From bdc191cd22ce3aa80a4dfe2cfc672f8d3212b518 Mon Sep 17 00:00:00 2001
From: khyperia <953151+khyperia@users.noreply.github.com>
Date: Sat, 28 Mar 2026 10:36:14 +0100
Subject: [PATCH 1/2] Explain how nested generic args are represented

---
 src/ty-module/generic-arguments.md | 32 ++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/src/ty-module/generic-arguments.md b/src/ty-module/generic-arguments.md
index 3339d31142..3d6124c2ec 100644
--- a/src/ty-module/generic-arguments.md
+++ b/src/ty-module/generic-arguments.md
@@ -126,3 +126,35 @@ 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))]`
 - And finally a `TyKind::Adt` with the `AdtDef` and `GenericArgs` listed above.
+
+## Nested generic args
+
+```rust
+struct MyStruct<T>(T);
+
+impl<T> MyStruct<T> {
+    fn func<T2, T3>() {}
+}
+
+fn main() {
+    MyStruct::<u32>::func::<bool, char>();
+}
+```
+
+The construct `MyStruct::<u32>::func::<bool, char>` is represented by a tuple: a DefId pointing at `func`, and then a
+`GenericArgs` list that "walks" all containing generic parameters - in this case, the list would be `[u32, bool, char]`.
+
+The [`ty::Generics`] type (returned by the [`generics_of`] query) contains the information of how a nested hierarchy
+gets flattened down to a list, and lets you figure out which index in the `GenericArgs` list corresponds to which
+generic. The general theme of how it works is outermost to innermost (`T` before `T2` in the example), left to right
+(`T2` before `T3`), but there are several complications:
+
+- `Self` is sometimes a generic parameter, and should sometimes be included in the list.
+- Only early-bound generic parameters are included, [late-bound generics] are not.
+- ... and more...
+
+Check out [`ty::Generics`] for exact specifics on how the flattening works.
+
+[`ty::Generics`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.Generics.html
+[`generics_of`]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_middle/ty/struct.TyCtxt.html#method.generics_of
+[late-bound generics]: ../early-late-parameters.md

From 383636a98b771a41fbac96b1c0344966a4fe9c0d Mon Sep 17 00:00:00 2001
From: Boxy <rust@boxyuwu.dev>
Date: Mon, 30 Mar 2026 11:20:31 +0100
Subject: [PATCH 2/2] reword `Self` parameter bullet point

---
 src/ty-module/generic-arguments.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ty-module/generic-arguments.md b/src/ty-module/generic-arguments.md
index 3d6124c2ec..cbf7b2c682 100644
--- a/src/ty-module/generic-arguments.md
+++ b/src/ty-module/generic-arguments.md
@@ -149,7 +149,7 @@ gets flattened down to a list, and lets you figure out which index in the `Gener
 generic. The general theme of how it works is outermost to innermost (`T` before `T2` in the example), left to right
 (`T2` before `T3`), but there are several complications:
 
-- `Self` is sometimes a generic parameter, and should sometimes be included in the list.
+- Traits have an implicit `Self` generic parameter which is the first (i.e. 0th) generic parameter. Note that `Self` doesn't mean a generic parameter in all situations, see [Res::SelfTyAlias](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def/enum.Res.html#variant.SelfTyAlias) and [Res::SelfCtor](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/def/enum.Res.html#variant.SelfCtor).
 - Only early-bound generic parameters are included, [late-bound generics] are not.
 - ... and more...