Auto merge of #126651 - fmease:consec-shorthand-proj, r=<try>

Implement consecutive shorthand projections (associated type paths) like `T::AssocA::AssocB`

I'd like to resolve / get feedback on the `FIXME` concerning "`Identity<T::Assoc>::Assoc`".
Then I'll polish up this PR and make it ready for a types FCP (i.e., tests, tests, tests).

Addresses #126360 (comment).
CC #22519 (arbitrary shorthand projections).

compiler/rustc_hir_analysis/src/collect.rs

@@ -19,15 +19,19 @@ use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_data_structures::unord::UnordMap;
 use rustc_errors::{struct_span_code_err, Applicability, Diag, ErrorGuaranteed, StashKey, E0228};
+use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::intravisit::{self, walk_generics, Visitor};
-use rustc_hir::{self as hir};
 use rustc_hir::{GenericParamKind, Node};
 use rustc_infer::infer::{InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::hir::nested_filter;
 use rustc_middle::query::Providers;
+use rustc_middle::ty::typeck_results::{
+    HasTypeDependentDefs, LocalTableInContext, LocalTableInContextMut, TypeDependentDef,
+    TypeDependentDefs,
+};
 use rustc_middle::ty::util::{Discr, IntTypeExt};
 use rustc_middle::ty::{self, AdtKind, Const, IsSuggestable, Ty, TyCtxt, Upcast};
 use rustc_middle::{bug, span_bug};
@@ -38,7 +42,7 @@ use rustc_target::spec::abi;
 use rustc_trait_selection::infer::InferCtxtExt;
 use rustc_trait_selection::traits::error_reporting::suggestions::NextTypeParamName;
 use rustc_trait_selection::traits::ObligationCtxt;
-use std::cell::Cell;
+use std::cell::{Cell, RefCell};
 use std::iter;
 use std::ops::Bound;
 
@@ -120,6 +124,7 @@ pub fn provide(providers: &mut Providers) {
 pub struct ItemCtxt<'tcx> {
     tcx: TyCtxt<'tcx>,
     item_def_id: LocalDefId,
+    type_dependent_defs: RefCell<TypeDependentDefs>,
     tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
 }
 
@@ -342,7 +347,12 @@ fn bad_placeholder<'tcx>(
 
 impl<'tcx> ItemCtxt<'tcx> {
     pub fn new(tcx: TyCtxt<'tcx>, item_def_id: LocalDefId) -> ItemCtxt<'tcx> {
-        ItemCtxt { tcx, item_def_id, tainted_by_errors: Cell::new(None) }
+        ItemCtxt {
+            tcx,
+            item_def_id,
+            type_dependent_defs: Default::default(),
+            tainted_by_errors: Cell::new(None),
+        }
     }
 
     pub fn lower_ty(&self, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
@@ -505,6 +515,14 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
         // There's no place to record types from signatures?
     }
 
+    fn record_res(&self, hir_id: hir::HirId, result: TypeDependentDef) {
+        LocalTableInContextMut::new(
+            self.hir_id().owner,
+            &mut self.type_dependent_defs.borrow_mut(),
+        )
+        .insert(hir_id, result);
+    }
+
     fn infcx(&self) -> Option<&InferCtxt<'tcx>> {
         None
     }
@@ -595,6 +613,19 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
 
         (input_tys, output_ty)
     }
+
+    fn upcast(&self) -> &dyn HasTypeDependentDefs {
+        self
+    }
+}
+
+impl HasTypeDependentDefs for ItemCtxt<'_> {
+    fn type_dependent_def(&self, id: hir::HirId) -> Option<(DefKind, DefId)> {
+        LocalTableInContext::new(self.hir_id().owner, &self.type_dependent_defs.borrow())
+            .get(id)
+            .copied()
+            .and_then(|result| result.ok())
+    }
 }
 
 /// Synthesize a new lifetime name that doesn't clash with any of the lifetimes already present.

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -145,11 +145,12 @@ fn anon_const_type_of<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> Ty<'tcx> {
             ..
         }) => {
             let body_owner = tcx.hir().enclosing_body_owner(hir_id);
-            let tables = tcx.typeck(body_owner);
+            let typeck_results = tcx.typeck(body_owner);
             // This may fail in case the method/path does not actually exist.
             // As there is no relevant param for `def_id`, we simply return
             // `None` here.
-            let Some(type_dependent_def) = tables.type_dependent_def_id(parent_node_id) else {
+            let Some(type_dependent_def) = typeck_results.type_dependent_def_id(parent_node_id)
+            else {
                 return Ty::new_error_with_message(
                     tcx,
                     span,

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -39,6 +39,7 @@ use rustc_infer::traits::ObligationCause;
 use rustc_middle::middle::stability::AllowUnstable;
 use rustc_middle::mir::interpret::{LitToConstError, LitToConstInput};
 use rustc_middle::ty::print::PrintPolyTraitRefExt as _;
+use rustc_middle::ty::typeck_results::{HasTypeDependentDefs, TypeDependentDef};
 use rustc_middle::ty::{
     self, Const, GenericArgKind, GenericArgsRef, GenericParamDefKind, ParamEnv, Ty, TyCtxt,
     TypeVisitableExt,
@@ -98,7 +99,7 @@ pub enum RegionInferReason<'a> {
 /// the [`rustc_middle::ty`] representation.
 ///
 /// This trait used to be called `AstConv`.
-pub trait HirTyLowerer<'tcx> {
+pub trait HirTyLowerer<'tcx>: HasTypeDependentDefs {
     fn tcx(&self) -> TyCtxt<'tcx>;
 
     /// Returns the [`LocalDefId`] of the overarching item whose constituents get lowered.
@@ -173,6 +174,8 @@ pub trait HirTyLowerer<'tcx> {
     /// Record the lowered type of a HIR node in this context.
     fn record_ty(&self, hir_id: HirId, ty: Ty<'tcx>, span: Span);
 
+    fn record_res(&self, hir_id: hir::HirId, result: TypeDependentDef);
+
     /// The inference context of the lowering context if applicable.
     fn infcx(&self) -> Option<&InferCtxt<'tcx>>;
 
@@ -192,6 +195,8 @@ pub trait HirTyLowerer<'tcx> {
     {
         self
     }
+
+    fn upcast(&self) -> &dyn HasTypeDependentDefs;
 }
 
 /// New-typed boolean indicating whether explicit late-bound lifetimes
@@ -992,6 +997,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
     /// [type-relative]: hir::QPath::TypeRelative
     /// [#22519]: https://github.com/rust-lang/rust/issues/22519
     /// [iat]: https://github.com/rust-lang/rust/issues/8995#issuecomment-1569208403
+    // FIXME(fmease): Update docs
     //
     // NOTE: When this function starts resolving `Trait::AssocTy` successfully
     // it should also start reporting the `BARE_TRAIT_OBJECTS` lint.
@@ -1006,13 +1012,33 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
         permit_variants: bool,
     ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
         debug!(%qself_ty, ?assoc_segment.ident);
+        let result = self.lower_assoc_path_inner(
+            hir_ref_id,
+            span,
+            qself_ty,
+            qself,
+            assoc_segment,
+            permit_variants,
+        );
+        self.record_res(hir_ref_id, result.map(|(_, def_kind, def_id)| (def_kind, def_id)));
+        result
+    }
+
+    fn lower_assoc_path_inner(
+        &self,
+        hir_ref_id: HirId,
+        span: Span,
+        qself_ty: Ty<'tcx>,
+        qself: &'tcx hir::Ty<'tcx>,
+        assoc_segment: &'tcx hir::PathSegment<'tcx>,
+        permit_variants: bool,
+    ) -> Result<(Ty<'tcx>, DefKind, DefId), ErrorGuaranteed> {
         let tcx = self.tcx();
 
         let assoc_ident = assoc_segment.ident;
-        let qself_res = if let hir::TyKind::Path(hir::QPath::Resolved(_, path)) = &qself.kind {
-            path.res
-        } else {
-            Res::Err
+        let qself_res = match &qself.kind {
+            hir::TyKind::Path(qpath) => self.upcast().qpath_res(qpath, qself.hir_id),
+            _ => Res::Err,
         };
 
         // Check if we have an enum variant or an inherent associated type.
@@ -1038,15 +1064,15 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             }
 
             // FIXME(inherent_associated_types, #106719): Support self types other than ADTs.
-            if let Some((ty, did)) = self.probe_inherent_assoc_ty(
+            if let Some((ty, def_id)) = self.probe_inherent_assoc_ty(
                 assoc_ident,
                 assoc_segment,
                 adt_def.did(),
                 qself_ty,
                 hir_ref_id,
                 span,
             )? {
-                return Ok((ty, DefKind::AssocTy, did));
+                return Ok((ty, DefKind::AssocTy, def_id));
             }
         }
 
@@ -1077,13 +1103,37 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 )?
             }
             (
-                &ty::Param(_),
-                Res::SelfTyParam { trait_: param_did } | Res::Def(DefKind::TyParam, param_did),
+                ty::Param(_),
+                Res::SelfTyParam { trait_: param_def_id }
+                | Res::Def(DefKind::TyParam, param_def_id),
             ) => self.probe_single_ty_param_bound_for_assoc_ty(
-                param_did.expect_local(),
+                param_def_id.expect_local(),
                 assoc_ident,
                 span,
             )?,
+            (ty::Alias(ty::Projection, alias_ty), Res::Def(DefKind::AssocTy, _)) => {
+                // FIXME: Utilizing `item_bounds` for this is cycle-prone.
+                let predicates = tcx.item_bounds(alias_ty.def_id).instantiate(tcx, alias_ty.args);
+
+                self.probe_single_bound_for_assoc_item(
+                    || {
+                        let trait_refs = predicates.iter().filter_map(|pred| {
+                            pred.as_trait_clause().map(|t| t.map_bound(|t| t.trait_ref))
+                        });
+                        traits::transitive_bounds_that_define_assoc_item(
+                            tcx,
+                            trait_refs,
+                            assoc_ident,
+                        )
+                    },
+                    qself_ty,
+                    None,
+                    ty::AssocKind::Type,
+                    assoc_ident,
+                    span,
+                    None,
+                )?
+            }
             _ => {
                 let reported = if variant_resolution.is_some() {
                     // Variant in type position
@@ -1187,6 +1237,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
                 );
             });
         }
+
         Ok((ty, DefKind::AssocTy, assoc_ty.def_id))
     }
 

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -170,9 +170,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     pub(crate) fn write_resolution(
         &self,
         hir_id: HirId,
-        r: Result<(DefKind, DefId), ErrorGuaranteed>,
+        result: Result<(DefKind, DefId), ErrorGuaranteed>,
     ) {
-        self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, r);
+        self.typeck_results.borrow_mut().type_dependent_defs_mut().insert(hir_id, result);
     }
 
     #[instrument(level = "debug", skip(self))]

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -1984,12 +1984,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     .map(|(ty, _, _)| ty)
                     .unwrap_or_else(|guar| Ty::new_error(self.tcx(), guar));
                 let ty = LoweredTy::from_raw(self, path_span, ty);
-                let result = result.map(|(_, kind, def_id)| (kind, def_id));
 
-                // Write back the new resolution.
-                self.write_resolution(hir_id, result);
-
-                (result.map_or(Res::Err, |(kind, def_id)| Res::Def(kind, def_id)), ty)
+                (result.map_or(Res::Err, |(_, kind, def_id)| Res::Def(kind, def_id)), ty)
             }
             QPath::LangItem(lang_item, span) => {
                 let (res, ty) = self.resolve_lang_item_path(lang_item, span, hir_id);

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -11,13 +11,14 @@ use crate::coercion::DynamicCoerceMany;
 use crate::fallback::DivergingFallbackBehavior;
 use crate::fn_ctxt::checks::DivergingBlockBehavior;
 use crate::{CoroutineTypes, Diverges, EnclosingBreakables, TypeckRootCtxt};
-use hir::def_id::CRATE_DEF_ID;
 use rustc_hir as hir;
-use rustc_hir::def_id::{DefId, LocalDefId};
+use rustc_hir::def::DefKind;
+use rustc_hir::def_id::{DefId, LocalDefId, CRATE_DEF_ID};
 use rustc_hir_analysis::hir_ty_lowering::{HirTyLowerer, RegionInferReason};
 use rustc_infer::infer;
 use rustc_infer::infer::error_reporting::sub_relations::SubRelations;
 use rustc_infer::infer::error_reporting::TypeErrCtxt;
+use rustc_middle::ty::typeck_results::{HasTypeDependentDefs, TypeDependentDef};
 use rustc_middle::ty::{self, Const, Ty, TyCtxt, TypeVisitableExt};
 use rustc_session::Session;
 use rustc_span::symbol::Ident;
@@ -334,6 +335,10 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         self.write_ty(hir_id, ty)
     }
 
+    fn record_res(&self, hir_id: hir::HirId, result: TypeDependentDef) {
+        self.write_resolution(hir_id, result);
+    }
+
     fn infcx(&self) -> Option<&infer::InferCtxt<'tcx>> {
         Some(&self.infcx)
     }
@@ -357,6 +362,16 @@ impl<'tcx> HirTyLowerer<'tcx> for FnCtxt<'_, 'tcx> {
         };
         (input_tys, output_ty)
     }
+
+    fn upcast(&self) -> &dyn HasTypeDependentDefs {
+        self
+    }
+}
+
+impl HasTypeDependentDefs for FnCtxt<'_, '_> {
+    fn type_dependent_def(&self, id: hir::HirId) -> Option<(DefKind, DefId)> {
+        self.typeck_results.borrow().type_dependent_def(id)
+    }
 }
 
 /// The `ty` representation of a user-provided type. Depending on the use-site

compiler/rustc_middle/src/ty/mod.rs

@@ -137,6 +137,7 @@ pub mod pattern;
 pub mod print;
 pub mod relate;
 pub mod trait_def;
+pub mod typeck_results;
 pub mod util;
 pub mod visit;
 pub mod vtable;
@@ -163,7 +164,6 @@ mod rvalue_scopes;
 mod structural_impls;
 #[allow(hidden_glob_reexports)]
 mod sty;
-mod typeck_results;
 
 // Data types