Rollup merge of rust-lang#111670 - compiler-errors:const-param-ty, r=BoxyUwU

Require that const param tys implement `ConstParamTy`

1. Require that const param tys implement `ConstParamTy` instead of using `search_for_adt_const_param_violation`
2. Add `StructuralPartialEq` as a supertrait for `ConstParamTy`, since we need to make sure that we derive *both* `PartialEq` and `Eq`
3. Implement `ConstParamTy` for tuples up to 12 (or whatever the default for tuples is)
4. Add some custom diagnostics to `ConstParamTy` errors, to avoid regressions from (1.). It's still not as great as it could be -- will point out inline in comments.

r? `@BoxyUwU`

Author: compiler-errors

core/src/marker.rs

@@ -205,6 +205,20 @@ pub trait StructuralPartialEq {
     // Empty.
 }
 
+marker_impls! {
+    #[unstable(feature = "structural_match", issue = "31434")]
+    StructuralPartialEq for
+        usize, u8, u16, u32, u64, u128,
+        isize, i8, i16, i32, i64, i128,
+        bool,
+        char,
+        str /* Technically requires `[u8]: StructuralEq` */,
+        (),
+        {T, const N: usize} [T; N],
+        {T} [T],
+        {T: ?Sized} &T,
+}
+
 /// Required trait for constants used in pattern matches.
 ///
 /// Any type that derives `Eq` automatically implements this trait, *regardless*
@@ -267,6 +281,7 @@ marker_impls! {
         bool,
         char,
         str /* Technically requires `[u8]: StructuralEq` */,
+        (),
         {T, const N: usize} [T; N],
         {T} [T],
         {T: ?Sized} &T,
@@ -974,7 +989,8 @@ pub trait PointerLike {}
 #[lang = "const_param_ty"]
 #[unstable(feature = "adt_const_params", issue = "95174")]
 #[rustc_on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
-pub trait ConstParamTy: StructuralEq {}
+#[allow(multiple_supertrait_upcastable)]
+pub trait ConstParamTy: StructuralEq + StructuralPartialEq {}
 
 /// Derive macro generating an impl of the trait `ConstParamTy`.
 #[rustc_builtin_macro]
@@ -983,8 +999,7 @@ pub macro ConstParamTy($item:item) {
     /* compiler built-in */
 }
 
-// FIXME(generic_const_parameter_types): handle `ty::FnDef`/`ty::Closure`
-// FIXME(generic_const_parameter_types): handle `ty::Tuple`
+// FIXME(adt_const_params): handle `ty::FnDef`/`ty::Closure`
 marker_impls! {
     #[unstable(feature = "adt_const_params", issue = "95174")]
     ConstParamTy for
@@ -998,6 +1013,11 @@ marker_impls! {
         {T: ?Sized + ConstParamTy} &T,
 }
 
+// FIXME(adt_const_params): Add to marker_impls call above once not in bootstrap
+#[unstable(feature = "adt_const_params", issue = "95174")]
+#[cfg(not(bootstrap))]
+impl ConstParamTy for () {}
+
 /// A common trait implemented by all function pointers.
 #[unstable(
     feature = "fn_ptr_trait",

core/src/mem/transmutability.rs

@@ -1,3 +1,5 @@
+use crate::marker::ConstParamTy;
+
 /// Are values of a type transmutable into values of another type?
 ///
 /// This trait is implemented on-the-fly by the compiler for types `Src` and `Self` when the bits of
@@ -33,6 +35,9 @@ pub struct Assume {
     pub validity: bool,
 }
 
+#[unstable(feature = "transmutability", issue = "99571")]
+impl ConstParamTy for Assume {}
+
 impl Assume {
     /// Do not assume that *you* have ensured any safety properties are met.
     #[unstable(feature = "transmutability", issue = "99571")]

core/src/tuple.rs

@@ -1,6 +1,9 @@
 // See src/libstd/primitive_docs.rs for documentation.
 
 use crate::cmp::Ordering::{self, *};
+#[cfg(not(bootstrap))]
+use crate::marker::ConstParamTy;
+use crate::marker::{StructuralEq, StructuralPartialEq};
 
 // Recursive macro for implementing n-ary tuple functions and operations
 //
@@ -45,6 +48,28 @@ macro_rules! tuple_impls {
             {}
         }
 
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            #[cfg(not(bootstrap))]
+            impl<$($T: ConstParamTy),+> ConstParamTy for ($($T,)+)
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            impl<$($T),+> StructuralPartialEq for ($($T,)+)
+            {}
+        }
+
+        maybe_tuple_doc! {
+            $($T)+ @
+            #[unstable(feature = "structural_match", issue = "31434")]
+            impl<$($T),+> StructuralEq for ($($T,)+)
+            {}
+        }
+
         maybe_tuple_doc! {
             $($T)+ @
             #[stable(feature = "rust1", since = "1.0.0")]