Mark assoc tys live only if the trait is live

compiler/rustc_passes/src/dead.rs

@@ -156,7 +156,10 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
 
     fn handle_res(&mut self, res: Res) {
         match res {
-            Res::Def(DefKind::Const | DefKind::AssocConst | DefKind::TyAlias, def_id) => {
+            Res::Def(
+                DefKind::Const | DefKind::AssocConst | DefKind::AssocTy | DefKind::TyAlias,
+                def_id,
+            ) => {
                 self.check_def_id(def_id);
             }
             _ if self.in_pat => {}
@@ -442,7 +445,7 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                     intravisit::walk_item(self, item)
                 }
                 hir::ItemKind::ForeignMod { .. } => {}
-                hir::ItemKind::Trait(..) => {
+                hir::ItemKind::Trait(_, _, _, _, trait_item_refs) => {
                     for impl_def_id in self.tcx.all_impls(item.owner_id.to_def_id()) {
                         if let Some(local_def_id) = impl_def_id.as_local()
                             && let ItemKind::Impl(impl_ref) =
@@ -455,7 +458,12 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                             intravisit::walk_path(self, impl_ref.of_trait.unwrap().path);
                         }
                     }
-
+                    // mark assoc ty live if the trait is live
+                    for trait_item in trait_item_refs {
+                        if let hir::AssocItemKind::Type = trait_item.kind {
+                            self.check_def_id(trait_item.id.owner_id.to_def_id());
+                        }
+                    }
                     intravisit::walk_item(self, item)
                 }
                 _ => intravisit::walk_item(self, item),
@@ -472,9 +480,8 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                             && let ItemKind::Impl(impl_ref) =
                                 self.tcx.hir().expect_item(local_impl_id).kind
                         {
-                            if !matches!(trait_item.kind, hir::TraitItemKind::Type(..))
-                                && !ty_ref_to_pub_struct(self.tcx, impl_ref.self_ty)
-                                    .ty_and_all_fields_are_public
+                            if !ty_ref_to_pub_struct(self.tcx, impl_ref.self_ty)
+                                .ty_and_all_fields_are_public
                             {
                                 // skip impl-items of non pure pub ty,
                                 // cause we don't know the ty is constructed or not,
@@ -813,9 +820,8 @@ fn check_item<'tcx>(
                 // for trait impl blocks,
                 // mark the method live if the self_ty is public,
                 // or the method is public and may construct self
-                if of_trait && matches!(tcx.def_kind(local_def_id), DefKind::AssocTy)
-                    || tcx.visibility(local_def_id).is_public()
-                        && (ty_and_all_fields_are_public || may_construct_self)
+                if tcx.visibility(local_def_id).is_public()
+                    && (ty_and_all_fields_are_public || may_construct_self)
                 {
                     // if the impl item is public,
                     // and the ty may be constructed or can be constructed in foreign crates,
@@ -852,10 +858,13 @@ fn check_trait_item(
     worklist: &mut Vec<(LocalDefId, ComesFromAllowExpect)>,
     id: hir::TraitItemId,
 ) {
-    use hir::TraitItemKind::{Const, Fn};
-    if matches!(tcx.def_kind(id.owner_id), DefKind::AssocConst | DefKind::AssocFn) {
+    use hir::TraitItemKind::{Const, Fn, Type};
+    if matches!(
+        tcx.def_kind(id.owner_id),
+        DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn
+    ) {
         let trait_item = tcx.hir().trait_item(id);
-        if matches!(trait_item.kind, Const(_, Some(_)) | Fn(..))
+        if matches!(trait_item.kind, Const(_, Some(_)) | Type(_, Some(_)) | Fn(..))
             && let Some(comes_from_allow) =
                 has_allow_dead_code_or_lang_attr(tcx, trait_item.owner_id.def_id)
         {
@@ -897,7 +906,7 @@ fn create_and_seed_worklist(
                     // checks impls, impl-items and pub structs with all public fields later
                     match tcx.def_kind(id) {
                         DefKind::Impl { .. } => false,
-                        DefKind::AssocConst | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
+                        DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn => !matches!(tcx.associated_item(id).container, AssocItemContainer::ImplContainer),
                         DefKind::Struct => struct_all_fields_are_public(tcx, id.to_def_id()) || has_allow_dead_code_or_lang_attr(tcx, id).is_some(),
                         _ => true
                     })
@@ -1132,6 +1141,7 @@ impl<'tcx> DeadVisitor<'tcx> {
         }
         match self.tcx.def_kind(def_id) {
             DefKind::AssocConst
+            | DefKind::AssocTy
             | DefKind::AssocFn
             | DefKind::Fn
             | DefKind::Static { .. }
@@ -1173,15 +1183,14 @@ fn check_mod_deathness(tcx: TyCtxt<'_>, module: LocalModDefId) {
             || (def_kind == DefKind::Trait && live_symbols.contains(&item.owner_id.def_id))
         {
             for &def_id in tcx.associated_item_def_ids(item.owner_id.def_id) {
-                // We have diagnosed unused assoc consts and fns in traits
+                // We have diagnosed unused assocs in traits
                 if matches!(def_kind, DefKind::Impl { of_trait: true })
-                    && matches!(tcx.def_kind(def_id), DefKind::AssocConst | DefKind::AssocFn)
+                    && matches!(tcx.def_kind(def_id), DefKind::AssocConst | DefKind::AssocTy | DefKind::AssocFn)
                     // skip unused public inherent methods,
                     // cause we have diagnosed unconstructed struct
                     || matches!(def_kind, DefKind::Impl { of_trait: false })
                         && tcx.visibility(def_id).is_public()
                         && ty_ref_to_pub_struct(tcx, tcx.hir().item(item).expect_impl().self_ty).ty_is_public
-                    || def_kind == DefKind::Trait && tcx.def_kind(def_id) == DefKind::AssocTy
                 {
                     continue;
                 }

tests/ui/const-generics/cross_crate_complex.rs

@@ -11,6 +11,7 @@ async fn foo() {
     async_in_foo(async_out_foo::<4>().await).await;
 }
 
+#[allow(dead_code)]
 struct Faz<const N: usize>;
 
 impl<const N: usize> Foo<N> for Faz<N> {}

tests/ui/generic-associated-types/missing-bounds.fixed

@@ -2,6 +2,7 @@
 
 use std::ops::Add;
 
+#[allow(dead_code)]
 struct A<B>(B);
 
 impl<B> Add for A<B> where B: Add<Output = B> {
@@ -12,6 +13,7 @@ impl<B> Add for A<B> where B: Add<Output = B> {
     }
 }
 
+#[allow(dead_code)]
 struct C<B>(B);
 
 impl<B: Add<Output = B>> Add for C<B> {
@@ -22,6 +24,7 @@ impl<B: Add<Output = B>> Add for C<B> {
     }
 }
 
+#[allow(dead_code)]
 struct D<B>(B);
 
 impl<B: std::ops::Add<Output = B>> Add for D<B> {
@@ -32,6 +35,7 @@ impl<B: std::ops::Add<Output = B>> Add for D<B> {
     }
 }
 
+#[allow(dead_code)]
 struct E<B>(B);
 
 impl<B: Add<Output = B>> Add for E<B> where B: Add<Output = B> {

tests/ui/generic-associated-types/missing-bounds.rs

@@ -2,6 +2,7 @@
 
 use std::ops::Add;
 
+#[allow(dead_code)]
 struct A<B>(B);
 
 impl<B> Add for A<B> where B: Add {
@@ -12,6 +13,7 @@ impl<B> Add for A<B> where B: Add {
     }
 }
 
+#[allow(dead_code)]
 struct C<B>(B);
 
 impl<B: Add> Add for C<B> {
@@ -22,6 +24,7 @@ impl<B: Add> Add for C<B> {
     }
 }
 
+#[allow(dead_code)]
 struct D<B>(B);
 
 impl<B> Add for D<B> {
@@ -32,6 +35,7 @@ impl<B> Add for D<B> {
     }
 }
 
+#[allow(dead_code)]
 struct E<B>(B);
 
 impl<B: Add> Add for E<B> where <B as Add>::Output = B {

tests/ui/generic-associated-types/missing-bounds.stderr

@@ -1,5 +1,5 @@
 error: equality constraints are not yet supported in `where` clauses
-  --> $DIR/missing-bounds.rs:37:33
+  --> $DIR/missing-bounds.rs:41:33
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |                                 ^^^^^^^^^^^^^^^^^^^^^^ not supported
@@ -11,7 +11,7 @@ LL | impl<B: Add> Add for E<B> where B: Add<Output = B> {
    |                                 ~~~~~~~~~~~~~~~~~~
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:11:11
+  --> $DIR/missing-bounds.rs:12:11
    |
 LL | impl<B> Add for A<B> where B: Add {
    |      - expected this type parameter
@@ -24,14 +24,14 @@ LL |         A(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 help: the type constructed contains `<B as Add>::Output` due to the type of the argument passed
-  --> $DIR/missing-bounds.rs:11:9
+  --> $DIR/missing-bounds.rs:12:9
    |
 LL |         A(self.0 + rhs.0)
    |         ^^--------------^
    |           |
    |           this argument influences the type of `A`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:5:8
+  --> $DIR/missing-bounds.rs:6:8
    |
 LL | struct A<B>(B);
    |        ^
@@ -41,7 +41,7 @@ LL | impl<B> Add for A<B> where B: Add<Output = B> {
    |                                  ++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:21:14
+  --> $DIR/missing-bounds.rs:23:14
    |
 LL | impl<B: Add> Add for C<B> {
    |      - expected this type parameter
@@ -54,7 +54,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:15:8
+  --> $DIR/missing-bounds.rs:17:8
    |
 LL | struct C<B>(B);
    |        ^
@@ -64,7 +64,7 @@ LL | impl<B: Add<Output = B>> Add for C<B> {
    |            ++++++++++++
 
 error[E0369]: cannot add `B` to `B`
-  --> $DIR/missing-bounds.rs:31:21
+  --> $DIR/missing-bounds.rs:34:21
    |
 LL |         Self(self.0 + rhs.0)
    |              ------ ^ ----- B
@@ -77,7 +77,7 @@ LL | impl<B: std::ops::Add<Output = B>> Add for D<B> {
    |       +++++++++++++++++++++++++++
 
 error[E0308]: mismatched types
-  --> $DIR/missing-bounds.rs:42:14
+  --> $DIR/missing-bounds.rs:46:14
    |
 LL | impl<B: Add> Add for E<B> where <B as Add>::Output = B {
    |      - expected this type parameter
@@ -90,7 +90,7 @@ LL |         Self(self.0 + rhs.0)
    = note: expected type parameter `B`
              found associated type `<B as Add>::Output`
 note: tuple struct defined here
-  --> $DIR/missing-bounds.rs:35:8
+  --> $DIR/missing-bounds.rs:39:8
    |
 LL | struct E<B>(B);
    |        ^

tests/ui/lint/dead-code/unused-trait-with-assoc-ty.rs

@@ -0,0 +1,11 @@
+#![deny(dead_code)]
+
+struct T1; //~ ERROR struct `T1` is never constructed
+
+trait Foo { type Unused; } //~ ERROR trait `Foo` is never used
+impl Foo for T1 { type Unused = Self; }
+
+pub trait Bar { type Used; }
+impl Bar for T1 { type Used = Self; }
+
+fn main() {}

tests/ui/lint/dead-code/unused-trait-with-assoc-ty.stderr

@@ -0,0 +1,20 @@
+error: struct `T1` is never constructed
+  --> $DIR/unused-trait-with-assoc-ty.rs:3:8
+   |
+LL | struct T1;
+   |        ^^
+   |
+note: the lint level is defined here
+  --> $DIR/unused-trait-with-assoc-ty.rs:1:9
+   |
+LL | #![deny(dead_code)]
+   |         ^^^^^^^^^
+
+error: trait `Foo` is never used
+  --> $DIR/unused-trait-with-assoc-ty.rs:5:7
+   |
+LL | trait Foo { type Unused; }
+   |       ^^^
+
+error: aborting due to 2 previous errors
+

tests/ui/pattern/issue-22546.rs

@@ -15,7 +15,7 @@ impl<T: ::std::fmt::Display> Foo<T> {
     }
 }
 
-trait Tr { //~ WARN trait `Tr` is never used
+trait Tr {
     type U;
 }