Lower our MSRV to 1.59.0 (#791)

Makes progress on #554

Cargo.toml

@@ -20,7 +20,7 @@ authors = ["Joshua Liebow-Feeser <[email protected]>"]
 description = "Utilities for zero-copy parsing and serialization"
 license = "BSD-2-Clause OR Apache-2.0 OR MIT"
 repository = "https://github.com/google/zerocopy"
-rust-version = "1.60.0"
+rust-version = "1.59.0"
 
 exclude = [".*"]
 
@@ -58,6 +58,10 @@ zerocopy-derive = { version = "=0.8.0-alpha.2", path = "zerocopy-derive" }
 [dev-dependencies]
 assert_matches = "1.5"
 itertools = "0.11"
+# We don't use this directly, but trybuild does. On the MSRV toolchain, the
+# version resolver fails to select any version for once_cell unless we
+# depend on it directly.
+once_cell = "=1.9"
 rand = { version = "0.8.5", features = ["small_rng"] }
 rustversion = "1.0"
 static_assertions = "1.1"
@@ -66,7 +70,7 @@ testutil = { path = "testutil" }
 # and the version used in CI are guaranteed to be the same. Future versions
 # sometimes change the output format slightly, so a version mismatch can cause
 # CI test failures.
-trybuild = { version = "=1.0.85", features = ["diff"] }
+trybuild = { version = "=1.0.89", features = ["diff"] }
 # In tests, unlike in production, zerocopy-derive is not optional
 zerocopy-derive = { version = "=0.8.0-alpha.2", path = "zerocopy-derive" }
 # TODO(#381) Remove this dependency once we have our own layout gadgets.

src/lib.rs

@@ -454,7 +454,7 @@ impl DstLayout {
             None => Self::MIN_ALIGN,
         };
 
-        assert!(align.is_power_of_two());
+        assert!(align.get().is_power_of_two());
 
         DstLayout { align, size_info: SizeInfo::Sized { _size: 0 } }
     }
@@ -542,7 +542,7 @@ impl DstLayout {
             None => Self::THEORETICAL_MAX_ALIGN,
         };
 
-        assert!(max_align.is_power_of_two());
+        assert!(max_align.get().is_power_of_two());
 
         // We use Kani to prove that this method is robust to future increases
         // in Rust's maximum allowed alignment. However, if such a change ever

src/macros.rs

@@ -125,7 +125,7 @@ macro_rules! unsafe_impl {
         => $trait:ident for $ty:ty $(; |$candidate:ident $(: MaybeAligned<$ref_repr:ty>)? $(: Maybe<$ptr_repr:ty>)?| $is_bit_valid:expr)?
     ) => {
         $(#[$attr])*
-        unsafe impl<$(const $constname: $constty,)* $($tyvar $(: $(? $optbound +)* $($bound +)*)?),*> $trait for $ty {
+        unsafe impl<$($tyvar $(: $(? $optbound +)* $($bound +)*)?),* $(, const $constname: $constty,)*> $trait for $ty {
             unsafe_impl!(@method $trait $(; |$candidate: $(MaybeAligned<$ref_repr>)? $(Maybe<$ptr_repr>)?| $is_bit_valid)?);
         }
     };
@@ -341,7 +341,7 @@ macro_rules! impl_known_layout {
             use core::ptr::NonNull;
 
             // SAFETY: Delegates safety to `DstLayout::for_type`.
-            unsafe impl<$(const $constvar : $constty,)? $($tyvar $(: ?$optbound)?)?> KnownLayout for $ty {
+            unsafe impl<$($tyvar $(: ?$optbound)?)? $(, const $constvar : $constty)?> KnownLayout for $ty {
                 #[allow(clippy::missing_inline_in_public_items)]
                 fn only_derive_is_allowed_to_implement_this_trait() where Self: Sized {}
 

src/pointer/ptr.rs

@@ -137,6 +137,7 @@ mod def {
     }
 }
 
+#[allow(unreachable_pub)] // This is a false positive on our MSRV toolchain.
 pub use def::Ptr;
 
 /// Used to define the system of [invariants][invariant] of `Ptr`.
@@ -1088,7 +1089,7 @@ mod tests {
 
         // - If `size_of::<T>() == 0`, `N == 4`
         // - Else, `N == 4 * size_of::<T>()`
-        fn test<const N: usize, T: ?Sized + KnownLayout + FromBytes>() {
+        fn test<T: ?Sized + KnownLayout + FromBytes, const N: usize>() {
             let mut bytes = [MaybeUninit::<u8>::uninit(); N];
             let initialized = [MaybeUninit::new(0u8); N];
             for start in 0..=bytes.len() {
@@ -1183,11 +1184,11 @@ mod tests {
             $({
                 const S: usize = core::mem::size_of::<$ty>();
                 const N: usize = if S == 0 { 4 } else { S * 4 };
-                test::<N, $ty>();
+                test::<$ty, N>();
                 // We don't support casting into DSTs whose trailing slice
                 // element is a ZST.
                 if S > 0 {
-                    test::<N, [$ty]>();
+                    test::<[$ty], N>();
                 }
                 // TODO: Test with a slice DST once we have any that
                 // implement `KnownLayout + FromBytes`.

tests/ui-msrv/transmute-mut-alignment-increase.stderr

@@ -16,13 +16,12 @@ error[E0658]: mutable references are not allowed in constants
    |
    = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
 
-error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], AU16>` in constants
+error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
   --> tests/ui-msrv/transmute-mut-alignment-increase.rs:19:39
    |
 19 | const INCREASE_ALIGNMENT: &mut AU16 = transmute_mut!(&mut [0u8; 2]);
    |                                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0716]: temporary value dropped while borrowed

tests/ui-msrv/transmute-mut-const.stderr

@@ -21,13 +21,12 @@ error[E0658]: mutable references are not allowed in constants
    |
    = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
 
-error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], [u8; 2]>` in constants
+error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
   --> tests/ui-msrv/transmute-mut-const.rs:20:37
    |
 20 | const CONST_CONTEXT: &mut [u8; 2] = transmute_mut!(&mut ARRAY_OF_U8S);
    |                                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0716]: temporary value dropped while borrowed

tests/ui-msrv/transmute-mut-size-decrease.stderr

@@ -16,13 +16,12 @@ error[E0658]: mutable references are not allowed in constants
    |
    = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
 
-error[E0015]: cannot call non-const fn `transmute_mut::<[u8; 2], u8>` in constants
+error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
   --> tests/ui-msrv/transmute-mut-size-decrease.rs:17:32
    |
 17 | const DECREASE_SIZE: &mut u8 = transmute_mut!(&mut [0u8; 2]);
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0716]: temporary value dropped while borrowed

tests/ui-msrv/transmute-mut-size-increase.stderr

@@ -16,13 +16,12 @@ error[E0658]: mutable references are not allowed in constants
    |
    = note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
 
-error[E0015]: cannot call non-const fn `transmute_mut::<u8, [u8; 2]>` in constants
+error[E0015]: calls in constants are limited to constant functions, tuple structs and tuple variants
   --> tests/ui-msrv/transmute-mut-size-increase.rs:17:37
    |
 17 | const INCREASE_SIZE: &mut [u8; 2] = transmute_mut!(&mut 0u8);
    |                                     ^^^^^^^^^^^^^^^^^^^^^^^^
    |
-   = note: calls in constants are limited to constant functions, tuple structs and tuple variants
    = note: this error originates in the macro `transmute_mut` (in Nightly builds, run with -Z macro-backtrace for more info)
 
 error[E0716]: temporary value dropped while borrowed

tests/ui-msrv/transmute-ptr-to-usize.stderr

@@ -4,12 +4,6 @@ error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
 20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
    |
-   = help: the following implementations were found:
-             <usize as AsBytes>
-             <f32 as AsBytes>
-             <f64 as AsBytes>
-             <i128 as AsBytes>
-           and $N others
 note: required by a bound in `AssertIsIntoBytes`
   --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
    |
@@ -23,12 +17,6 @@ error[E0277]: the trait bound `*const usize: AsBytes` is not satisfied
 20 | const POINTER_VALUE: usize = transmute!(&0usize as *const usize);
    |                              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `AsBytes` is not implemented for `*const usize`
    |
-   = help: the following implementations were found:
-             <usize as AsBytes>
-             <f32 as AsBytes>
-             <f64 as AsBytes>
-             <i128 as AsBytes>
-           and $N others
 note: required by a bound in `AssertIsIntoBytes`
   --> tests/ui-msrv/transmute-ptr-to-usize.rs:20:30
    |

zerocopy-derive/Cargo.toml

@@ -14,7 +14,7 @@ authors = ["Joshua Liebow-Feeser <[email protected]>"]
 description = "Custom derive for traits from the zerocopy crate"
 license = "BSD-2-Clause OR Apache-2.0 OR MIT"
 repository = "https://github.com/google/zerocopy"
-rust-version = "1.60.0"
+rust-version = "1.59.0"
 
 # We prefer to include tests when publishing to crates.io so that Crater [1] can
 # detect regressions in our test suite. These two tests are excessively large,
@@ -32,11 +32,15 @@ quote = "1.0.10"
 syn = "2.0.31"
 
 [dev-dependencies]
+# We don't use this directly, but trybuild does. On the MSRV toolchain, the
+# version resolver fails to select any version for once_cell unless we
+# depend on it directly.
+once_cell = "=1.9"
 static_assertions = "1.1"
 testutil = { path = "../testutil" }
 # Pinned to a specific version so that the version used for local development
 # and the version used in CI are guaranteed to be the same. Future versions
 # sometimes change the output format slightly, so a version mismatch can cause
 # CI test failures.
-trybuild = { version = "=1.0.85", features = ["diff"] }
+trybuild = { version = "=1.0.89", features = ["diff"] }
 zerocopy = { path = "../", features = ["derive"] }

zerocopy-derive/tests/enum_known_layout.rs

@@ -34,7 +34,7 @@ assert_impl_all!(Baz: KnownLayout);
 
 #[derive(KnownLayout)]
 #[repr(C)]
-enum WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + KnownLayout>
+enum WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + KnownLayout, const N: usize>
 where
     'a: 'b,
     'b: 'a,
@@ -43,4 +43,4 @@ where
     Variant([T; N], PhantomData<&'a &'b ()>),
 }
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: KnownLayout);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: KnownLayout);

zerocopy-derive/tests/enum_no_cell.rs

@@ -37,7 +37,7 @@ assert_impl_all!(Baz: NoCell);
 
 #[derive(NoCell)]
 #[repr(C)]
-enum WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + NoCell>
+enum WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + NoCell, const N: usize>
 where
     'a: 'b,
     'b: 'a,
@@ -47,4 +47,4 @@ where
     UnsafeCell(PhantomData<UnsafeCell<()>>, &'a UnsafeCell<()>),
 }
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: NoCell);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: NoCell);

zerocopy-derive/tests/struct_from_bytes.rs

@@ -67,7 +67,7 @@ assert_impl_all!(TypeParams<'static, [AU16], IntoIter<()>>: FromBytes);
 
 #[derive(FromZeros, FromBytes)]
 #[repr(transparent)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + FromBytes>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + FromBytes, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
 )
@@ -76,4 +76,4 @@ where
     'b: 'a,
     T: 'a + 'b + FromBytes;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: FromBytes);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: FromBytes);

zerocopy-derive/tests/struct_from_zeros.rs

@@ -65,7 +65,7 @@ assert_impl_all!(TypeParams<'static, [AU16], IntoIter<()>>: FromZeros);
 
 #[derive(FromZeros)]
 #[repr(transparent)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + FromZeros>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + FromZeros, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
 )
@@ -74,4 +74,4 @@ where
     'b: 'a,
     T: 'a + 'b + FromZeros;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: FromZeros);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: FromZeros);

zerocopy-derive/tests/struct_known_layout.rs

@@ -53,7 +53,7 @@ assert_impl_all!(TypeParams<'static, AU16, IntoIter<()>>: KnownLayout);
 
 #[derive(KnownLayout)]
 #[repr(C)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + KnownLayout>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + KnownLayout, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
 )
@@ -62,4 +62,4 @@ where
     'b: 'a,
     T: 'a + 'b + KnownLayout;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: KnownLayout);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: KnownLayout);

zerocopy-derive/tests/struct_no_cell.rs

@@ -87,7 +87,7 @@ assert_impl_all!(WithAssocType<UnsafeCell<u8>>: NoCell);
 
 #[derive(NoCell)]
 #[repr(C)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + NoCell>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + NoCell, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
     PhantomData<UnsafeCell<()>>,
@@ -98,4 +98,4 @@ where
     'b: 'a,
     T: 'a + 'b + NoCell;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: NoCell);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: NoCell);

zerocopy-derive/tests/struct_to_bytes.rs

@@ -149,7 +149,7 @@ assert_impl_all!(Unsized: IntoBytes);
 
 #[derive(IntoBytes)]
 #[repr(transparent)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + IntoBytes>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + IntoBytes, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
 )
@@ -158,4 +158,4 @@ where
     'b: 'a,
     T: 'a + 'b + IntoBytes;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: IntoBytes);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: IntoBytes);

zerocopy-derive/tests/struct_try_from_bytes.rs

@@ -133,7 +133,7 @@ assert_impl_all!(TypeParams<'static, [AU16], IntoIter<()>>: TryFromBytes);
 
 #[derive(TryFromBytes, FromZeros, FromBytes)]
 #[repr(transparent)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + TryFromBytes>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + TryFromBytes, const N: usize>(
     PhantomData<&'a &'b ()>,
     [T],
 )
@@ -142,7 +142,7 @@ where
     'b: 'a,
     T: 'a + 'b + TryFromBytes;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: TryFromBytes);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: TryFromBytes);
 
 #[derive(Debug, PartialEq, Eq, TryFromBytes, KnownLayout)]
 #[repr(C, packed)]

zerocopy-derive/tests/struct_unaligned.rs

@@ -88,7 +88,7 @@ assert_impl_all!(TypeParams<'static, [u8], IntoIter<()>>: Unaligned);
 
 #[derive(Unaligned)]
 #[repr(transparent)]
-struct WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + Unaligned>(
+struct WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + Unaligned, const N: usize>(
     [T; N],
     PhantomData<&'a &'b ()>,
 )
@@ -97,4 +97,4 @@ where
     'b: 'a,
     T: 'a + 'b + Unaligned;
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: Unaligned);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: Unaligned);

zerocopy-derive/tests/union_from_bytes.rs

@@ -59,7 +59,7 @@ assert_impl_all!(TypeParams<'static, (), IntoIter<()>>: FromBytes);
 
 #[derive(FromZeros, FromBytes)]
 #[repr(C)]
-union WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + FromBytes>
+union WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + FromBytes, const N: usize>
 where
     'a: 'b,
     'b: 'a,
@@ -69,4 +69,4 @@ where
     b: PhantomData<&'a &'b ()>,
 }
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: FromBytes);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: FromBytes);

zerocopy-derive/tests/union_from_zeros.rs

@@ -59,7 +59,7 @@ assert_impl_all!(TypeParams<'static, (), IntoIter<()>>: FromZeros);
 
 #[derive(FromZeros)]
 #[repr(C)]
-union WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + FromZeros>
+union WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + FromZeros, const N: usize>
 where
     'a: 'b,
     'b: 'a,
@@ -69,4 +69,4 @@ where
     b: PhantomData<&'a &'b ()>,
 }
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: FromZeros);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: FromZeros);

zerocopy-derive/tests/union_known_layout.rs

@@ -52,7 +52,7 @@ assert_impl_all!(TypeParams<'static, (), IntoIter<()>>: KnownLayout);
 
 #[derive(KnownLayout)]
 #[repr(C)]
-union WithParams<'a: 'b, 'b: 'a, const N: usize, T: 'a + 'b + KnownLayout>
+union WithParams<'a: 'b, 'b: 'a, T: 'a + 'b + KnownLayout, const N: usize>
 where
     'a: 'b,
     'b: 'a,
@@ -62,4 +62,4 @@ where
     b: PhantomData<&'a &'b ()>,
 }
 
-assert_impl_all!(WithParams<'static, 'static, 42, u8>: KnownLayout);
+assert_impl_all!(WithParams<'static, 'static, u8, 42>: KnownLayout);