Auto merge of rust-lang#109497 - matthiaskrgr:rollup-6txuxm0, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - rust-lang#109373 (Set LLVM `LLVM_UNREACHABLE_OPTIMIZE` to `OFF`)
 - rust-lang#109392 (Custom MIR: Allow optional RET type annotation)
 - rust-lang#109394 (adapt tests/codegen/vec-shrink-panik for LLVM 17)
 - rust-lang#109412 (rustdoc: Add GUI test for "Auto-hide item contents for large items" setting)
 - rust-lang#109452 (Ignore the vendor directory for tidy tests.)
 - rust-lang#109457 (Remove comment about reusing rib allocations)
 - rust-lang#109461 (rustdoc: remove redundant `.content` prefix from span/a colors)
 - rust-lang#109477 (`HirId` to `LocalDefId` cleanup)
 - rust-lang#109489 (More general captures)
 - rust-lang#109494 (Do not feed param_env for RPITITs impl side)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

core/src/intrinsics/mir.rs

@@ -49,6 +49,8 @@
 //!
 //! The input to the [`mir!`] macro is:
 //!
+//!  - An optional return type annotation in the form of `type RET = ...;`. This may be required
+//!    if the compiler cannot infer the type of RET.
 //!  - A possibly empty list of local declarations. Locals can also be declared inline on
 //!    assignments via `let`. Type inference generally works. Shadowing does not.
 //!  - A list of basic blocks. The first of these is the start block and is where execution begins.
@@ -124,6 +126,18 @@
 //!         }
 //!     )
 //! }
+//!
+//! #[custom_mir(dialect = "runtime", phase = "optimized")]
+//! fn annotated_return_type() -> (i32, bool) {
+//!     mir!(
+//!         type RET = (i32, bool);
+//!         {
+//!             RET.0 = 1;
+//!             RET.1 = true;
+//!             Return()
+//!         }
+//!     )
+//! }
 //! ```
 //!
 //! We can also set off compilation failures that happen in sufficiently late stages of the
@@ -342,6 +356,7 @@ define!(
 #[rustc_macro_transparency = "transparent"]
 pub macro mir {
     (
+        $(type RET = $ret_ty:ty ;)?
         $(let $local_decl:ident $(: $local_decl_ty:ty)? ;)*
 
         {
@@ -362,7 +377,7 @@ pub macro mir {
         {
             // Now all locals
             #[allow(non_snake_case)]
-            let RET;
+            let RET $(: $ret_ty)?;
             $(
                 let $local_decl $(: $local_decl_ty)? ;
             )*