Auto merge of #6046 - rail-rain:change_criteria_non_copy_const, r=flip1995

Change the criteria of `interior_mutable_const`

This implements my suggestion [here](https://github.com/rust-lang/rust-clippy/issues/5050#issuecomment-680310889), and so hopefully fixes #5050.

* stop linting associated types and generic type parameters
* start linting ones in trait impls
  whose corresponding definitions in the traits are generic
* remove the `is_copy` check
  as presumably the only purpose of it is to allow
  generics with `Copy` bounds as `Freeze` is internal
  and generics are no longer linted
* remove the term 'copy' from the tests
  as being `Copy` no longer have meaning

---

changelog: Change the criteria of `declare_interior_mutable_const` and `borrow_interior_mutable_const` to narrow the lints to only lint things that defenitly is a interior mutable type, not potentially.

5 files changed, 269 insertions, 135 deletions

diff --git a/clippy_lints/src/non_copy_const.rs b/clippy_lints/src/non_copy_const.rs
index 73eabd4207e..bb44eeb6adc 100644
--- a/clippy_lints/src/non_copy_const.rs
+++ b/clippy_lints/src/non_copy_const.rs
@@ -6,14 +6,16 @@ use std::ptr;
 
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::{Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, Node, TraitItem, TraitItemKind, UnOp};
+use rustc_infer::traits::specialization_graph;
 use rustc_lint::{LateContext, LateLintPass, Lint};
 use rustc_middle::ty::adjustment::Adjust;
-use rustc_middle::ty::{Ty, TypeFlags};
+use rustc_middle::ty::{AssocKind, Ty};
 use rustc_session::{declare_lint_pass, declare_tool_lint};
 use rustc_span::{InnerSpan, Span, DUMMY_SP};
 use rustc_typeck::hir_ty_to_ty;
 
-use crate::utils::{in_constant, is_copy, qpath_res, span_lint_and_then};
+use crate::utils::{in_constant, qpath_res, span_lint_and_then};
+use if_chain::if_chain;
 
 declare_clippy_lint! {
     /// **What it does:** Checks for declaration of `const` items which is interior
@@ -83,11 +85,10 @@ declare_clippy_lint! {
     "referencing `const` with interior mutability"
 }
 
-#[allow(dead_code)]
 #[derive(Copy, Clone)]
 enum Source {
     Item { item: Span },
-    Assoc { item: Span, ty: Span },
+    Assoc { item: Span },
     Expr { expr: Span },
 }
 
@@ -110,10 +111,15 @@ impl Source {
 }
 
 fn verify_ty_bound<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, source: Source) {
-    if ty.is_freeze(cx.tcx.at(DUMMY_SP), cx.param_env) || is_copy(cx, ty) {
-        // An `UnsafeCell` is `!Copy`, and an `UnsafeCell` is also the only type which
-        // is `!Freeze`, thus if our type is `Copy` we can be sure it must be `Freeze`
-        // as well.
+    // Ignore types whose layout is unknown since `is_freeze` reports every generic types as `!Freeze`,
+    // making it indistinguishable from `UnsafeCell`. i.e. it isn't a tool to prove a type is
+    // 'unfrozen'. However, this code causes a false negative in which
+    // a type contains a layout-unknown type, but also a unsafe cell like `const CELL: Cell<T>`.
+    // Yet, it's better than `ty.has_type_flags(TypeFlags::HAS_TY_PARAM | TypeFlags::HAS_PROJECTION)`
+    // since it works when a pointer indirection involves (`Cell<*const T>`).
+    // Making up a `ParamEnv` where every generic params and assoc types are `Freeze`is another option;
+    // but I'm not sure whether it's a decent way, if possible.
+    if cx.tcx.layout_of(cx.param_env.and(ty)).is_err() || ty.is_freeze(cx.tcx.at(DUMMY_SP), cx.param_env) {
         return;
     }
 
@@ -127,11 +133,7 @@ fn verify_ty_bound<'tcx>(cx: &LateContext<'tcx>, ty: Ty<'tcx>, source: Source) {
                 let const_kw_span = span.from_inner(InnerSpan::new(0, 5));
                 diag.span_label(const_kw_span, "make this a static item (maybe with lazy_static)");
             },
-            Source::Assoc { ty: ty_span, .. } => {
-                if ty.flags().intersects(TypeFlags::HAS_FREE_LOCAL_NAMES) {
-                    diag.span_label(ty_span, &format!("consider requiring `{}` to be `Copy`", ty));
-                }
-            },
+            Source::Assoc { .. } => (),
             Source::Expr { .. } => {
                 diag.help("assign this const to a local or static variable, and use the variable here");
             },
@@ -152,14 +154,10 @@ impl<'tcx> LateLintPass<'tcx> for NonCopyConst {
     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, trait_item: &'tcx TraitItem<'_>) {
         if let TraitItemKind::Const(hir_ty, ..) = &trait_item.kind {
             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
-            verify_ty_bound(
-                cx,
-                ty,
-                Source::Assoc {
-                    ty: hir_ty.span,
-                    item: trait_item.span,
-                },
-            );
+            // Normalize assoc types because ones originated from generic params
+            // bounded other traits could have their bound.
+            let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
+            verify_ty_bound(cx, normalized, Source::Assoc { item: trait_item.span });
         }
     }
 
@@ -167,17 +165,50 @@ impl<'tcx> LateLintPass<'tcx> for NonCopyConst {
         if let ImplItemKind::Const(hir_ty, ..) = &impl_item.kind {
             let item_hir_id = cx.tcx.hir().get_parent_node(impl_item.hir_id);
             let item = cx.tcx.hir().expect_item(item_hir_id);
-            // Ensure the impl is an inherent impl.
-            if let ItemKind::Impl { of_trait: None, .. } = item.kind {
-                let ty = hir_ty_to_ty(cx.tcx, hir_ty);
-                verify_ty_bound(
-                    cx,
-                    ty,
-                    Source::Assoc {
-                        ty: hir_ty.span,
-                        item: impl_item.span,
-                    },
-                );
+
+            match &item.kind {
+                ItemKind::Impl {
+                    of_trait: Some(of_trait_ref),
+                    ..
+                } => {
+                    if_chain! {
+                        // Lint a trait impl item only when the definition is a generic type,
+                        // assuming a assoc const is not meant to be a interior mutable type.
+                        if let Some(of_trait_def_id) = of_trait_ref.trait_def_id();
+                        if let Some(of_assoc_item) = specialization_graph::Node::Trait(of_trait_def_id)
+                            .item(cx.tcx, impl_item.ident, AssocKind::Const, of_trait_def_id);
+                        if cx
+                            .tcx
+                            .layout_of(cx.tcx.param_env(of_trait_def_id).and(
+                                // Normalize assoc types because ones originated from generic params
+                                // bounded other traits could have their bound at the trait defs;
+                                // and, in that case, the definition is *not* generic.
+                                cx.tcx.normalize_erasing_regions(
+                                    cx.tcx.param_env(of_trait_def_id),
+                                    cx.tcx.type_of(of_assoc_item.def_id),
+                                ),
+                            ))
+                            .is_err();
+                        then {
+                            let ty = hir_ty_to_ty(cx.tcx, hir_ty);
+                            let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
+                            verify_ty_bound(
+                                cx,
+                                normalized,
+                                Source::Assoc {
+                                    item: impl_item.span,
+                                },
+                            );
+                        }
+                    }
+                },
+                ItemKind::Impl { of_trait: None, .. } => {
+                    let ty = hir_ty_to_ty(cx.tcx, hir_ty);
+                    // Normalize assoc types originated from generic params.
+                    let normalized = cx.tcx.normalize_erasing_regions(cx.param_env, ty);
+                    verify_ty_bound(cx, normalized, Source::Assoc { item: impl_item.span });
+                },
+                _ => (),
             }
         }
     }
diff --git a/tests/ui/borrow_interior_mutable_const.rs b/tests/ui/borrow_interior_mutable_const.rs
index 39f87510548..9fcc9ece49b 100644
--- a/tests/ui/borrow_interior_mutable_const.rs
+++ b/tests/ui/borrow_interior_mutable_const.rs
@@ -19,16 +19,30 @@ const NO_ANN: &dyn Display = &70;
 static STATIC_TUPLE: (AtomicUsize, String) = (ATOMIC, STRING);
 const ONCE_INIT: Once = Once::new();
 
-trait Trait<T>: Copy {
-    type NonCopyType;
+trait Trait<T> {
+    type AssocType;
 
     const ATOMIC: AtomicUsize;
+    const INPUT: T;
+    const ASSOC: Self::AssocType;
+
+    fn function() {
+        let _ = &Self::INPUT;
+        let _ = &Self::ASSOC;
+    }
 }
 
 impl Trait<u32> for u64 {
-    type NonCopyType = u16;
+    type AssocType = AtomicUsize;
 
     const ATOMIC: AtomicUsize = AtomicUsize::new(9);
+    const INPUT: u32 = 10;
+    const ASSOC: Self::AssocType = AtomicUsize::new(11);
+
+    fn function() {
+        let _ = &Self::INPUT;
+        let _ = &Self::ASSOC; //~ ERROR interior mutability
+    }
 }
 
 // This is just a pointer that can be safely dereferended,
diff --git a/tests/ui/borrow_interior_mutable_const.stderr b/tests/ui/borrow_interior_mutable_const.stderr
index 5800af7e960..ed726a6b46e 100644
--- a/tests/ui/borrow_interior_mutable_const.stderr
+++ b/tests/ui/borrow_interior_mutable_const.stderr
@@ -1,14 +1,22 @@
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:66:5
+  --> $DIR/borrow_interior_mutable_const.rs:44:18
+   |
+LL |         let _ = &Self::ASSOC; //~ ERROR interior mutability
+   |                  ^^^^^^^^^^^
+   |
+   = note: `-D clippy::borrow-interior-mutable-const` implied by `-D warnings`
+   = help: assign this const to a local or static variable, and use the variable here
+
+error: a `const` item with interior mutability should not be borrowed
+  --> $DIR/borrow_interior_mutable_const.rs:80:5
    |
 LL |     ATOMIC.store(1, Ordering::SeqCst); //~ ERROR interior mutability
    |     ^^^^^^
    |
-   = note: `-D clippy::borrow-interior-mutable-const` implied by `-D warnings`
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:67:16
+  --> $DIR/borrow_interior_mutable_const.rs:81:16
    |
 LL |     assert_eq!(ATOMIC.load(Ordering::SeqCst), 5); //~ ERROR interior mutability
    |                ^^^^^^
@@ -16,7 +24,7 @@ LL |     assert_eq!(ATOMIC.load(Ordering::SeqCst), 5); //~ ERROR interior mutabi
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:70:22
+  --> $DIR/borrow_interior_mutable_const.rs:84:22
    |
 LL |     let _once_ref = &ONCE_INIT; //~ ERROR interior mutability
    |                      ^^^^^^^^^
@@ -24,7 +32,7 @@ LL |     let _once_ref = &ONCE_INIT; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:71:25
+  --> $DIR/borrow_interior_mutable_const.rs:85:25
    |
 LL |     let _once_ref_2 = &&ONCE_INIT; //~ ERROR interior mutability
    |                         ^^^^^^^^^
@@ -32,7 +40,7 @@ LL |     let _once_ref_2 = &&ONCE_INIT; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:72:27
+  --> $DIR/borrow_interior_mutable_const.rs:86:27
    |
 LL |     let _once_ref_4 = &&&&ONCE_INIT; //~ ERROR interior mutability
    |                           ^^^^^^^^^
@@ -40,7 +48,7 @@ LL |     let _once_ref_4 = &&&&ONCE_INIT; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:73:26
+  --> $DIR/borrow_interior_mutable_const.rs:87:26
    |
 LL |     let _once_mut = &mut ONCE_INIT; //~ ERROR interior mutability
    |                          ^^^^^^^^^
@@ -48,7 +56,7 @@ LL |     let _once_mut = &mut ONCE_INIT; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:84:14
+  --> $DIR/borrow_interior_mutable_const.rs:98:14
    |
 LL |     let _ = &ATOMIC_TUPLE; //~ ERROR interior mutability
    |              ^^^^^^^^^^^^
@@ -56,7 +64,7 @@ LL |     let _ = &ATOMIC_TUPLE; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:85:14
+  --> $DIR/borrow_interior_mutable_const.rs:99:14
    |
 LL |     let _ = &ATOMIC_TUPLE.0; //~ ERROR interior mutability
    |              ^^^^^^^^^^^^
@@ -64,7 +72,7 @@ LL |     let _ = &ATOMIC_TUPLE.0; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:86:19
+  --> $DIR/borrow_interior_mutable_const.rs:100:19
    |
 LL |     let _ = &(&&&&ATOMIC_TUPLE).0; //~ ERROR interior mutability
    |                   ^^^^^^^^^^^^
@@ -72,7 +80,7 @@ LL |     let _ = &(&&&&ATOMIC_TUPLE).0; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:87:14
+  --> $DIR/borrow_interior_mutable_const.rs:101:14
    |
 LL |     let _ = &ATOMIC_TUPLE.0[0]; //~ ERROR interior mutability
    |              ^^^^^^^^^^^^
@@ -80,7 +88,7 @@ LL |     let _ = &ATOMIC_TUPLE.0[0]; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:88:13
+  --> $DIR/borrow_interior_mutable_const.rs:102:13
    |
 LL |     let _ = ATOMIC_TUPLE.0[0].load(Ordering::SeqCst); //~ ERROR interior mutability
    |             ^^^^^^^^^^^^
@@ -88,7 +96,7 @@ LL |     let _ = ATOMIC_TUPLE.0[0].load(Ordering::SeqCst); //~ ERROR interior mu
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:94:13
+  --> $DIR/borrow_interior_mutable_const.rs:108:13
    |
 LL |     let _ = ATOMIC_TUPLE.0[0]; //~ ERROR interior mutability
    |             ^^^^^^^^^^^^
@@ -96,7 +104,7 @@ LL |     let _ = ATOMIC_TUPLE.0[0]; //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:99:5
+  --> $DIR/borrow_interior_mutable_const.rs:113:5
    |
 LL |     CELL.set(2); //~ ERROR interior mutability
    |     ^^^^
@@ -104,7 +112,7 @@ LL |     CELL.set(2); //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:100:16
+  --> $DIR/borrow_interior_mutable_const.rs:114:16
    |
 LL |     assert_eq!(CELL.get(), 6); //~ ERROR interior mutability
    |                ^^^^
@@ -112,7 +120,7 @@ LL |     assert_eq!(CELL.get(), 6); //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:113:5
+  --> $DIR/borrow_interior_mutable_const.rs:127:5
    |
 LL |     u64::ATOMIC.store(5, Ordering::SeqCst); //~ ERROR interior mutability
    |     ^^^^^^^^^^^
@@ -120,12 +128,12 @@ LL |     u64::ATOMIC.store(5, Ordering::SeqCst); //~ ERROR interior mutability
    = help: assign this const to a local or static variable, and use the variable here
 
 error: a `const` item with interior mutability should not be borrowed
-  --> $DIR/borrow_interior_mutable_const.rs:114:16
+  --> $DIR/borrow_interior_mutable_const.rs:128:16
    |
 LL |     assert_eq!(u64::ATOMIC.load(Ordering::SeqCst), 9); //~ ERROR interior mutability
    |                ^^^^^^^^^^^
    |
    = help: assign this const to a local or static variable, and use the variable here
 
-error: aborting due to 16 previous errors
+error: aborting due to 17 previous errors
 
diff --git a/tests/ui/declare_interior_mutable_const.rs b/tests/ui/declare_interior_mutable_const.rs
index b4003ed8932..3afcdca2f04 100644
--- a/tests/ui/declare_interior_mutable_const.rs
+++ b/tests/ui/declare_interior_mutable_const.rs
@@ -34,60 +34,141 @@ static STATIC_TUPLE: (AtomicUsize, String) = (ATOMIC, STRING);
 #[allow(clippy::declare_interior_mutable_const)]
 const ONCE_INIT: Once = Once::new();
 
-trait Trait<T>: Copy {
-    type NonCopyType;
-
+// a constant whose type is a concrete type should be linted at the definition site.
+trait ConcreteTypes {
     const ATOMIC: AtomicUsize; //~ ERROR interior mutable
     const INTEGER: u64;
     const STRING: String;
-    const SELF: Self; // (no error)
-    const INPUT: T;
-    //~^ ERROR interior mutable
-    //~| HELP consider requiring `T` to be `Copy`
-    const ASSOC: Self::NonCopyType;
-    //~^ ERROR interior mutable
-    //~| HELP consider requiring `<Self as Trait<T>>::NonCopyType` to be `Copy`
+    declare_const!(ANOTHER_ATOMIC: AtomicUsize = Self::ATOMIC); //~ ERROR interior mutable
+}
 
-    const AN_INPUT: T = Self::INPUT;
-    //~^ ERROR interior mutable
-    //~| ERROR consider requiring `T` to be `Copy`
-    declare_const!(ANOTHER_INPUT: T = Self::INPUT); //~ ERROR interior mutable
+impl ConcreteTypes for u64 {
+    const ATOMIC: AtomicUsize = AtomicUsize::new(9);
+    const INTEGER: u64 = 10;
+    const STRING: String = String::new();
 }
 
-trait Trait2 {
-    type CopyType: Copy;
+// a helper trait used below
+trait ConstDefault {
+    const DEFAULT: Self;
+}
+
+// a constant whose type is a generic type should be linted at the implementation site.
+trait GenericTypes<T, U> {
+    const TO_REMAIN_GENERIC: T;
+    const TO_BE_CONCRETE: U;
 
-    const SELF_2: Self;
-    //~^ ERROR interior mutable
-    //~| HELP consider requiring `Self` to be `Copy`
-    const ASSOC_2: Self::CopyType; // (no error)
+    const HAVING_DEFAULT: T = Self::TO_REMAIN_GENERIC;
+    declare_const!(IN_MACRO: T = Self::TO_REMAIN_GENERIC);
 }
 
-// we don't lint impl of traits, because an impl has no power to change the interface.
-impl Trait<u32> for u64 {
-    type NonCopyType = u16;
+impl<T: ConstDefault> GenericTypes<T, AtomicUsize> for u64 {
+    const TO_REMAIN_GENERIC: T = T::DEFAULT;
+    const TO_BE_CONCRETE: AtomicUsize = AtomicUsize::new(11); //~ ERROR interior mutable
+}
 
-    const ATOMIC: AtomicUsize = AtomicUsize::new(9);
-    const INTEGER: u64 = 10;
-    const STRING: String = String::new();
-    const SELF: Self = 11;
-    const INPUT: u32 = 12;
-    const ASSOC: Self::NonCopyType = 13;
+// a helper type used below
+struct Wrapper<T>(T);
+
+// a constant whose type is an associated type should be linted at the implementation site, too.
+trait AssocTypes {
+    type ToBeFrozen;
+    type ToBeUnfrozen;
+    type ToBeGenericParam;
+
+    const TO_BE_FROZEN: Self::ToBeFrozen;
+    const TO_BE_UNFROZEN: Self::ToBeUnfrozen;
+    const WRAPPED_TO_BE_UNFROZEN: Wrapper<Self::ToBeUnfrozen>;
+    // to ensure it can handle things when a generic type remains after normalization.
+    const WRAPPED_TO_BE_GENERIC_PARAM: Wrapper<Self::ToBeGenericParam>;
 }
 
-struct Local<T, U>(T, U);
+impl<T: ConstDefault> AssocTypes for Vec<T> {
+    type ToBeFrozen = u16;
+    type ToBeUnfrozen = AtomicUsize;
+    type ToBeGenericParam = T;
+
+    const TO_BE_FROZEN: Self::ToBeFrozen = 12;
+    const TO_BE_UNFROZEN: Self::ToBeUnfrozen = AtomicUsize::new(13); //~ ERROR interior mutable
+    const WRAPPED_TO_BE_UNFROZEN: Wrapper<Self::ToBeUnfrozen> = Wrapper(AtomicUsize::new(14)); //~ ERROR interior mutable
+    const WRAPPED_TO_BE_GENERIC_PARAM: Wrapper<Self::ToBeGenericParam> = Wrapper(T::DEFAULT);
+}
+
+// a helper trait used below
+trait AssocTypesHelper {
+    type NotToBeBounded;
+    type ToBeBounded;
+
+    const NOT_TO_BE_BOUNDED: Self::NotToBeBounded;
+}
 
-impl<T: Trait2 + Trait<u32>, U: Trait2> Local<T, U> {
-    const ASSOC_3: AtomicUsize = AtomicUsize::new(14); //~ ERROR interior mutable
+// a constant whose type is an assoc type originated from a generic param bounded at the definition
+// site should be linted at there.
+trait AssocTypesFromGenericParam<T>
+where
+    T: AssocTypesHelper<ToBeBounded = AtomicUsize>,
+{
+    const NOT_BOUNDED: T::NotToBeBounded;
+    const BOUNDED: T::ToBeBounded; //~ ERROR interior mutable
+}
+
+impl<T> AssocTypesFromGenericParam<T> for u64
+where
+    T: AssocTypesHelper<ToBeBounded = AtomicUsize>,
+{
+    // an associated type could remain unknown in a trait impl.
+    const NOT_BOUNDED: T::NotToBeBounded = T::NOT_TO_BE_BOUNDED;
+    const BOUNDED: T::ToBeBounded = AtomicUsize::new(15);
+}
+
+// a constant whose type is `Self` should be linted at the implementation site as well.
+// (`Option` requires `Sized` bound.)
+trait SelfType: Sized {
+    const SELF: Self;
+    // this was the one in the original issue (#5050).
+    const WRAPPED_SELF: Option<Self>;
+}
+
+impl SelfType for u64 {
+    const SELF: Self = 16;
+    const WRAPPED_SELF: Option<Self> = Some(20);
+}
+
+impl SelfType for AtomicUsize {
+    // this (interior mutable `Self` const) exists in `parking_lot`.
+    // `const_trait_impl` will replace it in the future, hopefully.
+    const SELF: Self = AtomicUsize::new(17); //~ ERROR interior mutable
+    const WRAPPED_SELF: Option<Self> = Some(AtomicUsize::new(21)); //~ ERROR interior mutable
+}
+
+// Even though a constant contains a generic type, if it also have a interior mutable type,
+// it should be linted at the definition site.
+trait BothOfCellAndGeneric<T> {
+    // this is a false negative in the current implementation.
+    const DIRECT: Cell<T>;
+    const INDIRECT: Cell<*const T>; //~ ERROR interior mutable
+}
+
+impl<T: ConstDefault> BothOfCellAndGeneric<T> for u64 {
+    const DIRECT: Cell<T> = Cell::new(T::DEFAULT);
+    const INDIRECT: Cell<*const T> = Cell::new(std::ptr::null());
+}
+
+struct Local<T>(T);
+
+// a constant in an inherent impl are essentially the same as a normal const item
+// except there can be a generic or associated type.
+impl<T> Local<T>
+where
+    T: ConstDefault + AssocTypesHelper<ToBeBounded = AtomicUsize>,
+{
+    const ATOMIC: AtomicUsize = AtomicUsize::new(18); //~ ERROR interior mutable
     const COW: Cow<'static, str> = Cow::Borrowed("tuvwxy");
-    const T_SELF: T = T::SELF_2;
-    const U_SELF: U = U::SELF_2;
-    //~^ ERROR interior mutable
-    //~| HELP consider requiring `U` to be `Copy`
-    const T_ASSOC: T::NonCopyType = T::ASSOC;
-    //~^ ERROR interior mutable
-    //~| HELP consider requiring `<T as Trait<u32>>::NonCopyType` to be `Copy`
-    const U_ASSOC: U::CopyType = U::ASSOC_2;
+
+    const GENERIC_TYPE: T = T::DEFAULT;
+
+    const ASSOC_TYPE: T::NotToBeBounded = T::NOT_TO_BE_BOUNDED;
+    const BOUNDED_ASSOC_TYPE: T::ToBeBounded = AtomicUsize::new(19); //~ ERROR interior mutable
 }
 
 fn main() {}
diff --git a/tests/ui/declare_interior_mutable_const.stderr b/tests/ui/declare_interior_mutable_const.stderr
index 6a9a57361f9..5cb10be88d8 100644
--- a/tests/ui/declare_interior_mutable_const.stderr
+++ b/tests/ui/declare_interior_mutable_const.stderr
@@ -36,75 +36,75 @@ LL | declare_const!(_ONCE: Once = Once::new()); //~ ERROR interior mutable
    = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:40:5
+  --> $DIR/declare_interior_mutable_const.rs:39:5
    |
 LL |     const ATOMIC: AtomicUsize; //~ ERROR interior mutable
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:44:5
+  --> $DIR/declare_interior_mutable_const.rs:16:9
+   |
+LL |         const $name: $ty = $e;
+   |         ^^^^^^^^^^^^^^^^^^^^^^
+...
+LL |     declare_const!(ANOTHER_ATOMIC: AtomicUsize = Self::ATOMIC); //~ ERROR interior mutable
+   |     ----------------------------------------------------------- in this macro invocation
    |
-LL |     const INPUT: T;
-   |     ^^^^^^^^^^^^^-^
-   |                  |
-   |                  consider requiring `T` to be `Copy`
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:47:5
+  --> $DIR/declare_interior_mutable_const.rs:67:5
    |
-LL |     const ASSOC: Self::NonCopyType;
-   |     ^^^^^^^^^^^^^-----------------^
-   |                  |
-   |                  consider requiring `<Self as Trait<T>>::NonCopyType` to be `Copy`
+LL |     const TO_BE_CONCRETE: AtomicUsize = AtomicUsize::new(11); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:51:5
+  --> $DIR/declare_interior_mutable_const.rs:92:5
    |
-LL |     const AN_INPUT: T = Self::INPUT;
-   |     ^^^^^^^^^^^^^^^^-^^^^^^^^^^^^^^^
-   |                     |
-   |                     consider requiring `T` to be `Copy`
+LL |     const TO_BE_UNFROZEN: Self::ToBeUnfrozen = AtomicUsize::new(13); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:16:9
+  --> $DIR/declare_interior_mutable_const.rs:93:5
    |
-LL |         const $name: $ty = $e;
-   |         ^^^^^^^^^^^^^^^^^^^^^^
-...
-LL |     declare_const!(ANOTHER_INPUT: T = Self::INPUT); //~ ERROR interior mutable
-   |     ----------------------------------------------- in this macro invocation
+LL |     const WRAPPED_TO_BE_UNFROZEN: Wrapper<Self::ToBeUnfrozen> = Wrapper(AtomicUsize::new(14)); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: a `const` item should never be interior mutable
+  --> $DIR/declare_interior_mutable_const.rs:112:5
    |
-   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+LL |     const BOUNDED: T::ToBeBounded; //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: a `const` item should never be interior mutable
+  --> $DIR/declare_interior_mutable_const.rs:140:5
+   |
+LL |     const SELF: Self = AtomicUsize::new(17); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:60:5
+  --> $DIR/declare_interior_mutable_const.rs:141:5
    |
-LL |     const SELF_2: Self;
-   |     ^^^^^^^^^^^^^^----^
-   |                   |
-   |                   consider requiring `Self` to be `Copy`
+LL |     const WRAPPED_SELF: Option<Self> = Some(AtomicUsize::new(21)); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:81:5
+  --> $DIR/declare_interior_mutable_const.rs:149:5
    |
-LL |     const ASSOC_3: AtomicUsize = AtomicUsize::new(14); //~ ERROR interior mutable
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     const INDIRECT: Cell<*const T>; //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:84:5
+  --> $DIR/declare_interior_mutable_const.rs:165:5
    |
-LL |     const U_SELF: U = U::SELF_2;
-   |     ^^^^^^^^^^^^^^-^^^^^^^^^^^^^
-   |                   |
-   |                   consider requiring `U` to be `Copy`
+LL |     const ATOMIC: AtomicUsize = AtomicUsize::new(18); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: a `const` item should never be interior mutable
-  --> $DIR/declare_interior_mutable_const.rs:87:5
+  --> $DIR/declare_interior_mutable_const.rs:171:5
    |
-LL |     const T_ASSOC: T::NonCopyType = T::ASSOC;
-   |     ^^^^^^^^^^^^^^^--------------^^^^^^^^^^^^
-   |                    |
-   |                    consider requiring `<T as Trait<u32>>::NonCopyType` to be `Copy`
+LL |     const BOUNDED_ASSOC_TYPE: T::ToBeBounded = AtomicUsize::new(19); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 13 previous errors
+error: aborting due to 15 previous errors