| use crate::infer::free_regions::FreeRegionMap; |
| use crate::infer::{GenericKind, InferCtxt}; |
| use crate::traits::query::OutlivesBound; |
| use rustc_data_structures::fx::FxHashMap; |
| use rustc_hir as hir; |
| use rustc_middle::ty; |
| |
| use super::explicit_outlives_bounds; |
| |
| /// The `OutlivesEnvironment` collects information about what outlives |
| /// what in a given type-checking setting. For example, if we have a |
| /// where-clause like `where T: 'a` in scope, then the |
| /// `OutlivesEnvironment` would record that (in its |
| /// `region_bound_pairs` field). Similarly, it contains methods for |
| /// processing and adding implied bounds into the outlives |
| /// environment. |
| /// |
| /// Other code at present does not typically take a |
| /// `&OutlivesEnvironment`, but rather takes some of its fields (e.g., |
| /// `process_registered_region_obligations` wants the |
| /// region-bound-pairs). There is no mistaking it: the current setup |
| /// of tracking region information is quite scattered! The |
| /// `OutlivesEnvironment`, for example, needs to sometimes be combined |
| /// with the `middle::RegionRelations`, to yield a full picture of how |
| /// (lexical) lifetimes interact. However, I'm reluctant to do more |
| /// refactoring here, since the setup with NLL is quite different. |
| /// For example, NLL has no need of `RegionRelations`, and is solely |
| /// interested in the `OutlivesEnvironment`. -nmatsakis |
| #[derive(Clone)] |
| pub struct OutlivesEnvironment<'tcx> { |
| pub param_env: ty::ParamEnv<'tcx>, |
| free_region_map: FreeRegionMap<'tcx>, |
| |
| // Contains, for each body B that we are checking (that is, the fn |
| // item, but also any nested closures), the set of implied region |
| // bounds that are in scope in that particular body. |
| // |
| // Example: |
| // |
| // ``` |
| // fn foo<'a, 'b, T>(x: &'a T, y: &'b ()) { |
| // bar(x, y, |y: &'b T| { .. } // body B1) |
| // } // body B0 |
| // ``` |
| // |
| // Here, for body B0, the list would be `[T: 'a]`, because we |
| // infer that `T` must outlive `'a` from the implied bounds on the |
| // fn declaration. |
| // |
| // For the body B1, the list would be `[T: 'a, T: 'b]`, because we |
| // also can see that -- within the closure body! -- `T` must |
| // outlive `'b`. This is not necessarily true outside the closure |
| // body, since the closure may never be called. |
| // |
| // We collect this map as we descend the tree. We then use the |
| // results when proving outlives obligations like `T: 'x` later |
| // (e.g., if `T: 'x` must be proven within the body B1, then we |
| // know it is true if either `'a: 'x` or `'b: 'x`). |
| region_bound_pairs_map: FxHashMap<hir::HirId, RegionBoundPairs<'tcx>>, |
| |
| // Used to compute `region_bound_pairs_map`: contains the set of |
| // in-scope region-bound pairs thus far. |
| region_bound_pairs_accum: RegionBoundPairs<'tcx>, |
| } |
| |
| /// "Region-bound pairs" tracks outlives relations that are known to |
| /// be true, either because of explicit where-clauses like `T: 'a` or |
| /// because of implied bounds. |
| pub type RegionBoundPairs<'tcx> = Vec<(ty::Region<'tcx>, GenericKind<'tcx>)>; |
| |
| impl<'a, 'tcx> OutlivesEnvironment<'tcx> { |
| pub fn new(param_env: ty::ParamEnv<'tcx>) -> Self { |
| let mut env = OutlivesEnvironment { |
| param_env, |
| free_region_map: Default::default(), |
| region_bound_pairs_map: Default::default(), |
| region_bound_pairs_accum: vec![], |
| }; |
| |
| env.add_outlives_bounds(None, explicit_outlives_bounds(param_env)); |
| |
| env |
| } |
| |
| /// Borrows current value of the `free_region_map`. |
| pub fn free_region_map(&self) -> &FreeRegionMap<'tcx> { |
| &self.free_region_map |
| } |
| |
| /// Borrows current value of the `region_bound_pairs`. |
| pub fn region_bound_pairs_map(&self) -> &FxHashMap<hir::HirId, RegionBoundPairs<'tcx>> { |
| &self.region_bound_pairs_map |
| } |
| |
| /// This is a hack to support the old-skool regionck, which |
| /// processes region constraints from the main function and the |
| /// closure together. In that context, when we enter a closure, we |
| /// want to be able to "save" the state of the surrounding a |
| /// function. We can then add implied bounds and the like from the |
| /// closure arguments into the environment -- these should only |
| /// apply in the closure body, so once we exit, we invoke |
| /// `pop_snapshot_post_closure` to remove them. |
| /// |
| /// Example: |
| /// |
| /// ``` |
| /// fn foo<T>() { |
| /// callback(for<'a> |x: &'a T| { |
| /// // ^^^^^^^ not legal syntax, but probably should be |
| /// // within this closure body, `T: 'a` holds |
| /// }) |
| /// } |
| /// ``` |
| /// |
| /// This "containment" of closure's effects only works so well. In |
| /// particular, we (intentionally) leak relationships between free |
| /// regions that are created by the closure's bounds. The case |
| /// where this is useful is when you have (e.g.) a closure with a |
| /// signature like `for<'a, 'b> fn(x: &'a &'b u32)` -- in this |
| /// case, we want to keep the relationship `'b: 'a` in the |
| /// free-region-map, so that later if we have to take `LUB('b, |
| /// 'a)` we can get the result `'b`. |
| /// |
| /// I have opted to keep **all modifications** to the |
| /// free-region-map, however, and not just those that concern free |
| /// variables bound in the closure. The latter seems more correct, |
| /// but it is not the existing behavior, and I could not find a |
| /// case where the existing behavior went wrong. In any case, it |
| /// seems like it'd be readily fixed if we wanted. There are |
| /// similar leaks around givens that seem equally suspicious, to |
| /// be honest. --nmatsakis |
| pub fn push_snapshot_pre_closure(&self) -> usize { |
| self.region_bound_pairs_accum.len() |
| } |
| |
| /// See `push_snapshot_pre_closure`. |
| pub fn pop_snapshot_post_closure(&mut self, len: usize) { |
| self.region_bound_pairs_accum.truncate(len); |
| } |
| |
| /// Save the current set of region-bound pairs under the given `body_id`. |
| pub fn save_implied_bounds(&mut self, body_id: hir::HirId) { |
| let old = |
| self.region_bound_pairs_map.insert(body_id, self.region_bound_pairs_accum.clone()); |
| assert!(old.is_none()); |
| } |
| |
| /// Processes outlives bounds that are known to hold, whether from implied or other sources. |
| /// |
| /// The `infcx` parameter is optional; if the implied bounds may |
| /// contain inference variables, it must be supplied, in which |
| /// case we will register "givens" on the inference context. (See |
| /// `RegionConstraintData`.) |
| pub fn add_outlives_bounds<I>( |
| &mut self, |
| infcx: Option<&InferCtxt<'a, 'tcx>>, |
| outlives_bounds: I, |
| ) where |
| I: IntoIterator<Item = OutlivesBound<'tcx>>, |
| { |
| // Record relationships such as `T:'x` that don't go into the |
| // free-region-map but which we use here. |
| for outlives_bound in outlives_bounds { |
| debug!("add_outlives_bounds: outlives_bound={:?}", outlives_bound); |
| match outlives_bound { |
| OutlivesBound::RegionSubRegion( |
| r_a @ (&ty::ReEarlyBound(_) | &ty::ReFree(_)), |
| &ty::ReVar(vid_b), |
| ) => { |
| infcx.expect("no infcx provided but region vars found").add_given(r_a, vid_b); |
| } |
| OutlivesBound::RegionSubParam(r_a, param_b) => { |
| self.region_bound_pairs_accum.push((r_a, GenericKind::Param(param_b))); |
| } |
| OutlivesBound::RegionSubProjection(r_a, projection_b) => { |
| self.region_bound_pairs_accum |
| .push((r_a, GenericKind::Projection(projection_b))); |
| } |
| OutlivesBound::RegionSubRegion(r_a, r_b) => { |
| // In principle, we could record (and take |
| // advantage of) every relationship here, but |
| // we are also free not to -- it simply means |
| // strictly less that we can successfully type |
| // check. Right now we only look for things |
| // relationships between free regions. (It may |
| // also be that we should revise our inference |
| // system to be more general and to make use |
| // of *every* relationship that arises here, |
| // but presently we do not.) |
| self.free_region_map.relate_regions(r_a, r_b); |
| } |
| } |
| } |
| } |
| } |
