Remove constants section as it is outdated

src/SUMMARY.md

@@ -142,7 +142,6 @@
     - [`EarlyBinder` and instantiating parameters](./ty_module/early_binder.md)
     - [`Binder` and Higher ranked regions](./ty_module/binders.md)
     - [Instantiating binders](./ty_module/instantiating_binders.md)
-    - [Constants in the type system](./constants.md)
 - [`TypeFolder` and `TypeFoldable`](./ty-fold.md)
 - [Parameter Environments](./param_env/param_env_summary.md)
     - [What is it?](./param_env/param_env_what_is_it.md)

src/constants.md

@@ -1,82 +0,0 @@
-# Constants in the type system
-
-Constants used in the type system are represented as [`ty::Const`].
-The variants of their [`const_kind::ConstKind`] mostly mirror the variants of [`ty_kind::TyKind`]
-with the two *additional* variants being `ConstKind::Value` and `ConstKind::Unevaluated`.
-
-## `WithOptConstParam` and dealing with the query system
-
-To typecheck constants used in the type system, we have to know their expected type.
-For const arguments in type dependent paths, e.g. `x.foo::<{ 3 + 4 }>()`, we don't know
-the expected type for `{ 3 + 4 }` until we are typechecking the containing function.
-
-As we may however have to evaluate that constant during this typecheck, we would get a cycle error.
-For more details, you can look at [this document](https://hackmd.io/@rust-const-generics/Bk5GHW-Iq).
-
-## Unevaluated constants
-
-*This section talks about what's happening with `feature(generic_const_exprs)` enabled.
-On stable we do not yet supply any generic parameters to anonymous constants,
-avoiding most of the issues mentioned here.*
-
-Unless a constant is either a simple literal, e.g. `[u8; 3]` or `foo::<{ 'c' }>()`,
-or a generic parameter, e.g. `[u8; N]`, converting a constant to its [`ty::Const`] representation
-returns an unevaluated constant. Even fully concrete constants which do not depend on
-generic parameters are not evaluated right away.
-
-Anonymous constants are typechecked separately from their containing item, e.g.
-```rust
-fn foo<const N: usize>() -> [u8; N + 1] {
-    [0; N + 1]
-}
-```
-is treated as
-```rust
-const ANON_CONST_1<const N: usize> = N + 1;
-const ANON_CONST_2<const N: usize> = N + 1;
-fn foo<const N: usize>() -> [u8; ANON_CONST_1::<N>] {
-    [0; ANON_CONST_2::<N>]
-}
-```
-
-### Unifying constants
-
-For the compiler, `ANON_CONST_1` and `ANON_CONST_2` are completely different, so
-we have to somehow look into unevaluated constants to check whether they should
-unify.
-
-For this we use [InferCtxt::try_unify_abstract_consts](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/infer/struct.InferCtxt.html#method.try_unify_abstract_consts).
-This builds a custom AST for the two inputs from their THIR. This is then used for
-the actual comparison.
-
-### Lazy normalization for constants
-
-We do not eagerly evaluate constant as they can be used in the `where`-clauses of their
-parent item, for example:
-
-```rust
-#[feature(generic_const_exprs)]
-fn foo<T: Trait>()
-where
-    [u8; <T as  Trait>::ASSOC + 1]: SomeOtherTrait,
-{}
-```
-
-The constant `<T as  Trait>::ASSOC + 1` depends on the `T: Trait` bound of
-its parents caller bounds, but is also part of another bound itself.
-If we were to eagerly evaluate this constant while computing its parents bounds
-this would cause a query cycle.
-
-### Unused generic arguments of anonymous constants
-
-Anonymous constants inherit the generic parameters of their parent, which is
-why the array length in `foo<const N: usize>() -> [u8; N + 1]` can use `N`.
-
-Without any manual adjustments, this causes us to include parameters even if
-the constant doesn't use them in any way. This can cause
-[some interesting errors][pcg-unused-substs] and breaks some already stable code.
-
-[`ty::Const`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Const.html
-[`const_kind::ConstKind`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_type_ir/const_kind/enum.ConstKind.html
-[`ty_kind::TyKind`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_type_ir/ty_kind/enum.TyKind.html
-[pcg-unused-substs]: https://github.com/rust-lang/project-const-generics/issues/33