Reviews

Author: BoxyUwU

src/ty.md

@@ -10,8 +10,7 @@ The `ty` module defines how the Rust compiler represents types internally. It al
 When we talk about how rustc represents types,  we usually refer to a type called `Ty` . There are
 quite a few modules and types for `Ty` in the compiler ([Ty documentation][ty]).
 
-[ty]: https://doc.rust-lang.org/nightly/nightly-rustc/ru
-]stc_middle/ty/index.html
+[ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/index.html
 
 The specific `Ty` we are referring to is [`rustc_middle::ty::Ty`][ty_ty] (and not
 [`rustc_hir::Ty`][hir_ty]). The distinction is important, so we will discuss it first before going

src/ty_module/binders.md

@@ -44,7 +44,7 @@ Binder(
     &[BoundVariarbleKind::Region(...)],
 )
 ```
-This would cause all kinds of issues as the region `'^1_0` refers to a binder at a higher level than the outtermost binder i.e. it is an escaping bound var. The `'^1` region (also writeable as `'^0_1`) is also ill formed as the binder it refers to does not introduce a second parameter. Modern day rustc will ICE when constructing this binder due to both of those regions, in the past we would have simply allowed this to work and then ran into issues in other parts of the codebase. 
+This would cause all kinds of issues as the region `'^1_0` refers to a binder at a higher level than the outermost binder i.e. it is an escaping bound var. The `'^1` region (also writeable as `'^0_1`) is also ill formed as the binder it refers to does not introduce a second parameter. Modern day rustc will ICE when constructing this binder due to both of those regions, in the past we would have simply allowed this to work and then ran into issues in other parts of the codebase. 
 
 [`Binder`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Binder.html
 [`BoundVar]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.BoundVar.html

src/ty_module/early_binder.md

@@ -10,7 +10,7 @@ fn main() {
 }
 ```
 
-When type checking `main` we cannot just naively look at the return type of `foo` and assign the type `T` to the variable `a`, after all the function `main` does not define any generic parameters, `T` is completely meaningless in this context. More generally whenever an item introduces (binds) generic parameters, when accessing types inside the item from outside, the generic parameters must be instantiated with values from the outer item.
+When type checking `main` we cannot just naively look at the return type of `foo` and assign the type `T` to the variable `c`, after all the function `main` does not define any generic parameters, `T` is completely meaningless in this context. More generally whenever an item introduces (binds) generic parameters, when accessing types inside the item from outside, the generic parameters must be instantiated with values from the outer item.
 
 In rustc we track this via the [`EarlyBinder`] type, the return type of `foo` is represented as an `EarlyBinder<Ty>` with the only way to acess `Ty` being to provide arguments for any generic parameters `Ty` might be using. This is implemented via the [`EarlyBinder::instantiate`] method which discharges the binder returning the inner value with all the generic parameters replaced by the provided arguments.
 

src/ty_module/generic_arguments.md

@@ -1,5 +1,7 @@
 # ADTs and Generic Arguments
 
+The term `ADT` stands for "Algebraic data type", in rust this refers to a struct, enum, or union.
+
 ## ADTs Representation
 
 Let's consider the example of a type like `MyStruct<u32>`, where `MyStruct` is defined like so:
@@ -123,4 +125,4 @@ For the `MyStruct<U>` written in the `Foo` type alias, we would represent it in
 
 - There would be an `AdtDef` (and corresponding `DefId`) for `MyStruct`.
 - There would be a `GenericArgs` containing the list `[GenericArgKind::Type(Ty(u32))]`
-- This is one `TyKind::Adt` containing the `AdtDef` of `MyStruct` with the `GenericArgs` above.
+- And finally a `TyKind::Adt` with the `AdtDef` and `GenericArgs` listed above.

src/ty_module/instantiating_binders.md

@@ -34,7 +34,7 @@ Instantiating binders with inference variables can be accomplished by using the
 
 ## Instantiating with placeholders
 
-Placeholders are very similar to `Ty/ConstKind::Param`/`ReEarlyParam`, they represent some unknown type that is only equal to itself. `Ty`/`Const` and `Region` all have a `Placeholder` variant that is comprised of a `Universe` and a `BoundVar`. 
+Placeholders are very similar to `Ty/ConstKind::Param`/`ReEarlyParam`, they represent some unknown type that is only equal to itself. `Ty`/`Const` and `Region` all have a [`Placeholder`] variant that is comprised of a [`Universe`] and a [`BoundVar`]. 
 
 The `Universe` tracks which binder the placeholder originated from, and the `BoundVar` tracks which parameter on said binder that this placeholder corresponds to. Equality of placeholders is determined solely by whether the universes are equal and the `BoundVar`s are equal. See the [chapter on Placeholders and Universes][ch_placeholders_universes] for more information.
 
@@ -139,4 +139,7 @@ As a concrete example, accessing the signature of a function we are type checkin
 [`instantiate_binder_with_fresh_vars`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/struct.InferCtxt.html#method.instantiate_binder_with_fresh_vars
 [`InferCtxt`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_trait_selection/infer/struct.InferCtxt.html
 [`EarlyBinder`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.EarlyBinder.html
-[`Binder`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/type.Binder.html
+[`Binder`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/type.Binder.html
+[`Placeholder`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Placeholder.html
+[`Universe`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.UniverseIndex.html
+[`BoundVar`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.BoundVar.html

src/ty_module/param_ty_const_regions.md

@@ -31,7 +31,7 @@ struct Foo<T>(Vec<T>);
 The `Vec<T>` type is represented as `TyKind::Adt(Vec, &[GenericArgKind::Type(Param("T", 0))])`.
 
 The name is somewhat self explanatory, it's the name of the type parameter. The index of the type parameter is an integer indicating
-its order in the list of generic parameters in scope (note: this includes parameters defined on items on outter scopes than the item the parameter is defined on). Consider the following examples:
+its order in the list of generic parameters in scope (note: this includes parameters defined on items on outer scopes than the item the parameter is defined on). Consider the following examples:
 
 ```rust,ignore
 struct Foo<A, B> {
@@ -50,7 +50,7 @@ impl<X, Y> Foo<X, Y> {
 }
 ```
 
-Concretely given the `ty::Generics` for the item the parameter is defined on, if the index is `10` then starting from the root `parent`, it will be the eleventh parameter to be introduced.
+Concretely given the `ty::Generics` for the item the parameter is defined on, if the index is `2` then starting from the root `parent`, it will be the third parameter to be introduced. For example in the above example, `Z` has index `2` and is the third generic parameter to be introduced, starting from the `impl` block. 
 
 The index fully defines the `Ty` and is the only part of `TyKind::Param` that matters for reasoning about the code we are compiling. 
 

src/what_is_ty_generics.md

@@ -10,9 +10,12 @@ trait Trait<T> {
 
 The `ty::Generics` used for `foo` would contain `[U]` and a parent of `Some(Trait)`. `Trait` would have a `ty::Generics` containing `[Self, T]` with a parent of `None`.
 
-The [`GenericParamDef`] struct is used to represent each individual generic parameter in a `ty::Generics` listing. The `GenericParamDef` struct contains information about the generic parameter, for example its name, defid, what kind of parameter it is (i.e. type, const, lifetime). It also contains a `u32` index representing what position the parameter is (starting from the outtermost parent).
+The [`GenericParamDef`] struct is used to represent each individual generic parameter in a `ty::Generics` listing. The `GenericParamDef` struct contains information about the generic parameter, for example its name, defid, what kind of parameter it is (i.e. type, const, lifetime). 
+
+`GenericParamDef` also contains a `u32` index representing what position the parameter is (starting from the outermost parent), this is the value used to represent usages of generic parameters (more on this in the [chapter on representing types][ch_representing_types]).
 
 Interestingly, `ty::Generics` does not currently contain _every_ generic parameter defined on an item. In the case of functions it only contains the _early bound_ lifetime parameters. See the next chapter for information on what "early bound" and "late bound" parameters are.
 
+[ch_representing_types]: ./ty.md
 [`ty::Generics`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Generics.html
 [`GenericParamDef`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/generics/struct.GenericParamDef.html