src/librustc/middle/resolve_lifetime.rs

   1 //! Name resolution for lifetimes: type declarations.
   2
   3 use crate::ty;
   4
   5 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
   6 use rustc_hir::def_id::{DefId, LocalDefId};
   7 use rustc_hir::{GenericParam, ItemLocalId};
   8 use rustc_hir::{GenericParamKind, LifetimeParamKind};
   9 use rustc_macros::HashStable;
  10
  11 /// The origin of a named lifetime definition.
  12 ///
  13 /// This is used to prevent the usage of in-band lifetimes in `Fn`/`fn` syntax.
  14 #[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, HashStable)]
  15 pub enum LifetimeDefOrigin {
  16     // Explicit binders like `fn foo<'a>(x: &'a u8)` or elided like `impl Foo<&u32>`
  17     ExplicitOrElided,
  18     // In-band declarations like `fn foo(x: &'a u8)`
  19     InBand,
  20     // Some kind of erroneous origin
  21     Error,
  22 }
  23
  24 impl LifetimeDefOrigin {
  25     pub fn from_param(param: &GenericParam<'_>) -> Self {
  26         match param.kind {
  27             GenericParamKind::Lifetime { kind } => match kind {
  28                 LifetimeParamKind::InBand => LifetimeDefOrigin::InBand,
  29                 LifetimeParamKind::Explicit => LifetimeDefOrigin::ExplicitOrElided,
  30                 LifetimeParamKind::Elided => LifetimeDefOrigin::ExplicitOrElided,
  31                 LifetimeParamKind::Error => LifetimeDefOrigin::Error,
  32             },
  33             _ => bug!("expected a lifetime param"),
  34         }
  35     }
  36 }
  37
  38 #[derive(Clone, Copy, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, Debug, HashStable)]
  39 pub enum Region {
  40     Static,
  41     EarlyBound(/* index */ u32, /* lifetime decl */ DefId, LifetimeDefOrigin),
  42     LateBound(ty::DebruijnIndex, /* lifetime decl */ DefId, LifetimeDefOrigin),
  43     LateBoundAnon(ty::DebruijnIndex, /* anon index */ u32),
  44     Free(DefId, /* lifetime decl */ DefId),
  45 }
  46
  47 /// A set containing, at most, one known element.
  48 /// If two distinct values are inserted into a set, then it
  49 /// becomes `Many`, which can be used to detect ambiguities.
  50 #[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Debug, HashStable)]
  51 pub enum Set1<T> {
  52     Empty,
  53     One(T),
  54     Many,
  55 }
  56
  57 impl<T: PartialEq> Set1<T> {
  58     pub fn insert(&mut self, value: T) {
  59         *self = match self {
  60             Set1::Empty => Set1::One(value),
  61             Set1::One(old) if *old == value => return,
  62             _ => Set1::Many,
  63         };
  64     }
  65 }
  66
  67 pub type ObjectLifetimeDefault = Set1<Region>;
  68
  69 /// Maps the id of each lifetime reference to the lifetime decl
  70 /// that it corresponds to.
  71 #[derive(Default, HashStable)]
  72 pub struct ResolveLifetimes {
  73     /// Maps from every use of a named (not anonymous) lifetime to a
  74     /// `Region` describing how that region is bound
  75     pub defs: FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Region>>,
  76
  77     /// Set of lifetime def ids that are late-bound; a region can
  78     /// be late-bound if (a) it does NOT appear in a where-clause and
  79     /// (b) it DOES appear in the arguments.
  80     pub late_bound: FxHashMap<LocalDefId, FxHashSet<ItemLocalId>>,
  81
  82     /// For each type and trait definition, maps type parameters
  83     /// to the trait object lifetime defaults computed from them.
  84     pub object_lifetime_defaults:
  85         FxHashMap<LocalDefId, FxHashMap<ItemLocalId, Vec<ObjectLifetimeDefault>>>,
  86 }