rewrite the test and fix a minor fp

* rewrite the test for `declare_interior_mutable_const from scratch`

* fix a minor false positive where `Cell<"const T>` gets linted twice

3 files changed, 166 insertions, 75 deletions

diff --git a/clippy_lints/src/non_copy_const.rs b/clippy_lints/src/non_copy_const.rs
index 28c68a2b68c..bb44eeb6adc 100644
--- a/clippy_lints/src/non_copy_const.rs
+++ b/clippy_lints/src/non_copy_const.rs
@@ -9,8 +9,7 @@ use rustc_hir::{Expr, ExprKind, ImplItem, ImplItemKind, Item, ItemKind, Node, Tr
 use rustc_infer::traits::specialization_graph;
 use rustc_lint::{LateContext, LateLintPass, Lint};
 use rustc_middle::ty::adjustment::Adjust;
-use rustc_middle::ty::fold::TypeFoldable as _;
-use rustc_middle::ty::{AssocKind, 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;
@@ -178,15 +177,18 @@ impl<'tcx> LateLintPass<'tcx> for NonCopyConst {
                         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
-                            // 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.
-                            .normalize_erasing_regions(
-                                cx.tcx.param_env(of_trait_def_id),
-                                cx.tcx.type_of(of_assoc_item.def_id),
-                            )
-                            .has_type_flags(TypeFlags::HAS_PROJECTION | TypeFlags::HAS_TY_PARAM);
+                        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);
diff --git a/tests/ui/declare_interior_mutable_const.rs b/tests/ui/declare_interior_mutable_const.rs
index 7471b360540..646d3ec8b47 100644
--- a/tests/ui/declare_interior_mutable_const.rs
+++ b/tests/ui/declare_interior_mutable_const.rs
@@ -34,64 +34,135 @@ static STATIC_TUPLE: (AtomicUsize, String) = (ATOMIC, STRING);
 #[allow(clippy::declare_interior_mutable_const)]
 const ONCE_INIT: Once = Once::new();
 
-struct Wrapper<T>(T);
-
-trait Trait<T: Trait2<AssocType5 = AtomicUsize>> {
-    type AssocType;
-    type AssocType2;
-    type AssocType3;
-
+// 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;
-    const INPUT: T;
-    const INPUT_ASSOC: T::AssocType4;
-    const INPUT_ASSOC_2: T::AssocType5; //~ ERROR interior mutable
-    const ASSOC: Self::AssocType;
-    const ASSOC_2: Self::AssocType2;
-    const WRAPPED_ASSOC_2: Wrapper<Self::AssocType2>;
-    const WRAPPED_ASSOC_3: Wrapper<Self::AssocType3>;
-
-    const AN_INPUT: T = Self::INPUT;
-    declare_const!(ANOTHER_INPUT: T = Self::INPUT);
     declare_const!(ANOTHER_ATOMIC: AtomicUsize = Self::ATOMIC); //~ ERROR interior mutable
 }
 
-trait Trait2 {
-    type AssocType4;
-    type AssocType5;
+impl ConcreteTypes for u64 {
+    const ATOMIC: AtomicUsize = AtomicUsize::new(9);
+    const INTEGER: u64 = 10;
+    const STRING: String = String::new();
+}
 
-    const SELF_2: Self;
-    const ASSOC_4: Self::AssocType4;
+// a helper trait used below
+trait ConstDefault {
+    const DEFAULT: Self;
 }
 
-impl<T: Trait2<AssocType5 = AtomicUsize>> Trait<T> for u64 {
-    type AssocType = u16;
-    type AssocType2 = AtomicUsize;
-    type AssocType3 = T;
+// 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 ATOMIC: AtomicUsize = AtomicUsize::new(9);
-    const INTEGER: u64 = 10;
-    const STRING: String = String::new();
-    const SELF: Self = 11;
-    const INPUT: T = T::SELF_2;
-    const INPUT_ASSOC: T::AssocType4 = T::ASSOC_4;
-    const INPUT_ASSOC_2: T::AssocType5 = AtomicUsize::new(16);
-    const ASSOC: Self::AssocType = 13;
-    const ASSOC_2: Self::AssocType2 = AtomicUsize::new(15); //~ ERROR interior mutable
-    const WRAPPED_ASSOC_2: Wrapper<Self::AssocType2> = Wrapper(AtomicUsize::new(16)); //~ ERROR interior mutable
-    const WRAPPED_ASSOC_3: Wrapper<Self::AssocType3> = Wrapper(T::SELF_2);
+    const HAVING_DEFAULT: T = Self::TO_REMAIN_GENERIC;
+    declare_const!(IN_MACRO: T = Self::TO_REMAIN_GENERIC);
+}
+
+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
+}
+
+// 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>;
+}
+
+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);
 }
 
-struct Local<T, U>(T, U);
+// a helper trait used below
+trait AssocTypesHelper {
+    type NotToBeBounded;
+    type ToBeBounded;
 
-impl<T: Trait<U>, U: Trait2<AssocType5 = AtomicUsize>> Local<T, U> {
-    const ASSOC_5: AtomicUsize = AtomicUsize::new(14); //~ ERROR interior mutable
+    const NOT_TO_BE_BOUNDED: Self::NotToBeBounded;
+}
+
+// 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);
+}
+
+trait SelfType {
+    const SELF: Self;
+}
+
+impl SelfType for u64 {
+    const SELF: Self = 16;
+}
+
+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
+}
+
+// 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 U_SELF: U = U::SELF_2;
-    const T_ASSOC: T::AssocType = T::ASSOC;
-    const U_ASSOC: U::AssocType5 = AtomicUsize::new(17); //~ ERROR interior mutable
+
+    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 0fcb726db46..0a0b818b8b7 100644
--- a/tests/ui/declare_interior_mutable_const.stderr
+++ b/tests/ui/declare_interior_mutable_const.stderr
@@ -36,18 +36,12 @@ 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:44:5
+  --> $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:50:5
-   |
-LL |     const INPUT_ASSOC_2: T::AssocType5; //~ ERROR interior mutable
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: a `const` item should never be interior mutable
   --> $DIR/declare_interior_mutable_const.rs:16:9
    |
 LL |         const $name: $ty = $e;
@@ -59,28 +53,52 @@ LL |     declare_const!(ANOTHER_ATOMIC: AtomicUsize = Self::ATOMIC); //~ ERROR i
    = 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:82:5
+  --> $DIR/declare_interior_mutable_const.rs:67:5
+   |
+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:92:5
+   |
+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:93:5
+   |
+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
+   |
+LL |     const BOUNDED: T::ToBeBounded; //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: a `const` item should never be interior mutable
+  --> $DIR/declare_interior_mutable_const.rs:135:5
    |
-LL |     const ASSOC_2: Self::AssocType2 = AtomicUsize::new(15); //~ ERROR interior mutable
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+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:83:5
+  --> $DIR/declare_interior_mutable_const.rs:143:5
    |
-LL |     const WRAPPED_ASSOC_2: Wrapper<Self::AssocType2> = Wrapper(AtomicUsize::new(16)); //~ 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:90:5
+  --> $DIR/declare_interior_mutable_const.rs:159:5
    |
-LL |     const ASSOC_5: AtomicUsize = AtomicUsize::new(14); //~ ERROR interior mutable
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+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:94:5
+  --> $DIR/declare_interior_mutable_const.rs:165:5
    |
-LL |     const U_ASSOC: U::AssocType5 = AtomicUsize::new(17); //~ ERROR interior mutable
-   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL |     const BOUNDED_ASSOC_TYPE: T::ToBeBounded = AtomicUsize::new(19); //~ ERROR interior mutable
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-error: aborting due to 11 previous errors
+error: aborting due to 14 previous errors