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 self::drop_ranges::DropRanges;
8 use rustc_data_structures::fx::{FxHashSet, FxIndexSet};
9 use rustc_errors::{pluralize, DelayDm};
11 use rustc_hir::def::{CtorKind, DefKind, Res};
12 use rustc_hir::def_id::DefId;
13 use rustc_hir::hir_id::HirIdSet;
14 use rustc_hir::intravisit::{self, Visitor};
15 use rustc_hir::{Arm, Expr, ExprKind, Guard, HirId, Pat, PatKind};
16 use rustc_infer::infer::RegionVariableOrigin;
17 use rustc_middle::middle::region::{self, Scope, ScopeData, YieldData};
18 use rustc_middle::ty::fold::FnMutDelegate;
19 use rustc_middle::ty::{self, BoundVariableKind, RvalueScopes, Ty, TyCtxt, TypeVisitable};
20 use rustc_span::symbol::sym;
22 use smallvec::{smallvec, SmallVec};
26 struct InteriorVisitor<'a, 'tcx> {
27 fcx: &'a FnCtxt<'a, 'tcx>,
28 region_scope_tree: &'a region::ScopeTree,
29 types: FxIndexSet<ty::GeneratorInteriorTypeCause<'tcx>>,
30 rvalue_scopes: &'a RvalueScopes,
32 kind: hir::GeneratorKind,
33 prev_unresolved_span: Option<Span>,
34 linted_values: HirIdSet,
35 drop_ranges: DropRanges,
38 impl<'a, 'tcx> InteriorVisitor<'a, 'tcx> {
43 scope: Option<region::Scope>,
44 expr: Option<&'tcx Expr<'tcx>>,
47 use rustc_span::DUMMY_SP;
49 let ty = self.fcx.resolve_vars_if_possible(ty);
52 "attempting to record type ty={:?}; hir_id={:?}; scope={:?}; expr={:?}; source_span={:?}; expr_count={:?}",
53 ty, hir_id, scope, expr, source_span, self.expr_count,
56 let live_across_yield = scope
58 self.region_scope_tree.yield_in_scope(s).and_then(|yield_data| {
59 // If we are recording an expression that is the last yield
60 // in the scope, or that has a postorder CFG index larger
61 // than the one of all of the yields, then its value can't
62 // be storage-live (and therefore live) at any of the yields.
64 // See the mega-comment at `yield_in_scope` for a proof.
70 "comparing counts yield: {} self: {}, source_span = {:?}",
71 yield_data.expr_and_pat_count, self.expr_count, source_span
74 if self.fcx.sess().opts.unstable_opts.drop_tracking
77 .is_dropped_at(hir_id, yield_data.expr_and_pat_count)
79 debug!("value is dropped at yield point; not recording");
83 // If it is a borrowing happening in the guard,
84 // it needs to be recorded regardless because they
85 // do live across this yield point.
86 yield_data.expr_and_pat_count >= self.expr_count
92 Some(YieldData { span: DUMMY_SP, expr_and_pat_count: 0, source: self.kind.into() })
95 if let Some(yield_data) = live_across_yield {
97 "type in expr = {:?}, scope = {:?}, type = {:?}, count = {}, yield_span = {:?}",
98 expr, scope, ty, self.expr_count, yield_data.span
101 if let Some((unresolved_type, unresolved_type_span)) =
102 self.fcx.unresolved_type_vars(&ty)
104 // If unresolved type isn't a ty_var then unresolved_type_span is None
106 .prev_unresolved_span
107 .unwrap_or_else(|| unresolved_type_span.unwrap_or(source_span));
109 // If we encounter an int/float variable, then inference fallback didn't
110 // finish due to some other error. Don't emit spurious additional errors.
111 if let ty::Infer(ty::InferTy::IntVar(_) | ty::InferTy::FloatVar(_)) =
112 unresolved_type.kind()
117 .delay_span_bug(span, &format!("Encountered var {:?}", unresolved_type));
120 "the type is part of the {} because of this {}",
121 self.kind, yield_data.source
125 .need_type_info_err_in_generator(self.kind, span, unresolved_type)
126 .span_note(yield_data.span, &*note)
130 // Insert the type into the ordered set.
131 let scope_span = scope.map(|s| s.span(self.fcx.tcx, self.region_scope_tree));
133 if !self.linted_values.contains(&hir_id) {
134 check_must_not_suspend_ty(
141 yield_span: yield_data.span,
146 self.linted_values.insert(hir_id);
149 self.types.insert(ty::GeneratorInteriorTypeCause {
153 yield_span: yield_data.span,
154 expr: expr.map(|e| e.hir_id),
159 "no type in expr = {:?}, count = {:?}, span = {:?}",
164 if let Some((unresolved_type, unresolved_type_span)) =
165 self.fcx.unresolved_type_vars(&ty)
168 "remained unresolved_type = {:?}, unresolved_type_span: {:?}",
169 unresolved_type, unresolved_type_span
171 self.prev_unresolved_span = unresolved_type_span;
177 pub fn resolve_interior<'a, 'tcx>(
178 fcx: &'a FnCtxt<'a, 'tcx>,
180 body_id: hir::BodyId,
182 kind: hir::GeneratorKind,
184 let body = fcx.tcx.hir().body(body_id);
185 let typeck_results = fcx.inh.typeck_results.borrow();
186 let mut visitor = InteriorVisitor {
188 types: FxIndexSet::default(),
189 region_scope_tree: fcx.tcx.region_scope_tree(def_id),
190 rvalue_scopes: &typeck_results.rvalue_scopes,
193 prev_unresolved_span: None,
194 linted_values: <_>::default(),
195 drop_ranges: drop_ranges::compute_drop_ranges(fcx, def_id, body),
197 intravisit::walk_body(&mut visitor, body);
199 // Check that we visited the same amount of expressions as the RegionResolutionVisitor
200 let region_expr_count = fcx.tcx.region_scope_tree(def_id).body_expr_count(body_id).unwrap();
201 assert_eq!(region_expr_count, visitor.expr_count);
203 // The types are already kept in insertion order.
204 let types = visitor.types;
206 // The types in the generator interior contain lifetimes local to the generator itself,
207 // which should not be exposed outside of the generator. Therefore, we replace these
208 // lifetimes with existentially-bound lifetimes, which reflect the exact value of the
209 // lifetimes not being known by users.
211 // These lifetimes are used in auto trait impl checking (for example,
212 // if a Sync generator contains an &'α T, we need to check whether &'α T: Sync),
213 // so knowledge of the exact relationships between them isn't particularly important.
215 debug!("types in generator {:?}, span = {:?}", types, body.value.span);
217 // We want to deduplicate if the lifetimes are the same modulo some non-informative counter.
218 // So, we need to actually do two passes: first by type to anonymize (preserving information
219 // required for diagnostics), then a second pass over all captured types to reassign disjoint
221 let mut captured_tys = FxHashSet::default();
222 let type_causes: Vec<_> = types
224 .filter_map(|mut cause| {
225 // Replace all regions inside the generator interior with late bound regions.
226 // Note that each region slot in the types gets a new fresh late bound region,
227 // which means that none of the regions inside relate to any other, even if
228 // typeck had previously found constraints that would cause them to be related.
231 let mut mk_bound_region = |span| {
232 let kind = ty::BrAnon(counter, span);
233 let var = ty::BoundVar::from_u32(counter);
235 ty::BoundRegion { var, kind }
237 let ty = fcx.normalize_associated_types_in(cause.span, cause.ty);
238 let ty = fcx.tcx.fold_regions(ty, |region, current_depth| {
239 let br = match region.kind() {
241 let origin = fcx.region_var_origin(vid);
243 RegionVariableOrigin::EarlyBoundRegion(span, _) => {
244 mk_bound_region(Some(span))
246 _ => mk_bound_region(None),
249 // FIXME: these should use `BrNamed`
250 ty::ReEarlyBound(region) => {
251 mk_bound_region(Some(fcx.tcx.def_span(region.def_id)))
253 ty::ReLateBound(_, ty::BoundRegion { kind, .. })
254 | ty::ReFree(ty::FreeRegion { bound_region: kind, .. }) => match kind {
255 ty::BoundRegionKind::BrAnon(_, span) => mk_bound_region(span),
256 ty::BoundRegionKind::BrNamed(def_id, _) => {
257 mk_bound_region(Some(fcx.tcx.def_span(def_id)))
259 ty::BoundRegionKind::BrEnv => mk_bound_region(None),
261 _ => mk_bound_region(None),
263 let r = fcx.tcx.mk_region(ty::ReLateBound(current_depth, br));
266 if captured_tys.insert(ty) {
275 let mut bound_vars: SmallVec<[BoundVariableKind; 4]> = smallvec![];
277 // Optimization: If there is only one captured type, then we don't actually
278 // need to fold and reindex (since the first type doesn't change).
279 let type_causes = if captured_tys.len() > 0 {
280 // Optimization: Use `replace_escaping_bound_vars_uncached` instead of
281 // `fold_regions`, since we only have late bound regions, and it skips
282 // types without bound regions.
283 fcx.tcx.replace_escaping_bound_vars_uncached(
287 let kind = match br.kind {
288 ty::BrAnon(_, span) => ty::BrAnon(counter, span),
291 let var = ty::BoundVar::from_usize(bound_vars.len());
292 bound_vars.push(ty::BoundVariableKind::Region(kind));
294 fcx.tcx.mk_region(ty::ReLateBound(ty::INNERMOST, ty::BoundRegion { var, kind }))
296 types: &mut |b| bug!("unexpected bound ty in binder: {b:?}"),
297 consts: &mut |b, ty| bug!("unexpected bound ct in binder: {b:?} {ty}"),
304 // Extract type components to build the witness type.
305 let type_list = fcx.tcx.mk_type_list(type_causes.iter().map(|cause| cause.ty));
306 let bound_vars = fcx.tcx.mk_bound_variable_kinds(bound_vars.iter());
308 fcx.tcx.mk_generator_witness(ty::Binder::bind_with_vars(type_list, bound_vars.clone()));
310 drop(typeck_results);
311 // Store the generator types and spans into the typeck results for this generator.
312 fcx.inh.typeck_results.borrow_mut().generator_interior_types =
313 ty::Binder::bind_with_vars(type_causes, bound_vars);
316 "types in generator after region replacement {:?}, span = {:?}",
317 witness, body.value.span
320 // Unify the type variable inside the generator with the new witness
321 match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
322 Ok(ok) => fcx.register_infer_ok_obligations(ok),
323 _ => bug!("failed to relate {interior} and {witness}"),
327 // This visitor has to have the same visit_expr calls as RegionResolutionVisitor in
328 // librustc_middle/middle/region.rs since `expr_count` is compared against the results
330 impl<'a, 'tcx> Visitor<'tcx> for InteriorVisitor<'a, 'tcx> {
331 fn visit_arm(&mut self, arm: &'tcx Arm<'tcx>) {
332 let Arm { guard, pat, body, .. } = arm;
334 if let Some(ref g) = guard {
336 // If there is a guard, we need to count all variables bound in the pattern as
337 // borrowed for the entire guard body, regardless of whether they are accessed.
338 // We do this by walking the pattern bindings and recording `&T` for any `x: T`
341 struct ArmPatCollector<'a, 'b, 'tcx> {
342 interior_visitor: &'a mut InteriorVisitor<'b, 'tcx>,
346 impl<'a, 'b, 'tcx> Visitor<'tcx> for ArmPatCollector<'a, 'b, 'tcx> {
347 fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) {
348 intravisit::walk_pat(self, pat);
349 if let PatKind::Binding(_, id, ident, ..) = pat.kind {
351 self.interior_visitor.fcx.typeck_results.borrow().node_type(id);
352 let tcx = self.interior_visitor.fcx.tcx;
354 // Use `ReErased` as `resolve_interior` is going to replace all the
356 tcx.mk_region(ty::ReErased),
357 ty::TypeAndMut { ty, mutbl: hir::Mutability::Not },
359 self.interior_visitor.record(
371 interior_visitor: self,
372 scope: Scope { id: g.body().hir_id.local_id, data: ScopeData::Node },
378 Guard::If(ref e) => {
381 Guard::IfLet(ref l) => {
382 self.visit_let_expr(l);
386 self.visit_expr(body);
389 fn visit_pat(&mut self, pat: &'tcx Pat<'tcx>) {
390 intravisit::walk_pat(self, pat);
392 self.expr_count += 1;
394 if let PatKind::Binding(..) = pat.kind {
395 let scope = self.region_scope_tree.var_scope(pat.hir_id.local_id).unwrap();
396 let ty = self.fcx.typeck_results.borrow().pat_ty(pat);
397 self.record(ty, pat.hir_id, Some(scope), None, pat.span);
401 fn visit_expr(&mut self, expr: &'tcx Expr<'tcx>) {
403 ExprKind::Call(callee, args) => match &callee.kind {
404 ExprKind::Path(qpath) => {
405 let res = self.fcx.typeck_results.borrow().qpath_res(qpath, callee.hir_id);
407 // Direct calls never need to keep the callee `ty::FnDef`
408 // ZST in a temporary, so skip its type, just in case it
409 // can significantly complicate the generator type.
411 DefKind::Fn | DefKind::AssocFn | DefKind::Ctor(_, CtorKind::Fn),
414 // NOTE(eddyb) this assumes a path expression has
415 // no nested expressions to keep track of.
416 self.expr_count += 1;
418 // Record the rest of the call expression normally.
420 self.visit_expr(arg);
423 _ => intravisit::walk_expr(self, expr),
426 _ => intravisit::walk_expr(self, expr),
428 _ => intravisit::walk_expr(self, expr),
431 self.expr_count += 1;
433 debug!("is_borrowed_temporary: {:?}", self.drop_ranges.is_borrowed_temporary(expr));
435 let ty = self.fcx.typeck_results.borrow().expr_ty_adjusted_opt(expr);
437 // Typically, the value produced by an expression is consumed by its parent in some way,
438 // so we only have to check if the parent contains a yield (note that the parent may, for
439 // example, store the value into a local variable, but then we already consider local
440 // variables to be live across their scope).
442 // However, in the case of temporary values, we are going to store the value into a
443 // temporary on the stack that is live for the current temporary scope and then return a
444 // reference to it. That value may be live across the entire temporary scope.
446 // There's another subtlety: if the type has an observable drop, it must be dropped after
447 // the yield, even if it's not borrowed or referenced after the yield. Ideally this would
448 // *only* happen for types with observable drop, not all types which wrap them, but that
449 // doesn't match the behavior of MIR borrowck and causes ICEs. See the FIXME comment in
450 // src/test/ui/generator/drop-tracking-parent-expression.rs.
451 let scope = if self.drop_ranges.is_borrowed_temporary(expr)
452 || ty.map_or(true, |ty| {
453 // Avoid ICEs in needs_drop.
454 let ty = self.fcx.resolve_vars_if_possible(ty);
455 let ty = self.fcx.tcx.erase_regions(ty);
456 if ty.needs_infer() {
460 .delay_span_bug(expr.span, &format!("inference variables in {ty}"));
463 ty.needs_drop(self.fcx.tcx, self.fcx.param_env)
466 self.rvalue_scopes.temporary_scope(self.region_scope_tree, expr.hir_id.local_id)
468 let parent_expr = self
472 .parent_iter(expr.hir_id)
473 .find(|(_, node)| matches!(node, hir::Node::Expr(_)))
475 debug!("parent_expr: {:?}", parent_expr);
477 Some(parent) => Some(Scope { id: parent.local_id, data: ScopeData::Node }),
479 self.rvalue_scopes.temporary_scope(self.region_scope_tree, expr.hir_id.local_id)
484 // If there are adjustments, then record the final type --
485 // this is the actual value that is being produced.
486 if let Some(adjusted_ty) = ty {
487 self.record(adjusted_ty, expr.hir_id, scope, Some(expr), expr.span);
490 // Also record the unadjusted type (which is the only type if
491 // there are no adjustments). The reason for this is that the
492 // unadjusted value is sometimes a "temporary" that would wind
493 // up in a MIR temporary.
495 // As an example, consider an expression like `vec![].push(x)`.
496 // Here, the `vec![]` would wind up MIR stored into a
497 // temporary variable `t` which we can borrow to invoke
498 // `<Vec<_>>::push(&mut t, x)`.
500 // Note that an expression can have many adjustments, and we
501 // are just ignoring those intermediate types. This is because
502 // those intermediate values are always linearly "consumed" by
503 // the other adjustments, and hence would never be directly
504 // captured in the MIR.
506 // (Note that this partly relies on the fact that the `Deref`
507 // traits always return references, which means their content
508 // can be reborrowed without needing to spill to a temporary.
509 // If this were not the case, then we could conceivably have
510 // to create intermediate temporaries.)
512 // The type table might not have information for this expression
513 // if it is in a malformed scope. (#66387)
514 if let Some(ty) = self.fcx.typeck_results.borrow().expr_ty_opt(expr) {
515 self.record(ty, expr.hir_id, scope, Some(expr), expr.span);
517 self.fcx.tcx.sess.delay_span_bug(expr.span, "no type for node");
523 struct SuspendCheckData<'a, 'tcx> {
524 expr: Option<&'tcx Expr<'tcx>>,
532 // Returns whether it emitted a diagnostic or not
533 // Note that this fn and the proceeding one are based on the code
534 // for creating must_use diagnostics
536 // Note that this technique was chosen over things like a `Suspend` marker trait
537 // as it is simpler and has precedent in the compiler
538 fn check_must_not_suspend_ty<'tcx>(
539 fcx: &FnCtxt<'_, 'tcx>,
542 data: SuspendCheckData<'_, 'tcx>,
545 // FIXME: should this check `Ty::is_inhabited_from`. This query is not available in this stage
546 // of typeck (before ReVar and RePlaceholder are removed), but may remove noise, like in
548 // || !ty.is_inhabited_from(fcx.tcx, fcx.tcx.parent_module(hir_id).to_def_id(), fcx.param_env)
553 let plural_suffix = pluralize!(data.plural_len);
555 debug!("Checking must_not_suspend for {}", ty);
558 ty::Adt(..) if ty.is_box() => {
559 let boxed_ty = ty.boxed_ty();
560 let descr_pre = &format!("{}boxed ", data.descr_pre);
561 check_must_not_suspend_ty(fcx, boxed_ty, hir_id, SuspendCheckData { descr_pre, ..data })
563 ty::Adt(def, _) => check_must_not_suspend_def(fcx.tcx, def.did(), hir_id, data),
564 // FIXME: support adding the attribute to TAITs
565 ty::Opaque(def, _) => {
566 let mut has_emitted = false;
567 for &(predicate, _) in fcx.tcx.explicit_item_bounds(def) {
568 // We only look at the `DefId`, so it is safe to skip the binder here.
569 if let ty::PredicateKind::Trait(ref poly_trait_predicate) =
570 predicate.kind().skip_binder()
572 let def_id = poly_trait_predicate.trait_ref.def_id;
573 let descr_pre = &format!("{}implementer{} of ", data.descr_pre, plural_suffix);
574 if check_must_not_suspend_def(
578 SuspendCheckData { descr_pre, ..data },
587 ty::Dynamic(binder, _, _) => {
588 let mut has_emitted = false;
589 for predicate in binder.iter() {
590 if let ty::ExistentialPredicate::Trait(ref trait_ref) = predicate.skip_binder() {
591 let def_id = trait_ref.def_id;
592 let descr_post = &format!(" trait object{}{}", plural_suffix, data.descr_post);
593 if check_must_not_suspend_def(
597 SuspendCheckData { descr_post, ..data },
606 ty::Tuple(fields) => {
607 let mut has_emitted = false;
608 let comps = match data.expr.map(|e| &e.kind) {
609 Some(hir::ExprKind::Tup(comps)) => {
610 debug_assert_eq!(comps.len(), fields.len());
615 for (i, ty) in fields.iter().enumerate() {
616 let descr_post = &format!(" in tuple element {i}");
617 let span = comps.and_then(|c| c.get(i)).map(|e| e.span).unwrap_or(data.source_span);
618 if check_must_not_suspend_ty(
624 expr: comps.and_then(|comps| comps.get(i)),
634 ty::Array(ty, len) => {
635 let descr_pre = &format!("{}array{} of ", data.descr_pre, plural_suffix);
636 check_must_not_suspend_ty(
642 plural_len: len.try_eval_usize(fcx.tcx, fcx.param_env).unwrap_or(0) as usize
648 // If drop tracking is enabled, we want to look through references, since the referrent
649 // may not be considered live across the await point.
650 ty::Ref(_region, ty, _mutability) if fcx.sess().opts.unstable_opts.drop_tracking => {
651 let descr_pre = &format!("{}reference{} to ", data.descr_pre, plural_suffix);
652 check_must_not_suspend_ty(fcx, ty, hir_id, SuspendCheckData { descr_pre, ..data })
658 fn check_must_not_suspend_def(
662 data: SuspendCheckData<'_, '_>,
664 if let Some(attr) = tcx.get_attr(def_id, sym::must_not_suspend) {
665 tcx.struct_span_lint_hir(
666 rustc_session::lint::builtin::MUST_NOT_SUSPEND,
671 "{}`{}`{} held across a suspend point, but should not be",
673 tcx.def_path_str(def_id),
678 // add span pointing to the offending yield/await
679 lint.span_label(data.yield_span, "the value is held across this suspend point");
681 // Add optional reason note
682 if let Some(note) = attr.value_str() {
683 // FIXME(guswynn): consider formatting this better
684 lint.span_note(data.source_span, note.as_str());
687 // Add some quick suggestions on what to do
688 // FIXME: can `drop` work as a suggestion here as well?
691 "consider using a block (`{ ... }`) \
692 to shrink the value's scope, ending before the suspend point",