rustc_hir_typeck/fn_ctxt/
_impl.rs

1use std::collections::hash_map::Entry;
2use std::slice;
3
4use rustc_abi::FieldIdx;
5use rustc_data_structures::fx::FxHashSet;
6use rustc_errors::{Applicability, Diag, ErrorGuaranteed, MultiSpan};
7use rustc_hir::def::{CtorOf, DefKind, Res};
8use rustc_hir::def_id::DefId;
9use rustc_hir::intravisit::VisitorExt;
10use rustc_hir::lang_items::LangItem;
11use rustc_hir::{self as hir, AmbigArg, ExprKind, GenericArg, HirId, Node, QPath, intravisit};
12use rustc_hir_analysis::hir_ty_lowering::errors::GenericsArgsErrExtend;
13use rustc_hir_analysis::hir_ty_lowering::generics::{
14    check_generic_arg_count_for_call, lower_generic_args,
15};
16use rustc_hir_analysis::hir_ty_lowering::{
17    ExplicitLateBound, FeedConstTy, GenericArgCountMismatch, GenericArgCountResult,
18    GenericArgsLowerer, GenericPathSegment, HirTyLowerer, IsMethodCall, RegionInferReason,
19};
20use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
21use rustc_infer::infer::{DefineOpaqueTypes, InferResult};
22use rustc_lint::builtin::SELF_CONSTRUCTOR_FROM_OUTER_ITEM;
23use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
24use rustc_middle::ty::{
25    self, AdtKind, CanonicalUserType, GenericArgsRef, GenericParamDefKind, IsIdentity, Ty, TyCtxt,
26    TypeFoldable, TypeVisitable, TypeVisitableExt, UserArgs, UserSelfTy,
27};
28use rustc_middle::{bug, span_bug};
29use rustc_session::lint;
30use rustc_span::Span;
31use rustc_span::def_id::LocalDefId;
32use rustc_span::hygiene::DesugaringKind;
33use rustc_trait_selection::error_reporting::infer::need_type_info::TypeAnnotationNeeded;
34use rustc_trait_selection::traits::{
35    self, NormalizeExt, ObligationCauseCode, StructurallyNormalizeExt,
36};
37use tracing::{debug, instrument};
38
39use crate::callee::{self, DeferredCallResolution};
40use crate::errors::{self, CtorIsPrivate};
41use crate::method::{self, MethodCallee};
42use crate::{BreakableCtxt, Diverges, Expectation, FnCtxt, LoweredTy, rvalue_scopes};
43
44impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
45    /// Produces warning on the given node, if the current point in the
46    /// function is unreachable, and there hasn't been another warning.
47    pub(crate) fn warn_if_unreachable(&self, id: HirId, span: Span, kind: &str) {
48        let Diverges::Always { span: orig_span, custom_note } = self.diverges.get() else {
49            return;
50        };
51
52        match span.desugaring_kind() {
53            // If span arose from a desugaring of `if` or `while`, then it is the condition
54            // itself, which diverges, that we are about to lint on. This gives suboptimal
55            // diagnostics. Instead, stop here so that the `if`- or `while`-expression's
56            // block is linted instead.
57            Some(DesugaringKind::CondTemporary) => return,
58
59            // Don't lint if the result of an async block or async function is `!`.
60            // This does not affect the unreachable lints *within* the body.
61            Some(DesugaringKind::Async) => return,
62
63            // Don't lint *within* the `.await` operator, since that's all just desugaring
64            // junk. We only want to lint if there is a subsequent expression after the
65            // `.await` operator.
66            Some(DesugaringKind::Await) => return,
67
68            _ => {}
69        }
70
71        // Don't warn twice.
72        self.diverges.set(Diverges::WarnedAlways);
73
74        debug!("warn_if_unreachable: id={:?} span={:?} kind={}", id, span, kind);
75
76        let msg = format!("unreachable {kind}");
77        self.tcx().node_span_lint(lint::builtin::UNREACHABLE_CODE, id, span, |lint| {
78            lint.primary_message(msg.clone());
79            lint.span_label(span, msg).span_label(
80                orig_span,
81                custom_note.unwrap_or("any code following this expression is unreachable"),
82            );
83        })
84    }
85
86    /// Resolves type and const variables in `t` if possible. Unlike the infcx
87    /// version (resolve_vars_if_possible), this version will
88    /// also select obligations if it seems useful, in an effort
89    /// to get more type information.
90    // FIXME(-Znext-solver): A lot of the calls to this method should
91    // probably be `try_structurally_resolve_type` or `structurally_resolve_type` instead.
92    #[instrument(skip(self), level = "debug", ret)]
93    pub(crate) fn resolve_vars_with_obligations<T: TypeFoldable<TyCtxt<'tcx>>>(
94        &self,
95        mut t: T,
96    ) -> T {
97        // No Infer()? Nothing needs doing.
98        if !t.has_non_region_infer() {
99            debug!("no inference var, nothing needs doing");
100            return t;
101        }
102
103        // If `t` is a type variable, see whether we already know what it is.
104        t = self.resolve_vars_if_possible(t);
105        if !t.has_non_region_infer() {
106            debug!(?t);
107            return t;
108        }
109
110        // If not, try resolving pending obligations as much as
111        // possible. This can help substantially when there are
112        // indirect dependencies that don't seem worth tracking
113        // precisely.
114        self.select_obligations_where_possible(|_| {});
115        self.resolve_vars_if_possible(t)
116    }
117
118    pub(crate) fn record_deferred_call_resolution(
119        &self,
120        closure_def_id: LocalDefId,
121        r: DeferredCallResolution<'tcx>,
122    ) {
123        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
124        deferred_call_resolutions.entry(closure_def_id).or_default().push(r);
125    }
126
127    pub(crate) fn remove_deferred_call_resolutions(
128        &self,
129        closure_def_id: LocalDefId,
130    ) -> Vec<DeferredCallResolution<'tcx>> {
131        let mut deferred_call_resolutions = self.deferred_call_resolutions.borrow_mut();
132        deferred_call_resolutions.remove(&closure_def_id).unwrap_or_default()
133    }
134
135    fn tag(&self) -> String {
136        format!("{self:p}")
137    }
138
139    pub(crate) fn local_ty(&self, span: Span, nid: HirId) -> Ty<'tcx> {
140        self.locals.borrow().get(&nid).cloned().unwrap_or_else(|| {
141            span_bug!(span, "no type for local variable {}", self.tcx.hir_id_to_string(nid))
142        })
143    }
144
145    #[inline]
146    pub(crate) fn write_ty(&self, id: HirId, ty: Ty<'tcx>) {
147        debug!("write_ty({:?}, {:?}) in fcx {}", id, self.resolve_vars_if_possible(ty), self.tag());
148        let mut typeck = self.typeck_results.borrow_mut();
149        let mut node_ty = typeck.node_types_mut();
150
151        if let Some(prev) = node_ty.insert(id, ty) {
152            if prev.references_error() {
153                node_ty.insert(id, prev);
154            } else if !ty.references_error() {
155                // Could change this to a bug, but there's lots of diagnostic code re-lowering
156                // or re-typechecking nodes that were already typecked.
157                // Lots of that diagnostics code relies on subtle effects of re-lowering, so we'll
158                // let it keep doing that and just ensure that compilation won't succeed.
159                self.dcx().span_delayed_bug(
160                    self.tcx.hir_span(id),
161                    format!("`{prev}` overridden by `{ty}` for {id:?} in {:?}", self.body_id),
162                );
163            }
164        }
165
166        if let Err(e) = ty.error_reported() {
167            self.set_tainted_by_errors(e);
168        }
169    }
170
171    pub(crate) fn write_field_index(&self, hir_id: HirId, index: FieldIdx) {
172        self.typeck_results.borrow_mut().field_indices_mut().insert(hir_id, index);
173    }
174
175    #[instrument(level = "debug", skip(self))]
176    pub(crate) fn write_resolution(
177        &self,
178        hir_id: HirId,
179        r: Result<(DefKind, DefId), ErrorGuaranteed>,
180    ) {
181        self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, r);
182    }
183
184    #[instrument(level = "debug", skip(self))]
185    pub(crate) fn write_method_call_and_enforce_effects(
186        &self,
187        hir_id: HirId,
188        span: Span,
189        method: MethodCallee<'tcx>,
190    ) {
191        self.enforce_context_effects(Some(hir_id), span, method.def_id, method.args);
192        self.write_resolution(hir_id, Ok((DefKind::AssocFn, method.def_id)));
193        self.write_args(hir_id, method.args);
194    }
195
196    fn write_args(&self, node_id: HirId, args: GenericArgsRef<'tcx>) {
197        if !args.is_empty() {
198            debug!("write_args({:?}, {:?}) in fcx {}", node_id, args, self.tag());
199
200            self.typeck_results.borrow_mut().node_args_mut().insert(node_id, args);
201        }
202    }
203
204    /// Given the args that we just converted from the HIR, try to
205    /// canonicalize them and store them as user-given parameters
206    /// (i.e., parameters that must be respected by the NLL check).
207    ///
208    /// This should be invoked **before any unifications have
209    /// occurred**, so that annotations like `Vec<_>` are preserved
210    /// properly.
211    #[instrument(skip(self), level = "debug")]
212    pub(crate) fn write_user_type_annotation_from_args(
213        &self,
214        hir_id: HirId,
215        def_id: DefId,
216        args: GenericArgsRef<'tcx>,
217        user_self_ty: Option<UserSelfTy<'tcx>>,
218    ) {
219        debug!("fcx {}", self.tag());
220
221        // Don't write user type annotations for const param types, since we give them
222        // identity args just so that we can trivially substitute their `EarlyBinder`.
223        // We enforce that they match their type in MIR later on.
224        if matches!(self.tcx.def_kind(def_id), DefKind::ConstParam) {
225            return;
226        }
227
228        if Self::can_contain_user_lifetime_bounds((args, user_self_ty)) {
229            let canonicalized = self.canonicalize_user_type_annotation(ty::UserType::new(
230                ty::UserTypeKind::TypeOf(def_id, UserArgs { args, user_self_ty }),
231            ));
232            debug!(?canonicalized);
233            self.write_user_type_annotation(hir_id, canonicalized);
234        }
235    }
236
237    #[instrument(skip(self), level = "debug")]
238    pub(crate) fn write_user_type_annotation(
239        &self,
240        hir_id: HirId,
241        canonical_user_type_annotation: CanonicalUserType<'tcx>,
242    ) {
243        debug!("fcx {}", self.tag());
244
245        // FIXME: is_identity being on `UserType` and not `Canonical<UserType>` is awkward
246        if !canonical_user_type_annotation.is_identity() {
247            self.typeck_results
248                .borrow_mut()
249                .user_provided_types_mut()
250                .insert(hir_id, canonical_user_type_annotation);
251        } else {
252            debug!("skipping identity args");
253        }
254    }
255
256    #[instrument(skip(self, expr), level = "debug")]
257    pub(crate) fn apply_adjustments(&self, expr: &hir::Expr<'_>, adj: Vec<Adjustment<'tcx>>) {
258        debug!("expr = {:#?}", expr);
259
260        if adj.is_empty() {
261            return;
262        }
263
264        let mut expr_ty = self.typeck_results.borrow().expr_ty_adjusted(expr);
265
266        for a in &adj {
267            match a.kind {
268                Adjust::NeverToAny => {
269                    if a.target.is_ty_var() {
270                        self.diverging_type_vars.borrow_mut().insert(a.target);
271                        debug!("apply_adjustments: adding `{:?}` as diverging type var", a.target);
272                    }
273                }
274                Adjust::Deref(Some(overloaded_deref)) => {
275                    self.enforce_context_effects(
276                        None,
277                        expr.span,
278                        overloaded_deref.method_call(self.tcx),
279                        self.tcx.mk_args(&[expr_ty.into()]),
280                    );
281                }
282                Adjust::Deref(None) => {
283                    // FIXME(const_trait_impl): We *could* enforce `&T: ~const Deref` here.
284                }
285                Adjust::Pointer(_pointer_coercion) => {
286                    // FIXME(const_trait_impl): We should probably enforce these.
287                }
288                Adjust::ReborrowPin(_mutability) => {
289                    // FIXME(const_trait_impl): We could enforce these; they correspond to
290                    // `&mut T: DerefMut` tho, so it's kinda moot.
291                }
292                Adjust::Borrow(_) => {
293                    // No effects to enforce here.
294                }
295            }
296
297            expr_ty = a.target;
298        }
299
300        let autoborrow_mut = adj.iter().any(|adj| {
301            matches!(
302                adj,
303                &Adjustment {
304                    kind: Adjust::Borrow(AutoBorrow::Ref(AutoBorrowMutability::Mut { .. })),
305                    ..
306                }
307            )
308        });
309
310        match self.typeck_results.borrow_mut().adjustments_mut().entry(expr.hir_id) {
311            Entry::Vacant(entry) => {
312                entry.insert(adj);
313            }
314            Entry::Occupied(mut entry) => {
315                debug!(" - composing on top of {:?}", entry.get());
316                match (&mut entry.get_mut()[..], &adj[..]) {
317                    (
318                        [Adjustment { kind: Adjust::NeverToAny, target }],
319                        &[.., Adjustment { target: new_target, .. }],
320                    ) => {
321                        // NeverToAny coercion can target any type, so instead of adding a new
322                        // adjustment on top we can change the target.
323                        //
324                        // This is required for things like `a == a` (where `a: !`) to produce
325                        // valid MIR -- we need borrow adjustment from things like `==` to change
326                        // the type to `&!` (or `&()` depending on the fallback). This might be
327                        // relevant even in unreachable code.
328                        *target = new_target;
329                    }
330
331                    (
332                        &mut [
333                            Adjustment { kind: Adjust::Deref(_), .. },
334                            Adjustment { kind: Adjust::Borrow(AutoBorrow::Ref(..)), .. },
335                        ],
336                        &[
337                            Adjustment { kind: Adjust::Deref(_), .. },
338                            .., // Any following adjustments are allowed.
339                        ],
340                    ) => {
341                        // A reborrow has no effect before a dereference, so we can safely replace adjustments.
342                        *entry.get_mut() = adj;
343                    }
344
345                    _ => {
346                        // FIXME: currently we never try to compose autoderefs
347                        // and ReifyFnPointer/UnsafeFnPointer, but we could.
348                        self.dcx().span_delayed_bug(
349                            expr.span,
350                            format!(
351                                "while adjusting {:?}, can't compose {:?} and {:?}",
352                                expr,
353                                entry.get(),
354                                adj
355                            ),
356                        );
357
358                        *entry.get_mut() = adj;
359                    }
360                }
361            }
362        }
363
364        // If there is an mutable auto-borrow, it is equivalent to `&mut <expr>`.
365        // In this case implicit use of `Deref` and `Index` within `<expr>` should
366        // instead be `DerefMut` and `IndexMut`, so fix those up.
367        if autoborrow_mut {
368            self.convert_place_derefs_to_mutable(expr);
369        }
370    }
371
372    /// Instantiates and normalizes the bounds for a given item
373    pub(crate) fn instantiate_bounds(
374        &self,
375        span: Span,
376        def_id: DefId,
377        args: GenericArgsRef<'tcx>,
378    ) -> ty::InstantiatedPredicates<'tcx> {
379        let bounds = self.tcx.predicates_of(def_id);
380        let result = bounds.instantiate(self.tcx, args);
381        let result = self.normalize(span, result);
382        debug!("instantiate_bounds(bounds={:?}, args={:?}) = {:?}", bounds, args, result);
383        result
384    }
385
386    pub(crate) fn normalize<T>(&self, span: Span, value: T) -> T
387    where
388        T: TypeFoldable<TyCtxt<'tcx>>,
389    {
390        self.register_infer_ok_obligations(
391            self.at(&self.misc(span), self.param_env).normalize(value),
392        )
393    }
394
395    pub(crate) fn require_type_meets(
396        &self,
397        ty: Ty<'tcx>,
398        span: Span,
399        code: traits::ObligationCauseCode<'tcx>,
400        def_id: DefId,
401    ) {
402        self.register_bound(ty, def_id, self.cause(span, code));
403    }
404
405    pub(crate) fn require_type_is_sized(
406        &self,
407        ty: Ty<'tcx>,
408        span: Span,
409        code: traits::ObligationCauseCode<'tcx>,
410    ) {
411        if !ty.references_error() {
412            let lang_item = self.tcx.require_lang_item(LangItem::Sized, span);
413            self.require_type_meets(ty, span, code, lang_item);
414        }
415    }
416
417    pub(crate) fn require_type_is_sized_deferred(
418        &self,
419        ty: Ty<'tcx>,
420        span: Span,
421        code: traits::ObligationCauseCode<'tcx>,
422    ) {
423        if !ty.references_error() {
424            self.deferred_sized_obligations.borrow_mut().push((ty, span, code));
425        }
426    }
427
428    pub(crate) fn require_type_has_static_alignment(&self, ty: Ty<'tcx>, span: Span) {
429        if !ty.references_error() {
430            let tail = self.tcx.struct_tail_raw(
431                ty,
432                |ty| {
433                    if self.next_trait_solver() {
434                        self.try_structurally_resolve_type(span, ty)
435                    } else {
436                        self.normalize(span, ty)
437                    }
438                },
439                || {},
440            );
441            // Sized types have static alignment, and so do slices.
442            if tail.is_trivially_sized(self.tcx) || matches!(tail.kind(), ty::Slice(..)) {
443                // Nothing else is required here.
444            } else {
445                // We can't be sure, let's required full `Sized`.
446                let lang_item = self.tcx.require_lang_item(LangItem::Sized, span);
447                self.require_type_meets(ty, span, ObligationCauseCode::Misc, lang_item);
448            }
449        }
450    }
451
452    pub(crate) fn register_bound(
453        &self,
454        ty: Ty<'tcx>,
455        def_id: DefId,
456        cause: traits::ObligationCause<'tcx>,
457    ) {
458        if !ty.references_error() {
459            self.fulfillment_cx.borrow_mut().register_bound(
460                self,
461                self.param_env,
462                ty,
463                def_id,
464                cause,
465            );
466        }
467    }
468
469    pub(crate) fn lower_ty(&self, hir_ty: &hir::Ty<'tcx>) -> LoweredTy<'tcx> {
470        let ty = self.lowerer().lower_ty(hir_ty);
471        self.register_wf_obligation(ty.into(), hir_ty.span, ObligationCauseCode::WellFormed(None));
472        LoweredTy::from_raw(self, hir_ty.span, ty)
473    }
474
475    /// Walk a `hir_ty` and collect any clauses that may have come from a type
476    /// within the `hir_ty`. These clauses will be canonicalized with a user type
477    /// annotation so that we can enforce these bounds in borrowck, too.
478    pub(crate) fn collect_impl_trait_clauses_from_hir_ty(
479        &self,
480        hir_ty: &'tcx hir::Ty<'tcx>,
481    ) -> ty::Clauses<'tcx> {
482        struct CollectClauses<'a, 'tcx> {
483            clauses: Vec<ty::Clause<'tcx>>,
484            fcx: &'a FnCtxt<'a, 'tcx>,
485        }
486
487        impl<'tcx> intravisit::Visitor<'tcx> for CollectClauses<'_, 'tcx> {
488            fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx, AmbigArg>) {
489                if let Some(clauses) = self.fcx.trait_ascriptions.borrow().get(&ty.hir_id.local_id)
490                {
491                    self.clauses.extend(clauses.iter().cloned());
492                }
493                intravisit::walk_ty(self, ty)
494            }
495        }
496
497        let mut clauses = CollectClauses { clauses: vec![], fcx: self };
498        clauses.visit_ty_unambig(hir_ty);
499        self.tcx.mk_clauses(&clauses.clauses)
500    }
501
502    #[instrument(level = "debug", skip_all)]
503    pub(crate) fn lower_ty_saving_user_provided_ty(&self, hir_ty: &'tcx hir::Ty<'tcx>) -> Ty<'tcx> {
504        let ty = self.lower_ty(hir_ty);
505        debug!(?ty);
506
507        if Self::can_contain_user_lifetime_bounds(ty.raw) {
508            let c_ty = self.canonicalize_response(ty::UserType::new(ty::UserTypeKind::Ty(ty.raw)));
509            debug!(?c_ty);
510            self.typeck_results.borrow_mut().user_provided_types_mut().insert(hir_ty.hir_id, c_ty);
511        }
512
513        ty.normalized
514    }
515
516    pub(super) fn user_args_for_adt(ty: LoweredTy<'tcx>) -> UserArgs<'tcx> {
517        match (ty.raw.kind(), ty.normalized.kind()) {
518            (ty::Adt(_, args), _) => UserArgs { args, user_self_ty: None },
519            (_, ty::Adt(adt, args)) => UserArgs {
520                args,
521                user_self_ty: Some(UserSelfTy { impl_def_id: adt.did(), self_ty: ty.raw }),
522            },
523            _ => bug!("non-adt type {:?}", ty),
524        }
525    }
526
527    pub(crate) fn lower_const_arg(
528        &self,
529        const_arg: &'tcx hir::ConstArg<'tcx>,
530        feed: FeedConstTy<'_, 'tcx>,
531    ) -> ty::Const<'tcx> {
532        let ct = self.lowerer().lower_const_arg(const_arg, feed);
533        self.register_wf_obligation(
534            ct.into(),
535            self.tcx.hir_span(const_arg.hir_id),
536            ObligationCauseCode::WellFormed(None),
537        );
538        ct
539    }
540
541    // If the type given by the user has free regions, save it for later, since
542    // NLL would like to enforce those. Also pass in types that involve
543    // projections, since those can resolve to `'static` bounds (modulo #54940,
544    // which hopefully will be fixed by the time you see this comment, dear
545    // reader, although I have my doubts). Also pass in types with inference
546    // types, because they may be repeated. Other sorts of things are already
547    // sufficiently enforced with erased regions. =)
548    fn can_contain_user_lifetime_bounds<T>(t: T) -> bool
549    where
550        T: TypeVisitable<TyCtxt<'tcx>>,
551    {
552        t.has_free_regions() || t.has_aliases() || t.has_infer_types()
553    }
554
555    pub(crate) fn node_ty(&self, id: HirId) -> Ty<'tcx> {
556        match self.typeck_results.borrow().node_types().get(id) {
557            Some(&t) => t,
558            None if let Some(e) = self.tainted_by_errors() => Ty::new_error(self.tcx, e),
559            None => {
560                bug!("no type for node {} in fcx {}", self.tcx.hir_id_to_string(id), self.tag());
561            }
562        }
563    }
564
565    pub(crate) fn node_ty_opt(&self, id: HirId) -> Option<Ty<'tcx>> {
566        match self.typeck_results.borrow().node_types().get(id) {
567            Some(&t) => Some(t),
568            None if let Some(e) = self.tainted_by_errors() => Some(Ty::new_error(self.tcx, e)),
569            None => None,
570        }
571    }
572
573    /// Registers an obligation for checking later, during regionck, that `arg` is well-formed.
574    pub(crate) fn register_wf_obligation(
575        &self,
576        term: ty::Term<'tcx>,
577        span: Span,
578        code: traits::ObligationCauseCode<'tcx>,
579    ) {
580        // WF obligations never themselves fail, so no real need to give a detailed cause:
581        let cause = self.cause(span, code);
582        self.register_predicate(traits::Obligation::new(
583            self.tcx,
584            cause,
585            self.param_env,
586            ty::ClauseKind::WellFormed(term),
587        ));
588    }
589
590    /// Registers obligations that all `args` are well-formed.
591    pub(crate) fn add_wf_bounds(&self, args: GenericArgsRef<'tcx>, span: Span) {
592        for term in args.iter().filter_map(ty::GenericArg::as_term) {
593            self.register_wf_obligation(term, span, ObligationCauseCode::WellFormed(None));
594        }
595    }
596
597    // FIXME(arielb1): use this instead of field.ty everywhere
598    // Only for fields! Returns <none> for methods>
599    // Indifferent to privacy flags
600    pub(crate) fn field_ty(
601        &self,
602        span: Span,
603        field: &'tcx ty::FieldDef,
604        args: GenericArgsRef<'tcx>,
605    ) -> Ty<'tcx> {
606        self.normalize(span, field.ty(self.tcx, args))
607    }
608
609    pub(crate) fn resolve_rvalue_scopes(&self, def_id: DefId) {
610        let scope_tree = self.tcx.region_scope_tree(def_id);
611        let rvalue_scopes = { rvalue_scopes::resolve_rvalue_scopes(self, scope_tree, def_id) };
612        let mut typeck_results = self.typeck_results.borrow_mut();
613        typeck_results.rvalue_scopes = rvalue_scopes;
614    }
615
616    /// Unify the inference variables corresponding to coroutine witnesses, and save all the
617    /// predicates that were stalled on those inference variables.
618    ///
619    /// This process allows to conservatively save all predicates that do depend on the coroutine
620    /// interior types, for later processing by `check_coroutine_obligations`.
621    ///
622    /// We must not attempt to select obligations after this method has run, or risk query cycle
623    /// ICE.
624    #[instrument(level = "debug", skip(self))]
625    pub(crate) fn resolve_coroutine_interiors(&self) {
626        // Try selecting all obligations that are not blocked on inference variables.
627        // Once we start unifying coroutine witnesses, trying to select obligations on them will
628        // trigger query cycle ICEs, as doing so requires MIR.
629        self.select_obligations_where_possible(|_| {});
630
631        let coroutines = std::mem::take(&mut *self.deferred_coroutine_interiors.borrow_mut());
632        debug!(?coroutines);
633
634        let mut obligations = vec![];
635
636        if !self.next_trait_solver() {
637            for &(coroutine_def_id, interior) in coroutines.iter() {
638                debug!(?coroutine_def_id);
639
640                // Create the `CoroutineWitness` type that we will unify with `interior`.
641                let args = ty::GenericArgs::identity_for_item(
642                    self.tcx,
643                    self.tcx.typeck_root_def_id(coroutine_def_id.to_def_id()),
644                );
645                let witness =
646                    Ty::new_coroutine_witness(self.tcx, coroutine_def_id.to_def_id(), args);
647
648                // Unify `interior` with `witness` and collect all the resulting obligations.
649                let span = self.tcx.hir_body_owned_by(coroutine_def_id).value.span;
650                let ty::Infer(ty::InferTy::TyVar(_)) = interior.kind() else {
651                    span_bug!(span, "coroutine interior witness not infer: {:?}", interior.kind())
652                };
653                let ok = self
654                    .at(&self.misc(span), self.param_env)
655                    // Will never define opaque types, as all we do is instantiate a type variable.
656                    .eq(DefineOpaqueTypes::Yes, interior, witness)
657                    .expect("Failed to unify coroutine interior type");
658
659                obligations.extend(ok.obligations);
660            }
661        }
662
663        if !coroutines.is_empty() {
664            obligations.extend(
665                self.fulfillment_cx
666                    .borrow_mut()
667                    .drain_stalled_obligations_for_coroutines(&self.infcx),
668            );
669        }
670
671        self.typeck_results
672            .borrow_mut()
673            .coroutine_stalled_predicates
674            .extend(obligations.into_iter().map(|o| (o.predicate, o.cause)));
675    }
676
677    #[instrument(skip(self), level = "debug")]
678    pub(crate) fn report_ambiguity_errors(&self) {
679        let mut errors = self.fulfillment_cx.borrow_mut().collect_remaining_errors(self);
680
681        if !errors.is_empty() {
682            self.adjust_fulfillment_errors_for_expr_obligation(&mut errors);
683            self.err_ctxt().report_fulfillment_errors(errors);
684        }
685    }
686
687    /// Select as many obligations as we can at present.
688    pub(crate) fn select_obligations_where_possible(
689        &self,
690        mutate_fulfillment_errors: impl Fn(&mut Vec<traits::FulfillmentError<'tcx>>),
691    ) {
692        let mut result = self.fulfillment_cx.borrow_mut().select_where_possible(self);
693        if !result.is_empty() {
694            mutate_fulfillment_errors(&mut result);
695            self.adjust_fulfillment_errors_for_expr_obligation(&mut result);
696            self.err_ctxt().report_fulfillment_errors(result);
697        }
698    }
699
700    /// For the overloaded place expressions (`*x`, `x[3]`), the trait
701    /// returns a type of `&T`, but the actual type we assign to the
702    /// *expression* is `T`. So this function just peels off the return
703    /// type by one layer to yield `T`.
704    pub(crate) fn make_overloaded_place_return_type(&self, method: MethodCallee<'tcx>) -> Ty<'tcx> {
705        // extract method return type, which will be &T;
706        let ret_ty = method.sig.output();
707
708        // method returns &T, but the type as visible to user is T, so deref
709        ret_ty.builtin_deref(true).unwrap()
710    }
711
712    pub(crate) fn type_var_is_sized(&self, self_ty: ty::TyVid) -> bool {
713        let sized_did = self.tcx.lang_items().sized_trait();
714        self.obligations_for_self_ty(self_ty).into_iter().any(|obligation| {
715            match obligation.predicate.kind().skip_binder() {
716                ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => {
717                    Some(data.def_id()) == sized_did
718                }
719                _ => false,
720            }
721        })
722    }
723
724    pub(crate) fn err_args(&self, len: usize, guar: ErrorGuaranteed) -> Vec<Ty<'tcx>> {
725        let ty_error = Ty::new_error(self.tcx, guar);
726        vec![ty_error; len]
727    }
728
729    pub(crate) fn resolve_lang_item_path(
730        &self,
731        lang_item: hir::LangItem,
732        span: Span,
733        hir_id: HirId,
734    ) -> (Res, Ty<'tcx>) {
735        let def_id = self.tcx.require_lang_item(lang_item, span);
736        let def_kind = self.tcx.def_kind(def_id);
737
738        let item_ty = if let DefKind::Variant = def_kind {
739            self.tcx.type_of(self.tcx.parent(def_id))
740        } else {
741            self.tcx.type_of(def_id)
742        };
743        let args = self.fresh_args_for_item(span, def_id);
744        let ty = item_ty.instantiate(self.tcx, args);
745
746        self.write_args(hir_id, args);
747        self.write_resolution(hir_id, Ok((def_kind, def_id)));
748
749        let code = match lang_item {
750            hir::LangItem::IntoFutureIntoFuture => {
751                if let hir::Node::Expr(into_future_call) = self.tcx.parent_hir_node(hir_id)
752                    && let hir::ExprKind::Call(_, [arg0]) = &into_future_call.kind
753                {
754                    Some(ObligationCauseCode::AwaitableExpr(arg0.hir_id))
755                } else {
756                    None
757                }
758            }
759            hir::LangItem::IteratorNext | hir::LangItem::IntoIterIntoIter => {
760                Some(ObligationCauseCode::ForLoopIterator)
761            }
762            hir::LangItem::TryTraitFromOutput
763            | hir::LangItem::TryTraitFromResidual
764            | hir::LangItem::TryTraitBranch => Some(ObligationCauseCode::QuestionMark),
765            _ => None,
766        };
767        if let Some(code) = code {
768            self.add_required_obligations_with_code(span, def_id, args, move |_, _| code.clone());
769        } else {
770            self.add_required_obligations_for_hir(span, def_id, args, hir_id);
771        }
772
773        (Res::Def(def_kind, def_id), ty)
774    }
775
776    /// Resolves an associated value path into a base type and associated constant, or method
777    /// resolution. The newly resolved definition is written into `type_dependent_defs`.
778    #[instrument(level = "trace", skip(self), ret)]
779    pub(crate) fn resolve_ty_and_res_fully_qualified_call(
780        &self,
781        qpath: &'tcx QPath<'tcx>,
782        hir_id: HirId,
783        span: Span,
784    ) -> (Res, Option<LoweredTy<'tcx>>, &'tcx [hir::PathSegment<'tcx>]) {
785        let (ty, qself, item_segment) = match *qpath {
786            QPath::Resolved(ref opt_qself, path) => {
787                return (
788                    path.res,
789                    opt_qself.as_ref().map(|qself| self.lower_ty(qself)),
790                    path.segments,
791                );
792            }
793            QPath::TypeRelative(ref qself, ref segment) => {
794                // Don't use `self.lower_ty`, since this will register a WF obligation.
795                // If we're trying to call a nonexistent method on a trait
796                // (e.g. `MyTrait::missing_method`), then resolution will
797                // give us a `QPath::TypeRelative` with a trait object as
798                // `qself`. In that case, we want to avoid registering a WF obligation
799                // for `dyn MyTrait`, since we don't actually need the trait
800                // to be dyn-compatible.
801                // We manually call `register_wf_obligation` in the success path
802                // below.
803                let ty = self.lowerer().lower_ty(qself);
804                (LoweredTy::from_raw(self, span, ty), qself, segment)
805            }
806            QPath::LangItem(..) => {
807                bug!("`resolve_ty_and_res_fully_qualified_call` called on `LangItem`")
808            }
809        };
810
811        self.register_wf_obligation(
812            ty.raw.into(),
813            qself.span,
814            ObligationCauseCode::WellFormed(None),
815        );
816        self.select_obligations_where_possible(|_| {});
817
818        if let Some(&cached_result) = self.typeck_results.borrow().type_dependent_defs().get(hir_id)
819        {
820            // Return directly on cache hit. This is useful to avoid doubly reporting
821            // errors with default match binding modes. See #44614.
822            let def = cached_result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id));
823            return (def, Some(ty), slice::from_ref(&**item_segment));
824        }
825        let item_name = item_segment.ident;
826        let result = self
827            .resolve_fully_qualified_call(span, item_name, ty.normalized, qself.span, hir_id)
828            .or_else(|error| {
829                let guar = self
830                    .dcx()
831                    .span_delayed_bug(span, "method resolution should've emitted an error");
832                let result = match error {
833                    method::MethodError::PrivateMatch(kind, def_id, _) => Ok((kind, def_id)),
834                    _ => Err(guar),
835                };
836
837                let trait_missing_method =
838                    matches!(error, method::MethodError::NoMatch(_)) && ty.normalized.is_trait();
839                self.report_method_error(
840                    hir_id,
841                    ty.normalized,
842                    error,
843                    Expectation::NoExpectation,
844                    trait_missing_method && span.edition().at_least_rust_2021(), // emits missing method for trait only after edition 2021
845                );
846
847                result
848            });
849
850        // Write back the new resolution.
851        self.write_resolution(hir_id, result);
852        (
853            result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)),
854            Some(ty),
855            slice::from_ref(&**item_segment),
856        )
857    }
858
859    /// Given a `HirId`, return the `HirId` of the enclosing function and its `FnDecl`.
860    pub(crate) fn get_fn_decl(
861        &self,
862        blk_id: HirId,
863    ) -> Option<(LocalDefId, &'tcx hir::FnDecl<'tcx>)> {
864        // Get enclosing Fn, if it is a function or a trait method, unless there's a `loop` or
865        // `while` before reaching it, as block tail returns are not available in them.
866        self.tcx.hir_get_fn_id_for_return_block(blk_id).and_then(|item_id| {
867            match self.tcx.hir_node(item_id) {
868                Node::Item(&hir::Item {
869                    kind: hir::ItemKind::Fn { sig, .. }, owner_id, ..
870                }) => Some((owner_id.def_id, sig.decl)),
871                Node::TraitItem(&hir::TraitItem {
872                    kind: hir::TraitItemKind::Fn(ref sig, ..),
873                    owner_id,
874                    ..
875                }) => Some((owner_id.def_id, sig.decl)),
876                Node::ImplItem(&hir::ImplItem {
877                    kind: hir::ImplItemKind::Fn(ref sig, ..),
878                    owner_id,
879                    ..
880                }) => Some((owner_id.def_id, sig.decl)),
881                Node::Expr(&hir::Expr {
882                    hir_id,
883                    kind: hir::ExprKind::Closure(&hir::Closure { def_id, kind, fn_decl, .. }),
884                    ..
885                }) => {
886                    match kind {
887                        hir::ClosureKind::CoroutineClosure(_) => {
888                            // FIXME(async_closures): Implement this.
889                            return None;
890                        }
891                        hir::ClosureKind::Closure => Some((def_id, fn_decl)),
892                        hir::ClosureKind::Coroutine(hir::CoroutineKind::Desugared(
893                            _,
894                            hir::CoroutineSource::Fn,
895                        )) => {
896                            let (sig, owner_id) = match self.tcx.parent_hir_node(hir_id) {
897                                Node::Item(&hir::Item {
898                                    kind: hir::ItemKind::Fn { ref sig, .. },
899                                    owner_id,
900                                    ..
901                                }) => (sig, owner_id),
902                                Node::TraitItem(&hir::TraitItem {
903                                    kind: hir::TraitItemKind::Fn(ref sig, ..),
904                                    owner_id,
905                                    ..
906                                }) => (sig, owner_id),
907                                Node::ImplItem(&hir::ImplItem {
908                                    kind: hir::ImplItemKind::Fn(ref sig, ..),
909                                    owner_id,
910                                    ..
911                                }) => (sig, owner_id),
912                                _ => return None,
913                            };
914                            Some((owner_id.def_id, sig.decl))
915                        }
916                        _ => None,
917                    }
918                }
919                _ => None,
920            }
921        })
922    }
923
924    pub(crate) fn note_internal_mutation_in_method(
925        &self,
926        err: &mut Diag<'_>,
927        expr: &hir::Expr<'_>,
928        expected: Option<Ty<'tcx>>,
929        found: Ty<'tcx>,
930    ) {
931        if found != self.tcx.types.unit {
932            return;
933        }
934
935        let ExprKind::MethodCall(path_segment, rcvr, ..) = expr.kind else {
936            return;
937        };
938
939        let rcvr_has_the_expected_type = self
940            .typeck_results
941            .borrow()
942            .expr_ty_adjusted_opt(rcvr)
943            .zip(expected)
944            .is_some_and(|(ty, expected_ty)| expected_ty.peel_refs() == ty.peel_refs());
945
946        let prev_call_mutates_and_returns_unit = || {
947            self.typeck_results
948                .borrow()
949                .type_dependent_def_id(expr.hir_id)
950                .map(|def_id| self.tcx.fn_sig(def_id).skip_binder().skip_binder())
951                .and_then(|sig| sig.inputs_and_output.split_last())
952                .is_some_and(|(output, inputs)| {
953                    output.is_unit()
954                        && inputs
955                            .get(0)
956                            .and_then(|self_ty| self_ty.ref_mutability())
957                            .is_some_and(rustc_ast::Mutability::is_mut)
958                })
959        };
960
961        if !(rcvr_has_the_expected_type || prev_call_mutates_and_returns_unit()) {
962            return;
963        }
964
965        let mut sp = MultiSpan::from_span(path_segment.ident.span);
966        sp.push_span_label(
967            path_segment.ident.span,
968            format!(
969                "this call modifies {} in-place",
970                match rcvr.kind {
971                    ExprKind::Path(QPath::Resolved(
972                        None,
973                        hir::Path { segments: [segment], .. },
974                    )) => format!("`{}`", segment.ident),
975                    _ => "its receiver".to_string(),
976                }
977            ),
978        );
979
980        let modifies_rcvr_note =
981            format!("method `{}` modifies its receiver in-place", path_segment.ident);
982        if rcvr_has_the_expected_type {
983            sp.push_span_label(
984                rcvr.span,
985                "you probably want to use this value after calling the method...",
986            );
987            err.span_note(sp, modifies_rcvr_note);
988            err.note(format!("...instead of the `()` output of method `{}`", path_segment.ident));
989        } else if let ExprKind::MethodCall(..) = rcvr.kind {
990            err.span_note(
991                sp,
992                modifies_rcvr_note + ", it is not meant to be used in method chains.",
993            );
994        } else {
995            err.span_note(sp, modifies_rcvr_note);
996        }
997    }
998
999    // Instantiates the given path, which must refer to an item with the given
1000    // number of type parameters and type.
1001    #[instrument(skip(self, span), level = "debug")]
1002    pub(crate) fn instantiate_value_path(
1003        &self,
1004        segments: &'tcx [hir::PathSegment<'tcx>],
1005        self_ty: Option<LoweredTy<'tcx>>,
1006        res: Res,
1007        span: Span,
1008        path_span: Span,
1009        hir_id: HirId,
1010    ) -> (Ty<'tcx>, Res) {
1011        let tcx = self.tcx;
1012
1013        let generic_segments = match res {
1014            Res::Local(_) | Res::SelfCtor(_) => vec![],
1015            Res::Def(kind, def_id) => self.lowerer().probe_generic_path_segments(
1016                segments,
1017                self_ty.map(|ty| ty.raw),
1018                kind,
1019                def_id,
1020                span,
1021            ),
1022            Res::Err => {
1023                return (
1024                    Ty::new_error(
1025                        tcx,
1026                        tcx.dcx().span_delayed_bug(span, "could not resolve path {:?}"),
1027                    ),
1028                    res,
1029                );
1030            }
1031            _ => bug!("instantiate_value_path on {:?}", res),
1032        };
1033
1034        let mut user_self_ty = None;
1035        let mut is_alias_variant_ctor = false;
1036        let mut err_extend = GenericsArgsErrExtend::None;
1037        match res {
1038            Res::Def(DefKind::Ctor(CtorOf::Variant, _), _) if let Some(self_ty) = self_ty => {
1039                let adt_def = self_ty.normalized.ty_adt_def().unwrap();
1040                user_self_ty =
1041                    Some(UserSelfTy { impl_def_id: adt_def.did(), self_ty: self_ty.raw });
1042                is_alias_variant_ctor = true;
1043                err_extend = GenericsArgsErrExtend::DefVariant(segments);
1044            }
1045            Res::Def(DefKind::Ctor(CtorOf::Variant, _), _) => {
1046                err_extend = GenericsArgsErrExtend::DefVariant(segments);
1047            }
1048            Res::Def(DefKind::AssocFn | DefKind::AssocConst, def_id) => {
1049                let assoc_item = tcx.associated_item(def_id);
1050                let container = assoc_item.container;
1051                let container_id = assoc_item.container_id(tcx);
1052                debug!(?def_id, ?container, ?container_id);
1053                match container {
1054                    ty::AssocItemContainer::Trait => {
1055                        if let Err(e) = callee::check_legal_trait_for_method_call(
1056                            tcx,
1057                            path_span,
1058                            None,
1059                            span,
1060                            container_id,
1061                            self.body_id.to_def_id(),
1062                        ) {
1063                            self.set_tainted_by_errors(e);
1064                        }
1065                    }
1066                    ty::AssocItemContainer::Impl => {
1067                        if segments.len() == 1 {
1068                            // `<T>::assoc` will end up here, and so
1069                            // can `T::assoc`. If this came from an
1070                            // inherent impl, we need to record the
1071                            // `T` for posterity (see `UserSelfTy` for
1072                            // details).
1073                            let self_ty = self_ty.expect("UFCS sugared assoc missing Self").raw;
1074                            user_self_ty = Some(UserSelfTy { impl_def_id: container_id, self_ty });
1075                        }
1076                    }
1077                }
1078            }
1079            _ => {}
1080        }
1081
1082        // Now that we have categorized what space the parameters for each
1083        // segment belong to, let's sort out the parameters that the user
1084        // provided (if any) into their appropriate spaces. We'll also report
1085        // errors if type parameters are provided in an inappropriate place.
1086
1087        let indices: FxHashSet<_> =
1088            generic_segments.iter().map(|GenericPathSegment(_, index)| index).collect();
1089        let generics_err = self.lowerer().prohibit_generic_args(
1090            segments.iter().enumerate().filter_map(|(index, seg)| {
1091                if !indices.contains(&index) || is_alias_variant_ctor { Some(seg) } else { None }
1092            }),
1093            err_extend,
1094        );
1095
1096        if let Res::Local(hid) = res {
1097            let ty = self.local_ty(span, hid);
1098            let ty = self.normalize(span, ty);
1099            return (ty, res);
1100        }
1101
1102        if let Err(_) = generics_err {
1103            // Don't try to infer type parameters when prohibited generic arguments were given.
1104            user_self_ty = None;
1105        }
1106
1107        // Now we have to compare the types that the user *actually*
1108        // provided against the types that were *expected*. If the user
1109        // did not provide any types, then we want to instantiate inference
1110        // variables. If the user provided some types, we may still need
1111        // to add defaults. If the user provided *too many* types, that's
1112        // a problem.
1113
1114        let mut infer_args_for_err = None;
1115
1116        let mut explicit_late_bound = ExplicitLateBound::No;
1117        for &GenericPathSegment(def_id, index) in &generic_segments {
1118            let seg = &segments[index];
1119            let generics = tcx.generics_of(def_id);
1120
1121            // Argument-position `impl Trait` is treated as a normal generic
1122            // parameter internally, but we don't allow users to specify the
1123            // parameter's value explicitly, so we have to do some error-
1124            // checking here.
1125            let arg_count =
1126                check_generic_arg_count_for_call(self, def_id, generics, seg, IsMethodCall::No);
1127
1128            if let ExplicitLateBound::Yes = arg_count.explicit_late_bound {
1129                explicit_late_bound = ExplicitLateBound::Yes;
1130            }
1131
1132            if let Err(GenericArgCountMismatch { reported, .. }) = arg_count.correct {
1133                infer_args_for_err
1134                    .get_or_insert_with(|| (reported, FxHashSet::default()))
1135                    .1
1136                    .insert(index);
1137                self.set_tainted_by_errors(reported); // See issue #53251.
1138            }
1139        }
1140
1141        let has_self = generic_segments
1142            .last()
1143            .is_some_and(|GenericPathSegment(def_id, _)| tcx.generics_of(*def_id).has_self);
1144
1145        let (res, implicit_args) = if let Res::Def(DefKind::ConstParam, def) = res {
1146            // types of const parameters are somewhat special as they are part of
1147            // the same environment as the const parameter itself. this means that
1148            // unlike most paths `type-of(N)` can return a type naming parameters
1149            // introduced by the containing item, rather than provided through `N`.
1150            //
1151            // for example given `<T, const M: usize, const N: [T; M]>` and some
1152            // `let a = N;` expression. The path to `N` would wind up with no args
1153            // (as it has no args), but instantiating the early binder on `typeof(N)`
1154            // requires providing generic arguments for `[T, M, N]`.
1155            (res, Some(ty::GenericArgs::identity_for_item(tcx, tcx.parent(def))))
1156        } else if let Res::SelfCtor(impl_def_id) = res {
1157            let ty = LoweredTy::from_raw(
1158                self,
1159                span,
1160                tcx.at(span).type_of(impl_def_id).instantiate_identity(),
1161            );
1162
1163            // Firstly, check that this SelfCtor even comes from the item we're currently
1164            // typechecking. This can happen because we never validated the resolution of
1165            // SelfCtors, and when we started doing so, we noticed regressions. After
1166            // sufficiently long time, we can remove this check and turn it into a hard
1167            // error in `validate_res_from_ribs` -- it's just difficult to tell whether the
1168            // self type has any generic types during rustc_resolve, which is what we use
1169            // to determine if this is a hard error or warning.
1170            if std::iter::successors(Some(self.body_id.to_def_id()), |def_id| {
1171                self.tcx.generics_of(def_id).parent
1172            })
1173            .all(|def_id| def_id != impl_def_id)
1174            {
1175                let sugg = ty.normalized.ty_adt_def().map(|def| errors::ReplaceWithName {
1176                    span: path_span,
1177                    name: self.tcx.item_name(def.did()).to_ident_string(),
1178                });
1179                if ty.raw.has_param() {
1180                    let guar = self.dcx().emit_err(errors::SelfCtorFromOuterItem {
1181                        span: path_span,
1182                        impl_span: tcx.def_span(impl_def_id),
1183                        sugg,
1184                    });
1185                    return (Ty::new_error(self.tcx, guar), res);
1186                } else {
1187                    self.tcx.emit_node_span_lint(
1188                        SELF_CONSTRUCTOR_FROM_OUTER_ITEM,
1189                        hir_id,
1190                        path_span,
1191                        errors::SelfCtorFromOuterItemLint {
1192                            impl_span: tcx.def_span(impl_def_id),
1193                            sugg,
1194                        },
1195                    );
1196                }
1197            }
1198
1199            match ty.normalized.ty_adt_def() {
1200                Some(adt_def) if adt_def.has_ctor() => {
1201                    let (ctor_kind, ctor_def_id) = adt_def.non_enum_variant().ctor.unwrap();
1202                    // Check the visibility of the ctor.
1203                    let vis = tcx.visibility(ctor_def_id);
1204                    if !vis.is_accessible_from(tcx.parent_module(hir_id).to_def_id(), tcx) {
1205                        self.dcx()
1206                            .emit_err(CtorIsPrivate { span, def: tcx.def_path_str(adt_def.did()) });
1207                    }
1208                    let new_res = Res::Def(DefKind::Ctor(CtorOf::Struct, ctor_kind), ctor_def_id);
1209                    let user_args = Self::user_args_for_adt(ty);
1210                    user_self_ty = user_args.user_self_ty;
1211                    (new_res, Some(user_args.args))
1212                }
1213                _ => {
1214                    let mut err = self.dcx().struct_span_err(
1215                        span,
1216                        "the `Self` constructor can only be used with tuple or unit structs",
1217                    );
1218                    if let Some(adt_def) = ty.normalized.ty_adt_def() {
1219                        match adt_def.adt_kind() {
1220                            AdtKind::Enum => {
1221                                err.help("did you mean to use one of the enum's variants?");
1222                            }
1223                            AdtKind::Struct | AdtKind::Union => {
1224                                err.span_suggestion(
1225                                    span,
1226                                    "use curly brackets",
1227                                    "Self { /* fields */ }",
1228                                    Applicability::HasPlaceholders,
1229                                );
1230                            }
1231                        }
1232                    }
1233                    let reported = err.emit();
1234                    return (Ty::new_error(tcx, reported), res);
1235                }
1236            }
1237        } else {
1238            (res, None)
1239        };
1240        let def_id = res.def_id();
1241
1242        let (correct, infer_args_for_err) = match infer_args_for_err {
1243            Some((reported, args)) => {
1244                (Err(GenericArgCountMismatch { reported, invalid_args: vec![] }), args)
1245            }
1246            None => (Ok(()), Default::default()),
1247        };
1248
1249        let arg_count = GenericArgCountResult { explicit_late_bound, correct };
1250
1251        struct CtorGenericArgsCtxt<'a, 'tcx> {
1252            fcx: &'a FnCtxt<'a, 'tcx>,
1253            span: Span,
1254            generic_segments: &'a [GenericPathSegment],
1255            infer_args_for_err: &'a FxHashSet<usize>,
1256            segments: &'tcx [hir::PathSegment<'tcx>],
1257        }
1258        impl<'a, 'tcx> GenericArgsLowerer<'a, 'tcx> for CtorGenericArgsCtxt<'a, 'tcx> {
1259            fn args_for_def_id(
1260                &mut self,
1261                def_id: DefId,
1262            ) -> (Option<&'a hir::GenericArgs<'tcx>>, bool) {
1263                if let Some(&GenericPathSegment(_, index)) =
1264                    self.generic_segments.iter().find(|&GenericPathSegment(did, _)| *did == def_id)
1265                {
1266                    // If we've encountered an `impl Trait`-related error, we're just
1267                    // going to infer the arguments for better error messages.
1268                    if !self.infer_args_for_err.contains(&index) {
1269                        // Check whether the user has provided generic arguments.
1270                        if let Some(data) = self.segments[index].args {
1271                            return (Some(data), self.segments[index].infer_args);
1272                        }
1273                    }
1274                    return (None, self.segments[index].infer_args);
1275                }
1276
1277                (None, true)
1278            }
1279
1280            fn provided_kind(
1281                &mut self,
1282                preceding_args: &[ty::GenericArg<'tcx>],
1283                param: &ty::GenericParamDef,
1284                arg: &GenericArg<'tcx>,
1285            ) -> ty::GenericArg<'tcx> {
1286                match (&param.kind, arg) {
1287                    (GenericParamDefKind::Lifetime, GenericArg::Lifetime(lt)) => self
1288                        .fcx
1289                        .lowerer()
1290                        .lower_lifetime(lt, RegionInferReason::Param(param))
1291                        .into(),
1292                    (GenericParamDefKind::Type { .. }, GenericArg::Type(ty)) => {
1293                        // We handle the ambig portions of `Ty` in match arm below
1294                        self.fcx.lower_ty(ty.as_unambig_ty()).raw.into()
1295                    }
1296                    (GenericParamDefKind::Type { .. }, GenericArg::Infer(inf)) => {
1297                        self.fcx.lower_ty(&inf.to_ty()).raw.into()
1298                    }
1299                    (GenericParamDefKind::Const { .. }, GenericArg::Const(ct)) => self
1300                        .fcx
1301                        // Ambiguous parts of `ConstArg` are handled in the match arms below
1302                        .lower_const_arg(
1303                            ct.as_unambig_ct(),
1304                            FeedConstTy::Param(param.def_id, preceding_args),
1305                        )
1306                        .into(),
1307                    (&GenericParamDefKind::Const { .. }, GenericArg::Infer(inf)) => {
1308                        self.fcx.ct_infer(Some(param), inf.span).into()
1309                    }
1310                    _ => unreachable!(),
1311                }
1312            }
1313
1314            fn inferred_kind(
1315                &mut self,
1316                preceding_args: &[ty::GenericArg<'tcx>],
1317                param: &ty::GenericParamDef,
1318                infer_args: bool,
1319            ) -> ty::GenericArg<'tcx> {
1320                let tcx = self.fcx.tcx();
1321                if !infer_args && let Some(default) = param.default_value(tcx) {
1322                    // If we have a default, then it doesn't matter that we're not inferring
1323                    // the type/const arguments: We provide the default where any is missing.
1324                    return default.instantiate(tcx, preceding_args);
1325                }
1326                // If no type/const arguments were provided, we have to infer them.
1327                // This case also occurs as a result of some malformed input, e.g.,
1328                // a lifetime argument being given instead of a type/const parameter.
1329                // Using inference instead of `Error` gives better error messages.
1330                self.fcx.var_for_def(self.span, param)
1331            }
1332        }
1333
1334        let args_raw = implicit_args.unwrap_or_else(|| {
1335            lower_generic_args(
1336                self,
1337                def_id,
1338                &[],
1339                has_self,
1340                self_ty.map(|s| s.raw),
1341                &arg_count,
1342                &mut CtorGenericArgsCtxt {
1343                    fcx: self,
1344                    span,
1345                    generic_segments: &generic_segments,
1346                    infer_args_for_err: &infer_args_for_err,
1347                    segments,
1348                },
1349            )
1350        });
1351
1352        // First, store the "user args" for later.
1353        self.write_user_type_annotation_from_args(hir_id, def_id, args_raw, user_self_ty);
1354
1355        // Normalize only after registering type annotations.
1356        let args = self.normalize(span, args_raw);
1357
1358        self.add_required_obligations_for_hir(span, def_id, args, hir_id);
1359
1360        // Instantiate the values for the type parameters into the type of
1361        // the referenced item.
1362        let ty = tcx.type_of(def_id);
1363        assert!(!args.has_escaping_bound_vars());
1364        assert!(!ty.skip_binder().has_escaping_bound_vars());
1365        let ty_instantiated = self.normalize(span, ty.instantiate(tcx, args));
1366
1367        if let Some(UserSelfTy { impl_def_id, self_ty }) = user_self_ty {
1368            // In the case of `Foo<T>::method` and `<Foo<T>>::method`, if `method`
1369            // is inherent, there is no `Self` parameter; instead, the impl needs
1370            // type parameters, which we can infer by unifying the provided `Self`
1371            // with the instantiated impl type.
1372            // This also occurs for an enum variant on a type alias.
1373            let impl_ty = self.normalize(span, tcx.type_of(impl_def_id).instantiate(tcx, args));
1374            let self_ty = self.normalize(span, self_ty);
1375            match self.at(&self.misc(span), self.param_env).eq(
1376                DefineOpaqueTypes::Yes,
1377                impl_ty,
1378                self_ty,
1379            ) {
1380                Ok(ok) => self.register_infer_ok_obligations(ok),
1381                Err(_) => {
1382                    self.dcx().span_bug(
1383                        span,
1384                        format!(
1385                            "instantiate_value_path: (UFCS) {self_ty:?} was a subtype of {impl_ty:?} but now is not?",
1386                        ),
1387                    );
1388                }
1389            }
1390        }
1391
1392        debug!("instantiate_value_path: type of {:?} is {:?}", hir_id, ty_instantiated);
1393        self.write_args(hir_id, args);
1394
1395        (ty_instantiated, res)
1396    }
1397
1398    /// Add all the obligations that are required, instantiated and normalized appropriately.
1399    pub(crate) fn add_required_obligations_for_hir(
1400        &self,
1401        span: Span,
1402        def_id: DefId,
1403        args: GenericArgsRef<'tcx>,
1404        hir_id: HirId,
1405    ) {
1406        self.add_required_obligations_with_code(span, def_id, args, |idx, span| {
1407            ObligationCauseCode::WhereClauseInExpr(def_id, span, hir_id, idx)
1408        })
1409    }
1410
1411    #[instrument(level = "debug", skip(self, code, span, args))]
1412    fn add_required_obligations_with_code(
1413        &self,
1414        span: Span,
1415        def_id: DefId,
1416        args: GenericArgsRef<'tcx>,
1417        code: impl Fn(usize, Span) -> ObligationCauseCode<'tcx>,
1418    ) {
1419        let param_env = self.param_env;
1420
1421        let bounds = self.instantiate_bounds(span, def_id, args);
1422
1423        for obligation in traits::predicates_for_generics(
1424            |idx, predicate_span| self.cause(span, code(idx, predicate_span)),
1425            param_env,
1426            bounds,
1427        ) {
1428            self.register_predicate(obligation);
1429        }
1430    }
1431
1432    /// Try to resolve `ty` to a structural type, normalizing aliases.
1433    ///
1434    /// In case there is still ambiguity, the returned type may be an inference
1435    /// variable. This is different from `structurally_resolve_type` which errors
1436    /// in this case.
1437    #[instrument(level = "debug", skip(self, sp), ret)]
1438    pub(crate) fn try_structurally_resolve_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
1439        let ty = self.resolve_vars_with_obligations(ty);
1440
1441        if self.next_trait_solver()
1442            && let ty::Alias(..) = ty.kind()
1443        {
1444            // We need to use a separate variable here as otherwise the temporary for
1445            // `self.fulfillment_cx.borrow_mut()` is alive in the `Err` branch, resulting
1446            // in a reentrant borrow, causing an ICE.
1447            let result = self
1448                .at(&self.misc(sp), self.param_env)
1449                .structurally_normalize_ty(ty, &mut **self.fulfillment_cx.borrow_mut());
1450            match result {
1451                Ok(normalized_ty) => normalized_ty,
1452                Err(errors) => {
1453                    let guar = self.err_ctxt().report_fulfillment_errors(errors);
1454                    return Ty::new_error(self.tcx, guar);
1455                }
1456            }
1457        } else {
1458            ty
1459        }
1460    }
1461
1462    #[instrument(level = "debug", skip(self, sp), ret)]
1463    pub(crate) fn try_structurally_resolve_const(
1464        &self,
1465        sp: Span,
1466        ct: ty::Const<'tcx>,
1467    ) -> ty::Const<'tcx> {
1468        let ct = self.resolve_vars_with_obligations(ct);
1469
1470        if self.next_trait_solver()
1471            && let ty::ConstKind::Unevaluated(..) = ct.kind()
1472        {
1473            // We need to use a separate variable here as otherwise the temporary for
1474            // `self.fulfillment_cx.borrow_mut()` is alive in the `Err` branch, resulting
1475            // in a reentrant borrow, causing an ICE.
1476            let result = self
1477                .at(&self.misc(sp), self.param_env)
1478                .structurally_normalize_const(ct, &mut **self.fulfillment_cx.borrow_mut());
1479            match result {
1480                Ok(normalized_ct) => normalized_ct,
1481                Err(errors) => {
1482                    let guar = self.err_ctxt().report_fulfillment_errors(errors);
1483                    return ty::Const::new_error(self.tcx, guar);
1484                }
1485            }
1486        } else if self.tcx.features().generic_const_exprs() {
1487            rustc_trait_selection::traits::evaluate_const(&self.infcx, ct, self.param_env)
1488        } else {
1489            ct
1490        }
1491    }
1492
1493    /// Resolves `ty` by a single level if `ty` is a type variable.
1494    ///
1495    /// When the new solver is enabled, this will also attempt to normalize
1496    /// the type if it's a projection (note that it will not deeply normalize
1497    /// projections within the type, just the outermost layer of the type).
1498    ///
1499    /// If no resolution is possible, then an error is reported.
1500    /// Numeric inference variables may be left unresolved.
1501    pub(crate) fn structurally_resolve_type(&self, sp: Span, ty: Ty<'tcx>) -> Ty<'tcx> {
1502        let ty = self.try_structurally_resolve_type(sp, ty);
1503
1504        if !ty.is_ty_var() {
1505            ty
1506        } else {
1507            let e = self.tainted_by_errors().unwrap_or_else(|| {
1508                self.err_ctxt()
1509                    .emit_inference_failure_err(
1510                        self.body_id,
1511                        sp,
1512                        ty.into(),
1513                        TypeAnnotationNeeded::E0282,
1514                        true,
1515                    )
1516                    .emit()
1517            });
1518            let err = Ty::new_error(self.tcx, e);
1519            self.demand_suptype(sp, err, ty);
1520            err
1521        }
1522    }
1523
1524    pub(crate) fn structurally_resolve_const(
1525        &self,
1526        sp: Span,
1527        ct: ty::Const<'tcx>,
1528    ) -> ty::Const<'tcx> {
1529        let ct = self.try_structurally_resolve_const(sp, ct);
1530
1531        if !ct.is_ct_infer() {
1532            ct
1533        } else {
1534            let e = self.tainted_by_errors().unwrap_or_else(|| {
1535                self.err_ctxt()
1536                    .emit_inference_failure_err(
1537                        self.body_id,
1538                        sp,
1539                        ct.into(),
1540                        TypeAnnotationNeeded::E0282,
1541                        true,
1542                    )
1543                    .emit()
1544            });
1545            // FIXME: Infer `?ct = {const error}`?
1546            ty::Const::new_error(self.tcx, e)
1547        }
1548    }
1549
1550    pub(crate) fn with_breakable_ctxt<F: FnOnce() -> R, R>(
1551        &self,
1552        id: HirId,
1553        ctxt: BreakableCtxt<'tcx>,
1554        f: F,
1555    ) -> (BreakableCtxt<'tcx>, R) {
1556        let index;
1557        {
1558            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
1559            index = enclosing_breakables.stack.len();
1560            enclosing_breakables.by_id.insert(id, index);
1561            enclosing_breakables.stack.push(ctxt);
1562        }
1563        let result = f();
1564        let ctxt = {
1565            let mut enclosing_breakables = self.enclosing_breakables.borrow_mut();
1566            debug_assert!(enclosing_breakables.stack.len() == index + 1);
1567            // FIXME(#120456) - is `swap_remove` correct?
1568            enclosing_breakables.by_id.swap_remove(&id).expect("missing breakable context");
1569            enclosing_breakables.stack.pop().expect("missing breakable context")
1570        };
1571        (ctxt, result)
1572    }
1573
1574    /// Instantiate a QueryResponse in a probe context, without a
1575    /// good ObligationCause.
1576    pub(crate) fn probe_instantiate_query_response(
1577        &self,
1578        span: Span,
1579        original_values: &OriginalQueryValues<'tcx>,
1580        query_result: &Canonical<'tcx, QueryResponse<'tcx, Ty<'tcx>>>,
1581    ) -> InferResult<'tcx, Ty<'tcx>> {
1582        self.instantiate_query_response_and_region_obligations(
1583            &self.misc(span),
1584            self.param_env,
1585            original_values,
1586            query_result,
1587        )
1588    }
1589
1590    /// Returns `true` if an expression is contained inside the LHS of an assignment expression.
1591    pub(crate) fn expr_in_place(&self, mut expr_id: HirId) -> bool {
1592        let mut contained_in_place = false;
1593
1594        while let hir::Node::Expr(parent_expr) = self.tcx.parent_hir_node(expr_id) {
1595            match &parent_expr.kind {
1596                hir::ExprKind::Assign(lhs, ..) | hir::ExprKind::AssignOp(_, lhs, ..) => {
1597                    if lhs.hir_id == expr_id {
1598                        contained_in_place = true;
1599                        break;
1600                    }
1601                }
1602                _ => (),
1603            }
1604            expr_id = parent_expr.hir_id;
1605        }
1606
1607        contained_in_place
1608    }
1609}