Auto merge of #102513 - RalfJung:no-more-unaligned-reference, r=cjgillot,scottmcm

make unaligned_reference a hard error

The `unaligned_references` lint has been warn-by-default since Rust 1.53 (https://github.com/rust-lang/rust/pull/82525) and deny-by-default with mention in cargo future-incompat reports since Rust 1.62 (https://github.com/rust-lang/rust/pull/95372). Current nightly will become Rust 1.66, so (unless major surprises show up with crater) I think it is time we make this a hard error, and close this old soundness gap in the language.

EDIT: Turns out this will only land for Rust 1.67, so there is another 6 weeks of time here for crates to adjust.

Fixes https://github.com/rust-lang/rust/issues/82523.

1 files changed, 17 insertions, 26 deletions

diff --git a/compiler/rustc_mir_transform/src/check_packed_ref.rs b/compiler/rustc_mir_transform/src/check_packed_ref.rs
index 3e7571aa7a2..9dc8dba23a4 100644
--- a/compiler/rustc_mir_transform/src/check_packed_ref.rs
+++ b/compiler/rustc_mir_transform/src/check_packed_ref.rs
@@ -1,7 +1,7 @@
+use rustc_errors::struct_span_err;
 use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, TyCtxt};
-use rustc_session::lint::builtin::UNALIGNED_REFERENCES;
 
 use crate::util;
 use crate::MirLint;
@@ -49,31 +49,22 @@ impl<'tcx> Visitor<'tcx> for PackedRefChecker<'_, 'tcx> {
                     // shouldn't do.
                     unreachable!();
                 } else {
-                    let source_info = self.source_info;
-                    let lint_root = self.body.source_scopes[source_info.scope]
-                        .local_data
-                        .as_ref()
-                        .assert_crate_local()
-                        .lint_root;
-                    self.tcx.struct_span_lint_hir(
-                        UNALIGNED_REFERENCES,
-                        lint_root,
-                        source_info.span,
-                        "reference to packed field is unaligned",
-                        |lint| {
-                            lint
-                                .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)"
-                                )
-                        },
-                    );
+                    struct_span_err!(
+                        self.tcx.sess,
+                        self.source_info.span,
+                        E0793,
+                        "reference to packed field is unaligned"
+                    )
+                    .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)"
+                    )
+                    .emit();
                 }
             }
         }