1 //! This calculates the types which has storage which lives across a suspension point in a
2 //! generator from the perspective of typeck. The actual types used at runtime
3 //! is calculated in `rustc_mir::transform::generator` and may be a subset of the
4 //! types computed here.
6 use rustc::hir::def_id::DefId;
7 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
8 use rustc::hir::{self, Pat, PatKind, Expr};
9 use rustc::middle::region;
10 use rustc::ty::{self, Ty};
13 use crate::util::nodemap::FxHashMap;
15 struct InteriorVisitor<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
16 fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
17 types: FxHashMap<Ty<'tcx>, usize>,
18 region_scope_tree: &'gcx region::ScopeTree,
22 impl<'a, 'gcx, 'tcx> InteriorVisitor<'a, 'gcx, 'tcx> {
25 scope: Option<region::Scope>,
26 expr: Option<&'tcx Expr>,
28 use syntax_pos::DUMMY_SP;
30 let live_across_yield = scope.map_or(Some(DUMMY_SP), |s| {
31 self.region_scope_tree.yield_in_scope(s).and_then(|(yield_span, expr_count)| {
32 // If we are recording an expression that is the last yield
33 // in the scope, or that has a postorder CFG index larger
34 // than the one of all of the yields, then its value can't
35 // be storage-live (and therefore live) at any of the yields.
37 // See the mega-comment at `yield_in_scope` for a proof.
39 debug!("comparing counts yield: {} self: {}, source_span = {:?}",
40 expr_count, self.expr_count, source_span);
42 if expr_count >= self.expr_count {
50 if let Some(yield_span) = live_across_yield {
51 let ty = self.fcx.resolve_vars_if_possible(&ty);
53 debug!("type in expr = {:?}, scope = {:?}, type = {:?}, count = {}, yield_span = {:?}",
54 expr, scope, ty, self.expr_count, yield_span);
56 if let Some((unresolved_type, unresolved_type_span)) =
57 self.fcx.unresolved_type_vars(&ty)
59 // If unresolved type isn't a ty_var then unresolved_type_span is None
60 self.fcx.need_type_info_err_in_generator(
61 unresolved_type_span.unwrap_or(yield_span),
63 .span_note(yield_span,
64 "the type is part of the generator because of this `yield`")
67 // Map the type to the number of types added before it
68 let entries = self.types.len();
69 self.types.entry(&ty).or_insert(entries);
72 debug!("no type in expr = {:?}, count = {:?}, span = {:?}",
73 expr, self.expr_count, expr.map(|e| e.span));
78 pub fn resolve_interior<'a, 'gcx, 'tcx>(fcx: &'a FnCtxt<'a, 'gcx, 'tcx>,
82 let body = fcx.tcx.hir().body(body_id);
83 let mut visitor = InteriorVisitor {
85 types: FxHashMap::default(),
86 region_scope_tree: fcx.tcx.region_scope_tree(def_id),
89 intravisit::walk_body(&mut visitor, body);
91 // Check that we visited the same amount of expressions and the RegionResolutionVisitor
92 let region_expr_count = visitor.region_scope_tree.body_expr_count(body_id).unwrap();
93 assert_eq!(region_expr_count, visitor.expr_count);
95 let mut types: Vec<_> = visitor.types.drain().collect();
97 // Sort types by insertion order
98 types.sort_by_key(|t| t.1);
100 // Extract type components
101 let type_list = fcx.tcx.mk_type_list(types.into_iter().map(|t| t.0));
103 // The types in the generator interior contain lifetimes local to the generator itself,
104 // which should not be exposed outside of the generator. Therefore, we replace these
105 // lifetimes with existentially-bound lifetimes, which reflect the exact value of the
106 // lifetimes not being known by users.
108 // These lifetimes are used in auto trait impl checking (for example,
109 // if a Sync generator contains an &'α T, we need to check whether &'α T: Sync),
110 // so knowledge of the exact relationships between them isn't particularly important.
112 debug!("Types in generator {:?}, span = {:?}", type_list, body.value.span);
114 // Replace all regions inside the generator interior with late bound regions
115 // Note that each region slot in the types gets a new fresh late bound region,
116 // which means that none of the regions inside relate to any other, even if
117 // typeck had previously found constraints that would cause them to be related.
119 let type_list = fcx.tcx.fold_regions(&type_list, &mut false, |_, current_depth| {
121 fcx.tcx.mk_region(ty::ReLateBound(current_depth, ty::BrAnon(counter)))
124 let witness = fcx.tcx.mk_generator_witness(ty::Binder::bind(type_list));
126 debug!("Types in generator after region replacement {:?}, span = {:?}",
127 witness, body.value.span);
129 // Unify the type variable inside the generator with the new witness
130 match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
131 Ok(ok) => fcx.register_infer_ok_obligations(ok),
136 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor in
137 // librustc/middle/region.rs since `expr_count` is compared against the results
139 impl<'a, 'gcx, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'gcx, 'tcx> {
140 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
141 NestedVisitorMap::None
144 fn visit_pat(&mut self, pat: &'tcx Pat) {
145 intravisit::walk_pat(self, pat);
147 self.expr_count += 1;
149 if let PatKind::Binding(..) = pat.node {
150 let scope = self.region_scope_tree.var_scope(pat.hir_id.local_id);
151 let ty = self.fcx.tables.borrow().pat_ty(pat);
152 self.record(ty, Some(scope), None, pat.span);
156 fn visit_expr(&mut self, expr: &'tcx Expr) {
157 intravisit::walk_expr(self, expr);
159 self.expr_count += 1;
161 let scope = self.region_scope_tree.temporary_scope(expr.hir_id.local_id);
163 // Record the unadjusted type
164 let ty = self.fcx.tables.borrow().expr_ty(expr);
165 self.record(ty, scope, Some(expr), expr.span);
167 // Also include the adjusted types, since these can result in MIR locals
168 for adjustment in self.fcx.tables.borrow().expr_adjustments(expr) {
169 self.record(adjustment.target, scope, Some(expr), expr.span);