//! Name resolution for lifetimes and late-bound type and const variables: type declarations.

use rustc_data_structures::fx::FxIndexMap;
use rustc_errors::ErrorGuaranteed;
use rustc_hir::def_id::{DefId, LocalDefId};
use rustc_hir::{ItemLocalId, OwnerId};
use rustc_macros::{Decodable, Encodable, HashStable, TyDecodable, TyEncodable};

use crate::ty;

#[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable, Debug, HashStable)]
pub enum ResolvedArg {
    StaticLifetime,
    EarlyBound(/* decl */ LocalDefId),
    LateBound(ty::DebruijnIndex, /* late-bound index */ u32, /* decl */ LocalDefId),
    Free(LocalDefId, /* lifetime decl */ LocalDefId),
    Error(ErrorGuaranteed),
}

/// A set containing, at most, one known element.
/// If two distinct values are inserted into a set, then it
/// becomes `Many`, which can be used to detect ambiguities.
#[derive(Copy, Clone, PartialEq, Eq, TyEncodable, TyDecodable, Debug, HashStable)]
pub enum Set1<T> {
    Empty,
    One(T),
    Many,
}

impl<T: PartialEq> Set1<T> {
    pub fn insert(&mut self, value: T) {
        *self = match self {
            Set1::Empty => Set1::One(value),
            Set1::One(old) if *old == value => return,
            _ => Set1::Many,
        };
    }
}

#[derive(Copy, Clone, Debug, HashStable, Encodable, Decodable)]
pub enum ObjectLifetimeDefault {
    Empty,
    Static,
    Ambiguous,
    Param(DefId),
}

/// Maps the id of each lifetime reference to the lifetime decl
/// that it corresponds to.
#[derive(Default, HashStable, Debug)]
pub struct ResolveBoundVars {
    /// Maps from every use of a named (not anonymous) lifetime to a
    /// `Region` describing how that region is bound
    pub defs: FxIndexMap<OwnerId, FxIndexMap<ItemLocalId, ResolvedArg>>,

    pub late_bound_vars: FxIndexMap<OwnerId, FxIndexMap<ItemLocalId, Vec<ty::BoundVariableKind>>>,
}