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.
7 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
9 use rustc_hir::def::{CtorKind, DefKind, Res};
10 use rustc_hir::def_id::DefId;
11 use rustc_hir::intravisit::{self, NestedVisitorMap, Visitor};
12 use rustc_hir::{Expr, ExprKind, Pat, PatKind};
13 use rustc_middle::middle::region::{self, YieldData};
14 use rustc_middle::ty::{self, Ty};
17 struct InteriorVisitor<'a, 'tcx> {
18 fcx: &'a FnCtxt<'a, 'tcx>,
19 types: FxHashMap<ty::GeneratorInteriorTypeCause<'tcx>, usize>,
20 region_scope_tree: &'tcx region::ScopeTree,
22 kind: hir::GeneratorKind,
23 prev_unresolved_span: Option<Span>,
26 impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
30 scope: Option<region::Scope>,
31 expr: Option<&'tcx Expr<'tcx>>,
34 use rustc_span::DUMMY_SP;
37 "generator_interior: attempting to record type {:?} {:?} {:?} {:?}",
38 ty, scope, expr, source_span
41 let live_across_yield = scope
43 self.region_scope_tree.yield_in_scope(s).and_then(|yield_data| {
44 // If we are recording an expression that is the last yield
45 // in the scope, or that has a postorder CFG index larger
46 // than the one of all of the yields, then its value can't
47 // be storage-live (and therefore live) at any of the yields.
49 // See the mega-comment at `yield_in_scope` for a proof.
52 "comparing counts yield: {} self: {}, source_span = {:?}",
53 yield_data.expr_and_pat_count, self.expr_count, source_span
56 if yield_data.expr_and_pat_count >= self.expr_count {
64 Some(YieldData { span: DUMMY_SP, expr_and_pat_count: 0, source: self.kind.into() })
67 if let Some(yield_data) = live_across_yield {
68 let ty = self.fcx.resolve_vars_if_possible(&ty);
70 "type in expr = {:?}, scope = {:?}, type = {:?}, count = {}, yield_span = {:?}",
71 expr, scope, ty, self.expr_count, yield_data.span
74 if let Some((unresolved_type, unresolved_type_span)) =
75 self.fcx.unresolved_type_vars(&ty)
78 "the type is part of the {} because of this {}",
79 self.kind, yield_data.source
82 // If unresolved type isn't a ty_var then unresolved_type_span is None
85 .unwrap_or_else(|| unresolved_type_span.unwrap_or(source_span));
87 .need_type_info_err_in_generator(self.kind, span, unresolved_type)
88 .span_note(yield_data.span, &*note)
91 // Map the type to the number of types added before it
92 let entries = self.types.len();
93 let scope_span = scope.map(|s| s.span(self.fcx.tcx, self.region_scope_tree));
95 .entry(ty::GeneratorInteriorTypeCause {
99 expr: expr.map(|e| e.hir_id),
105 "no type in expr = {:?}, count = {:?}, span = {:?}",
110 let ty = self.fcx.resolve_vars_if_possible(&ty);
111 if let Some((unresolved_type, unresolved_type_span)) =
112 self.fcx.unresolved_type_vars(&ty)
115 "remained unresolved_type = {:?}, unresolved_type_span: {:?}",
116 unresolved_type, unresolved_type_span
118 self.prev_unresolved_span = unresolved_type_span;
124 pub fn resolve_interior<'a, 'tcx>(
125 fcx: &'a FnCtxt<'a, 'tcx>,
127 body_id: hir::BodyId,
129 kind: hir::GeneratorKind,
131 let body = fcx.tcx.hir().body(body_id);
132 let mut visitor = InteriorVisitor {
134 types: FxHashMap::default(),
135 region_scope_tree: fcx.tcx.region_scope_tree(def_id),
138 prev_unresolved_span: None,
140 intravisit::walk_body(&mut visitor, body);
142 // Check that we visited the same amount of expressions and the RegionResolutionVisitor
143 let region_expr_count = visitor.region_scope_tree.body_expr_count(body_id).unwrap();
144 assert_eq!(region_expr_count, visitor.expr_count);
146 let mut types: Vec<_> = visitor.types.drain().collect();
148 // Sort types by insertion order
149 types.sort_by_key(|t| t.1);
151 // The types in the generator interior contain lifetimes local to the generator itself,
152 // which should not be exposed outside of the generator. Therefore, we replace these
153 // lifetimes with existentially-bound lifetimes, which reflect the exact value of the
154 // lifetimes not being known by users.
156 // These lifetimes are used in auto trait impl checking (for example,
157 // if a Sync generator contains an &'α T, we need to check whether &'α T: Sync),
158 // so knowledge of the exact relationships between them isn't particularly important.
160 debug!("types in generator {:?}, span = {:?}", types, body.value.span);
163 let mut captured_tys = FxHashSet::default();
164 let type_causes: Vec<_> = types
166 .filter_map(|(mut cause, _)| {
167 // Erase regions and canonicalize late-bound regions to deduplicate as many types as we
169 let erased = fcx.tcx.erase_regions(&cause.ty);
170 if captured_tys.insert(erased) {
171 // Replace all regions inside the generator interior with late bound regions.
172 // Note that each region slot in the types gets a new fresh late bound region,
173 // which means that none of the regions inside relate to any other, even if
174 // typeck had previously found constraints that would cause them to be related.
175 let folded = fcx.tcx.fold_regions(&erased, &mut false, |_, current_depth| {
177 fcx.tcx.mk_region(ty::ReLateBound(current_depth, ty::BrAnon(counter)))
188 // Extract type components to build the witness type.
189 let type_list = fcx.tcx.mk_type_list(type_causes.iter().map(|cause| cause.ty));
190 let witness = fcx.tcx.mk_generator_witness(ty::Binder::bind(type_list));
192 // Store the generator types and spans into the tables for this generator.
193 visitor.fcx.inh.tables.borrow_mut().generator_interior_types = type_causes;
196 "types in generator after region replacement {:?}, span = {:?}",
197 witness, body.value.span
200 // Unify the type variable inside the generator with the new witness
201 match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
202 Ok(ok) => fcx.register_infer_ok_obligations(ok),
207 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor in
208 // librustc_middle/middle/region.rs since `expr_count` is compared against the results
210 impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
211 type Map = intravisit::ErasedMap<'tcx>;
213 fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
214 NestedVisitorMap::None
217 fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) {
218 intravisit::walk_pat(self, pat);
220 self.expr_count += 1;
222 if let PatKind::Binding(..) = pat.kind {
223 let scope = self.region_scope_tree.var_scope(pat.hir_id.local_id);
224 let ty = self.fcx.tables.borrow().pat_ty(pat);
225 self.record(ty, Some(scope), None, pat.span);
229 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
231 ExprKind::Call(callee, args) => match &callee.kind {
232 ExprKind::Path(qpath) => {
233 let res = self.fcx.tables.borrow().qpath_res(qpath, callee.hir_id);
235 // Direct calls never need to keep the callee `ty::FnDef`
236 // ZST in a temporary, so skip its type, just in case it
237 // can significantly complicate the generator type.
238 Res::Def(DefKind::Fn, _)
239 | Res::Def(DefKind::AssocFn, _)
240 | Res::Def(DefKind::Ctor(_, CtorKind::Fn), _) => {
241 // NOTE(eddyb) this assumes a path expression has
242 // no nested expressions to keep track of.
243 self.expr_count += 1;
245 // Record the rest of the call expression normally.
247 self.visit_expr(arg);
250 _ => intravisit::walk_expr(self, expr),
253 _ => intravisit::walk_expr(self, expr),
255 _ => intravisit::walk_expr(self, expr),
258 self.expr_count += 1;
260 let scope = self.region_scope_tree.temporary_scope(expr.hir_id.local_id);
262 // If there are adjustments, then record the final type --
263 // this is the actual value that is being produced.
264 if let Some(adjusted_ty) = self.fcx.tables.borrow().expr_ty_adjusted_opt(expr) {
265 self.record(adjusted_ty, scope, Some(expr), expr.span);
268 // Also record the unadjusted type (which is the only type if
269 // there are no adjustments). The reason for this is that the
270 // unadjusted value is sometimes a "temporary" that would wind
271 // up in a MIR temporary.
273 // As an example, consider an expression like `vec![].push()`.
274 // Here, the `vec![]` would wind up MIR stored into a
275 // temporary variable `t` which we can borrow to invoke
276 // `<Vec<_>>::push(&mut t)`.
278 // Note that an expression can have many adjustments, and we
279 // are just ignoring those intermediate types. This is because
280 // those intermediate values are always linearly "consumed" by
281 // the other adjustments, and hence would never be directly
282 // captured in the MIR.
284 // (Note that this partly relies on the fact that the `Deref`
285 // traits always return references, which means their content
286 // can be reborrowed without needing to spill to a temporary.
287 // If this were not the case, then we could conceivably have
288 // to create intermediate temporaries.)
290 // The type table might not have information for this expression
291 // if it is in a malformed scope. (#66387)
292 if let Some(ty) = self.fcx.tables.borrow().expr_ty_opt(expr) {
293 self.record(ty, scope, Some(expr), expr.span);
295 self.fcx.tcx.sess.delay_span_bug(expr.span, "no type for node");