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

hir_ty/lower/
path.rs
