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::{CtorKind, DefKind, Res};
7 use rustc::hir::def_id::DefId;
8 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
9 use rustc::hir::{self, Pat, PatKind, Expr, ExprKind};
10 use rustc::middle::region::{self, YieldData};
11 use rustc::ty::{self, Ty};
14 use crate::util::nodemap::FxHashMap;
16 struct InteriorVisitor<'a, 'tcx> {
17 fcx: &'a FnCtxt<'a, 'tcx>,
18 types: FxHashMap<ty::GeneratorInteriorTypeCause<'tcx>, usize>,
19 region_scope_tree: &'tcx region::ScopeTree,
21 kind: hir::GeneratorKind,
24 impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
27 scope: Option<region::Scope>,
28 expr: Option<&'tcx Expr>,
30 use syntax_pos::DUMMY_SP;
32 debug!("generator_interior: attempting to record type {:?} {:?} {:?} {:?}",
33 ty, scope, expr, source_span);
36 let live_across_yield = scope.map(|s| {
37 self.region_scope_tree.yield_in_scope(s).and_then(|yield_data| {
38 // If we are recording an expression that is the last yield
39 // in the scope, or that has a postorder CFG index larger
40 // than the one of all of the yields, then its value can't
41 // be storage-live (and therefore live) at any of the yields.
43 // See the mega-comment at `yield_in_scope` for a proof.
45 debug!("comparing counts yield: {} self: {}, source_span = {:?}",
46 yield_data.expr_and_pat_count, self.expr_count, source_span);
48 if yield_data.expr_and_pat_count >= self.expr_count {
54 }).unwrap_or_else(|| Some(YieldData {
56 expr_and_pat_count: 0,
57 source: match self.kind { // Guess based on the kind of the current generator.
58 hir::GeneratorKind::Gen => hir::YieldSource::Yield,
59 hir::GeneratorKind::Async(_) => hir::YieldSource::Await,
63 if let Some(yield_data) = live_across_yield {
64 let ty = self.fcx.resolve_vars_if_possible(&ty);
66 debug!("type in expr = {:?}, scope = {:?}, type = {:?}, count = {}, yield_span = {:?}",
67 expr, scope, ty, self.expr_count, yield_data.span);
69 if let Some((unresolved_type, unresolved_type_span)) =
70 self.fcx.unresolved_type_vars(&ty)
72 let note = format!("the type is part of the {} because of this {}",
76 // If unresolved type isn't a ty_var then unresolved_type_span is None
77 self.fcx.need_type_info_err_in_generator(
79 unresolved_type_span.unwrap_or(source_span),
82 .span_note(yield_data.span, &*note)
85 // Map the type to the number of types added before it
86 let entries = self.types.len();
87 let scope_span = scope.map(|s| s.span(self.fcx.tcx, self.region_scope_tree));
88 self.types.entry(ty::GeneratorInteriorTypeCause {
92 }).or_insert(entries);
95 debug!("no type in expr = {:?}, count = {:?}, span = {:?}",
96 expr, self.expr_count, expr.map(|e| e.span));
101 pub fn resolve_interior<'a, 'tcx>(
102 fcx: &'a FnCtxt<'a, 'tcx>,
104 body_id: hir::BodyId,
106 kind: hir::GeneratorKind,
108 let body = fcx.tcx.hir().body(body_id);
109 let mut visitor = InteriorVisitor {
111 types: FxHashMap::default(),
112 region_scope_tree: fcx.tcx.region_scope_tree(def_id),
116 intravisit::walk_body(&mut visitor, body);
118 // Check that we visited the same amount of expressions and the RegionResolutionVisitor
119 let region_expr_count = visitor.region_scope_tree.body_expr_count(body_id).unwrap();
120 assert_eq!(region_expr_count, visitor.expr_count);
122 let mut types: Vec<_> = visitor.types.drain().collect();
124 // Sort types by insertion order
125 types.sort_by_key(|t| t.1);
127 // The types in the generator interior contain lifetimes local to the generator itself,
128 // which should not be exposed outside of the generator. Therefore, we replace these
129 // lifetimes with existentially-bound lifetimes, which reflect the exact value of the
130 // lifetimes not being known by users.
132 // These lifetimes are used in auto trait impl checking (for example,
133 // if a Sync generator contains an &'α T, we need to check whether &'α T: Sync),
134 // so knowledge of the exact relationships between them isn't particularly important.
136 debug!("types in generator {:?}, span = {:?}", types, body.value.span);
138 // Replace all regions inside the generator interior with late bound regions
139 // Note that each region slot in the types gets a new fresh late bound region,
140 // which means that none of the regions inside relate to any other, even if
141 // typeck had previously found constraints that would cause them to be related.
143 let types = fcx.tcx.fold_regions(&types, &mut false, |_, current_depth| {
145 fcx.tcx.mk_region(ty::ReLateBound(current_depth, ty::BrAnon(counter)))
148 // Store the generator types and spans into the tables for this generator.
149 let interior_types = types.iter().map(|t| t.0.clone()).collect::<Vec<_>>();
150 visitor.fcx.inh.tables.borrow_mut().generator_interior_types = interior_types;
152 // Extract type components
153 let type_list = fcx.tcx.mk_type_list(types.into_iter().map(|t| (t.0).ty));
155 let witness = fcx.tcx.mk_generator_witness(ty::Binder::bind(type_list));
157 debug!("types in generator after region replacement {:?}, span = {:?}",
158 witness, body.value.span);
160 // Unify the type variable inside the generator with the new witness
161 match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
162 Ok(ok) => fcx.register_infer_ok_obligations(ok),
167 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor in
168 // librustc/middle/region.rs since `expr_count` is compared against the results
170 impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
171 fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'tcx> {
172 NestedVisitorMap::None
175 fn visit_pat(&mut self, pat: &'tcx Pat) {
176 intravisit::walk_pat(self, pat);
178 self.expr_count += 1;
180 if let PatKind::Binding(..) = pat.kind {
181 let scope = self.region_scope_tree.var_scope(pat.hir_id.local_id);
182 let ty = self.fcx.tables.borrow().pat_ty(pat);
183 self.record(ty, Some(scope), None, pat.span);
187 fn visit_expr(&mut self, expr: &'tcx Expr) {
189 ExprKind::Call(callee, args) => match &callee.kind {
190 ExprKind::Path(qpath) => {
191 let res = self.fcx.tables.borrow().qpath_res(qpath, callee.hir_id);
193 // Direct calls never need to keep the callee `ty::FnDef`
194 // ZST in a temporary, so skip its type, just in case it
195 // can significantly complicate the generator type.
196 Res::Def(DefKind::Fn, _) |
197 Res::Def(DefKind::Method, _) |
198 Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => {
199 // NOTE(eddyb) this assumes a path expression has
200 // no nested expressions to keep track of.
201 self.expr_count += 1;
203 // Record the rest of the call expression normally.
205 self.visit_expr(arg);
208 _ => intravisit::walk_expr(self, expr),
211 _ => intravisit::walk_expr(self, expr),
213 _ => intravisit::walk_expr(self, expr),
216 self.expr_count += 1;
218 let scope = self.region_scope_tree.temporary_scope(expr.hir_id.local_id);
220 // If there are adjustments, then record the final type --
221 // this is the actual value that is being produced.
222 if let Some(adjusted_ty) = self.fcx.tables.borrow().expr_ty_adjusted_opt(expr) {
223 self.record(adjusted_ty, scope, Some(expr), expr.span);
226 // Also record the unadjusted type (which is the only type if
227 // there are no adjustments). The reason for this is that the
228 // unadjusted value is sometimes a "temporary" that would wind
229 // up in a MIR temporary.
231 // As an example, consider an expression like `vec![].push()`.
232 // Here, the `vec![]` would wind up MIR stored into a
233 // temporary variable `t` which we can borrow to invoke
234 // `<Vec<_>>::push(&mut t)`.
236 // Note that an expression can have many adjustments, and we
237 // are just ignoring those intermediate types. This is because
238 // those intermediate values are always linearly "consumed" by
239 // the other adjustments, and hence would never be directly
240 // captured in the MIR.
242 // (Note that this partly relies on the fact that the `Deref`
243 // traits always return references, which means their content
244 // can be reborrowed without needing to spill to a temporary.
245 // If this were not the case, then we could conceivably have
246 // to create intermediate temporaries.)
247 let ty = self.fcx.tables.borrow().expr_ty(expr);
248 self.record(ty, scope, Some(expr), expr.span);