delegation: emit error when there is an error in lowered user-specified generic args

compiler/rustc_hir_analysis/src/collect.rs

@@ -46,7 +46,7 @@ use rustc_trait_selection::traits::{
 };
 use tracing::{debug, instrument};
 
-use crate::errors;
+use crate::errors::{self, ElidedLifetimesAreNotAllowedInDelegations};
 use crate::hir_ty_lowering::{HirTyLowerer, InherentAssocCandidate, RegionInferReason};
 
 pub(crate) mod dump;
@@ -131,6 +131,7 @@ pub(crate) struct ItemCtxt<'tcx> {
     tcx: TyCtxt<'tcx>,
     item_def_id: LocalDefId,
     tainted_by_errors: Cell<Option<ErrorGuaranteed>>,
+    lowering_delegation_segment: bool,
 }
 
 ///////////////////////////////////////////////////////////////////////////
@@ -241,7 +242,24 @@ fn bad_placeholder<'cx, 'tcx>(
 
 impl<'tcx> ItemCtxt<'tcx> {
     pub(crate) fn new(tcx: TyCtxt<'tcx>, item_def_id: LocalDefId) -> ItemCtxt<'tcx> {
-        ItemCtxt { tcx, item_def_id, tainted_by_errors: Cell::new(None) }
+        ItemCtxt::new_internal(tcx, item_def_id, false)
+    }
+
+    fn new_internal(
+        tcx: TyCtxt<'tcx>,
+        item_def_id: LocalDefId,
+        delegation: bool,
+    ) -> ItemCtxt<'tcx> {
+        ItemCtxt {
+            tcx,
+            item_def_id,
+            tainted_by_errors: Cell::new(None),
+            lowering_delegation_segment: delegation,
+        }
+    }
+
+    pub(crate) fn new_for_delegation(tcx: TyCtxt<'tcx>, item_def_id: LocalDefId) -> ItemCtxt<'tcx> {
+        ItemCtxt::new_internal(tcx, item_def_id, true)
     }
 
     pub(crate) fn lower_ty(&self, hir_ty: &hir::Ty<'tcx>) -> Ty<'tcx> {
@@ -335,6 +353,13 @@ impl<'tcx> HirTyLowerer<'tcx> for ItemCtxt<'tcx> {
                 .emit();
             ty::Region::new_error(self.tcx(), guar)
         } else {
+            // If we found elided lifetime during lowering of delegation parent or child
+            // segment then emit an error, as we need a named lifetime for proper signature
+            // inheritance (#156848).
+            if self.lowering_delegation_segment {
+                self.tcx.dcx().emit_err(ElidedLifetimesAreNotAllowedInDelegations { span });
+            }
+
             // This indicates an illegal lifetime in a non-assoc-trait position
             ty::Region::new_error_with_message(self.tcx(), span, "unelided lifetime in signature")
         }

compiler/rustc_hir_analysis/src/delegation.rs

@@ -7,7 +7,7 @@ use std::debug_assert_matches;
 use rustc_data_structures::fx::FxHashMap;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LocalDefId};
-use rustc_hir::{DelegationInfo, HirId, PathSegment};
+use rustc_hir::{DelegationInfo, PathSegment};
 use rustc_middle::ty::{
     self, EarlyBinder, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
 };
@@ -551,7 +551,7 @@ pub(crate) fn inherit_predicates_for_delegation_item<'tcx>(
         }
     }
 
-    let (parent_args, child_args) = get_delegation_user_specified_args(tcx, def_id);
+    let (parent_args, child_args) = tcx.get_delegation_user_specified_args(def_id);
     let (folder, args) = create_folder_and_args(tcx, def_id, sig_id, parent_args, child_args);
     let self_pos_kind = create_self_position_kind(tcx, def_id, sig_id);
     let filter_self_preds = matches!(self_pos_kind, SelfPositionKind::AfterLifetimes(true));
@@ -627,7 +627,7 @@ pub(crate) fn inherit_sig_for_delegation_item<'tcx>(
         return tcx.arena.alloc_from_iter((0..sig_len).map(|_| err_type));
     }
 
-    let (parent_args, child_args) = get_delegation_user_specified_args(tcx, def_id);
+    let (parent_args, child_args) = tcx.get_delegation_user_specified_args(def_id);
     let (mut folder, args) = create_folder_and_args(tcx, def_id, sig_id, parent_args, child_args);
     let caller_sig = EarlyBinder::bind(caller_sig.skip_binder().fold_with(&mut folder));
 
@@ -640,18 +640,18 @@ pub(crate) fn inherit_sig_for_delegation_item<'tcx>(
 // they will be used during delegation signature and predicates inheritance.
 // Example: reuse Trait::<'static, i32, 1>::foo::<A, B>
 // we want to extract [Self, 'static, i32, 1] for parent and [A, B] for child.
-fn get_delegation_user_specified_args<'tcx>(
+pub(crate) fn get_delegation_user_specified_args<'tcx>(
     tcx: TyCtxt<'tcx>,
     delegation_id: LocalDefId,
 ) -> (&'tcx [ty::GenericArg<'tcx>], &'tcx [ty::GenericArg<'tcx>]) {
     let info = get_delegation_info(tcx, delegation_id);
 
-    let get_segment = |hir_id: HirId| -> Option<(&'tcx PathSegment<'tcx>, DefId)> {
+    let get_segment = |hir_id| -> Option<(&'tcx PathSegment<'tcx>, DefId)> {
         let segment = tcx.hir_node(hir_id).expect_path_segment();
         segment.res.opt_def_id().map(|def_id| (segment, def_id))
     };
 
-    let ctx = ItemCtxt::new(tcx, delegation_id);
+    let ctx = ItemCtxt::new_for_delegation(tcx, delegation_id);
     let lowerer = ctx.lowerer();
 
     let parent_args = info.parent_args_segment_id.and_then(get_segment).map(|(segment, def_id)| {

compiler/rustc_hir_analysis/src/errors.rs

@@ -1680,6 +1680,13 @@ pub(crate) struct DelegationSelfTypeNotSpecified {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag("elided lifetimes are not allowed in delegations as we need to inherit signature")]
+pub(crate) struct ElidedLifetimesAreNotAllowedInDelegations {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag("method should be `async` or return a future, but it is synchronous")]
 pub(crate) struct MethodShouldReturnFuture {

compiler/rustc_hir_analysis/src/lib.rs

@@ -137,6 +137,7 @@ pub fn provide(providers: &mut Providers) {
         inferred_outlives_crate: outlives::inferred_outlives_crate,
         inferred_outlives_of: outlives::inferred_outlives_of,
         inherit_sig_for_delegation_item: delegation::inherit_sig_for_delegation_item,
+        get_delegation_user_specified_args: delegation::get_delegation_user_specified_args,
         enforce_impl_non_lifetime_params_are_constrained:
             impl_wf_check::enforce_impl_non_lifetime_params_are_constrained,
         crate_variances: variance::crate_variances,

compiler/rustc_middle/src/queries.rs

@@ -2065,6 +2065,10 @@ rustc_queries! {
         desc { "inheriting delegation signature" }
     }
 
+    query get_delegation_user_specified_args(def_id: LocalDefId) -> (&'tcx [GenericArg<'tcx>], &'tcx [GenericArg<'tcx>]) {
+        desc { "getting delegation user-specified args" }
+    }
+
     /// Does lifetime resolution on items. Importantly, we can't resolve
     /// lifetimes directly on things like trait methods, because of trait params.
     /// See `rustc_resolve::late::lifetimes` for details.

compiler/rustc_middle/src/query/erase.rs

@@ -147,6 +147,10 @@ impl<T0, T1> Erasable for (&'_ T0, &'_ T1) {
     type Storage = [u8; size_of::<(&'_ (), &'_ ())>()];
 }
 
+impl<T0, T1> Erasable for (&'_ [T0], &'_ [T1]) {
+    type Storage = [u8; size_of::<(&'_ [()], &'_ [()])>()];
+}
+
 macro_rules! impl_erasable_for_types_with_no_type_params {
     ($($ty:ty),+ $(,)?) => {
         $(

tests/ui/delegation/generics/generics-gen-args-errors.rs

@@ -36,6 +36,7 @@ mod test_1 {
         //~| ERROR can't use generic parameters from outer item
         //~| ERROR: unresolved item provided when a constant was expected
         //~| ERROR: function takes 2 lifetime arguments but 0 lifetime arguments were supplied
+        //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
     }
 }
 
@@ -44,36 +45,45 @@ mod test_2 {
 
     reuse foo::<> as bar1;
     //~^ ERROR: the placeholder `_` is not allowed within types on item signatures for functions
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<String, String> as bar2;
     //~^ ERROR: function takes 3 generic arguments but 2 generic arguments were supplied
     //~| ERROR: function takes 2 lifetime arguments but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<'static, _, 'asdasd, 'static, 'static, 'static, _> as bar3;
     //~^ ERROR: use of undeclared lifetime name `'asdasd`
     //~| ERROR: function takes 2 lifetime arguments but 5 lifetime arguments were supplied
     //~| ERROR: function takes 3 generic arguments but 2 generic arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
+
     reuse foo::<String, 'static, 123, asdasd> as bar4;
     //~^ ERROR: cannot find type `asdasd` in this scope
     //~| ERROR: function takes 2 lifetime arguments but 1 lifetime argument was supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<1, 2, _, 4, 5, _> as bar5;
     //~^ ERROR: function takes 3 generic arguments but 6 generic arguments were supplied
     //~| ERROR: function takes 2 lifetime arguments but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<1, 2,asd,String, { let x = 0; }> as bar6;
     //~^ ERROR: cannot find type `asd` in this scope
     //~| ERROR: function takes 3 generic arguments but 5 generic arguments were supplied
     //~| ERROR: function takes 2 lifetime arguments but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<"asdasd", asd, "askdn", 'static, 'a> as bar7;
     //~^ ERROR: use of undeclared lifetime name `'a`
     //~| ERROR: cannot find type `asd` in this scope
     //~| ERROR: constant provided when a type was expected
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse foo::<{}, {}, {}> as bar8;
     //~^ ERROR: constant provided when a type was expected
     //~| ERROR: function takes 2 lifetime arguments but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 }
 
 mod test_3 {
@@ -90,34 +100,43 @@ mod test_3 {
     //~| ERROR: cannot find type `asdasa` in this scope
     //~| ERROR: trait takes 3 lifetime arguments but 0 lifetime arguments were supplied
     //~| ERROR: trait takes 2 generic arguments but 6 generic arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse Trait::<'static, 'static>::foo as bar2;
     //~^ ERROR: trait takes 3 lifetime arguments but 2 lifetime arguments were supplied
     //~| ERROR: the placeholder `_` is not allowed within types on item signatures for functions
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
     reuse Trait::<1, 2, 3, 4, 5>::foo as bar3;
     //~^ ERROR: trait takes 3 lifetime arguments but 0 lifetime arguments were supplied
     //~| ERROR: trait takes 2 generic arguments but 5 generic arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse Trait::<1, 2, true>::foo as bar4;
     //~^ ERROR: trait takes 3 lifetime arguments but 0 lifetime arguments were supplied
     //~| ERROR: trait takes 2 generic arguments but 3 generic arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse Trait::<'static>::foo as bar5;
     //~^ ERROR: trait takes 3 lifetime arguments but 1 lifetime argument was supplied
     //~| ERROR: the placeholder `_` is not allowed within types on item signatures for functions
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse Trait::<1, 2, 'static, DDDD>::foo::<1, 2, 3, 4, 5, 6> as bar6;
     //~^ ERROR: cannot find type `DDDD` in this scope [E0425]
     //~| ERROR: trait takes 3 lifetime arguments but 1 lifetime argument was supplied
     //~| ERROR: trait takes 2 generic arguments but 3 generic arguments were supplied
     //~| ERROR: method takes 2 generic arguments but 6 generic arguments were supplied
     //~| ERROR: method takes 1 lifetime argument but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 
     reuse Trait::<Trait, Clone, _, 'static, dyn Send, _>::foo::<1, 2, 3, _, 6> as bar7;
     //~^ ERROR: trait takes 3 lifetime arguments but 1 lifetime argument was supplied
     //~| ERROR: trait takes 2 generic arguments but 5 generic arguments were supplied
     //~| ERROR: method takes 2 generic arguments but 5 generic arguments were supplied
     //~| ERROR: method takes 1 lifetime argument but 0 lifetime arguments were supplied
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
+    //~| ERROR: elided lifetimes are not allowed in delegations as we need to inherit signature
 }
 
 fn main() {}