Rollup merge of rust-lang#101698 - raldone01:feat/const_cmp_typeid, r…

…=scottmcm

Constify `TypeId` ordering impls

Tracking issue: rust-lang#101871

Adding const ordering to `TypeId` allows rtti crates to optimize some casting scenarios (without transmuting to `u64`). This would also prevent these crates from breaking if the underlying type is changed from `u64` to something different.

Feature gate: `#![feature(const_cmp_type_id)]`

library/core/src/any.rs

@@ -662,7 +662,8 @@ impl dyn Any + Send + Sync {
 /// While `TypeId` implements `Hash`, `PartialOrd`, and `Ord`, it is worth
 /// noting that the hashes and ordering will vary between Rust releases. Beware
 /// of relying on them inside of your code!
-#[derive(Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Debug, Hash)]
+#[derive(Clone, Copy, Debug, Hash, Eq)]
+#[derive_const(PartialEq, PartialOrd, Ord)]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct TypeId {
     t: u64,

tests/ui/const-generics/issues/issue-90318.rs

@@ -12,14 +12,14 @@ impl True for If<true> {}
 fn consume<T: 'static>(_val: T)
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-    //~^ ERROR: can't compare
+    //~^ overly complex generic constant
 {
 }
 
 fn test<T: 'static>()
 where
     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-    //~^ ERROR: can't compare
+    //~^ overly complex generic constant
 {
 }
 

tests/ui/const-generics/issues/issue-90318.stderr

@@ -1,29 +1,24 @@
-error[E0277]: can't compare `TypeId` with `_` in const contexts
-  --> $DIR/issue-90318.rs:14:28
+error: overly complex generic constant
+  --> $DIR/issue-90318.rs:14:8
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |                            ^^ no implementation for `TypeId == _`
+   |        ^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
+   |          |
+   |          borrowing is not supported in generic constants
    |
-   = help: the trait `~const PartialEq<_>` is not implemented for `TypeId`
-note: the trait `PartialEq<_>` is implemented for `TypeId`, but that implementation is not `const`
-  --> $DIR/issue-90318.rs:14:28
-   |
-LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |                            ^^
+   = help: consider moving this anonymous constant into a `const` function
+   = note: this operation may be supported in the future
 
-error[E0277]: can't compare `TypeId` with `_` in const contexts
-  --> $DIR/issue-90318.rs:21:28
+error: overly complex generic constant
+  --> $DIR/issue-90318.rs:21:8
    |
 LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |                            ^^ no implementation for `TypeId == _`
+   |        ^^-----------------^^^^^^^^^^^^^^^^^^^^^^^^
+   |          |
+   |          borrowing is not supported in generic constants
    |
-   = help: the trait `~const PartialEq<_>` is not implemented for `TypeId`
-note: the trait `PartialEq<_>` is implemented for `TypeId`, but that implementation is not `const`
-  --> $DIR/issue-90318.rs:21:28
-   |
-LL |     If<{ TypeId::of::<T>() != TypeId::of::<()>() }>: True,
-   |                            ^^
+   = help: consider moving this anonymous constant into a `const` function
+   = note: this operation may be supported in the future
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0277`.

tests/ui/consts/const_cmp_type_id.rs

@@ -0,0 +1,12 @@
+// run-pass
+#![feature(const_type_id)]
+#![feature(const_trait_impl)]
+
+use std::any::TypeId;
+
+const fn main() {
+    assert!(TypeId::of::<u8>() == TypeId::of::<u8>());
+    assert!(TypeId::of::<()>() != TypeId::of::<u8>());
+    const _A: bool = TypeId::of::<u8>() < TypeId::of::<u16>();
+    // can't assert `_A` because it is not deterministic
+}

tests/ui/consts/issue-73976-monomorphic.rs

@@ -7,6 +7,7 @@
 
 #![feature(const_type_id)]
 #![feature(const_type_name)]
+#![feature(const_trait_impl)]
 
 use std::any::{self, TypeId};
 
@@ -17,7 +18,7 @@ impl<T: 'static> GetTypeId<T> {
 }
 
 const fn check_type_id<T: 'static>() -> bool {
-    matches!(GetTypeId::<T>::VALUE, GetTypeId::<usize>::VALUE)
+    GetTypeId::<T>::VALUE == GetTypeId::<usize>::VALUE
 }
 
 pub struct GetTypeNameLen<T>(T);