Updating lints page to reflect recent changes

src/doc/rustc/src/lints/index.md

@@ -39,19 +39,32 @@ provides detailed information and an opportunity for feedback. This gives
 users some time to fix the code to accommodate the change. After some time,
 the warning may become an error.
 
-The following is an example of what a future-incompatible looks like:
-
-```text
-warning: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
- --> lint_example.rs:11:13
- |
-11 | let y = &x.data.0;
- | ^^^^^^^^^
- |
- = note: `#[warn(safe_packed_borrows)]` on by default
- = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
- = note: for more information, see issue #46043 <https://github.com/rust-lang/rust/issues/46043>
- = note: fields of packed structs might be misaligned: dereferencing a misaligned pointer or even just creating a misaligned reference is undefined behavior
+The following is an example of what future-incompatible code looks like:
+
+```bash
+$ cat main.rs
+#[repr(packed)]
+struct Packed {
+ f1: u8,
+ f2: u16,
+}
+
+fn main() {
+ let packed = Packed { f1: 1, f2: 2 };
+ let _ = &packed.f2; // This line triggers the warning
+}
+
+$ rustc main.rs
+
+error[E0793]: reference to packed field is unaligned
+ --> src/main.rs:9:13
+ |
+9 | let _ = &packed.f2; // This line triggers the warning
+ | ^^^^^^^^^^
+ |
+ = note: packed structs are only aligned by one byte, and many modern architectures penalize unaligned field accesses
+ = note: creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+ = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
 ```
 
 For more information about the process and policy of future-incompatible