Rollup merge of #117556 - obeis:static-mut-ref-lint, r=davidtwco

Disallow reference to `static mut` and adding `static_mut_ref` lint

Closes #114447

r? `@scottmcm`

2 files changed, 23 insertions, 0 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index 1028d43f9c5..a1391cceb71 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -515,6 +515,7 @@ E0792: include_str!("./error_codes/E0792.md"),
 E0793: include_str!("./error_codes/E0793.md"),
 E0794: include_str!("./error_codes/E0794.md"),
 E0795: include_str!("./error_codes/E0795.md"),
+E0796: include_str!("./error_codes/E0796.md"),
 }
 
 // Undocumented removed error codes. Note that many removed error codes are kept in the list above
diff --git a/compiler/rustc_error_codes/src/error_codes/E0796.md b/compiler/rustc_error_codes/src/error_codes/E0796.md
new file mode 100644
index 00000000000..cea18f8db85
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0796.md
@@ -0,0 +1,22 @@
+Reference of mutable static.
+
+Erroneous code example:
+
+```compile_fail,edition2024,E0796
+static mut X: i32 = 23;
+static mut Y: i32 = 24;
+
+unsafe {
+  let y = &X;
+  let ref x = X;
+  let (x, y) = (&X, &Y);
+  foo(&X);
+}
+
+fn foo<'a>(_x: &'a i32) {}
+```
+
+Mutable statics can be written to by multiple threads: aliasing violations or
+data races will cause undefined behavior.
+
+Reference of mutable static is a hard error from 2024 edition.