Prepare for removal of safe_packed_borrows lint

src/lib.rs

@@ -590,18 +590,25 @@ macro_rules! __pin_project_internal {
 
             // Ensure that it's impossible to use pin projections on a #[repr(packed)] struct.
             //
-            // Taking a reference to a packed field is unsafe, amd appplying
-            // #[forbid(safe_packed_borrows)] makes sure that doing this without
-            // an 'unsafe' block (which we deliberately do not generate)
-            // is a hard error.
+            // Taking a reference to a packed field is UB, and applying
+            // `#[forbid(unaligned_references)]` makes sure that doing this is a hard error.
             //
             // If the struct ends up having #[repr(packed)] applied somehow,
             // this will generate an (unfriendly) error message. Under all reasonable
             // circumstances, we'll detect the #[repr(packed)] attribute, and generate
             // a much nicer error above.
             //
             // See /~https://github.com/taiki-e/pin-project/pull/34 for more details.
-            #[forbid(safe_packed_borrows)]
+            //
+            // Note:
+            // - Lint-based tricks aren't perfect, but they're much better than nothing:
+            //   /~https://github.com/taiki-e/pin-project-lite/issues/26
+            //
+            // - Enable both unaligned_references and safe_packed_borrows lints
+            //   because unaligned_references lint does not exist in older compilers:
+            //   /~https://github.com/taiki-e/pin-project-lite/pull/55
+            //   /~https://github.com/rust-lang/rust/pull/82525
+            #[forbid(unaligned_references, safe_packed_borrows)]
             fn __assert_not_repr_packed <$($impl_generics)*> (this: &$ident <$($ty_generics)*>)
             $(where
                 $($where_clause)*)?

tests/expand/default/struct.expanded.rs

@@ -75,7 +75,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/expand/multifields/struct.expanded.rs

@@ -141,7 +141,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned1;
         let _ = &this.pinned2;

tests/expand/naming/struct-all.expanded.rs

@@ -108,7 +108,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/expand/naming/struct-mut.expanded.rs

@@ -75,7 +75,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/expand/naming/struct-none.expanded.rs

@@ -75,7 +75,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/expand/naming/struct-ref.expanded.rs

@@ -75,7 +75,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/expand/pub/struct.expanded.rs

@@ -75,7 +75,7 @@ const _: () = {
     #[allow(clippy::drop_bounds, drop_bounds)]
     impl<T: ::pin_project_lite::__private::Drop> MustNotImplDrop for T {}
     impl<T, U> MustNotImplDrop for Struct<T, U> {}
-    #[forbid(safe_packed_borrows)]
+    #[forbid(unaligned_references, safe_packed_borrows)]
     fn __assert_not_repr_packed<T, U>(this: &Struct<T, U>) {
         let _ = &this.pinned;
         let _ = &this.unpinned;

tests/ui/pin_project/packed.rs

@@ -1,16 +1,16 @@
 use pin_project_lite::pin_project;
 
-pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+pin_project! { //~ ERROR reference to packed field is unaligned
     #[repr(packed, C)]
-    struct A {
+    struct Packed {
         #[pin]
         field: u16,
     }
 }
 
-pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+pin_project! { //~ ERROR reference to packed field is unaligned
     #[repr(packed(2))]
-    struct C {
+    struct PackedN {
         #[pin]
         field: u32,
     }

tests/ui/pin_project/packed.stderr

@@ -1,9 +1,61 @@
+error: reference to packed field is unaligned
+ --> $DIR/packed.rs:3:1
+  |
+3 | / pin_project! { //~ ERROR reference to packed field is unaligned
+4 | |     #[repr(packed, C)]
+5 | |     struct Packed {
+6 | |         #[pin]
+7 | |         field: u16,
+8 | |     }
+9 | | }
+  | |_^
+  |
+note: the lint level is defined here
+ --> $DIR/packed.rs:3:1
+  |
+3 | / pin_project! { //~ ERROR reference to packed field is unaligned
+4 | |     #[repr(packed, C)]
+5 | |     struct Packed {
+6 | |         #[pin]
+7 | |         field: u16,
+8 | |     }
+9 | | }
+  | |_^
+  = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+  = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: reference to packed field is unaligned
+  --> $DIR/packed.rs:11:1
+   |
+11 | / pin_project! { //~ ERROR reference to packed field is unaligned
+12 | |     #[repr(packed(2))]
+13 | |     struct PackedN {
+14 | |         #[pin]
+15 | |         field: u32,
+16 | |     }
+17 | | }
+   | |_^
+   |
+note: the lint level is defined here
+  --> $DIR/packed.rs:11:1
+   |
+11 | / pin_project! { //~ ERROR reference to packed field is unaligned
+12 | |     #[repr(packed(2))]
+13 | |     struct PackedN {
+14 | |         #[pin]
+15 | |         field: u32,
+16 | |     }
+17 | | }
+   | |_^
+   = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced)
+   = note: this error originates in a macro (in Nightly builds, run with -Z macro-backtrace for more info)
+
 error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
  --> $DIR/packed.rs:3:1
   |
-3 | / pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+3 | / pin_project! { //~ ERROR reference to packed field is unaligned
 4 | |     #[repr(packed, C)]
-5 | |     struct A {
+5 | |     struct Packed {
 6 | |         #[pin]
 7 | |         field: u16,
 8 | |     }
@@ -13,9 +65,9 @@ error: borrow of packed field is unsafe and requires unsafe function or block (e
 note: the lint level is defined here
  --> $DIR/packed.rs:3:1
   |
-3 | / pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+3 | / pin_project! { //~ ERROR reference to packed field is unaligned
 4 | |     #[repr(packed, C)]
-5 | |     struct A {
+5 | |     struct Packed {
 6 | |         #[pin]
 7 | |         field: u16,
 8 | |     }
@@ -29,9 +81,9 @@ note: the lint level is defined here
 error: borrow of packed field is unsafe and requires unsafe function or block (error E0133)
   --> $DIR/packed.rs:11:1
    |
-11 | / pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+11 | / pin_project! { //~ ERROR reference to packed field is unaligned
 12 | |     #[repr(packed(2))]
-13 | |     struct C {
+13 | |     struct PackedN {
 14 | |         #[pin]
 15 | |         field: u32,
 16 | |     }
@@ -41,9 +93,9 @@ error: borrow of packed field is unsafe and requires unsafe function or block (e
 note: the lint level is defined here
   --> $DIR/packed.rs:11:1
    |
-11 | / pin_project! { //~ ERROR borrow of packed field is unsafe and requires unsafe function or block
+11 | / pin_project! { //~ ERROR reference to packed field is unaligned
 12 | |     #[repr(packed(2))]
-13 | |     struct C {
+13 | |     struct PackedN {
 14 | |         #[pin]
 15 | |         field: u32,
 16 | |     }