hir_ty/lower/
path.rs

1//! A wrapper around [`TyLoweringContext`] specifically for lowering paths.
2
3use either::Either;
4use hir_def::{
5    GenericDefId, GenericParamId, Lookup, TraitId, TypeParamId,
6    expr_store::{
7        ExpressionStore, HygieneId,
8        path::{
9            GenericArg as HirGenericArg, GenericArgs as HirGenericArgs, GenericArgsParentheses,
10            Path, PathSegment, PathSegments,
11        },
12    },
13    hir::generics::{
14        GenericParamDataRef, TypeOrConstParamData, TypeParamData, TypeParamProvenance,
15    },
16    resolver::{ResolveValueResult, TypeNs, ValueNs},
17    signatures::{TraitFlags, TraitSignature},
18    type_ref::{TypeRef, TypeRefId},
19};
20use rustc_type_ir::{
21    AliasTerm, AliasTy, AliasTyKind,
22    inherent::{GenericArgs as _, Region as _, Ty as _},
23};
24use smallvec::SmallVec;
25
26use crate::{
27    GenericArgsProhibitedReason, IncorrectGenericsLenKind, PathGenericsSource,
28    PathLoweringDiagnostic, Span, TyDefId, ValueTyDefId,
29    db::HirDatabase,
30    generics::{Generics, generics},
31    infer::unify::InferenceTable,
32    lower::{
33        AssocTypeShorthandResolution, ForbidParamsAfterReason, GenericPredicateSource,
34        LifetimeElisionKind, PathDiagnosticCallbackData, const_param_ty,
35    },
36    next_solver::{
37        AliasTermKind, Binder, Clause, Const, DbInterner, EarlyBinder, ErrorGuaranteed, GenericArg,
38        GenericArgs, Predicate, ProjectionPredicate, Region, TraitRef, Ty,
39    },
40};
41
42use super::{
43    ImplTraitLoweringMode, TyLoweringContext,
44    associated_type_by_name_including_super_traits_allow_ambiguity, ty_query,
45};
46
47type CallbackData<'a> =
48    Either<PathDiagnosticCallbackData, crate::infer::diagnostics::PathDiagnosticCallbackData<'a>>;
49
50// We cannot use `&mut dyn FnMut()` because of lifetime issues, and we don't want to use `Box<dyn FnMut()>`
51// because of the allocation, so we create a lifetime-less callback, tailored for our needs.
52pub(crate) struct PathDiagnosticCallback<'a, 'db> {
53    pub(crate) data: CallbackData<'a>,
54    pub(crate) callback:
55        fn(&CallbackData<'_>, &mut TyLoweringContext<'db, '_>, PathLoweringDiagnostic),
56}
57
58pub(crate) struct PathLoweringContext<'a, 'b, 'db> {
59    ctx: &'a mut TyLoweringContext<'db, 'b>,
60    on_diagnostic: PathDiagnosticCallback<'a, 'db>,
61    path: &'a Path,
62    segments: PathSegments<'a>,
63    current_segment_idx: usize,
64    /// Contains the previous segment if `current_segment_idx == segments.len()`
65    current_or_prev_segment: PathSegment<'a>,
66}
67
68impl<'a, 'b, 'db> PathLoweringContext<'a, 'b, 'db> {
69    #[inline]
70    pub(crate) fn new(
71        ctx: &'a mut TyLoweringContext<'db, 'b>,
72        on_diagnostic: PathDiagnosticCallback<'a, 'db>,
73        path: &'a Path,
74    ) -> Self {
75        let segments = path.segments();
76        let first_segment = segments.first().unwrap_or(PathSegment::MISSING);
77        Self {
78            ctx,
79            on_diagnostic,
80            path,
81            segments,
82            current_segment_idx: 0,
83            current_or_prev_segment: first_segment,
84        }
85    }
86
87    #[track_caller]
88    pub(crate) fn expect_table(&mut self) -> &mut InferenceTable<'db> {
89        self.ctx.expect_table()
90    }
91
92    #[inline]
93    #[cold]
94    fn on_diagnostic(&mut self, diag: PathLoweringDiagnostic) {
95        (self.on_diagnostic.callback)(&self.on_diagnostic.data, self.ctx, diag);
96    }
97
98    #[inline]
99    pub(crate) fn ty_ctx(&mut self) -> &mut TyLoweringContext<'db, 'b> {
100        self.ctx
101    }
102
103    #[inline]
104    fn current_segment_u32(&self) -> u32 {
105        self.current_segment_idx as u32
106    }
107
108    #[inline]
109    fn skip_resolved_segment(&mut self) {
110        if !matches!(self.path, Path::LangItem(..)) {
111            // In lang items, the resolved "segment" is not one of the segments. Perhaps we should've put it
112            // point at -1, but I don't feel this is clearer.
113            self.current_segment_idx += 1;
114        }
115        self.update_current_segment();
116    }
117
118    #[inline]
119    fn update_current_segment(&mut self) {
120        self.current_or_prev_segment =
121            self.segments.get(self.current_segment_idx).unwrap_or(self.current_or_prev_segment);
122    }
123
124    #[inline]
125    pub(crate) fn ignore_last_segment(&mut self) {
126        self.segments = self.segments.strip_last();
127    }
128
129    #[inline]
130    pub(crate) fn set_current_segment(&mut self, segment: usize) {
131        self.current_segment_idx = segment;
132        self.current_or_prev_segment = self
133            .segments
134            .get(segment)
135            .expect("invalid segment passed to PathLoweringContext::set_current_segment()");
136    }
137
138    #[inline]
139    fn with_lifetime_elision<T>(
140        &mut self,
141        lifetime_elision: LifetimeElisionKind<'db>,
142        f: impl FnOnce(&mut PathLoweringContext<'_, '_, 'db>) -> T,
143    ) -> T {
144        let old_lifetime_elision =
145            std::mem::replace(&mut self.ctx.lifetime_elision, lifetime_elision);
146        let result = f(self);
147        self.ctx.lifetime_elision = old_lifetime_elision;
148        result
149    }
150
151    pub(crate) fn lower_ty_relative_path(
152        &mut self,
153        ty: Ty<'db>,
154        // We need the original resolution to lower `Self::AssocTy` correctly
155        res: Option<TypeNs>,
156        infer_args: bool,
157        span: Span,
158    ) -> (Ty<'db>, Option<TypeNs>) {
159        let remaining_segments = self.segments.len() - self.current_segment_idx;
160        match remaining_segments {
161            0 => (ty, res),
162            1 => {
163                // resolve unselected assoc types
164                (self.select_associated_type(res, infer_args, span), None)
165            }
166            _ => {
167                // FIXME report error (ambiguous associated type)
168                (self.ctx.types.types.error, None)
169            }
170        }
171    }
172
173    // When calling this, the current segment is the resolved segment (we don't advance it yet).
174    pub(crate) fn lower_partly_resolved_path(
175        &mut self,
176        resolution: TypeNs,
177        infer_args: bool,
178        span: Span,
179    ) -> (Ty<'db>, Option<TypeNs>) {
180        let remaining_segments = self.segments.skip(self.current_segment_idx + 1);
181        tracing::debug!(?remaining_segments);
182        let rem_seg_len = remaining_segments.len();
183        tracing::debug!(?rem_seg_len);
184
185        let ty = match resolution {
186            TypeNs::TraitId(trait_) => {
187                let ty = match remaining_segments.len() {
188                    1 => {
189                        let trait_ref = self.lower_trait_ref_from_resolved_path(
190                            trait_,
191                            self.ctx.types.types.error,
192                            infer_args,
193                            span,
194                        );
195                        tracing::debug!(?trait_ref);
196                        self.skip_resolved_segment();
197                        let segment = self.current_or_prev_segment;
198                        let trait_id = trait_ref.def_id.0;
199                        let found =
200                            trait_id.trait_items(self.ctx.db).associated_type_by_name(segment.name);
201
202                        tracing::debug!(?found);
203                        match found {
204                            Some(associated_ty) => {
205                                // FIXME: `substs_from_path_segment()` pushes `TyKind::Error` for every parent
206                                // generic params. It's inefficient to splice the `Substitution`s, so we may want
207                                // that method to optionally take parent `Substitution` as we already know them at
208                                // this point (`trait_ref.substitution`).
209                                let substitution = self.substs_from_path_segment(
210                                    associated_ty.into(),
211                                    infer_args,
212                                    None,
213                                    true,
214                                    span,
215                                );
216                                let args = GenericArgs::new_from_iter(
217                                    self.ctx.interner,
218                                    trait_ref
219                                        .args
220                                        .iter()
221                                        .chain(substitution.iter().skip(trait_ref.args.len())),
222                                );
223                                Ty::new_alias(
224                                    self.ctx.interner,
225                                    AliasTy::new_from_args(
226                                        self.ctx.interner,
227                                        AliasTyKind::Projection { def_id: associated_ty.into() },
228                                        args,
229                                    ),
230                                )
231                            }
232                            None => {
233                                // FIXME: report error (associated type not found)
234                                self.ctx.types.types.error
235                            }
236                        }
237                    }
238                    0 => {
239                        // Trait object type without dyn; this should be handled in upstream. See
240                        // `lower_path()`.
241                        stdx::never!("unexpected fully resolved trait path");
242                        self.ctx.types.types.error
243                    }
244                    _ => {
245                        // FIXME report error (ambiguous associated type)
246                        self.ctx.types.types.error
247                    }
248                };
249                return (ty, None);
250            }
251            TypeNs::GenericParam(param_id) => {
252                let generics = self.ctx.generics();
253                let idx = generics.type_or_const_param_idx(param_id.into());
254                self.ctx.type_param(param_id, idx)
255            }
256            TypeNs::SelfType(impl_id) => self.ctx.db.impl_self_ty(impl_id).skip_binder(),
257            TypeNs::AdtSelfType(adt) => {
258                let args = GenericArgs::identity_for_item(self.ctx.interner, adt.into());
259                Ty::new_adt(self.ctx.interner, adt, args)
260            }
261
262            TypeNs::AdtId(it) => self.lower_path_inner(it.into(), infer_args, span),
263            TypeNs::BuiltinType(it) => self.lower_path_inner(it.into(), infer_args, span),
264            TypeNs::TypeAliasId(it) => self.lower_path_inner(it.into(), infer_args, span),
265            // FIXME: report error
266            TypeNs::EnumVariantId(_) | TypeNs::ModuleId(_) => {
267                return (self.ctx.types.types.error, None);
268            }
269        };
270
271        tracing::debug!(?ty);
272
273        self.skip_resolved_segment();
274        self.lower_ty_relative_path(ty, Some(resolution), infer_args, span)
275    }
276
277    /// This returns whether to keep the resolution (`true`) of throw it (`false`).
278    #[must_use]
279    fn handle_type_ns_resolution(&mut self, resolution: &TypeNs) -> bool {
280        let mut prohibit_generics_on_resolved = |reason| {
281            if self.current_or_prev_segment.args_and_bindings.is_some() {
282                let segment = self.current_segment_u32();
283                self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
284                    segment,
285                    reason,
286                });
287            }
288        };
289
290        match resolution {
291            TypeNs::SelfType(_) => {
292                prohibit_generics_on_resolved(GenericArgsProhibitedReason::SelfTy)
293            }
294            TypeNs::GenericParam(_) => {
295                prohibit_generics_on_resolved(GenericArgsProhibitedReason::TyParam)
296            }
297            TypeNs::AdtSelfType(_) => {
298                prohibit_generics_on_resolved(GenericArgsProhibitedReason::SelfTy);
299
300                if self.ctx.forbid_params_after.is_some()
301                    && self.ctx.forbid_params_after_reason
302                        == ForbidParamsAfterReason::LoweringParamDefault
303                {
304                    // FIXME: Handle other reasons.
305                    let segment = self.current_segment_u32();
306                    self.on_diagnostic(PathLoweringDiagnostic::GenericDefaultRefersToSelf {
307                        segment,
308                    });
309                    return false;
310                }
311            }
312            TypeNs::BuiltinType(_) => {
313                prohibit_generics_on_resolved(GenericArgsProhibitedReason::PrimitiveTy)
314            }
315            TypeNs::ModuleId(_) => {
316                prohibit_generics_on_resolved(GenericArgsProhibitedReason::Module)
317            }
318            TypeNs::AdtId(_)
319            | TypeNs::EnumVariantId(_)
320            | TypeNs::TypeAliasId(_)
321            | TypeNs::TraitId(_) => {}
322        }
323
324        true
325    }
326
327    pub(crate) fn resolve_path_in_type_ns_fully(&mut self) -> Option<TypeNs> {
328        let (res, unresolved) = self.resolve_path_in_type_ns()?;
329        if unresolved.is_some() {
330            return None;
331        }
332        Some(res)
333    }
334
335    #[tracing::instrument(skip(self), ret)]
336    pub(crate) fn resolve_path_in_type_ns(&mut self) -> Option<(TypeNs, Option<usize>)> {
337        let (resolution, remaining_index, _, prefix_info, _) =
338            self.ctx.resolver.resolve_path_in_type_ns_with_prefix_info(self.ctx.db, self.path)?;
339
340        let segments = self.segments;
341        if segments.is_empty() || matches!(self.path, Path::LangItem(..)) {
342            // `segments.is_empty()` can occur with `self`.
343            return Some((resolution, remaining_index));
344        }
345
346        let (module_segments, resolved_segment_idx, enum_segment) = match remaining_index {
347            None if prefix_info.enum_variant => {
348                (segments.strip_last_two(), segments.len() - 1, Some(segments.len() - 2))
349            }
350            None => (segments.strip_last(), segments.len() - 1, None),
351            Some(i) => (segments.take(i - 1), i - 1, None),
352        };
353
354        self.current_segment_idx = resolved_segment_idx;
355        self.current_or_prev_segment =
356            segments.get(resolved_segment_idx).expect("should have resolved segment");
357
358        for (i, mod_segment) in module_segments.iter().enumerate() {
359            if mod_segment.args_and_bindings.is_some() {
360                self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
361                    segment: i as u32,
362                    reason: GenericArgsProhibitedReason::Module,
363                });
364            }
365        }
366
367        if let Some(enum_segment) = enum_segment
368            && segments.get(enum_segment).is_some_and(|it| it.args_and_bindings.is_some())
369            && segments.get(enum_segment + 1).is_some_and(|it| it.args_and_bindings.is_some())
370        {
371            self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
372                segment: (enum_segment + 1) as u32,
373                reason: GenericArgsProhibitedReason::EnumVariant,
374            });
375        }
376
377        if !self.handle_type_ns_resolution(&resolution) {
378            return None;
379        }
380
381        Some((resolution, remaining_index))
382    }
383
384    pub(crate) fn resolve_path_in_value_ns(
385        &mut self,
386        hygiene_id: HygieneId,
387    ) -> Option<ResolveValueResult> {
388        let (res, prefix_info, _) = self.ctx.resolver.resolve_path_in_value_ns_with_prefix_info(
389            self.ctx.db,
390            self.path,
391            hygiene_id,
392        )?;
393
394        let segments = self.segments;
395        if segments.is_empty() || matches!(self.path, Path::LangItem(..)) {
396            // `segments.is_empty()` can occur with `self`.
397            return Some(res);
398        }
399
400        let (mod_segments, enum_segment, resolved_segment_idx) = match res {
401            ResolveValueResult::Partial(_, unresolved_segment) => {
402                (segments.take(unresolved_segment - 1), None, unresolved_segment - 1)
403            }
404            ResolveValueResult::ValueNs(ValueNs::EnumVariantId(_)) if prefix_info.enum_variant => {
405                (segments.strip_last_two(), segments.len().checked_sub(2), segments.len() - 1)
406            }
407            ResolveValueResult::ValueNs(..) => (segments.strip_last(), None, segments.len() - 1),
408        };
409
410        self.current_segment_idx = resolved_segment_idx;
411        self.current_or_prev_segment =
412            segments.get(resolved_segment_idx).expect("should have resolved segment");
413
414        for (i, mod_segment) in mod_segments.iter().enumerate() {
415            if mod_segment.args_and_bindings.is_some() {
416                self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
417                    segment: i as u32,
418                    reason: GenericArgsProhibitedReason::Module,
419                });
420            }
421        }
422
423        if let Some(enum_segment) = enum_segment
424            && segments.get(enum_segment).is_some_and(|it| it.args_and_bindings.is_some())
425            && segments.get(enum_segment + 1).is_some_and(|it| it.args_and_bindings.is_some())
426        {
427            self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
428                segment: (enum_segment + 1) as u32,
429                reason: GenericArgsProhibitedReason::EnumVariant,
430            });
431        }
432
433        match &res {
434            ResolveValueResult::ValueNs(resolution) => {
435                let resolved_segment_idx = self.current_segment_u32();
436                let resolved_segment = self.current_or_prev_segment;
437
438                let mut prohibit_generics_on_resolved = |reason| {
439                    if resolved_segment.args_and_bindings.is_some() {
440                        self.on_diagnostic(PathLoweringDiagnostic::GenericArgsProhibited {
441                            segment: resolved_segment_idx,
442                            reason,
443                        });
444                    }
445                };
446
447                match resolution {
448                    ValueNs::ImplSelf(_) => {
449                        prohibit_generics_on_resolved(GenericArgsProhibitedReason::SelfTy);
450                    }
451                    // FIXME: rustc generates E0107 (incorrect number of generic arguments) and not
452                    // E0109 (generic arguments provided for a type that doesn't accept them) for
453                    // consts and statics, presumably as a defense against future in which consts
454                    // and statics can be generic, or just because it was easier for rustc implementors.
455                    // That means we'll show the wrong error code. Because of us it's easier to do it
456                    // this way :)
457                    ValueNs::GenericParam(_) => {
458                        prohibit_generics_on_resolved(GenericArgsProhibitedReason::Const)
459                    }
460                    ValueNs::StaticId(_) => {
461                        prohibit_generics_on_resolved(GenericArgsProhibitedReason::Static)
462                    }
463                    ValueNs::LocalBinding(_) => {
464                        prohibit_generics_on_resolved(GenericArgsProhibitedReason::LocalVariable)
465                    }
466                    ValueNs::FunctionId(_)
467                    | ValueNs::StructId(_)
468                    | ValueNs::EnumVariantId(_)
469                    | ValueNs::ConstId(_) => {}
470                }
471            }
472            ResolveValueResult::Partial(resolution, _) => {
473                if !self.handle_type_ns_resolution(resolution) {
474                    return None;
475                }
476            }
477        };
478        Some(res)
479    }
480
481    #[tracing::instrument(skip(self), ret)]
482    fn select_associated_type(
483        &mut self,
484        res: Option<TypeNs>,
485        infer_args: bool,
486        span: Span,
487    ) -> Ty<'db> {
488        let interner = self.ctx.interner;
489        let db = self.ctx.db;
490        let def = self.ctx.generic_def;
491        let segment = self.current_or_prev_segment;
492        let assoc_name = segment.name;
493        let (assoc_type, trait_args) = match res {
494            Some(TypeNs::GenericParam(param)) => {
495                let AssocTypeShorthandResolution::Resolved(assoc_type) =
496                    super::resolve_type_param_assoc_type_shorthand(
497                        db,
498                        def,
499                        param,
500                        assoc_name.clone(),
501                    )
502                else {
503                    // FIXME: Emit an error.
504                    return self.ctx.types.types.error;
505                };
506                assoc_type
507                    .get_with(|(assoc_type, trait_args)| (*assoc_type, trait_args.as_ref()))
508                    .skip_binder()
509            }
510            Some(TypeNs::SelfType(impl_)) => {
511                let Some(impl_trait) = db.impl_trait(impl_) else {
512                    return self.ctx.types.types.error;
513                };
514                let impl_trait = impl_trait.instantiate_identity().skip_norm_wip();
515                // Searching for `Self::Assoc` in `impl Trait for Type` is like searching for `Self::Assoc` in `Trait`.
516                let AssocTypeShorthandResolution::Resolved(assoc_type) =
517                    super::resolve_type_param_assoc_type_shorthand(
518                        db,
519                        impl_trait.def_id.0.into(),
520                        TypeParamId::trait_self(impl_trait.def_id.0),
521                        assoc_name.clone(),
522                    )
523                else {
524                    // FIXME: Emit an error.
525                    return self.ctx.types.types.error;
526                };
527                let (assoc_type, trait_args) = assoc_type
528                    .get_with(|(assoc_type, trait_args)| (*assoc_type, trait_args.as_ref()))
529                    .skip_binder();
530                (
531                    assoc_type,
532                    EarlyBinder::bind(trait_args)
533                        .instantiate(interner, impl_trait.args)
534                        .skip_norm_wip(),
535                )
536            }
537            _ => return self.ctx.types.types.error,
538        };
539
540        // FIXME: `substs_from_path_segment()` pushes `TyKind::Error` for every parent
541        // generic params. It's inefficient to splice the `Substitution`s, so we may want
542        // that method to optionally take parent `Substitution` as we already know them at
543        // this point (`t.substitution`).
544        let substs = self.substs_from_path_segment(assoc_type.into(), infer_args, None, true, span);
545
546        let substs = GenericArgs::new_from_iter(
547            interner,
548            trait_args.iter().chain(substs.iter().skip(trait_args.len())),
549        );
550
551        Ty::new_projection_from_args(interner, assoc_type.into(), substs)
552    }
553
554    fn lower_path_inner(&mut self, typeable: TyDefId, infer_args: bool, span: Span) -> Ty<'db> {
555        let generic_def = match typeable {
556            TyDefId::BuiltinType(builtinty) => {
557                return Ty::from_builtin_type(self.ctx.interner, builtinty);
558            }
559            TyDefId::AdtId(it) => it.into(),
560            TyDefId::TypeAliasId(it) => it.into(),
561        };
562        let args = self.substs_from_path_segment(generic_def, infer_args, None, false, span);
563        let ty = ty_query(self.ctx.db, typeable);
564        ty.instantiate(self.ctx.interner, args).skip_norm_wip()
565    }
566
567    /// Collect generic arguments from a path into a `Substs`. See also
568    /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
569    pub(crate) fn substs_from_path(
570        &mut self,
571        // Note that we don't call `db.value_type(resolved)` here,
572        // `ValueTyDefId` is just a convenient way to pass generics and
573        // special-case enum variants
574        resolved: ValueTyDefId,
575        infer_args: bool,
576        lowering_assoc_type_generics: bool,
577        span: Span,
578    ) -> GenericArgs<'db> {
579        let prev_current_segment_idx = self.current_segment_idx;
580        let prev_current_segment = self.current_or_prev_segment;
581
582        let generic_def = match resolved {
583            ValueTyDefId::FunctionId(it) => it.into(),
584            ValueTyDefId::StructId(it) => it.into(),
585            ValueTyDefId::UnionId(it) => it.into(),
586            ValueTyDefId::ConstId(it) => it.into(),
587            ValueTyDefId::StaticId(_) => {
588                return GenericArgs::empty();
589            }
590            ValueTyDefId::EnumVariantId(var) => {
591                // the generic args for an enum variant may be either specified
592                // on the segment referring to the enum, or on the segment
593                // referring to the variant. So `Option::<T>::None` and
594                // `Option::None::<T>` are both allowed (though the former is
595                // FIXME: This isn't strictly correct, enum variants may be used not through the enum
596                // (via `use Enum::Variant`). The resolver returns whether they were, but we don't have its result
597                // available here. The worst that can happen is that we will show some confusing diagnostics to the user,
598                // if generics exist on the module and they don't match with the variant.
599                // preferred). See also `def_ids_for_path_segments` in rustc.
600                //
601                // `wrapping_sub(1)` will return a number which `get` will return None for if current_segment_idx<2.
602                // This simplifies the code a bit.
603                let penultimate_idx = self.current_segment_idx.wrapping_sub(1);
604                let penultimate = self.segments.get(penultimate_idx);
605                if let Some(penultimate) = penultimate
606                    && self.current_or_prev_segment.args_and_bindings.is_none()
607                    && penultimate.args_and_bindings.is_some()
608                {
609                    self.current_segment_idx = penultimate_idx;
610                    self.current_or_prev_segment = penultimate;
611                }
612                var.lookup(self.ctx.db).parent.into()
613            }
614        };
615        let result = self.substs_from_path_segment(
616            generic_def,
617            infer_args,
618            None,
619            lowering_assoc_type_generics,
620            span,
621        );
622        self.current_segment_idx = prev_current_segment_idx;
623        self.current_or_prev_segment = prev_current_segment;
624        result
625    }
626
627    pub(crate) fn substs_from_path_segment(
628        &mut self,
629        def: GenericDefId,
630        infer_args: bool,
631        explicit_self_ty: Option<Ty<'db>>,
632        lowering_assoc_type_generics: bool,
633        span: Span,
634    ) -> GenericArgs<'db> {
635        let old_lifetime_elision = self.ctx.lifetime_elision;
636
637        if let Some(args) = self.current_or_prev_segment.args_and_bindings
638            && args.parenthesized != GenericArgsParentheses::No
639        {
640            let prohibit_parens = match def {
641                GenericDefId::TraitId(trait_) => {
642                    // RTN is prohibited anyways if we got here.
643                    let is_rtn = args.parenthesized == GenericArgsParentheses::ReturnTypeNotation;
644                    let is_fn_trait = TraitSignature::of(self.ctx.db, trait_)
645                        .flags
646                        .contains(TraitFlags::RUSTC_PAREN_SUGAR);
647                    is_rtn || !is_fn_trait
648                }
649                _ => true,
650            };
651
652            if prohibit_parens {
653                let segment = self.current_segment_u32();
654                self.on_diagnostic(
655                    PathLoweringDiagnostic::ParenthesizedGenericArgsWithoutFnTrait { segment },
656                );
657
658                return GenericArgs::error_for_item(self.ctx.interner, def.into());
659            }
660
661            // `Fn()`-style generics are treated like functions for the purpose of lifetime elision.
662            self.ctx.lifetime_elision =
663                LifetimeElisionKind::AnonymousCreateParameter { report_in_path: false };
664        }
665
666        let result = self.substs_from_args_and_bindings(
667            self.current_or_prev_segment.args_and_bindings,
668            def,
669            infer_args,
670            explicit_self_ty,
671            PathGenericsSource::Segment(self.current_segment_u32()),
672            lowering_assoc_type_generics,
673            self.ctx.lifetime_elision,
674            span,
675        );
676        self.ctx.lifetime_elision = old_lifetime_elision;
677        result
678    }
679
680    pub(super) fn substs_from_args_and_bindings(
681        &mut self,
682        args_and_bindings: Option<&HirGenericArgs>,
683        def: GenericDefId,
684        infer_args: bool,
685        explicit_self_ty: Option<Ty<'db>>,
686        generics_source: PathGenericsSource,
687        lowering_assoc_type_generics: bool,
688        lifetime_elision: LifetimeElisionKind<'db>,
689        span: Span,
690    ) -> GenericArgs<'db> {
691        struct LowererCtx<'a, 'b, 'c, 'db> {
692            ctx: &'a mut PathLoweringContext<'b, 'c, 'db>,
693            generics_source: PathGenericsSource,
694            span: Span,
695        }
696
697        impl<'db> GenericArgsLowerer<'db> for LowererCtx<'_, '_, '_, 'db> {
698            fn report_len_mismatch(
699                &mut self,
700                def: GenericDefId,
701                provided_count: u32,
702                expected_count: u32,
703                kind: IncorrectGenericsLenKind,
704            ) {
705                self.ctx.on_diagnostic(PathLoweringDiagnostic::IncorrectGenericsLen {
706                    generics_source: self.generics_source,
707                    provided_count,
708                    expected_count,
709                    kind,
710                    def,
711                });
712            }
713
714            fn report_arg_mismatch(
715                &mut self,
716                param_id: GenericParamId,
717                arg_idx: u32,
718                has_self_arg: bool,
719            ) {
720                self.ctx.on_diagnostic(PathLoweringDiagnostic::IncorrectGenericsOrder {
721                    generics_source: self.generics_source,
722                    param_id,
723                    arg_idx,
724                    has_self_arg,
725                });
726            }
727
728            fn provided_kind(
729                &mut self,
730                param_id: GenericParamId,
731                param: GenericParamDataRef<'_>,
732                arg: &HirGenericArg,
733            ) -> GenericArg<'db> {
734                match (param, *arg) {
735                    (
736                        GenericParamDataRef::LifetimeParamData(_),
737                        HirGenericArg::Lifetime(lifetime),
738                    ) => self.ctx.ctx.lower_lifetime(lifetime).into(),
739                    (GenericParamDataRef::TypeParamData(_), HirGenericArg::Type(type_ref)) => {
740                        self.ctx.ctx.lower_ty(type_ref).into()
741                    }
742                    (GenericParamDataRef::ConstParamData(_), HirGenericArg::Const(konst)) => {
743                        let GenericParamId::ConstParamId(const_id) = param_id else {
744                            unreachable!("non-const param ID for const param");
745                        };
746                        self.ctx
747                            .ctx
748                            .lower_const(konst, const_param_ty(self.ctx.ctx.db, const_id))
749                            .into()
750                    }
751                    _ => unreachable!("unmatching param kinds were passed to `provided_kind()`"),
752                }
753            }
754
755            fn provided_type_like_const(
756                &mut self,
757                type_ref: TypeRefId,
758                const_ty: Ty<'db>,
759                arg: TypeLikeConst<'_>,
760            ) -> Const<'db> {
761                match arg {
762                    TypeLikeConst::Path(path) => self.ctx.ctx.lower_path_as_const(path, const_ty),
763                    TypeLikeConst::Infer => self.ctx.ctx.next_const_var(type_ref.into()),
764                }
765            }
766
767            fn inferred_kind(
768                &mut self,
769                def: GenericDefId,
770                param_id: GenericParamId,
771                param: GenericParamDataRef<'_>,
772                infer_args: bool,
773                preceding_args: &[GenericArg<'db>],
774                had_count_error: bool,
775            ) -> GenericArg<'db> {
776                let default = || {
777                    self.ctx.ctx.db.generic_defaults(def).get(preceding_args.len()).map(|default| {
778                        default.instantiate(self.ctx.ctx.interner, preceding_args).skip_norm_wip()
779                    })
780                };
781                // If `!infer_args`, we've already emitted an error, so put a dummy span.
782                let span = if !infer_args || had_count_error { Span::Dummy } else { self.span };
783                match param {
784                    GenericParamDataRef::LifetimeParamData(_) => {
785                        self.ctx.ctx.next_region_var(span).into()
786                    }
787                    GenericParamDataRef::TypeParamData(param) => {
788                        if !infer_args
789                            && param.default.is_some()
790                            && let Some(default) = default()
791                        {
792                            return default;
793                        }
794                        self.ctx.ctx.next_ty_var(span).into()
795                    }
796                    GenericParamDataRef::ConstParamData(param) => {
797                        if !infer_args
798                            && param.default.is_some()
799                            && let Some(default) = default()
800                        {
801                            return default;
802                        }
803                        let GenericParamId::ConstParamId(_) = param_id else {
804                            unreachable!("non-const param ID for const param");
805                        };
806                        self.ctx.ctx.next_const_var(span).into()
807                    }
808                }
809            }
810
811            fn parent_arg(&mut self, _param_idx: u32, param_id: GenericParamId) -> GenericArg<'db> {
812                match param_id {
813                    GenericParamId::TypeParamId(_) => {
814                        Ty::new_error(self.ctx.ctx.interner, ErrorGuaranteed).into()
815                    }
816                    GenericParamId::ConstParamId(_) => self.ctx.ctx.types.consts.error.into(),
817                    GenericParamId::LifetimeParamId(_) => self.ctx.ctx.types.regions.error.into(),
818                }
819            }
820
821            fn report_elided_lifetimes_in_path(
822                &mut self,
823                def: GenericDefId,
824                expected_count: u32,
825                hard_error: bool,
826            ) {
827                self.ctx.on_diagnostic(PathLoweringDiagnostic::ElidedLifetimesInPath {
828                    generics_source: self.generics_source,
829                    def,
830                    expected_count,
831                    hard_error,
832                });
833            }
834
835            fn report_elision_failure(&mut self, def: GenericDefId, expected_count: u32) {
836                self.ctx.on_diagnostic(PathLoweringDiagnostic::ElisionFailure {
837                    generics_source: self.generics_source,
838                    def,
839                    expected_count,
840                });
841            }
842
843            fn report_missing_lifetime(&mut self, def: GenericDefId, expected_count: u32) {
844                self.ctx.on_diagnostic(PathLoweringDiagnostic::MissingLifetime {
845                    generics_source: self.generics_source,
846                    def,
847                    expected_count,
848                });
849            }
850        }
851
852        substs_from_args_and_bindings(
853            self.ctx.db,
854            self.ctx.store,
855            args_and_bindings,
856            def,
857            infer_args,
858            lifetime_elision,
859            lowering_assoc_type_generics,
860            explicit_self_ty,
861            &mut LowererCtx { ctx: self, generics_source, span },
862        )
863    }
864
865    pub(crate) fn lower_trait_ref_from_resolved_path(
866        &mut self,
867        resolved: TraitId,
868        explicit_self_ty: Ty<'db>,
869        infer_args: bool,
870        span: Span,
871    ) -> TraitRef<'db> {
872        let args = self.trait_ref_substs_from_path(resolved, explicit_self_ty, infer_args, span);
873        TraitRef::new_from_args(self.ctx.interner, resolved.into(), args)
874    }
875
876    fn trait_ref_substs_from_path(
877        &mut self,
878        resolved: TraitId,
879        explicit_self_ty: Ty<'db>,
880        infer_args: bool,
881        span: Span,
882    ) -> GenericArgs<'db> {
883        self.substs_from_path_segment(
884            resolved.into(),
885            infer_args,
886            Some(explicit_self_ty),
887            false,
888            span,
889        )
890    }
891
892    pub(super) fn assoc_type_bindings_from_type_bound(
893        mut self,
894        trait_ref: TraitRef<'db>,
895        span: Span,
896    ) -> Option<impl Iterator<Item = (Clause<'db>, GenericPredicateSource)> + use<'a, 'b, 'db>>
897    {
898        let interner = self.ctx.interner;
899        self.current_or_prev_segment.args_and_bindings.map(|args_and_bindings| {
900            args_and_bindings.bindings.iter().enumerate().flat_map(move |(binding_idx, binding)| {
901                let found = associated_type_by_name_including_super_traits_allow_ambiguity(
902                    self.ctx.db,
903                    trait_ref,
904                    binding.name.clone(),
905                );
906                let (associated_ty, super_trait_args) = match found {
907                    None => return SmallVec::new(),
908                    Some(t) => t,
909                };
910                let args =
911                    self.with_lifetime_elision(LifetimeElisionKind::AnonymousReportError, |this| {
912                        // FIXME: `substs_from_path_segment()` pushes `TyKind::Error` for every parent
913                        // generic params. It's inefficient to splice the `Substitution`s, so we may want
914                        // that method to optionally take parent `Substitution` as we already know them at
915                        // this point (`super_trait_ref.substitution`).
916                        this.substs_from_args_and_bindings(
917                            binding.args.as_ref(),
918                            associated_ty.into(),
919                            false, // this is not relevant
920                            Some(super_trait_args.type_at(0)),
921                            PathGenericsSource::AssocType {
922                                segment: this.current_segment_u32(),
923                                assoc_type: binding_idx as u32,
924                            },
925                            false,
926                            this.ctx.lifetime_elision,
927                            span,
928                        )
929                    });
930                let args = GenericArgs::new_from_iter(
931                    interner,
932                    super_trait_args.iter().chain(args.iter().skip(super_trait_args.len())),
933                );
934                let projection_term = AliasTerm::new_from_args(
935                    interner,
936                    AliasTermKind::ProjectionTy { def_id: associated_ty.into() },
937                    args,
938                );
939                let mut predicates: SmallVec<[_; 1]> = SmallVec::with_capacity(
940                    binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
941                );
942                if let Some(type_ref) = binding.type_ref {
943                    let lifetime_elision =
944                        if args_and_bindings.parenthesized == GenericArgsParentheses::ParenSugar {
945                            // `Fn()`-style generics are elided like functions. This is `Output` (we lower to it in hir-def).
946                            LifetimeElisionKind::for_fn_ret(self.ctx.interner)
947                        } else {
948                            self.ctx.lifetime_elision
949                        };
950                    self.with_lifetime_elision(lifetime_elision, |this| {
951                        match (&this.ctx.store[type_ref], this.ctx.impl_trait_mode.mode) {
952                            (TypeRef::ImplTrait(_), ImplTraitLoweringMode::Disallowed) => (),
953                            (
954                                _,
955                                ImplTraitLoweringMode::Disallowed | ImplTraitLoweringMode::Opaque,
956                            ) => {
957                                let ty = this.ctx.lower_ty(type_ref);
958                                let bound_vars = this.ctx.peek_bound_vars();
959                                let pred = Clause(Predicate::new(
960                                    interner,
961                                    Binder::bind_with_vars(
962                                        rustc_type_ir::PredicateKind::Clause(
963                                            rustc_type_ir::ClauseKind::Projection(
964                                                ProjectionPredicate {
965                                                    projection_term,
966                                                    term: ty.into(),
967                                                },
968                                            ),
969                                        ),
970                                        bound_vars,
971                                    ),
972                                ));
973                                predicates.push((pred, GenericPredicateSource::SelfOnly));
974                            }
975                        }
976                    })
977                }
978                for bound in binding.bounds.iter() {
979                    predicates.extend(
980                        self.ctx
981                            .lower_type_bound(
982                                bound,
983                                Ty::new_alias(
984                                    self.ctx.interner,
985                                    AliasTy::new_from_args(
986                                        self.ctx.interner,
987                                        AliasTyKind::Projection { def_id: associated_ty.into() },
988                                        args,
989                                    ),
990                                ),
991                                false,
992                            )
993                            .map(|(pred, _)| (pred, GenericPredicateSource::AssocTyBound)),
994                    );
995                }
996                predicates
997            })
998        })
999    }
1000
1001    pub(crate) fn interner(&self) -> DbInterner<'db> {
1002        self.ctx.interner
1003    }
1004}
1005
1006/// A const that were parsed like a type.
1007pub(crate) enum TypeLikeConst<'a> {
1008    Infer,
1009    Path(&'a Path),
1010}
1011
1012pub(crate) trait GenericArgsLowerer<'db> {
1013    fn report_elided_lifetimes_in_path(
1014        &mut self,
1015        def: GenericDefId,
1016        expected_count: u32,
1017        hard_error: bool,
1018    );
1019
1020    fn report_elision_failure(&mut self, def: GenericDefId, expected_count: u32);
1021
1022    fn report_missing_lifetime(&mut self, def: GenericDefId, expected_count: u32);
1023
1024    fn report_len_mismatch(
1025        &mut self,
1026        def: GenericDefId,
1027        provided_count: u32,
1028        expected_count: u32,
1029        kind: IncorrectGenericsLenKind,
1030    );
1031
1032    fn report_arg_mismatch(&mut self, param_id: GenericParamId, arg_idx: u32, has_self_arg: bool);
1033
1034    fn provided_kind(
1035        &mut self,
1036        param_id: GenericParamId,
1037        param: GenericParamDataRef<'_>,
1038        arg: &HirGenericArg,
1039    ) -> GenericArg<'db>;
1040
1041    fn provided_type_like_const(
1042        &mut self,
1043        type_ref: TypeRefId,
1044        const_ty: Ty<'db>,
1045        arg: TypeLikeConst<'_>,
1046    ) -> Const<'db>;
1047
1048    fn inferred_kind(
1049        &mut self,
1050        def: GenericDefId,
1051        param_id: GenericParamId,
1052        param: GenericParamDataRef<'_>,
1053        infer_args: bool,
1054        preceding_args: &[GenericArg<'db>],
1055        had_count_error: bool,
1056    ) -> GenericArg<'db>;
1057
1058    fn parent_arg(&mut self, param_idx: u32, param_id: GenericParamId) -> GenericArg<'db>;
1059}
1060
1061/// Returns true if there was an error.
1062fn check_generic_args_len<'db>(
1063    args_and_bindings: Option<&HirGenericArgs>,
1064    def: GenericDefId,
1065    def_generics: &Generics<'db>,
1066    infer_args: bool,
1067    lifetime_elision: &LifetimeElisionKind<'db>,
1068    lowering_assoc_type_generics: bool,
1069    ctx: &mut impl GenericArgsLowerer<'db>,
1070) -> bool {
1071    let mut had_error = false;
1072
1073    let (mut provided_lifetimes_count, mut provided_types_and_consts_count) = (0usize, 0usize);
1074    if let Some(args_and_bindings) = args_and_bindings {
1075        let args_no_self = &args_and_bindings.args[usize::from(args_and_bindings.has_self_type)..];
1076        for arg in args_no_self {
1077            match arg {
1078                HirGenericArg::Lifetime(_) => provided_lifetimes_count += 1,
1079                HirGenericArg::Type(_) | HirGenericArg::Const(_) => {
1080                    provided_types_and_consts_count += 1
1081                }
1082            }
1083        }
1084    }
1085
1086    let lifetime_args_len = def_generics.len_lifetimes_self();
1087    if provided_lifetimes_count == 0
1088        && lifetime_args_len > 0
1089        && (!lowering_assoc_type_generics || infer_args)
1090    {
1091        // In generic associated types, we never allow inferring the lifetimes, but only in type context, that is
1092        // when `infer_args == false`. In expression/pattern context we always allow inferring them, even for GATs.
1093        match lifetime_elision {
1094            &LifetimeElisionKind::AnonymousCreateParameter { report_in_path } => {
1095                ctx.report_elided_lifetimes_in_path(def, lifetime_args_len as u32, report_in_path);
1096                had_error |= report_in_path;
1097            }
1098            LifetimeElisionKind::AnonymousReportError => {
1099                ctx.report_missing_lifetime(def, lifetime_args_len as u32);
1100                had_error = true
1101            }
1102            LifetimeElisionKind::ElisionFailure => {
1103                ctx.report_elision_failure(def, lifetime_args_len as u32);
1104                had_error = true;
1105            }
1106            LifetimeElisionKind::StaticIfNoLifetimeInScope { only_lint: _ } => {
1107                // FIXME: Check there are other lifetimes in scope, and error/lint.
1108            }
1109            LifetimeElisionKind::Elided(_) => {
1110                ctx.report_elided_lifetimes_in_path(def, lifetime_args_len as u32, false);
1111            }
1112            LifetimeElisionKind::Infer => {
1113                // Allow eliding lifetimes.
1114            }
1115        }
1116    } else if lifetime_args_len != provided_lifetimes_count {
1117        ctx.report_len_mismatch(
1118            def,
1119            provided_lifetimes_count as u32,
1120            lifetime_args_len as u32,
1121            IncorrectGenericsLenKind::Lifetimes,
1122        );
1123        had_error = true;
1124    }
1125
1126    let defaults_count =
1127        def_generics.iter_self_type_or_consts().filter(|(_, param)| param.has_default()).count();
1128    let named_type_and_const_params_count = def_generics
1129        .iter_self_type_or_consts()
1130        .filter(|(_, param)| match param {
1131            TypeOrConstParamData::TypeParamData(param) => {
1132                param.provenance == TypeParamProvenance::TypeParamList
1133            }
1134            TypeOrConstParamData::ConstParamData(_) => true,
1135        })
1136        .count();
1137    let expected_max = named_type_and_const_params_count;
1138    let expected_min =
1139        if infer_args { 0 } else { named_type_and_const_params_count - defaults_count };
1140    if provided_types_and_consts_count < expected_min
1141        || expected_max < provided_types_and_consts_count
1142    {
1143        ctx.report_len_mismatch(
1144            def,
1145            provided_types_and_consts_count as u32,
1146            named_type_and_const_params_count as u32,
1147            IncorrectGenericsLenKind::TypesAndConsts,
1148        );
1149        had_error = true;
1150    }
1151
1152    had_error
1153}
1154
1155pub(crate) fn substs_from_args_and_bindings<'db>(
1156    db: &'db dyn HirDatabase,
1157    store: &ExpressionStore,
1158    args_and_bindings: Option<&HirGenericArgs>,
1159    def: GenericDefId,
1160    mut infer_args: bool,
1161    lifetime_elision: LifetimeElisionKind<'db>,
1162    lowering_assoc_type_generics: bool,
1163    explicit_self_ty: Option<Ty<'db>>,
1164    ctx: &mut impl GenericArgsLowerer<'db>,
1165) -> GenericArgs<'db> {
1166    let interner = DbInterner::new_no_crate(db);
1167
1168    tracing::debug!(?args_and_bindings);
1169
1170    // Order is
1171    // - Parent parameters
1172    // - Optional Self parameter
1173    // - Lifetime parameters
1174    // - Type or Const parameters
1175    let def_generics = generics(db, def);
1176    let args_slice = args_and_bindings.map(|it| &*it.args).unwrap_or_default();
1177
1178    // We do not allow inference if there are specified args, i.e. we do not allow partial inference.
1179    let has_non_lifetime_args =
1180        args_slice.iter().any(|arg| !matches!(arg, HirGenericArg::Lifetime(_)));
1181    infer_args &= !has_non_lifetime_args;
1182
1183    let had_count_error = check_generic_args_len(
1184        args_and_bindings,
1185        def,
1186        &def_generics,
1187        infer_args,
1188        &lifetime_elision,
1189        lowering_assoc_type_generics,
1190        ctx,
1191    );
1192
1193    let mut substs = Vec::with_capacity(def_generics.len(true));
1194
1195    substs.extend(
1196        def_generics.iter_parent_id().enumerate().map(|(idx, id)| ctx.parent_arg(idx as u32, id)),
1197    );
1198
1199    let mut args = args_slice.iter().enumerate().peekable();
1200    let mut params = def_generics.iter_self().peekable();
1201
1202    // If we encounter a type or const when we expect a lifetime, we infer the lifetimes.
1203    // If we later encounter a lifetime, we know that the arguments were provided in the
1204    // wrong order. `force_infer_lt` records the type or const that forced lifetimes to be
1205    // inferred, so we can use it for diagnostics later.
1206    let mut force_infer_lt = None;
1207
1208    let has_self_arg = args_and_bindings.is_some_and(|it| it.has_self_type);
1209    // First, handle `Self` parameter. Consume it from the args if provided, otherwise from `explicit_self_ty`,
1210    // and lastly infer it.
1211    if let Some(&(
1212        self_param_id,
1213        self_param @ GenericParamDataRef::TypeParamData(TypeParamData {
1214            provenance: TypeParamProvenance::TraitSelf,
1215            ..
1216        }),
1217    )) = params.peek()
1218    {
1219        let self_ty = if has_self_arg {
1220            let (_, self_ty) = args.next().expect("has_self_type=true, should have Self type");
1221            ctx.provided_kind(self_param_id, self_param, self_ty)
1222        } else {
1223            explicit_self_ty.map(|it| it.into()).unwrap_or_else(|| {
1224                ctx.inferred_kind(
1225                    def,
1226                    self_param_id,
1227                    self_param,
1228                    infer_args,
1229                    &substs,
1230                    had_count_error,
1231                )
1232            })
1233        };
1234        params.next();
1235        substs.push(self_ty);
1236    } else if has_self_arg {
1237        // A qualified path `<T as Trait>::Assoc` where `Trait` resolved to something without a
1238        // `Self` parameter, e.g. a struct. `check_generic_args_len()` skips the self type
1239        // unconditionally, so drop it here too instead of matching it against a real parameter.
1240        // FIXME: Report a diagnostic here, rustc emits `E0404: expected trait, found struct`.
1241        args.next();
1242    }
1243
1244    loop {
1245        // We're going to iterate through the generic arguments that the user
1246        // provided, matching them with the generic parameters we expect.
1247        // Mismatches can occur as a result of elided lifetimes, or for malformed
1248        // input. We try to handle both sensibly.
1249        match (args.peek(), params.peek()) {
1250            (Some(&(arg_idx, arg)), Some(&(param_id, param))) => match (arg, param) {
1251                (HirGenericArg::Type(_), GenericParamDataRef::TypeParamData(type_param))
1252                    if type_param.provenance == TypeParamProvenance::ArgumentImplTrait =>
1253                {
1254                    // Do not allow specifying `impl Trait` explicitly. We already err at that, but if we won't handle it here
1255                    // we will handle it as if it was specified, instead of inferring it.
1256                    substs.push(ctx.inferred_kind(
1257                        def,
1258                        param_id,
1259                        param,
1260                        infer_args,
1261                        &substs,
1262                        had_count_error,
1263                    ));
1264                    params.next();
1265                }
1266                (HirGenericArg::Lifetime(_), GenericParamDataRef::LifetimeParamData(_))
1267                | (HirGenericArg::Type(_), GenericParamDataRef::TypeParamData(_))
1268                | (HirGenericArg::Const(_), GenericParamDataRef::ConstParamData(_)) => {
1269                    substs.push(ctx.provided_kind(param_id, param, arg));
1270                    args.next();
1271                    params.next();
1272                }
1273                (
1274                    HirGenericArg::Type(_) | HirGenericArg::Const(_),
1275                    GenericParamDataRef::LifetimeParamData(_),
1276                ) => {
1277                    // We expected a lifetime argument, but got a type or const
1278                    // argument. That means we're inferring the lifetime.
1279                    substs.push(ctx.inferred_kind(
1280                        def,
1281                        param_id,
1282                        param,
1283                        infer_args,
1284                        &substs,
1285                        had_count_error,
1286                    ));
1287                    params.next();
1288                    force_infer_lt = Some((arg_idx as u32, param_id));
1289                }
1290                (HirGenericArg::Type(type_ref), GenericParamDataRef::ConstParamData(_)) => {
1291                    if let Some(konst) = type_looks_like_const(store, *type_ref) {
1292                        let GenericParamId::ConstParamId(param_id) = param_id else {
1293                            panic!("unmatching param kinds");
1294                        };
1295                        let const_ty = const_param_ty(db, param_id);
1296                        substs
1297                            .push(ctx.provided_type_like_const(*type_ref, const_ty, konst).into());
1298                        args.next();
1299                        params.next();
1300                    } else {
1301                        // See the `_ => { ... }` branch.
1302                        if !had_count_error {
1303                            ctx.report_arg_mismatch(param_id, arg_idx as u32, has_self_arg);
1304                        }
1305                        while args.next().is_some() {}
1306                    }
1307                }
1308                _ => {
1309                    // We expected one kind of parameter, but the user provided
1310                    // another. This is an error. However, if we already know that
1311                    // the arguments don't match up with the parameters, we won't issue
1312                    // an additional error, as the user already knows what's wrong.
1313                    if !had_count_error {
1314                        ctx.report_arg_mismatch(param_id, arg_idx as u32, has_self_arg);
1315                    }
1316
1317                    // We've reported the error, but we want to make sure that this
1318                    // problem doesn't bubble down and create additional, irrelevant
1319                    // errors. In this case, we're simply going to ignore the argument
1320                    // and any following arguments. The rest of the parameters will be
1321                    // inferred.
1322                    while args.next().is_some() {}
1323                }
1324            },
1325
1326            (Some(&(_, arg)), None) => {
1327                // We should never be able to reach this point with well-formed input.
1328                // There are two situations in which we can encounter this issue.
1329                //
1330                //  1. The number of arguments is incorrect. In this case, an error
1331                //     will already have been emitted, and we can ignore it.
1332                //  2. We've inferred some lifetimes, which have been provided later (i.e.
1333                //     after a type or const). We want to throw an error in this case.
1334                if !had_count_error {
1335                    assert!(
1336                        matches!(arg, HirGenericArg::Lifetime(_)),
1337                        "the only possible situation here is incorrect lifetime order"
1338                    );
1339                    let (provided_arg_idx, param_id) =
1340                        force_infer_lt.expect("lifetimes ought to have been inferred");
1341                    ctx.report_arg_mismatch(param_id, provided_arg_idx, has_self_arg);
1342                }
1343
1344                break;
1345            }
1346
1347            (None, Some(&(param_id, param))) => {
1348                // If there are fewer arguments than parameters, it means we're inferring the remaining arguments.
1349                let param = if let GenericParamId::LifetimeParamId(_) = param_id {
1350                    match &lifetime_elision {
1351                        LifetimeElisionKind::ElisionFailure
1352                        | LifetimeElisionKind::AnonymousCreateParameter { report_in_path: true }
1353                        | LifetimeElisionKind::AnonymousReportError => {
1354                            assert!(had_count_error);
1355                            ctx.inferred_kind(
1356                                def,
1357                                param_id,
1358                                param,
1359                                infer_args,
1360                                &substs,
1361                                had_count_error,
1362                            )
1363                        }
1364                        LifetimeElisionKind::StaticIfNoLifetimeInScope { only_lint: _ } => {
1365                            Region::new_static(interner).into()
1366                        }
1367                        LifetimeElisionKind::Elided(lifetime) => (*lifetime).into(),
1368                        LifetimeElisionKind::AnonymousCreateParameter { report_in_path: false }
1369                        | LifetimeElisionKind::Infer => {
1370                            // FIXME: With `AnonymousCreateParameter`, we need to create a new lifetime parameter here
1371                            // (but this will probably be done in hir-def lowering instead).
1372                            ctx.inferred_kind(
1373                                def,
1374                                param_id,
1375                                param,
1376                                infer_args,
1377                                &substs,
1378                                had_count_error,
1379                            )
1380                        }
1381                    }
1382                } else {
1383                    ctx.inferred_kind(def, param_id, param, infer_args, &substs, had_count_error)
1384                };
1385                substs.push(param);
1386                params.next();
1387            }
1388
1389            (None, None) => break,
1390        }
1391    }
1392
1393    GenericArgs::new_from_slice(&substs)
1394}
1395
1396fn type_looks_like_const(
1397    store: &ExpressionStore,
1398    type_ref: TypeRefId,
1399) -> Option<TypeLikeConst<'_>> {
1400    // A path/`_` const will be parsed as a type, instead of a const, because when parsing/lowering
1401    // in hir-def we don't yet know the expected argument kind. rustc does this a bit differently,
1402    // when lowering to HIR it resolves the path, and if it doesn't resolve to the type namespace
1403    // it is lowered as a const. Our behavior could deviate from rustc when the value is resolvable
1404    // in both the type and value namespaces, but I believe we only allow more code.
1405    let type_ref = &store[type_ref];
1406    match type_ref {
1407        TypeRef::Path(path) => Some(TypeLikeConst::Path(path)),
1408        TypeRef::Placeholder => Some(TypeLikeConst::Infer),
1409        _ => None,
1410    }
1411}
hir_ty/lower/path.rs

hir_ty/lower/
path.rs
