Auto merge of #112629 - compiler-errors:atb-imply, r=jackh726

Make associated type bounds in supertrait position implied

`trait A: B<Assoc: C> {}` should be able to imply both `Self: B` and `<Self as B>::Assoc: C`. Adjust the way that we collect implied predicates to do so.

Fixes #112573
Fixes #112568

Author: bors

compiler/rustc_hir_analysis/src/astconv/bounds.rs

@@ -9,12 +9,12 @@ use rustc_span::symbol::Ident;
 use rustc_span::{ErrorGuaranteed, Span};
 use rustc_trait_selection::traits;
 
-use crate::astconv::{AstConv, ConvertedBinding, ConvertedBindingKind};
+use crate::astconv::{
+    AstConv, ConvertedBinding, ConvertedBindingKind, OnlySelfBounds, PredicateFilter,
+};
 use crate::bounds::Bounds;
 use crate::errors::{MultipleRelaxedDefaultBounds, ValueOfAssociatedStructAlreadySpecified};
 
-use super::OnlySelfBounds;
-
 impl<'tcx> dyn AstConv<'tcx> + '_ {
     /// Sets `implicitly_sized` to true on `Bounds` if necessary
     pub(crate) fn add_implicitly_sized(
@@ -176,47 +176,39 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
         &self,
         param_ty: Ty<'tcx>,
         ast_bounds: &[hir::GenericBound<'_>],
-        only_self_bounds: OnlySelfBounds,
+        filter: PredicateFilter,
     ) -> Bounds<'tcx> {
         let mut bounds = Bounds::default();
-        self.add_bounds(
-            param_ty,
-            ast_bounds.iter(),
-            &mut bounds,
-            ty::List::empty(),
-            only_self_bounds,
-        );
-        debug!(?bounds);
 
-        bounds
-    }
-
-    /// Convert the bounds in `ast_bounds` that refer to traits which define an associated type
-    /// named `assoc_name` into ty::Bounds. Ignore the rest.
-    pub(crate) fn compute_bounds_that_match_assoc_item(
-        &self,
-        param_ty: Ty<'tcx>,
-        ast_bounds: &[hir::GenericBound<'_>],
-        assoc_name: Ident,
-    ) -> Bounds<'tcx> {
-        let mut result = Vec::new();
-
-        for ast_bound in ast_bounds {
-            if let Some(trait_ref) = ast_bound.trait_ref()
-                && let Some(trait_did) = trait_ref.trait_def_id()
-                && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
-            {
-                result.push(ast_bound.clone());
+        let only_self_bounds = match filter {
+            PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                OnlySelfBounds(false)
             }
-        }
+            PredicateFilter::SelfOnly | PredicateFilter::SelfThatDefines(_) => OnlySelfBounds(true),
+        };
 
-        let mut bounds = Bounds::default();
         self.add_bounds(
             param_ty,
-            result.iter(),
+            ast_bounds.iter().filter(|bound| {
+                match filter {
+                PredicateFilter::All
+                | PredicateFilter::SelfOnly
+                | PredicateFilter::SelfAndAssociatedTypeBounds => true,
+                PredicateFilter::SelfThatDefines(assoc_name) => {
+                    if let Some(trait_ref) = bound.trait_ref()
+                        && let Some(trait_did) = trait_ref.trait_def_id()
+                        && self.tcx().trait_may_define_assoc_item(trait_did, assoc_name)
+                    {
+                        true
+                    } else {
+                        false
+                    }
+                }
+            }
+            }),
             &mut bounds,
             ty::List::empty(),
-            OnlySelfBounds(true),
+            only_self_bounds,
         );
         debug!(?bounds);
 

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -58,6 +58,24 @@ pub struct PathSeg(pub DefId, pub usize);
 #[derive(Copy, Clone, Debug)]
 pub struct OnlySelfBounds(pub bool);
 
+#[derive(Copy, Clone, Debug)]
+pub enum PredicateFilter {
+    /// All predicates may be implied by the trait.
+    All,
+
+    /// Only traits that reference `Self: ..` are implied by the trait.
+    SelfOnly,
+
+    /// Only traits that reference `Self: ..` and define an associated type
+    /// with the given ident are implied by the trait.
+    SelfThatDefines(Ident),
+
+    /// Only traits that reference `Self: ..` and their associated type bounds.
+    /// For example, given `Self: Tr<A: B>`, this would expand to `Self: Tr`
+    /// and `<Self as Tr>::A: B`.
+    SelfAndAssociatedTypeBounds,
+}
+
 pub trait AstConv<'tcx> {
     fn tcx(&self) -> TyCtxt<'tcx>;
 

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -1,5 +1,5 @@
 use super::ItemCtxt;
-use crate::astconv::{AstConv, OnlySelfBounds};
+use crate::astconv::{AstConv, PredicateFilter};
 use rustc_hir as hir;
 use rustc_infer::traits::util;
 use rustc_middle::ty::subst::InternalSubsts;
@@ -26,7 +26,7 @@ fn associated_type_bounds<'tcx>(
     );
 
     let icx = ItemCtxt::new(tcx, assoc_item_def_id);
-    let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, OnlySelfBounds(false));
+    let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
     // Associated types are implicitly sized unless a `?Sized` bound is found
     icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
 
@@ -68,7 +68,7 @@ fn opaque_type_bounds<'tcx>(
 ) -> &'tcx [(ty::Clause<'tcx>, Span)] {
     ty::print::with_no_queries!({
         let icx = ItemCtxt::new(tcx, opaque_def_id);
-        let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, OnlySelfBounds(false));
+        let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds, PredicateFilter::All);
         // Opaque types are implicitly sized unless a `?Sized` bound is found
         icx.astconv().add_implicitly_sized(&mut bounds, item_ty, ast_bounds, None, span);
         debug!(?bounds);

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -1,4 +1,4 @@
-use crate::astconv::{AstConv, OnlySelfBounds};
+use crate::astconv::{AstConv, OnlySelfBounds, PredicateFilter};
 use crate::bounds::Bounds;
 use crate::collect::ItemCtxt;
 use crate::constrained_generic_params as cgp;
@@ -125,7 +125,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     if let Some(self_bounds) = is_trait {
         predicates.extend(
             icx.astconv()
-                .compute_bounds(tcx.types.self_param, self_bounds, OnlySelfBounds(false))
+                .compute_bounds(tcx.types.self_param, self_bounds, PredicateFilter::All)
                 .clauses(),
         );
     }
@@ -530,19 +530,6 @@ pub(super) fn explicit_predicates_of<'tcx>(
     }
 }
 
-#[derive(Copy, Clone, Debug)]
-pub enum PredicateFilter {
-    /// All predicates may be implied by the trait
-    All,
-
-    /// Only traits that reference `Self: ..` are implied by the trait
-    SelfOnly,
-
-    /// Only traits that reference `Self: ..` and define an associated type
-    /// with the given ident are implied by the trait
-    SelfThatDefines(Ident),
-}
-
 /// Ensures that the super-predicates of the trait with a `DefId`
 /// of `trait_def_id` are converted and stored. This also ensures that
 /// the transitive super-predicates are converted.
@@ -564,11 +551,15 @@ pub(super) fn implied_predicates_of(
     tcx: TyCtxt<'_>,
     trait_def_id: LocalDefId,
 ) -> ty::GenericPredicates<'_> {
-    if tcx.is_trait_alias(trait_def_id.to_def_id()) {
-        implied_predicates_with_filter(tcx, trait_def_id.to_def_id(), PredicateFilter::All)
-    } else {
-        tcx.super_predicates_of(trait_def_id)
-    }
+    implied_predicates_with_filter(
+        tcx,
+        trait_def_id.to_def_id(),
+        if tcx.is_trait_alias(trait_def_id.to_def_id()) {
+            PredicateFilter::All
+        } else {
+            PredicateFilter::SelfAndAssociatedTypeBounds
+        },
+    )
 }
 
 /// Ensures that the super-predicates of the trait with a `DefId`
@@ -601,44 +592,14 @@ pub(super) fn implied_predicates_with_filter(
     let icx = ItemCtxt::new(tcx, trait_def_id);
 
     let self_param_ty = tcx.types.self_param;
-    let (superbounds, where_bounds_that_match) = match filter {
-        PredicateFilter::All => (
-            // Convert the bounds that follow the colon (or equal in trait aliases)
-            icx.astconv().compute_bounds(self_param_ty, bounds, OnlySelfBounds(false)),
-            // Also include all where clause bounds
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(false),
-                None,
-            ),
-        ),
-        PredicateFilter::SelfOnly => (
-            // Convert the bounds that follow the colon (or equal in trait aliases)
-            icx.astconv().compute_bounds(self_param_ty, bounds, OnlySelfBounds(true)),
-            // Include where clause bounds for `Self`
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(true),
-                None,
-            ),
-        ),
-        PredicateFilter::SelfThatDefines(assoc_name) => (
-            // Convert the bounds that follow the colon (or equal) that reference the associated name
-            icx.astconv().compute_bounds_that_match_assoc_item(self_param_ty, bounds, assoc_name),
-            // Include where clause bounds for `Self` that reference the associated name
-            icx.type_parameter_bounds_in_generics(
-                generics,
-                item.owner_id.def_id,
-                self_param_ty,
-                OnlySelfBounds(true),
-                Some(assoc_name),
-            ),
-        ),
-    };
+    let superbounds = icx.astconv().compute_bounds(self_param_ty, bounds, filter);
+
+    let where_bounds_that_match = icx.type_parameter_bounds_in_generics(
+        generics,
+        item.owner_id.def_id,
+        self_param_ty,
+        filter,
+    );
 
     // Combine the two lists to form the complete set of superbounds:
     let implied_bounds =
@@ -743,8 +704,7 @@ pub(super) fn type_param_predicates(
             ast_generics,
             def_id,
             ty,
-            OnlySelfBounds(true),
-            Some(assoc_name),
+            PredicateFilter::SelfThatDefines(assoc_name),
         )
         .into_iter()
         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
@@ -768,8 +728,7 @@ impl<'tcx> ItemCtxt<'tcx> {
         ast_generics: &'tcx hir::Generics<'tcx>,
         param_def_id: LocalDefId,
         ty: Ty<'tcx>,
-        only_self_bounds: OnlySelfBounds,
-        assoc_name: Option<Ident>,
+        filter: PredicateFilter,
     ) -> Vec<(ty::Clause<'tcx>, Span)> {
         let mut bounds = Bounds::default();
 
@@ -778,9 +737,23 @@ impl<'tcx> ItemCtxt<'tcx> {
                 continue;
             };
 
+            let (only_self_bounds, assoc_name) = match filter {
+                PredicateFilter::All | PredicateFilter::SelfAndAssociatedTypeBounds => {
+                    (OnlySelfBounds(false), None)
+                }
+                PredicateFilter::SelfOnly => (OnlySelfBounds(true), None),
+                PredicateFilter::SelfThatDefines(assoc_name) => {
+                    (OnlySelfBounds(true), Some(assoc_name))
+                }
+            };
+
+            // Subtle: If we're collecting `SelfAndAssociatedTypeBounds`, then we
+            // want to only consider predicates with `Self: ...`, but we don't want
+            // `OnlySelfBounds(true)` since we want to collect the nested associated
+            // type bound as well.
             let bound_ty = if predicate.is_param_bound(param_def_id.to_def_id()) {
                 ty
-            } else if !only_self_bounds.0 {
+            } else if matches!(filter, PredicateFilter::All) {
                 self.to_ty(predicate.bounded_ty)
             } else {
                 continue;

tests/ui/associated-type-bounds/implied-in-supertrait.rs

@@ -0,0 +1,19 @@
+// check-pass
+
+#![feature(associated_type_bounds)]
+
+trait Trait: Super<Assoc: Bound> {}
+
+trait Super {
+    type Assoc;
+}
+
+trait Bound {}
+
+fn foo<T>(x: T)
+where
+    T: Trait,
+{
+}
+
+fn main() {}

tests/ui/async-await/return-type-notation/rtn-implied-in-supertrait.rs

@@ -0,0 +1,28 @@
+// edition:2021
+// check-pass
+
+#![feature(async_fn_in_trait, return_position_impl_trait_in_trait, return_type_notation)]
+//~^ WARN the feature `return_type_notation` is incomplete
+
+use std::future::Future;
+
+struct JoinHandle<T>(fn() -> T);
+
+fn spawn<T>(_: impl Future<Output = T>) -> JoinHandle<T> {
+    todo!()
+}
+
+trait Foo {
+    async fn bar(&self) -> i32;
+}
+
+trait SendFoo: Foo<bar(): Send> + Send {}
+
+fn foobar(foo: impl SendFoo) -> JoinHandle<i32> {
+    spawn(async move {
+        let future = foo.bar();
+        future.await
+    })
+}
+
+fn main() {}

tests/ui/async-await/return-type-notation/rtn-implied-in-supertrait.stderr

@@ -0,0 +1,11 @@
+warning: the feature `return_type_notation` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/rtn-implied-in-supertrait.rs:4:68
+   |
+LL | #![feature(async_fn_in_trait, return_position_impl_trait_in_trait, return_type_notation)]
+   |                                                                    ^^^^^^^^^^^^^^^^^^^^
+   |
+   = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
+   = note: `#[warn(incomplete_features)]` on by default
+
+warning: 1 warning emitted
+