Don't assume primitive type alignments

zerocopy-derive/tests/struct_as_bytes.rs

@@ -4,10 +4,14 @@
 
 #![allow(warnings)]
 
+mod util;
+
 use std::{marker::PhantomData, option::IntoIter};
 
 use zerocopy::AsBytes;
 
+use crate::util::AU16;
+
 struct IsAsBytes<T: AsBytes>(T);
 
 // Fail compilation if `$ty: !AsBytes`.
@@ -36,7 +40,7 @@ is_as_bytes!(CZst);
 struct C {
     a: u8,
     b: u8,
-    c: u16,
+    c: AU16,
 }
 
 is_as_bytes!(C);
@@ -60,6 +64,13 @@ is_as_bytes!(CZstPacked);
 #[repr(C, packed)]
 struct CPacked {
     a: u8,
+    // NOTE: The `u16` type is not guaranteed to have alignment 2, although it
+    // does on many platforms. However, to fix this would require a custom type
+    // with a `#[repr(align(2))]` attribute, and `#[repr(packed)]` types are not
+    // allowed to transitively contain `#[repr(align(...))]` types. Thus, we
+    // have no choice but to use `u16` here. Luckily, these tests run in CI on
+    // platforms on which `u16` has alignment 2, so this isn't that big of a
+    // deal.
     b: u16,
 }
 

zerocopy-derive/tests/struct_unaligned.rs

@@ -44,6 +44,13 @@ is_unaligned!(Bar);
 #[derive(Unaligned)]
 #[repr(packed)]
 struct Baz {
+    // NOTE: The `u16` type is not guaranteed to have alignment 2, although it
+    // does on many platforms. However, to fix this would require a custom type
+    // with a `#[repr(align(2))]` attribute, and `#[repr(packed)]` types are not
+    // allowed to transitively contain `#[repr(align(...))]` types. Thus, we
+    // have no choice but to use `u16` here. Luckily, these tests run in CI on
+    // platforms on which `u16` has alignment 2, so this isn't that big of a
+    // deal.
     a: u16,
 }
 

zerocopy-derive/tests/ui-msrv/late_compile_pass.stderr

@@ -1,53 +1,44 @@
 error[E0277]: the trait bound `&'static str: FromBytes` is not satisfied
-  --> tests/ui-msrv/late_compile_pass.rs:18:10
+  --> tests/ui-msrv/late_compile_pass.rs:23:10
    |
-18 | #[derive(FromBytes)]
+23 | #[derive(FromBytes)]
    |          ^^^^^^^^^ the trait `FromBytes` is not implemented for `&'static str`
    |
    = help: see issue #48214
    = note: this error originates in the derive macro `FromBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `NotAsBytes: AsBytes` is not satisfied
-  --> tests/ui-msrv/late_compile_pass.rs:30:10
+  --> tests/ui-msrv/late_compile_pass.rs:35:10
    |
-30 | #[derive(AsBytes)]
+35 | #[derive(AsBytes)]
    |          ^^^^^^^ the trait `AsBytes` is not implemented for `NotAsBytes`
    |
    = help: see issue #48214
    = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-msrv/late_compile_pass.rs:40:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:45:10
    |
-40 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+45 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
-   = help: the following implementations were found:
-             <i8 as Unaligned>
-             <u8 as Unaligned>
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-msrv/late_compile_pass.rs:48:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:53:10
    |
-48 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
-   = help: the following implementations were found:
-             <i8 as Unaligned>
-             <u8 as Unaligned>
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-msrv/late_compile_pass.rs:55:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:60:10
    |
-55 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+60 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
-   = help: the following implementations were found:
-             <i8 as Unaligned>
-             <u8 as Unaligned>
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)

zerocopy-derive/tests/ui-msrv/struct.stderr

@@ -1,51 +1,51 @@
 error: unsupported on types with type parameters
-  --> tests/ui-msrv/struct.rs:14:10
+  --> tests/ui-msrv/struct.rs:19:10
    |
-14 | #[derive(AsBytes)]
+19 | #[derive(AsBytes)]
    |          ^^^^^^^
    |
    = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/struct.rs:34:11
+  --> tests/ui-msrv/struct.rs:35:11
    |
-34 | #[repr(C, align(2))]
+35 | #[repr(C, align(2))]
    |           ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/struct.rs:38:21
+  --> tests/ui-msrv/struct.rs:39:21
    |
-38 | #[repr(transparent, align(2))]
+39 | #[repr(transparent, align(2))]
    |                     ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/struct.rs:44:16
+  --> tests/ui-msrv/struct.rs:45:16
    |
-44 | #[repr(packed, align(2))]
+45 | #[repr(packed, align(2))]
    |                ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/struct.rs:48:18
+  --> tests/ui-msrv/struct.rs:49:18
    |
-48 | #[repr(align(1), align(2))]
+49 | #[repr(align(1), align(2))]
    |                  ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/struct.rs:52:8
+  --> tests/ui-msrv/struct.rs:53:8
    |
-52 | #[repr(align(2), align(4))]
+53 | #[repr(align(2), align(4))]
    |        ^^^^^^^^
 
 error[E0692]: transparent struct cannot have other repr hints
-  --> tests/ui-msrv/struct.rs:38:8
+  --> tests/ui-msrv/struct.rs:39:8
    |
-38 | #[repr(transparent, align(2))]
+39 | #[repr(transparent, align(2))]
    |        ^^^^^^^^^^^  ^^^^^^^^
 
 error[E0277]: the trait bound `HasPadding<AsBytes2, true>: ShouldBe<false>` is not satisfied
-  --> tests/ui-msrv/struct.rs:22:10
+  --> tests/ui-msrv/struct.rs:23:10
    |
-22 | #[derive(AsBytes)]
+23 | #[derive(AsBytes)]
    |          ^^^^^^^ the trait `ShouldBe<false>` is not implemented for `HasPadding<AsBytes2, true>`
    |
    = help: the following implementations were found:

zerocopy-derive/tests/ui-msrv/union.stderr

@@ -1,39 +1,39 @@
 error: unsupported on types with type parameters
-  --> tests/ui-msrv/union.rs:16:10
+  --> tests/ui-msrv/union.rs:21:10
    |
-16 | #[derive(AsBytes)]
+21 | #[derive(AsBytes)]
    |          ^^^^^^^
    |
    = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/union.rs:34:11
+  --> tests/ui-msrv/union.rs:39:11
    |
-34 | #[repr(C, align(2))]
+39 | #[repr(C, align(2))]
    |           ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/union.rs:50:16
+  --> tests/ui-msrv/union.rs:55:16
    |
-50 | #[repr(packed, align(2))]
+55 | #[repr(packed, align(2))]
    |                ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/union.rs:56:18
+  --> tests/ui-msrv/union.rs:61:18
    |
-56 | #[repr(align(1), align(2))]
+61 | #[repr(align(1), align(2))]
    |                  ^^^^^^^^
 
 error: cannot derive Unaligned with repr(align(N > 1))
-  --> tests/ui-msrv/union.rs:62:8
+  --> tests/ui-msrv/union.rs:67:8
    |
-62 | #[repr(align(2), align(4))]
+67 | #[repr(align(2), align(4))]
    |        ^^^^^^^^
 
 error[E0277]: the trait bound `HasPadding<AsBytes2, true>: ShouldBe<false>` is not satisfied
-  --> tests/ui-msrv/union.rs:22:10
+  --> tests/ui-msrv/union.rs:27:10
    |
-22 | #[derive(AsBytes)]
+27 | #[derive(AsBytes)]
    |          ^^^^^^^ the trait `ShouldBe<false>` is not implemented for `HasPadding<AsBytes2, true>`
    |
    = help: the following implementations were found:

zerocopy-derive/tests/ui-stable/late_compile_pass.stderr

@@ -1,7 +1,7 @@
 error[E0277]: the trait bound `&'static str: FromBytes` is not satisfied
-  --> tests/ui-stable/late_compile_pass.rs:18:10
+  --> tests/ui-stable/late_compile_pass.rs:23:10
    |
-18 | #[derive(FromBytes)]
+23 | #[derive(FromBytes)]
    |          ^^^^^^^^^ the trait `FromBytes` is not implemented for `&'static str`
    |
    = help: the following other types implement trait `FromBytes`:
@@ -18,56 +18,77 @@ error[E0277]: the trait bound `&'static str: FromBytes` is not satisfied
    = note: this error originates in the derive macro `FromBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0277]: the trait bound `NotAsBytes: AsBytes` is not satisfied
-  --> tests/ui-stable/late_compile_pass.rs:30:10
+  --> tests/ui-stable/late_compile_pass.rs:35:10
    |
-30 | #[derive(AsBytes)]
+35 | #[derive(AsBytes)]
    |          ^^^^^^^ the trait `AsBytes` is not implemented for `NotAsBytes`
    |
    = help: the following other types implement trait `AsBytes`:
              ()
+             AU16
              AsBytes1
              F32<O>
              F64<O>
              I128<O>
              I16<O>
              I32<O>
-             I64<O>
            and $N others
    = help: see issue #48214
    = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-stable/late_compile_pass.rs:40:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:45:10
    |
-40 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+45 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
    = help: the following other types implement trait `Unaligned`:
-             i8
-             u8
+             ()
+             F32<O>
+             F64<O>
+             I128<O>
+             I16<O>
+             I32<O>
+             I64<O>
+             PhantomData<T>
+           and $N others
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-stable/late_compile_pass.rs:48:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:53:10
    |
-48 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
    = help: the following other types implement trait `Unaligned`:
-             i8
-             u8
+             ()
+             F32<O>
+             F64<O>
+             I128<O>
+             I16<O>
+             I32<O>
+             I64<O>
+             PhantomData<T>
+           and $N others
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
 
-error[E0277]: the trait bound `u16: Unaligned` is not satisfied
-  --> tests/ui-stable/late_compile_pass.rs:55:10
+error[E0277]: the trait bound `AU16: Unaligned` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:60:10
    |
-55 | #[derive(Unaligned)]
-   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+60 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `AU16`
    |
    = help: the following other types implement trait `Unaligned`:
-             i8
-             u8
+             ()
+             F32<O>
+             F64<O>
+             I128<O>
+             I16<O>
+             I32<O>
+             I64<O>
+             PhantomData<T>
+           and $N others
    = help: see issue #48214
    = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)