Auto merge of #107220 - JohnTitor:rollup-5pvuz0z, r=JohnTitor

Rollup of 7 pull requests

Successful merges:

 - #106796 (BPF: Disable atomic CAS)
 - #106886 (Make stage2 rustdoc and proc-macro-srv disableable in x.py install)
 - #107101 (Filter param-env predicates for errors before calling `to_opt_poly_trait_pred`)
 - #107109 (ThinBox: Add intra-doc-links for Metadata)
 - #107148 (remove error code from `E0789`, add UI test/docs)
 - #107151 (Instantiate dominators algorithm only once)
 - #107153 (Consistently use dominates instead of is_dominated_by)

Failed merges:

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

2 files changed, 31 insertions, 1 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index 9d5f4ad7520..4ae372bb904 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -506,6 +506,7 @@ E0785: include_str!("./error_codes/E0785.md"),
 E0786: include_str!("./error_codes/E0786.md"),
 E0787: include_str!("./error_codes/E0787.md"),
 E0788: include_str!("./error_codes/E0788.md"),
+E0789: include_str!("./error_codes/E0789.md"),
 E0790: include_str!("./error_codes/E0790.md"),
 E0791: include_str!("./error_codes/E0791.md"),
 E0792: include_str!("./error_codes/E0792.md"),
@@ -645,5 +646,4 @@ E0792: include_str!("./error_codes/E0792.md"),
 //  E0721, // `await` keyword
 //  E0723, // unstable feature in `const` context
 //  E0738, // Removed; errored on `#[track_caller] fn`s in `extern "Rust" { ... }`.
-    E0789, // rustc_allowed_through_unstable_modules without stability attribute
 }
diff --git a/compiler/rustc_error_codes/src/error_codes/E0789.md b/compiler/rustc_error_codes/src/error_codes/E0789.md
new file mode 100644
index 00000000000..89b7cd422fe
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0789.md
@@ -0,0 +1,30 @@
+#### This error code is internal to the compiler and will not be emitted with normal Rust code.
+
+The internal `rustc_allowed_through_unstable_modules` attribute must be used
+on an item with a `stable` attribute.
+
+Erroneous code example:
+
+```compile_fail,E0789
+// NOTE: both of these attributes are perma-unstable and should *never* be
+//       used outside of the compiler and standard library.
+#![feature(rustc_attrs)]
+#![feature(staged_api)]
+
+#![unstable(feature = "foo_module", reason = "...", issue = "123")]
+
+#[rustc_allowed_through_unstable_modules]
+// #[stable(feature = "foo", since = "1.0")]
+struct Foo;
+// ^^^ error: `rustc_allowed_through_unstable_modules` attribute must be
+//            paired with a `stable` attribute
+```
+
+Typically when an item is marked with a `stable` attribute, the modules that
+enclose the item must also be marked with `stable` attributes, otherwise the
+item becomes *de facto* unstable. `#[rustc_allowed_through_unstable_modules]`
+is a workaround which allows an item to "escape" its unstable parent modules.
+This error occurs when an item is marked with
+`#[rustc_allowed_through_unstable_modules]` but no supplementary `stable`
+attribute exists. See [#99288](https://github.com/rust-lang/rust/pull/99288)
+for an example of `#[rustc_allowed_through_unstable_modules]` in use.