make unaligned_reference warning visible in future compat report

compiler/rustc_lint_defs/src/builtin.rs

@@ -1141,6 +1141,7 @@ declare_lint! {
     "detects unaligned references to fields of packed structs",
     @future_incompatible = FutureIncompatibleInfo {
         reference: "issue #82523 <https://github.com/rust-lang/rust/issues/82523>",
+        reason: FutureIncompatibilityReason::FutureReleaseErrorReportNow,
     };
     report_in_external_macro
 }

src/test/ui/binding/issue-53114-safety-checks.stderr

@@ -102,3 +102,55 @@ LL |     match (&u2.a,) { (_,) => { } }
 error: aborting due to 11 previous errors
 
 For more information about this error, try `rustc --explain E0133`.
+Future incompatibility report: Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-53114-safety-checks.rs:23:13
+   |
+LL |     let _ = &p.b;
+   |             ^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-53114-safety-checks.rs:29:17
+   |
+LL |     let (_,) = (&p.b,);
+   |                 ^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-53114-safety-checks.rs:39:11
+   |
+LL |     match &p.b  { _ => { } }
+   |           ^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-53114-safety-checks.rs:45:12
+   |
+LL |     match (&p.b,)  { (_,) => { } }
+   |            ^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+

src/test/ui/closures/2229_closure_analysis/diagnostics/repr_packed.stderr

@@ -13,3 +13,17 @@ LL |         println!("{}", foo.x);
 
 error: aborting due to previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/repr_packed.rs:21:24
+   |
+LL |         println!("{}", foo.x);
+   |                        ^^^^^
+   |
+   = note: `#[deny(unaligned_references)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = help: copy the field contents to a local variable, or replace the reference with a raw pointer and use `read_unaligned`/`write_unaligned` (loads and stores via `*p` must be properly aligned even when using raw pointers)
+   = note: this error originates in the macro `$crate::format_args_nl` (in Nightly builds, run with -Z macro-backtrace for more info)
+

src/test/ui/derives/deriving-with-repr-packed.stderr

@@ -45,3 +45,67 @@ LL | #[derive(PartialEq)]
 
 error: aborting due to 4 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: `#[derive]` can't be used on a `#[repr(packed)]` struct with type or const parameters (error E0133)
+  --> $DIR/deriving-with-repr-packed.rs:8:16
+   |
+LL | #[derive(Copy, Clone, PartialEq, Eq)]
+   |                ^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deriving-with-repr-packed.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: this error originates in the derive macro `Clone` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+Future breakage diagnostic:
+error: `#[derive]` can't be used on a `#[repr(packed)]` struct with type or const parameters (error E0133)
+  --> $DIR/deriving-with-repr-packed.rs:8:23
+   |
+LL | #[derive(Copy, Clone, PartialEq, Eq)]
+   |                       ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deriving-with-repr-packed.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+Future breakage diagnostic:
+error: `#[derive]` can't be used on a `#[repr(packed)]` struct that does not derive Copy (error E0133)
+  --> $DIR/deriving-with-repr-packed.rs:16:10
+   |
+LL | #[derive(PartialEq, Eq)]
+   |          ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deriving-with-repr-packed.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+Future breakage diagnostic:
+error: `#[derive]` can't be used on a `#[repr(packed)]` struct that does not derive Copy (error E0133)
+  --> $DIR/deriving-with-repr-packed.rs:25:10
+   |
+LL | #[derive(PartialEq)]
+   |          ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/deriving-with-repr-packed.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: this error originates in the derive macro `PartialEq` (in Nightly builds, run with -Z macro-backtrace for more info)
+

src/test/ui/lint/unaligned_references.stderr

@@ -82,3 +82,122 @@ LL |         let _ = &packed2.x;
 
 error: aborting due to 7 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:22:17
+   |
+LL |         let _ = &good.ptr;
+   |                 ^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:24:17
+   |
+LL |         let _ = &good.data;
+   |                 ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:27:17
+   |
+LL |         let _ = &good.data as *const _;
+   |                 ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:29:27
+   |
+LL |         let _: *const _ = &good.data;
+   |                           ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:32:17
+   |
+LL |         let _ = good.data.clone();
+   |                 ^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:35:17
+   |
+LL |         let _ = &good.data2[0];
+   |                 ^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references.rs:45:17
+   |
+LL |         let _ = &packed2.x;
+   |                 ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references.rs:1:9
+   |
+LL | #![deny(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+

src/test/ui/lint/unaligned_references_external_macro.stderr

@@ -29,3 +29,33 @@ LL | | }
 
 error: aborting due to previous error
 
+Future incompatibility report: Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/unaligned_references_external_macro.rs:5:1
+   |
+LL | / unaligned_references_external_crate::mac! {
+LL | |
+LL | |     #[repr(packed)]
+LL | |     pub struct X {
+LL | |         pub field: u16
+LL | |     }
+LL | | }
+   | |_^
+   |
+note: the lint level is defined here
+  --> $DIR/unaligned_references_external_macro.rs:5:1
+   |
+LL | / unaligned_references_external_crate::mac! {
+LL | |
+LL | |     #[repr(packed)]
+LL | |     pub struct X {
+LL | |         pub field: u16
+LL | |     }
+LL | | }
+   | |_^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+   = note: this error originates in the macro `unaligned_references_external_crate::mac` (in Nightly builds, run with -Z macro-backtrace for more info)
+

src/test/ui/packed/issue-27060-rpass.stderr

@@ -0,0 +1,68 @@
+Future incompatibility report: Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/issue-27060-rpass.rs:15:13
+   |
+LL |     let _ = &good.data; // ok
+   |             ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-27060-rpass.rs:11:9
+   |
+LL | #[allow(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/issue-27060-rpass.rs:16:13
+   |
+LL |     let _ = &good.data2[0]; // ok
+   |             ^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-27060-rpass.rs:11:9
+   |
+LL | #[allow(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/issue-27060-rpass.rs:18:13
+   |
+LL |     let _ = &good.data;
+   |             ^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-27060-rpass.rs:11:9
+   |
+LL | #[allow(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/issue-27060-rpass.rs:19:13
+   |
+LL |     let _ = &good.data2[0];
+   |             ^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/issue-27060-rpass.rs:11:9
+   |
+LL | #[allow(unaligned_references)]
+   |         ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+

src/test/ui/packed/issue-27060.stderr

@@ -45,3 +45,55 @@ LL |     let _ = &good.data2[0];
 
 error: aborting due to 4 previous errors
 
+Future incompatibility report: Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-27060.rs:15:13
+   |
+LL |     let _ = &good.data;
+   |             ^^^^^^^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-27060.rs:17:13
+   |
+LL |     let _ = &good.data2[0];
+   |             ^^^^^^^^^^^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-27060.rs:20:13
+   |
+LL |     let _ = &good.data;
+   |             ^^^^^^^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+error: reference to packed field is unaligned
+  --> $DIR/issue-27060.rs:22:13
+   |
+LL |     let _ = &good.data2[0];
+   |             ^^^^^^^^^^^^^^
+   |
+   = note: `#[deny(unaligned_references)]` 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+

src/test/ui/packed/packed-struct-borrow-element-64bit.stderr

@@ -16,3 +16,20 @@ LL | #[warn(unaligned_references)]
 
 warning: 1 warning emitted
 
+Future incompatibility report: Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/packed-struct-borrow-element-64bit.rs:15:15
+   |
+LL |     let brw = &foo.baz;
+   |               ^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/packed-struct-borrow-element-64bit.rs:12:8
+   |
+LL | #[warn(unaligned_references)]
+   |        ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+

src/test/ui/packed/packed-struct-borrow-element.stderr

@@ -27,3 +27,37 @@ LL |     let brw = &foo.baz;
 
 warning: 2 warnings emitted
 
+Future incompatibility report: Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/packed-struct-borrow-element.rs:26:15
+   |
+LL |     let brw = &foo.baz;
+   |               ^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/packed-struct-borrow-element.rs:23:8
+   |
+LL | #[warn(unaligned_references)]
+   |        ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+
+Future breakage diagnostic:
+warning: reference to packed field is unaligned
+  --> $DIR/packed-struct-borrow-element.rs:31:15
+   |
+LL |     let brw = &foo.baz;
+   |               ^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/packed-struct-borrow-element.rs:23:8
+   |
+LL | #[warn(unaligned_references)]
+   |        ^^^^^^^^^^^^^^^^^^^^
+   = 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 #82523 <https://github.com/rust-lang/rust/issues/82523>
+   = note: fields of packed structs are not properly aligned, and 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)
+