Rollup merge of #142743 - tshepang:rdg-push, r=jieyouxu

rustc-dev-guide subtree update

r? `@ghost`

Author: Kobzol

src/doc/rustc-dev-guide/rust-version

@@ -1 +1 @@
-14346303d760027e53214e705109a62c0f00b214
+d1d8e386c5e84c4ba857f56c3291f73c27e2d62a

src/doc/rustc-dev-guide/src/SUMMARY.md

@@ -101,6 +101,8 @@
 	- [The `rustdoc` test suite](./rustdoc-internals/rustdoc-test-suite.md)
 	- [The `rustdoc-gui` test suite](./rustdoc-internals/rustdoc-gui-test-suite.md)
 	- [The `rustdoc-json` test suite](./rustdoc-internals/rustdoc-json-test-suite.md)
+- [GPU offload internals](./offload/internals.md)
+    - [Installation](./offload/installation.md)
 - [Autodiff internals](./autodiff/internals.md)
     - [Installation](./autodiff/installation.md)
     - [How to debug](./autodiff/debugging.md)
@@ -121,8 +123,9 @@
     - [Feature gate checking](./feature-gate-ck.md)
     - [Lang Items](./lang-items.md)
 - [The HIR (High-level IR)](./hir.md)
-    - [Lowering AST to HIR](./ast-lowering.md)
-    - [Debugging](./hir-debugging.md)
+    - [Lowering AST to HIR](./hir/lowering.md)
+    - [Ambig/Unambig Types and Consts](./hir/ambig-unambig-ty-and-consts.md)
+    - [Debugging](./hir/debugging.md)
 - [The THIR (Typed High-level IR)](./thir.md)
 - [The MIR (Mid-level IR)](./mir/index.md)
     - [MIR construction](./mir/construction.md)
@@ -181,15 +184,15 @@
         - [Significant changes and quirks](./solve/significant-changes.md)
     - [`Unsize` and `CoerceUnsized` traits](./traits/unsize.md)
 - [Type checking](./type-checking.md)
-    - [Method Lookup](./method-lookup.md)
+    - [Method lookup](./method-lookup.md)
     - [Variance](./variance.md)
     - [Coherence checking](./coherence.md)
     - [Opaque types](./opaque-types-type-alias-impl-trait.md)
         - [Inference details](./opaque-types-impl-trait-inference.md)
         - [Return Position Impl Trait In Trait](./return-position-impl-trait-in-trait.md)
         - [Region inference restrictions][opaque-infer]
 - [Const condition checking](./effects.md)
-- [Pattern and Exhaustiveness Checking](./pat-exhaustive-checking.md)
+- [Pattern and exhaustiveness checking](./pat-exhaustive-checking.md)
 - [Unsafety checking](./unsafety-checking.md)
 - [MIR dataflow](./mir/dataflow.md)
 - [Drop elaboration](./mir/drop-elaboration.md)
@@ -209,7 +212,7 @@
 - [Closure capture inference](./closure.md)
 - [Async closures/"coroutine-closures"](coroutine-closures.md)
 
-# MIR to Binaries
+# MIR to binaries
 
 - [Prologue](./part-5-intro.md)
 - [MIR optimizations](./mir/optimizations.md)
@@ -218,15 +221,15 @@
     - [Interpreter](./const-eval/interpret.md)
 - [Monomorphization](./backend/monomorph.md)
 - [Lowering MIR](./backend/lowering-mir.md)
-- [Code Generation](./backend/codegen.md)
+- [Code generation](./backend/codegen.md)
     - [Updating LLVM](./backend/updating-llvm.md)
     - [Debugging LLVM](./backend/debugging.md)
     - [Backend Agnostic Codegen](./backend/backend-agnostic.md)
-    - [Implicit Caller Location](./backend/implicit-caller-location.md)
-- [Libraries and Metadata](./backend/libs-and-metadata.md)
-- [Profile-guided Optimization](./profile-guided-optimization.md)
-- [LLVM Source-Based Code Coverage](./llvm-coverage-instrumentation.md)
-- [Sanitizers Support](./sanitizers.md)
+    - [Implicit caller location](./backend/implicit-caller-location.md)
+- [Libraries and metadata](./backend/libs-and-metadata.md)
+- [Profile-guided optimization](./profile-guided-optimization.md)
+- [LLVM source-based code coverage](./llvm-coverage-instrumentation.md)
+- [Sanitizers support](./sanitizers.md)
 - [Debugging support in the Rust compiler](./debugging-support-in-rustc.md)
 
 ---

src/doc/rustc-dev-guide/src/backend/implicit-caller-location.md

@@ -1,4 +1,4 @@
-# Implicit Caller Location
+# Implicit caller location
 
 <!-- toc -->
 
@@ -8,7 +8,7 @@ adds the [`#[track_caller]`][attr-reference] attribute for functions, the
 [`caller_location`][intrinsic] intrinsic, and the stabilization-friendly
 [`core::panic::Location::caller`][wrapper] wrapper.
 
-## Motivating Example
+## Motivating example
 
 Take this example program:
 
@@ -39,7 +39,7 @@ These error messages are achieved through a combination of changes to `panic!` i
 of `core::panic::Location::caller` and a number of `#[track_caller]` annotations in the standard
 library which propagate caller information.
 
-## Reading Caller Location
+## Reading caller location
 
 Previously, `panic!` made use of the `file!()`, `line!()`, and `column!()` macros to construct a
 [`Location`] pointing to where the panic occurred. These macros couldn't be given an overridden
@@ -51,7 +51,7 @@ was expanded. This function is itself annotated with `#[track_caller]` and wraps
 [`caller_location`][intrinsic] compiler intrinsic implemented by rustc. This intrinsic is easiest
 explained in terms of how it works in a `const` context.
 
-## Caller Location in `const`
+## Caller location in `const`
 
 There are two main phases to returning the caller location in a const context: walking up the stack
 to find the right location and allocating a const value to return.
@@ -138,7 +138,7 @@ fn main() {
 }
 ```
 
-### Dynamic Dispatch
+### Dynamic dispatch
 
 In codegen contexts we have to modify the callee ABI to pass this information down the stack, but
 the attribute expressly does *not* modify the type of the function. The ABI change must be
@@ -156,7 +156,7 @@ probably the best we can do without modifying fully-stabilized type signatures.
 > whether we'll be called in a const context (safe to ignore shim) or in a codegen context (unsafe
 > to ignore shim). Even if we did know, the results from const and codegen contexts must agree.
 
-## The Attribute
+## The attribute
 
 The `#[track_caller]` attribute is checked alongside other codegen attributes to ensure the
 function:

src/doc/rustc-dev-guide/src/backend/libs-and-metadata.md

@@ -1,4 +1,4 @@
-# Libraries and Metadata
+# Libraries and metadata
 
 When the compiler sees a reference to an external crate, it needs to load some
 information about that crate. This chapter gives an overview of that process,

src/doc/rustc-dev-guide/src/building/new-target.md

@@ -174,8 +174,8 @@ compiler, you can use it instead of the JSON file for both arguments.
 ## Promoting a target from tier 2 (target) to tier 2 (host)
 
 There are two levels of tier 2 targets:
-  a) Targets that are only cross-compiled (`rustup target add`)
-  b) Targets that [have a native toolchain][tier2-native] (`rustup toolchain install`)
+- Targets that are only cross-compiled (`rustup target add`)
+- Targets that [have a native toolchain][tier2-native] (`rustup toolchain install`)
 
 [tier2-native]: https://doc.rust-lang.org/nightly/rustc/target-tier-policy.html#tier-2-with-host-tools
 

src/doc/rustc-dev-guide/src/contributing.md

@@ -364,7 +364,7 @@ To find documentation-related issues, use the [A-docs label].
 
 You can find documentation style guidelines in [RFC 1574].
 
-To build the standard library documentation, use `x doc --stage 0 library --open`.
+To build the standard library documentation, use `x doc --stage 1 library --open`.
 To build the documentation for a book (e.g. the unstable book), use `x doc src/doc/unstable-book.`
 Results should appear in `build/host/doc`, as well as automatically open in your default browser.
 See [Building Documentation](./building/compiler-documenting.md#building-documentation) for more

src/doc/rustc-dev-guide/src/diagnostics.md

@@ -553,7 +553,7 @@ compiler](#linting-early-in-the-compiler).
 
 
 [AST nodes]: the-parser.md
-[AST lowering]: ast-lowering.md
+[AST lowering]: ./hir/lowering.md
 [HIR nodes]: hir.md
 [MIR nodes]: mir/index.md
 [macro expansion]: macro-expansion.md

src/doc/rustc-dev-guide/src/hir.md

@@ -5,7 +5,7 @@
 The HIR – "High-Level Intermediate Representation" – is the primary IR used
 in most of rustc. It is a compiler-friendly representation of the abstract
 syntax tree (AST) that is generated after parsing, macro expansion, and name
-resolution (see [Lowering](./ast-lowering.html) for how the HIR is created).
+resolution (see [Lowering](./hir/lowering.md) for how the HIR is created).
 Many parts of HIR resemble Rust surface syntax quite closely, with
 the exception that some of Rust's expression forms have been desugared away.
 For example, `for` loops are converted into a `loop` and do not appear in

src/doc/rustc-dev-guide/src/hir/ambig-unambig-ty-and-consts.md

@@ -0,0 +1,63 @@
+# Ambig/Unambig Types and Consts
+
+Types and Consts args in the HIR can be in two kinds of positions ambiguous (ambig) or unambiguous (unambig). Ambig positions are where
+it would be valid to parse either a type or a const, unambig positions are where only one kind would be valid to
+parse.
+
+```rust
+fn func<T, const N: usize>(arg: T) {
+    //                           ^ Unambig type position
+    let a: _ = arg; 
+    //     ^ Unambig type position
+
+    func::<T, N>(arg);
+    //     ^  ^
+    //     ^^^^ Ambig position 
+
+    let _: [u8; 10];
+    //      ^^  ^^ Unambig const position
+    //      ^^ Unambig type position
+}
+
+```
+
+Most types/consts in ambig positions are able to be disambiguated as either a type or const during parsing. Single segment paths are always represented as types in the AST but may get resolved to a const parameter during name resolution, then lowered to a const argument during ast-lowering. The only generic arguments which remain ambiguous after lowering are inferred generic arguments (`_`) in path segments. For example, in `Foo<_>` it is not clear whether the `_` argument is an inferred type argument, or an inferred const argument.
+
+In unambig positions, inferred arguments are represented with [`hir::TyKind::Infer`][ty_infer] or [`hir::ConstArgKind::Infer`][const_infer] depending on whether it is a type or const position respectively.
+In ambig positions, inferred arguments are represented with `hir::GenericArg::Infer`.
+
+A naive implementation of this would result in there being potentially 5 places where you might think an inferred type/const could be found in the HIR from looking at the structure of the HIR:
+1. In unambig type position as a `hir::TyKind::Infer`
+2. In unambig const arg position as a `hir::ConstArgKind::Infer`
+3. In an ambig position as a [`GenericArg::Type(TyKind::Infer)`][generic_arg_ty]
+4. In an ambig position as a [`GenericArg::Const(ConstArgKind::Infer)`][generic_arg_const]
+5. In an ambig position as a [`GenericArg::Infer`][generic_arg_infer]
+
+Note that places 3 and 4 would never actually be possible to encounter as we always lower to `GenericArg::Infer` in generic arg position. 
+
+This has a few failure modes:
+- People may write visitors which check for `GenericArg::Infer` but forget to check for `hir::TyKind/ConstArgKind::Infer`, only handling infers in ambig positions by accident.
+- People may write visitors which check for `hir::TyKind/ConstArgKind::Infer` but forget to check for `GenericArg::Infer`, only handling infers in unambig positions by accident.
+- People may write visitors which check for `GenerArg::Type/Const(TyKind/ConstArgKind::Infer)` and `GenerigArg::Infer`, not realising that we never represent inferred types/consts in ambig positions as a `GenericArg::Type/Const`.
+- People may write visitors which check for *only* `TyKind::Infer` and not `ConstArgKind::Infer` forgetting that there are also inferred const arguments (and vice versa).
+
+To make writing HIR visitors less error prone when caring about inferred types/consts we have a relatively complex system:
+
+1. We have different types in the compiler for when a type or const is in an unambig or ambig position, `hir::Ty<AmbigArg>` and `hir::Ty<()>`. [`AmbigArg`][ambig_arg] is an uninhabited type which we use in the `Infer` variant of `TyKind` and `ConstArgKind` to selectively "disable" it if we are in an ambig position.
+
+2. The [`visit_ty`][visit_ty] and [`visit_const_arg`][visit_const_arg] methods on HIR visitors only accept the ambig position versions of types/consts. Unambig types/consts are implicitly converted to ambig types/consts during the visiting process, with the `Infer` variant handled by a dedicated [`visit_infer`][visit_infer] method.
+
+This has a number of benefits:
+- It's clear that `GenericArg::Type/Const` cannot represent inferred type/const arguments
+- Implementors of `visit_ty` and `visit_const_arg` will never encounter inferred types/consts making it impossible to write a visitor that seems to work right but handles edge cases wrong 
+- The `visit_infer` method handles *all* cases of inferred type/consts in the HIR making it easy for visitors to handle inferred type/consts in one dedicated place and not forget cases
+
+[ty_infer]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.TyKind.html#variant.Infer
+[const_infer]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.ConstArgKind.html#variant.Infer
+[generic_arg_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.GenericArg.html#variant.Type
+[generic_arg_const]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.GenericArg.html#variant.Const
+[generic_arg_infer]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.GenericArg.html#variant.Infer
+[ambig_arg]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/hir/enum.AmbigArg.html
+[visit_ty]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/intravisit/trait.Visitor.html#method.visit_ty
+[visit_const_arg]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/intravisit/trait.Visitor.html#method.visit_const_arg
+[visit_infer]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_hir/intravisit/trait.Visitor.html#method.visit_infer