rustc_hir_typeck/fn_ctxt/
mod.rs

1mod _impl;
2mod adjust_fulfillment_errors;
3mod arg_matrix;
4mod checks;
5mod inspect_obligations;
6mod suggestions;
7
8use std::cell::{Cell, RefCell};
9use std::ops::Deref;
10
11use hir::def_id::CRATE_DEF_ID;
12use rustc_errors::DiagCtxtHandle;
13use rustc_hir::def_id::{DefId, LocalDefId};
14use rustc_hir::{self as hir, HirId, ItemLocalMap};
15use rustc_hir_analysis::hir_ty_lowering::{
16    HirTyLowerer, InherentAssocCandidate, RegionInferReason,
17};
18use rustc_infer::infer;
19use rustc_infer::traits::{DynCompatibilityViolation, Obligation};
20use rustc_middle::ty::{self, Const, Ty, TyCtxt, TypeVisitableExt};
21use rustc_session::Session;
22use rustc_span::{self, DUMMY_SP, ErrorGuaranteed, Ident, Span, sym};
23use rustc_trait_selection::error_reporting::TypeErrCtxt;
24use rustc_trait_selection::error_reporting::infer::sub_relations::SubRelations;
25use rustc_trait_selection::traits::{
26    self, FulfillmentError, ObligationCause, ObligationCauseCode, ObligationCtxt,
27};
28
29use crate::coercion::DynamicCoerceMany;
30use crate::fallback::DivergingFallbackBehavior;
31use crate::fn_ctxt::checks::DivergingBlockBehavior;
32use crate::{CoroutineTypes, Diverges, EnclosingBreakables, TypeckRootCtxt};
33
34/// The `FnCtxt` stores type-checking context needed to type-check bodies of
35/// functions, closures, and `const`s, including performing type inference
36/// with [`InferCtxt`].
37///
38/// This is in contrast to `rustc_hir_analysis::collect::ItemCtxt`, which is
39/// used to type-check item *signatures* and thus does not perform type
40/// inference.
41///
42/// See `ItemCtxt`'s docs for more.
43///
44/// [`InferCtxt`]: infer::InferCtxt
45pub(crate) struct FnCtxt<'a, 'tcx> {
46    pub(super) body_id: LocalDefId,
47
48    /// The parameter environment used for proving trait obligations
49    /// in this function. This can change when we descend into
50    /// closures (as they bring new things into scope), hence it is
51    /// not part of `Inherited` (as of the time of this writing,
52    /// closures do not yet change the environment, but they will
53    /// eventually).
54    pub(super) param_env: ty::ParamEnv<'tcx>,
55
56    /// If `Some`, this stores coercion information for returned
57    /// expressions. If `None`, this is in a context where return is
58    /// inappropriate, such as a const expression.
59    ///
60    /// This is a `RefCell<DynamicCoerceMany>`, which means that we
61    /// can track all the return expressions and then use them to
62    /// compute a useful coercion from the set, similar to a match
63    /// expression or other branching context. You can use methods
64    /// like `expected_ty` to access the declared return type (if
65    /// any).
66    pub(super) ret_coercion: Option<RefCell<DynamicCoerceMany<'tcx>>>,
67
68    /// First span of a return site that we find. Used in error messages.
69    pub(super) ret_coercion_span: Cell<Option<Span>>,
70
71    pub(super) coroutine_types: Option<CoroutineTypes<'tcx>>,
72
73    /// Whether the last checked node generates a divergence (e.g.,
74    /// `return` will set this to `Always`). In general, when entering
75    /// an expression or other node in the tree, the initial value
76    /// indicates whether prior parts of the containing expression may
77    /// have diverged. It is then typically set to `Maybe` (and the
78    /// old value remembered) for processing the subparts of the
79    /// current expression. As each subpart is processed, they may set
80    /// the flag to `Always`, etc. Finally, at the end, we take the
81    /// result and "union" it with the original value, so that when we
82    /// return the flag indicates if any subpart of the parent
83    /// expression (up to and including this part) has diverged. So,
84    /// if you read it after evaluating a subexpression `X`, the value
85    /// you get indicates whether any subexpression that was
86    /// evaluating up to and including `X` diverged.
87    ///
88    /// We currently use this flag for the following purposes:
89    ///
90    /// - To warn about unreachable code: if, after processing a
91    ///   sub-expression but before we have applied the effects of the
92    ///   current node, we see that the flag is set to `Always`, we
93    ///   can issue a warning. This corresponds to something like
94    ///   `foo(return)`; we warn on the `foo()` expression. (We then
95    ///   update the flag to `WarnedAlways` to suppress duplicate
96    ///   reports.) Similarly, if we traverse to a fresh statement (or
97    ///   tail expression) from an `Always` setting, we will issue a
98    ///   warning. This corresponds to something like `{return;
99    ///   foo();}` or `{return; 22}`, where we would warn on the
100    ///   `foo()` or `22`.
101    /// - To assign the `!` type to block expressions with diverging
102    ///   statements.
103    ///
104    /// An expression represents dead code if, after checking it,
105    /// the diverges flag is set to something other than `Maybe`.
106    pub(super) diverges: Cell<Diverges>,
107
108    /// If one of the function arguments is a never pattern, this counts as diverging code. This
109    /// affect typechecking of the function body.
110    pub(super) function_diverges_because_of_empty_arguments: Cell<Diverges>,
111
112    /// Whether the currently checked node is the whole body of the function.
113    pub(super) is_whole_body: Cell<bool>,
114
115    pub(super) enclosing_breakables: RefCell<EnclosingBreakables<'tcx>>,
116
117    pub(super) root_ctxt: &'a TypeckRootCtxt<'tcx>,
118
119    pub(super) fallback_has_occurred: Cell<bool>,
120
121    pub(super) diverging_fallback_behavior: DivergingFallbackBehavior,
122    pub(super) diverging_block_behavior: DivergingBlockBehavior,
123
124    /// Clauses that we lowered as part of the `impl_trait_in_bindings` feature.
125    ///
126    /// These are stored here so we may collect them when canonicalizing user
127    /// type ascriptions later.
128    pub(super) trait_ascriptions: RefCell<ItemLocalMap<Vec<ty::Clause<'tcx>>>>,
129}
130
131impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
132    pub(crate) fn new(
133        root_ctxt: &'a TypeckRootCtxt<'tcx>,
134        param_env: ty::ParamEnv<'tcx>,
135        body_id: LocalDefId,
136    ) -> FnCtxt<'a, 'tcx> {
137        let (diverging_fallback_behavior, diverging_block_behavior) =
138            never_type_behavior(root_ctxt.tcx);
139        FnCtxt {
140            body_id,
141            param_env,
142            ret_coercion: None,
143            ret_coercion_span: Cell::new(None),
144            coroutine_types: None,
145            diverges: Cell::new(Diverges::Maybe),
146            function_diverges_because_of_empty_arguments: Cell::new(Diverges::Maybe),
147            is_whole_body: Cell::new(false),
148            enclosing_breakables: RefCell::new(EnclosingBreakables {
149                stack: Vec::new(),
150                by_id: Default::default(),
151            }),
152            root_ctxt,
153            fallback_has_occurred: Cell::new(false),
154            diverging_fallback_behavior,
155            diverging_block_behavior,
156            trait_ascriptions: Default::default(),
157        }
158    }
159
160    pub(crate) fn dcx(&self) -> DiagCtxtHandle<'a> {
161        self.root_ctxt.infcx.dcx()
162    }
163
164    pub(crate) fn cause(
165        &self,
166        span: Span,
167        code: ObligationCauseCode<'tcx>,
168    ) -> ObligationCause<'tcx> {
169        ObligationCause::new(span, self.body_id, code)
170    }
171
172    pub(crate) fn misc(&self, span: Span) -> ObligationCause<'tcx> {
173        self.cause(span, ObligationCauseCode::Misc)
174    }
175
176    pub(crate) fn sess(&self) -> &Session {
177        self.tcx.sess
178    }
179
180    /// Creates an `TypeErrCtxt` with a reference to the in-progress
181    /// `TypeckResults` which is used for diagnostics.
182    /// Use [`InferCtxtErrorExt::err_ctxt`] to start one without a `TypeckResults`.
183    ///
184    /// [`InferCtxtErrorExt::err_ctxt`]: rustc_trait_selection::error_reporting::InferCtxtErrorExt::err_ctxt
185    pub(crate) fn err_ctxt(&'a self) -> TypeErrCtxt<'a, 'tcx> {
186        let mut sub_relations = SubRelations::default();
187        sub_relations.add_constraints(
188            self,
189            self.fulfillment_cx.borrow_mut().pending_obligations().iter().map(|o| o.predicate),
190        );
191        TypeErrCtxt {
192            infcx: &self.infcx,
193            sub_relations: RefCell::new(sub_relations),
194            typeck_results: Some(self.typeck_results.borrow()),
195            fallback_has_occurred: self.fallback_has_occurred.get(),
196            normalize_fn_sig: Box::new(|fn_sig| {
197                if fn_sig.has_escaping_bound_vars() {
198                    return fn_sig;
199                }
200                self.probe(|_| {
201                    let ocx = ObligationCtxt::new(self);
202                    let normalized_fn_sig =
203                        ocx.normalize(&ObligationCause::dummy(), self.param_env, fn_sig);
204                    if ocx.select_all_or_error().is_empty() {
205                        let normalized_fn_sig = self.resolve_vars_if_possible(normalized_fn_sig);
206                        if !normalized_fn_sig.has_infer() {
207                            return normalized_fn_sig;
208                        }
209                    }
210                    fn_sig
211                })
212            }),
213            autoderef_steps: Box::new(|ty| {
214                let mut autoderef = self.autoderef(DUMMY_SP, ty).silence_errors();
215                let mut steps = vec![];
216                while let Some((ty, _)) = autoderef.next() {
217                    steps.push((ty, autoderef.current_obligations()));
218                }
219                steps
220            }),
221        }
222    }
223}
224
225impl<'a, 'tcx> Deref for FnCtxt<'a, 'tcx> {
226    type Target = TypeckRootCtxt<'tcx>;
227    fn deref(&self) -> &Self::Target {
228        self.root_ctxt
229    }
230}
231
232impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
233    fn tcx(&self) -> TyCtxt<'tcx> {
234        self.tcx
235    }
236
237    fn dcx(&self) -> DiagCtxtHandle<'_> {
238        self.root_ctxt.dcx()
239    }
240
241    fn item_def_id(&self) -> LocalDefId {
242        self.body_id
243    }
244
245    fn re_infer(&self, span: Span, reason: RegionInferReason<'_>) -> ty::Region<'tcx> {
246        let v = match reason {
247            RegionInferReason::Param(def) => infer::RegionParameterDefinition(span, def.name),
248            _ => infer::MiscVariable(span),
249        };
250        self.next_region_var(v)
251    }
252
253    fn ty_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Ty<'tcx> {
254        match param {
255            Some(param) => self.var_for_def(span, param).as_type().unwrap(),
256            None => self.next_ty_var(span),
257        }
258    }
259
260    fn ct_infer(&self, param: Option<&ty::GenericParamDef>, span: Span) -> Const<'tcx> {
261        // FIXME ideally this shouldn't use unwrap
262        match param {
263            Some(param) => self.var_for_def(span, param).as_const().unwrap(),
264            None => self.next_const_var(span),
265        }
266    }
267
268    fn register_trait_ascription_bounds(
269        &self,
270        bounds: Vec<(ty::Clause<'tcx>, Span)>,
271        hir_id: HirId,
272        _span: Span,
273    ) {
274        for (clause, span) in bounds {
275            if clause.has_escaping_bound_vars() {
276                self.dcx().span_delayed_bug(span, "clause should have no escaping bound vars");
277                continue;
278            }
279
280            self.trait_ascriptions.borrow_mut().entry(hir_id.local_id).or_default().push(clause);
281
282            let clause = self.normalize(span, clause);
283            self.register_predicate(Obligation::new(
284                self.tcx,
285                self.misc(span),
286                self.param_env,
287                clause,
288            ));
289        }
290    }
291
292    fn probe_ty_param_bounds(
293        &self,
294        _: Span,
295        def_id: LocalDefId,
296        _: Ident,
297    ) -> ty::EarlyBinder<'tcx, &'tcx [(ty::Clause<'tcx>, Span)]> {
298        let tcx = self.tcx;
299        let item_def_id = tcx.hir_ty_param_owner(def_id);
300        let generics = tcx.generics_of(item_def_id);
301        let index = generics.param_def_id_to_index[&def_id.to_def_id()];
302        // HACK(eddyb) should get the original `Span`.
303        let span = tcx.def_span(def_id);
304
305        ty::EarlyBinder::bind(tcx.arena.alloc_from_iter(
306            self.param_env.caller_bounds().iter().filter_map(|predicate| {
307                match predicate.kind().skip_binder() {
308                    ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
309                        Some((predicate, span))
310                    }
311                    _ => None,
312                }
313            }),
314        ))
315    }
316
317    fn select_inherent_assoc_candidates(
318        &self,
319        span: Span,
320        self_ty: Ty<'tcx>,
321        candidates: Vec<InherentAssocCandidate>,
322    ) -> (Vec<InherentAssocCandidate>, Vec<FulfillmentError<'tcx>>) {
323        let tcx = self.tcx();
324        let infcx = &self.infcx;
325        let mut fulfillment_errors = vec![];
326
327        let mut filter_iat_candidate = |self_ty, impl_| {
328            let ocx = ObligationCtxt::new_with_diagnostics(self);
329            let self_ty = ocx.normalize(&ObligationCause::dummy(), self.param_env, self_ty);
330
331            let impl_args = infcx.fresh_args_for_item(span, impl_);
332            let impl_ty = tcx.type_of(impl_).instantiate(tcx, impl_args);
333            let impl_ty = ocx.normalize(&ObligationCause::dummy(), self.param_env, impl_ty);
334
335            // Check that the self types can be related.
336            if ocx.eq(&ObligationCause::dummy(), self.param_env, impl_ty, self_ty).is_err() {
337                return false;
338            }
339
340            // Check whether the impl imposes obligations we have to worry about.
341            let impl_bounds = tcx.predicates_of(impl_).instantiate(tcx, impl_args);
342            let impl_bounds = ocx.normalize(&ObligationCause::dummy(), self.param_env, impl_bounds);
343            let impl_obligations = traits::predicates_for_generics(
344                |_, _| ObligationCause::dummy(),
345                self.param_env,
346                impl_bounds,
347            );
348            ocx.register_obligations(impl_obligations);
349
350            let mut errors = ocx.select_where_possible();
351            if !errors.is_empty() {
352                fulfillment_errors.append(&mut errors);
353                return false;
354            }
355
356            true
357        };
358
359        let mut universes = if self_ty.has_escaping_bound_vars() {
360            vec![None; self_ty.outer_exclusive_binder().as_usize()]
361        } else {
362            vec![]
363        };
364
365        let candidates =
366            traits::with_replaced_escaping_bound_vars(infcx, &mut universes, self_ty, |self_ty| {
367                candidates
368                    .into_iter()
369                    .filter(|&InherentAssocCandidate { impl_, .. }| {
370                        infcx.probe(|_| filter_iat_candidate(self_ty, impl_))
371                    })
372                    .collect()
373            });
374
375        (candidates, fulfillment_errors)
376    }
377
378    fn lower_assoc_item_path(
379        &self,
380        span: Span,
381        item_def_id: DefId,
382        item_segment: &rustc_hir::PathSegment<'tcx>,
383        poly_trait_ref: ty::PolyTraitRef<'tcx>,
384    ) -> Result<(DefId, ty::GenericArgsRef<'tcx>), ErrorGuaranteed> {
385        let trait_ref = self.instantiate_binder_with_fresh_vars(
386            span,
387            // FIXME(mgca): `item_def_id` can be an AssocConst; rename this variant.
388            infer::BoundRegionConversionTime::AssocTypeProjection(item_def_id),
389            poly_trait_ref,
390        );
391
392        let item_args = self.lowerer().lower_generic_args_of_assoc_item(
393            span,
394            item_def_id,
395            item_segment,
396            trait_ref.args,
397        );
398
399        Ok((item_def_id, item_args))
400    }
401
402    fn probe_adt(&self, span: Span, ty: Ty<'tcx>) -> Option<ty::AdtDef<'tcx>> {
403        match ty.kind() {
404            ty::Adt(adt_def, _) => Some(*adt_def),
405            // FIXME(#104767): Should we handle bound regions here?
406            ty::Alias(ty::Projection | ty::Inherent | ty::Free, _)
407                if !ty.has_escaping_bound_vars() =>
408            {
409                if self.next_trait_solver() {
410                    self.try_structurally_resolve_type(span, ty).ty_adt_def()
411                } else {
412                    self.normalize(span, ty).ty_adt_def()
413                }
414            }
415            _ => None,
416        }
417    }
418
419    fn record_ty(&self, hir_id: hir::HirId, ty: Ty<'tcx>, span: Span) {
420        // FIXME: normalization and escaping regions
421        let ty = if !ty.has_escaping_bound_vars() {
422            // NOTE: These obligations are 100% redundant and are implied by
423            // WF obligations that are registered elsewhere, but they have a
424            // better cause code assigned to them in `add_required_obligations_for_hir`.
425            // This means that they should shadow obligations with worse spans.
426            if let ty::Alias(ty::Projection | ty::Free, ty::AliasTy { args, def_id, .. }) =
427                ty.kind()
428            {
429                self.add_required_obligations_for_hir(span, *def_id, args, hir_id);
430            }
431
432            self.normalize(span, ty)
433        } else {
434            ty
435        };
436        self.write_ty(hir_id, ty)
437    }
438
439    fn infcx(&self) -> Option<&infer::InferCtxt<'tcx>> {
440        Some(&self.infcx)
441    }
442
443    fn lower_fn_sig(
444        &self,
445        decl: &rustc_hir::FnDecl<'tcx>,
446        _generics: Option<&rustc_hir::Generics<'_>>,
447        _hir_id: rustc_hir::HirId,
448        _hir_ty: Option<&hir::Ty<'_>>,
449    ) -> (Vec<Ty<'tcx>>, Ty<'tcx>) {
450        let input_tys = decl.inputs.iter().map(|a| self.lowerer().lower_ty(a)).collect();
451
452        let output_ty = match decl.output {
453            hir::FnRetTy::Return(output) => self.lowerer().lower_ty(output),
454            hir::FnRetTy::DefaultReturn(..) => self.tcx().types.unit,
455        };
456        (input_tys, output_ty)
457    }
458
459    fn dyn_compatibility_violations(&self, trait_def_id: DefId) -> Vec<DynCompatibilityViolation> {
460        self.tcx.dyn_compatibility_violations(trait_def_id).to_vec()
461    }
462}
463
464/// The `ty` representation of a user-provided type. Depending on the use-site
465/// we want to either use the unnormalized or the normalized form of this type.
466///
467/// This is a bridge between the interface of HIR ty lowering, which outputs a raw
468/// `Ty`, and the API in this module, which expect `Ty` to be fully normalized.
469#[derive(Clone, Copy, Debug)]
470pub(crate) struct LoweredTy<'tcx> {
471    /// The unnormalized type provided by the user.
472    pub raw: Ty<'tcx>,
473
474    /// The normalized form of `raw`, stored here for efficiency.
475    pub normalized: Ty<'tcx>,
476}
477
478impl<'tcx> LoweredTy<'tcx> {
479    fn from_raw(fcx: &FnCtxt<'_, 'tcx>, span: Span, raw: Ty<'tcx>) -> LoweredTy<'tcx> {
480        // FIXME(-Znext-solver=no): This is easier than requiring all uses of `LoweredTy`
481        // to call `try_structurally_resolve_type` instead. This seems like a lot of
482        // effort, especially as we're still supporting the old solver. We may revisit
483        // this in the future.
484        let normalized = if fcx.next_trait_solver() {
485            fcx.try_structurally_resolve_type(span, raw)
486        } else {
487            fcx.normalize(span, raw)
488        };
489        LoweredTy { raw, normalized }
490    }
491}
492
493fn never_type_behavior(tcx: TyCtxt<'_>) -> (DivergingFallbackBehavior, DivergingBlockBehavior) {
494    let (fallback, block) = parse_never_type_options_attr(tcx);
495    let fallback = fallback.unwrap_or_else(|| default_fallback(tcx));
496    let block = block.unwrap_or_default();
497
498    (fallback, block)
499}
500
501/// Returns the default fallback which is used when there is no explicit override via `#![never_type_options(...)]`.
502fn default_fallback(tcx: TyCtxt<'_>) -> DivergingFallbackBehavior {
503    // Edition 2024: fallback to `!`
504    if tcx.sess.edition().at_least_rust_2024() {
505        return DivergingFallbackBehavior::ToNever;
506    }
507
508    // `feature(never_type_fallback)`: fallback to `!` or `()` trying to not break stuff
509    if tcx.features().never_type_fallback() {
510        return DivergingFallbackBehavior::ContextDependent;
511    }
512
513    // Otherwise: fallback to `()`
514    DivergingFallbackBehavior::ToUnit
515}
516
517fn parse_never_type_options_attr(
518    tcx: TyCtxt<'_>,
519) -> (Option<DivergingFallbackBehavior>, Option<DivergingBlockBehavior>) {
520    // Error handling is dubious here (unwraps), but that's probably fine for an internal attribute.
521    // Just don't write incorrect attributes <3
522
523    let mut fallback = None;
524    let mut block = None;
525
526    let items = tcx
527        .get_attr(CRATE_DEF_ID, sym::rustc_never_type_options)
528        .map(|attr| attr.meta_item_list().unwrap())
529        .unwrap_or_default();
530
531    for item in items {
532        if item.has_name(sym::fallback) && fallback.is_none() {
533            let mode = item.value_str().unwrap();
534            match mode {
535                sym::unit => fallback = Some(DivergingFallbackBehavior::ToUnit),
536                sym::niko => fallback = Some(DivergingFallbackBehavior::ContextDependent),
537                sym::never => fallback = Some(DivergingFallbackBehavior::ToNever),
538                sym::no => fallback = Some(DivergingFallbackBehavior::NoFallback),
539                _ => {
540                    tcx.dcx().span_err(item.span(), format!("unknown never type fallback mode: `{mode}` (supported: `unit`, `niko`, `never` and `no`)"));
541                }
542            };
543            continue;
544        }
545
546        if item.has_name(sym::diverging_block_default) && block.is_none() {
547            let default = item.value_str().unwrap();
548            match default {
549                sym::unit => block = Some(DivergingBlockBehavior::Unit),
550                sym::never => block = Some(DivergingBlockBehavior::Never),
551                _ => {
552                    tcx.dcx().span_err(item.span(), format!("unknown diverging block default: `{default}` (supported: `unit` and `never`)"));
553                }
554            };
555            continue;
556        }
557
558        tcx.dcx().span_err(
559            item.span(),
560            format!(
561                "unknown or duplicate never type option: `{}` (supported: `fallback`, `diverging_block_default`)",
562                item.name().unwrap()
563            ),
564        );
565    }
566
567    (fallback, block)
568}
rustc_hir_typeck/fn_ctxt/mod.rs

rustc_hir_typeck/fn_ctxt/
mod.rs
