol),
  41     /// Multi-segment custom attribute living in a "tool module" (`#[rustfmt::skip]`).
  42     Tool,
  43     /// Single-segment custom attribute registered by a derive macro (`#[serde(default)]`).
  44     DeriveHelper,
  45     /// Single-segment custom attribute registered by a derive macro
  46     /// but used before that derive macro was expanded (deprecated).
  47     DeriveHelperCompat,
  48     /// Single-segment custom attribute registered with `#[register_attr]`.
  49     Registered,
  50 }
  51
  52 /// What kind of definition something is; e.g., `mod` vs `struct`.
  53 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
  54 #[derive(HashStable_Generic)]
  55 pub enum DefKind {
  56     // Type namespace
  57     Mod,
  58     /// Refers to the struct itself, [`DefKind::Ctor`] refers to its constructor if it exists.
  59     Struct,
  60     Union,
  61     Enum,
  62     /// Refers to the variant itself, [`DefKind::Ctor`] refers to its constructor if it exists.
  63     Variant,
  64     Trait,
  65     /// Type alias: `type Foo = Bar;`
  66     TyAlias,
  67     /// Type from an `extern` block.
  68     ForeignTy,
  69     /// Trait alias: `trait IntIterator = Iterator<Item = i32>;`
  70     TraitAlias,
  71     /// Associated type: `trait MyTrait { type Assoc; }`
  72     AssocTy,
  73     /// Type parameter: the `T` in `struct Vec<T> { ... }`
  74     TyParam,
  75
  76     // Value namespace
  77     Fn,
  78     Const,
  79     /// Constant generic parameter: `struct Foo<const N: usize> { ... }`
  80     ConstParam,
  81     Static(ast::Mutability),
  82     /// Refers to the struct or enum variant's constructor.
  83     ///
  84     /// The reason `Ctor` exists in addition to [`DefKind::Struct`] and
  85     /// [`DefKind::Variant`] is because structs and enum variants exist
  86     /// in the *type* namespace, whereas struct and enum variant *constructors*
  87     /// exist in the *value* namespace.
  88     ///
  89     /// You may wonder why enum variants exist in the type namespace as opposed
  90     /// to the value namespace. Check out [RFC 2593] for intuition on why that is.
  91     ///
  92     /// [RFC 2593]: https://github.com/rust-lang/rfcs/pull/2593
  93     Ctor(CtorOf, CtorKind),
  94     /// Associated function: `impl MyStruct { fn associated() {} }`
  95     AssocFn,
  96     /// Associated constant: `trait MyTrait { const ASSOC: usize; }`
  97     AssocConst,
  98
  99     // Macro namespace
 100     Macro(MacroKind),
 101
 102     // Not namespaced (or they are, but we don't treat them so)
 103     ExternCrate,
 104     Use,
 105     /// An `extern` block.
 106     ForeignMod,
 107     /// Anonymous constant, e.g. the `1 + 2` in `[u8; 1 + 2]`
 108     AnonConst,
 109     /// An inline constant, e.g. `const { 1 + 2 }`
 110     InlineConst,
 111     /// Opaque type, aka `impl Trait`.
 112     OpaqueTy,
 113     Field,
 114     /// Lifetime parameter: the `'a` in `struct Foo<'a> { ... }`
 115     LifetimeParam,
 116     /// A use of `global_asm!`.
 117     GlobalAsm,
 118     Impl,
 119     Closure,
 120     Generator,
 121 }
 122
 123 impl DefKind {
 124     pub fn descr(self, def_id: DefId) -> &'static str {
 125         match self {
 126             DefKind::Fn => "function",
 127             DefKind::Mod if def_id.is_crate_root() && !def_id.is_local() => "crate",
 128             DefKind::Mod => "module",
 129             DefKind::Static(..) => "static",
 130             DefKind::Enum => "enum",
 131             DefKind::Variant => "variant",
 132             DefKind::Ctor(CtorOf::Variant, CtorKind::Fn) => "tuple variant",
 133             DefKind::Ctor(CtorOf::Variant, CtorKind::Const) => "unit variant",
 134             DefKind::Ctor(CtorOf::Variant, CtorKind::Fictive) => "struct variant",
 135             DefKind::Struct => "struct",
 136             DefKind::Ctor(CtorOf::Struct, CtorKind::Fn) => "tuple struct",
 137             DefKind::Ctor(CtorOf::Struct, CtorKind::Const) => "unit struct",
 138             DefKind::Ctor(CtorOf::Struct, CtorKind::Fictive) => {
 139                 panic!("impossible struct constructor")
 140             }
 141             DefKind::OpaqueTy => "opaque type",
 142             DefKind::TyAlias => "type alias",
 143             DefKind::TraitAlias => "trait alias",
 144             DefKind::AssocTy => "associated type",
 145             DefKind::Union => "union",
 146             DefKind::Trait => "trait",
 147             DefKind::ForeignTy => "foreign type",
 148             DefKind::AssocFn => "associated function",
 149             DefKind::Const => "constant",
 150             DefKind::AssocConst => "associated constant",
 151             DefKind::TyParam => "type parameter",
 152             DefKind::ConstParam => "const parameter",
 153             DefKind::Macro(macro_kind) => macro_kind.descr(),
 154             DefKind::LifetimeParam => "lifetime parameter",
 155             DefKind::Use => "import",
 156             DefKind::ForeignMod => "foreign module",
 157             DefKind::AnonConst => "constant expression",
 158             DefKind::InlineConst => "inline constant",
 159             DefKind::Field => "field",
 160             DefKind::Impl => "implementation",
 161             DefKind::Closure => "closure",
 162             DefKind::Generator => "generator",
 163             DefKind::ExternCrate => "extern crate",
 164             DefKind::GlobalAsm => "global assembly block",
 165         }
 166     }
 167
 168     /// Gets an English article for the definition.
 169     pub fn article(&self) -> &'static str {
 170         match *self {
 171             DefKind::AssocTy
 172             | DefKind::AssocConst
 173             | DefKind::AssocFn
 174             | DefKind::Enum
 175             | DefKind::OpaqueTy
 176             | DefKind::Impl
 177             | DefKind::Use
 178             | DefKind::InlineConst
 179             | DefKind::ExternCrate => "an",
 180             DefKind::Macro(macro_kind) => macro_kind.article(),
 181             _ => "a",
 182         }
 183     }
 184
 185     pub fn ns(&self) -> Option<Namespace> {
 186         match self {
 187             DefKind::Mod
 188             | DefKind::Struct
 189             | DefKind::Union
 190             | DefKind::Enum
 191             | DefKind::Variant
 192             | DefKind::Trait
 193             | DefKind::OpaqueTy
 194             | DefKind::TyAlias
 195             | DefKind::ForeignTy
 196             | DefKind::TraitAlias
 197             | DefKind::AssocTy
 198             | DefKind::TyParam => Some(Namespace::TypeNS),
 199
 200             DefKind::Fn
 201             | DefKind::Const
 202             | DefKind::ConstParam
 203             | DefKind::Static(..)
 204             | DefKind::Ctor(..)
 205             | DefKind::AssocFn
 206             | DefKind::AssocConst => Some(Namespace::ValueNS),
 207
 208             DefKind::Macro(..) => Some(Namespace::MacroNS),
 209
 210             // Not namespaced.
 211             DefKind::AnonConst
 212             | DefKind::InlineConst
 213             | DefKind::Field
 214             | DefKind::LifetimeParam
 215             | DefKind::ExternCrate
 216             | DefKind::Closure
 217             | DefKind::Generator
 218             | DefKind::Use
 219             | DefKind::ForeignMod
 220             | DefKind::GlobalAsm
 221             | DefKind::Impl => None,
 222         }
 223     }
 224
 225     #[inline]
 226     pub fn is_fn_like(self) -> bool {
 227         match self {
 228             DefKind::Fn | DefKind::AssocFn | DefKind::Closure | DefKind::Generator => true,
 229             _ => false,
 230         }
 231     }
 232
 233     /// Whether `query get_codegen_attrs` should be used with this definition.
 234     pub fn has_codegen_attrs(self) -> bool {
 235         match self {
 236             DefKind::Fn
 237             | DefKind::AssocFn
 238             | DefKind::Ctor(..)
 239             | DefKind::Closure
 240             | DefKind::Generator
 241             | DefKind::Static(_) => true,
 242             DefKind::Mod
 243             | DefKind::Struct
 244             | DefKind::Union
 245             | DefKind::Enum
 246             | DefKind::Variant
 247             | DefKind::Trait
 248             | DefKind::TyAlias
 249             | DefKind::ForeignTy
 250             | DefKind::TraitAlias
 251             | DefKind::AssocTy
 252             | DefKind::Const
 253             | DefKind::AssocConst
 254             | DefKind::Macro(..)
 255             | DefKind::Use
 256             | DefKind::ForeignMod
 257             | DefKind::OpaqueTy
 258             | DefKind::Impl
 259             | DefKind::Field
 260             | DefKind::TyParam
 261             | DefKind::ConstParam
 262             | DefKind::LifetimeParam
 263             | DefKind::AnonConst
 264             | DefKind::InlineConst
 265             | DefKind::GlobalAsm
 266             | DefKind::ExternCrate => false,
 267         }
 268     }
 269 }
 270
 271 /// The resolution of a path or export.
 272 ///
 273 /// For every path or identifier in Rust, the compiler must determine
 274 /// what the path refers to. This process is called name resolution,
 275 /// and `Res` is the primary result of name resolution.
 276 ///
 277 /// For example, everything prefixed with `/* Res */` in this example has
 278 /// an associated `Res`:
 279 ///
 280 /// ```
 281 /// fn str_to_string(s: & /* Res */ str) -> /* Res */ String {
 282 ///     /* Res */ String::from(/* Res */ s)
 283 /// }
 284 ///
 285 /// /* Res */ str_to_string("hello");
 286 /// ```
 287 ///
 288 /// The associated `Res`s will be:
 289 ///
 290 /// - `str` will resolve to [`Res::PrimTy`];
 291 /// - `String` will resolve to [`Res::Def`], and the `Res` will include the [`DefId`]
 292 ///   for `String` as defined in the standard library;
 293 /// - `String::from` will also resolve to [`Res::Def`], with the [`DefId`]
 294 ///   pointing to `String::from`;
 295 /// - `s` will resolve to [`Res::Local`];
 296 /// - the call to `str_to_string` will resolve to [`Res::Def`], with the [`DefId`]
 297 ///   pointing to the definition of `str_to_string` in the current crate.
 298 //
 299 #[derive(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Debug)]
 300 #[derive(HashStable_Generic)]
 301 pub enum Res<Id = hir::HirId> {
 302     /// Definition having a unique ID (`DefId`), corresponds to something defined in user code.
 303     ///
 304     /// **Not bound to a specific namespace.**
 305     Def(DefKind, DefId),
 306
 307     // Type namespace
 308     /// A primitive type such as `i32` or `str`.
 309     ///
 310     /// **Belongs to the type namespace.**
 311     PrimTy(hir::PrimTy),
 312     /// The `Self` type, optionally with the [`DefId`] of the trait it belongs to and
 313     /// optionally with the [`DefId`] of the item introducing the `Self` type alias.
 314     ///
 315     /// **Belongs to the type namespace.**
 316     ///
 317     /// Examples:
 318     /// ```
 319     /// struct Bar(Box<Self>);
 320     /// // `Res::SelfTy { trait_: None, alias_of: Some(Bar) }`
 321     ///
 322     /// trait Foo {
 323     ///     fn foo() -> Box<Self>;
 324     ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: None }`
 325     /// }
 326     ///
 327     /// impl Bar {
 328     ///     fn blah() {
 329     ///         let _: Self;
 330     ///         // `Res::SelfTy { trait_: None, alias_of: Some(::{impl#0}) }`
 331     ///     }
 332     /// }
 333     ///
 334     /// impl Foo for Bar {
 335     ///     fn foo() -> Box<Self> {
 336     ///     // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
 337     ///         let _: Self;
 338     ///         // `Res::SelfTy { trait_: Some(Foo), alias_of: Some(::{impl#1}) }`
 339     ///
 340     ///         todo!()
 341     ///     }
 342     /// }
 343     /// ```
 344     ///
 345     /// *See also [`Res::SelfCtor`].*
 346     ///
 347     /// -----
 348     ///
 349     /// HACK(min_const_generics): self types also have an optional requirement to **not** mention
 350     /// any generic parameters to allow the following with `min_const_generics`:
 351     /// ```
 352     /// # struct Foo;
 353     /// impl Foo { fn test() -> [u8; std::mem::size_of::<Self>()] { todo!() } }
 354     ///
 355     /// struct Bar([u8; baz::<Self>()]);
 356     /// const fn baz<T>() -> usize { 10 }
 357     /// ```
 358     /// We do however allow `Self` in repeat expression even if it is generic to not break code
 359     /// which already works on stable while causing the `const_evaluatable_unchecked` future compat lint:
 360     /// ```
 361     /// fn foo<T>() {
 362     ///     let _bar = [1_u8; std::mem::size_of::<*mut T>()];
 363     /// }
 364     /// ```
 365     // FIXME(generic_const_exprs): Remove this bodge once that feature is stable.
 366     SelfTy {
 367         /// The trait this `Self` is a generic arg for.
 368         trait_: Option<DefId>,
 369         /// The item introducing the `Self` type alias. Can be used in the `type_of` query
 370         /// to get the underlying type. Additionally whether the `Self` type is disallowed
 371         /// from mentioning generics (i.e. when used in an anonymous constant).
 372         alias_to: Option<(DefId, bool)>,
 373     },
 374     /// A tool attribute module; e.g., the `rustfmt` in `#[rustfmt::skip]`.
 375     ///
 376     /// **Belongs to the type namespace.**
 377     ToolMod,
 378
 379     // Value namespace
 380     /// The `Self` constructor, along with the [`DefId`]
 381     /// of the impl it is associated with.
 382     ///
 383     /// **Belongs to the value namespace.**
 384     ///
 385     /// *See also [`Res::SelfTy`].*
 386     SelfCtor(DefId),
 387     /// A local variable or function parameter.
 388     ///
 389     /// **Belongs to the value namespace.**
 390     Local(Id),
 391
 392     // Macro namespace
 393     /// An attribute that is *not* implemented via macro.
 394     /// E.g., `#[inline]` and `#[rustfmt::skip]`, which are essentially directives,
 395     /// as opposed to `#[test]`, which is a builtin macro.
 396     ///
 397     /// **Belongs to the macro namespace.**
 398     NonMacroAttr(NonMacroAttrKind), // e.g., `#[inline]` or `#[rustfmt::skip]`
 399
 400     // All namespaces
 401     /// Name resolution failed. We use a dummy `Res` variant so later phases
 402     /// of the compiler won't crash and can instead report more errors.
 403     ///
 404     /// **Not bound to a specific namespace.**
 405     Err,
 406 }
 407
 408 /// The result of resolving a path before lowering to HIR,
 409 /// with "module" segments resolved and associated item
 410 /// segments deferred to type checking.
 411 /// `base_res` is the resolution of the resolved part of the
 412 /// path, `unresolved_segments` is the number of unresolved
 413 /// segments.
 414 ///
 415 /// ```text
 416 /// module::Type::AssocX::AssocY::MethodOrAssocType
 417 /// ^~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 418 /// base_res      unresolved_segments = 3
 419 ///
 420 /// <T as Trait>::AssocX::AssocY::MethodOrAssocType
 421 ///       ^~~~~~~~~~~~~~  ^~~~~~~~~~~~~~~~~~~~~~~~~
 422 ///       base_res        unresolved_segments = 2
 423 /// ```
 424 #[derive(Copy, Clone, Debug)]
 425 pub struct PartialRes {
 426     base_res: Res<NodeId>,
 427     unresolved_segments: usize,
 428 }
 429
 430 impl PartialRes {
 431     #[inline]
 432     pub fn new(base_res: Res<NodeId>) -> Self {
 433         PartialRes { base_res, unresolved_segments: 0 }
 434     }
 435
 436     #[inline]
 437     pub fn with_unresolved_segments(base_res: Res<NodeId>, mut unresolved_segments: usize) -> Self {
 438         if base_res == Res::Err {
 439             unresolved_segments = 0
 440         }
 441         PartialRes { base_res, unresolved_segments }
 442     }
 443
 444     #[inline]
 445     pub fn base_res(&self) -> Res<NodeId> {
 446         self.base_res
 447     }
 448
 449     #[inline]
 450     pub fn unresolved_segments(&self) -> usize {
 451         self.unresolved_segments
 452     }
 453 }
 454
 455 /// Different kinds of symbols can coexist even if they share the same textual name.
 456 /// Therefore, they each have a separate universe (known as a "namespace").
 457 #[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug)]
 458 pub enum Namespace {
 459     /// The type namespace includes `struct`s, `enum`s, `union`s, `trait`s, and `mod`s
 460     /// (and, by extension, crates).
 461     ///
 462     /// Note that the type namespace includes other items; this is not an
 463     /// exhaustive list.
 464     TypeNS,
 465     /// The value namespace includes `fn`s, `const`s, `static`s, and local variables (including function arguments).
 466     ValueNS,
 467     /// The macro namespace includes `macro_rules!` macros, declarative `macro`s,
 468     /// procedural macros, attribute macros, `derive` macros, and non-macro attributes
 469     /// like `#[inline]` and `#[rustfmt::skip]`.
 470     MacroNS,
 471 }
 472
 473 impl Namespace {
 474     /// The English description of the namespace.
 475     pub fn descr(self) -> &'static str {
 476         match self {
 477             Self::TypeNS => "type",
 478             Self::ValueNS => "value",
 479             Self::MacroNS => "macro",
 480         }
 481     }
 482 }
 483
 484 /// Just a helper ‒ separate structure for each namespace.
 485 #[derive(Copy, Clone, Default, Debug)]
 486 pub struct PerNS<T> {
 487     pub value_ns: T,
 488     pub type_ns: T,
 489     pub macro_ns: T,
 490 }
 491
 492 impl<T> PerNS<T> {
 493     pub fn map<U, F: FnMut(T) -> U>(self, mut f: F) -> PerNS<U> {
 494         PerNS { value_ns: f(self.value_ns), type_ns: f(self.type_ns), macro_ns: f(self.macro_ns) }
 495     }
 496
 497     pub fn into_iter(self) -> IntoIter<T, 3> {
 498         [self.value_ns, self.type_ns, self.macro_ns].into_iter()
 499     }
 500
 501     pub fn iter(&self) -> IntoIter<&T, 3> {
 502         [&self.value_ns, &self.type_ns, &self.macro_ns].into_iter()
 503     }
 504 }
 505
 506 impl<T> ::std::ops::Index<Namespace> for PerNS<T> {
 507     type Output = T;
 508
 509     fn index(&self, ns: Namespace) -> &T {
 510         match ns {
 511             Namespace::ValueNS => &self.value_ns,
 512             Namespace::TypeNS => &self.type_ns,
 513             Namespace::MacroNS => &self.macro_ns,
 514         }
 515     }
 516 }
 517
 518 impl<T> ::std::ops::IndexMut<Namespace> for PerNS<T> {
 519     fn index_mut(&mut self, ns: Namespace) -> &mut T {
 520         match ns {
 521             Namespace::ValueNS => &mut self.value_ns,
 522             Namespace::TypeNS => &mut self.type_ns,
 523             Namespace::MacroNS => &mut self.macro_ns,
 524         }
 525     }
 526 }
 527
 528 impl<T> PerNS<Option<T>> {
 529     /// Returns `true` if all the items in this collection are `None`.
 530     pub fn is_empty(&self) -> bool {
 531         self.type_ns.is_none() && self.value_ns.is_none() && self.macro_ns.is_none()
 532     }
 533
 534     /// Returns an iterator over the items which are `Some`.
 535     pub fn present_items(self) -> impl Iterator<Item = T> {
 536         [self.type_ns, self.value_ns, self.macro_ns].into_iter().flatten()
 537     }
 538 }
 539
 540 impl CtorKind {
 541     pub fn from_ast(vdata: &ast::VariantData) -> CtorKind {
 542         match *vdata {
 543             ast::VariantData::Tuple(..) => CtorKind::Fn,
 544             ast::VariantData::Unit(..) => CtorKind::Const,
 545             ast::VariantData::Struct(..) => CtorKind::Fictive,
 546         }
 547     }
 548
 549     pub fn from_hir(vdata: &hir::VariantData<'_>) -> CtorKind {
 550         match *vdata {
 551             hir::VariantData::Tuple(..) => CtorKind::Fn,
 552             hir::VariantData::Unit(..) => CtorKind::Const,
 553             hir::VariantData::Struct(..) => CtorKind::Fictive,
 554         }
 555     }
 556 }
 557
 558 impl NonMacroAttrKind {
 559     pub fn descr(self) -> &'static str {
 560         match self {
 561             NonMacroAttrKind::Builtin(..) => "built-in attribute",
 562             NonMacroAttrKind::Tool => "tool attribute",
 563             NonMacroAttrKind::DeriveHelper | NonMacroAttrKind::DeriveHelperCompat => {
 564                 "derive helper attribute"
 565             }
 566             NonMacroAttrKind::Registered => "explicitly registered attribute",
 567         }
 568     }
 569
 570     pub fn article(self) -> &'static str {
 571         match self {
 572             NonMacroAttrKind::Registered => "an",
 573             _ => "a",
 574         }
 575     }
 576
 577     /// Users of some attributes cannot mark them as used, so they are considered always used.
 578     pub fn is_used(self) -> bool {
 579         match self {
 580             NonMacroAttrKind::Tool
 581             | NonMacroAttrKind::DeriveHelper
 582             | NonMacroAttrKind::DeriveHelperCompat => true,
 583             NonMacroAttrKind::Builtin(..) | NonMacroAttrKind::Registered => false,
 584         }
 585     }
 586 }
 587
 588 impl<Id> Res<Id> {
 589     /// Return the `DefId` of this `Def` if it has an ID, else panic.
 590     pub fn def_id(&self) -> DefId
 591     where
 592         Id: Debug,
 593     {
 594         self.opt_def_id()
 595             .unwrap_or_else(|| panic!("attempted .def_id() on invalid res: {:?}", self))
 596     }
 597
 598     /// Return `Some(..)` with the `DefId` of this `Res` if it has a ID, else `None`.
 599     pub fn opt_def_id(&self) -> Option<DefId> {
 600         match *self {
 601             Res::Def(_, id) => Some(id),
 602
 603             Res::Local(..)
 604             | Res::PrimTy(..)
 605             | Res::SelfTy { .. }
 606             | Res::SelfCtor(..)
 607             | Res::ToolMod
 608             | Res::NonMacroAttr(..)
 609             | Res::Err => None,
 610         }
 611     }
 612
 613     /// Return the `DefId` of this `Res` if it represents a module.
 614     pub fn mod_def_id(&self) -> Option<DefId> {
 615         match *self {
 616             Res::Def(DefKind::Mod, id) => Some(id),
 617             _ => None,
 618         }
 619     }
 620
 621     /// A human readable name for the res kind ("function", "module", etc.).
 622     pub fn descr(&self) -> &'static str {
 623         match *self {
 624             Res::Def(kind, def_id) => kind.descr(def_id),
 625             Res::SelfCtor(..) => "self constructor",
 626             Res::PrimTy(..) => "builtin type",
 627             Res::Local(..) => "local variable",
 628             Res::SelfTy { .. } => "self type",
 629             Res::ToolMod => "tool module",
 630             Res::NonMacroAttr(attr_kind) => attr_kind.descr(),
 631             Res::Err => "unresolved item",
 632         }
 633     }
 634
 635     /// Gets an English article for the `Res`.
 636     pub fn article(&self) -> &'static str {
 637         match *self {
 638             Res::Def(kind, _) => kind.article(),
 639             Res::NonMacroAttr(kind) => kind.article(),
 640             Res::Err => "an",
 641             _ => "a",
 642         }
 643     }
 644
 645     pub fn map_id<R>(self, mut map: impl FnMut(Id) -> R) -> Res<R> {
 646         match self {
 647             Res::Def(kind, id) => Res::Def(kind, id),
 648             Res::SelfCtor(id) => Res::SelfCtor(id),
 649             Res::PrimTy(id) => Res::PrimTy(id),
 650             Res::Local(id) => Res::Local(map(id)),
 651             Res::SelfTy { trait_, alias_to } => Res::SelfTy { trait_, alias_to },
 652             Res::ToolMod => Res::ToolMod,
 653             Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
 654             Res::Err => Res::Err,
 655         }
 656     }
 657
 658     pub fn apply_id<R, E>(self, mut map: impl FnMut(Id) -> Result<R, E>) -> Result<Res<R>, E> {
 659         Ok(match self {
 660             Res::Def(kind, id) => Res::Def(kind, id),
 661             Res::SelfCtor(id) => Res::SelfCtor(id),
 662             Res::PrimTy(id) => Res::PrimTy(id),
 663             Res::Local(id) => Res::Local(map(id)?),
 664             Res::SelfTy { trait_, alias_to } => Res::SelfTy { trait_, alias_to },
 665             Res::ToolMod => Res::ToolMod,
 666             Res::NonMacroAttr(attr_kind) => Res::NonMacroAttr(attr_kind),
 667             Res::Err => Res::Err,
 668         })
 669     }
 670
 671     #[track_caller]
 672     pub fn expect_non_local<OtherId>(self) -> Res<OtherId> {
 673         self.map_id(|_| panic!("unexpected `Res::Local`"))
 674     }
 675
 676     pub fn macro_kind(self) -> Option<MacroKind> {
 677         match self {
 678             Res::Def(DefKind::Macro(kind), _) => Some(kind),
 679             Res::NonMacroAttr(..) => Some(MacroKind::Attr),
 680             _ => None,
 681         }
 682     }
 683
 684     /// Returns `None` if this is `Res::Err`
 685     pub fn ns(&self) -> Option<Namespace> {
 686         match self {
 687             Res::Def(kind, ..) => kind.ns(),
 688             Res::PrimTy(..) | Res::SelfTy { .. } | Res::ToolMod => Some(Namespace::TypeNS),
 689             Res::SelfCtor(..) | Res::Local(..) => Some(Namespace::ValueNS),
 690             Res::NonMacroAttr(..) => Some(Namespace::MacroNS),
 691             Res::Err => None,
 692         }
 693     }
 694
 695     /// Always returns `true` if `self` is `Res::Err`
 696     pub fn matches_ns(&self, ns: Namespace) -> bool {
 697         self.ns().map_or(true, |actual_ns| actual_ns == ns)
 698     }
 699
 700     /// Returns whether such a resolved path can occur in a tuple struct/variant pattern
 701     pub fn expected_in_tuple_struct_pat(&self) -> bool {
 702         matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) | Res::SelfCtor(..))
 703     }
 704
 705     /// Returns whether such a resolved path can occur in a unit struct/variant pattern
 706     pub fn expected_in_unit_struct_pat(&self) -> bool {
 707         matches!(self, Res::Def(DefKind::Ctor(_, CtorKind::Const), _) | Res::SelfCtor(..))
 708     }
 709 }