diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 04dfe5a203..738308d9b6 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -12,20 +12,17 @@ jobs:
 
     strategy:
       matrix:
-        # Nightly is specificied at a particular date since not all nightlies
-        # have a working Miri. See here for details:
-        # https://rust-lang.github.io/rustup-components-history/
-        channel: [ "1.56.1", "stable", "beta", "nightly-2022-09-26" ]
+        # See `INTERNAL.md` for an explanation of these pinned toolchain
+        # versions.
+        channel: [ "1.56.1", "1.64.0", "nightly-2022-09-26" ]
         target: [ "i686-unknown-linux-gnu", "x86_64-unknown-linux-gnu", "arm-unknown-linux-gnueabi", "aarch64-unknown-linux-gnu", "powerpc-unknown-linux-gnu", "powerpc64-unknown-linux-gnu", "wasm32-wasi" ]
-        features: [ "" , "alloc,simd", "alloc,simd,simd-nightly"]
+        features: [ "" , "alloc,simd", "alloc,simd,simd-nightly" ]
         exclude:
           # Exclude any combination which uses a non-nightly toolchain but
           # enables nightly features.
           - channel: "1.56.1"
             features: "alloc,simd,simd-nightly"
-          - channel: "stable"
-            features: "alloc,simd,simd-nightly"
-          - channel: "beta"
+          - channel: "1.64.0"
             features: "alloc,simd,simd-nightly"
 
     name: Build & Test (${{ matrix.channel }} for ${{ matrix.target }}, features set to "${{ matrix.features }}")
@@ -54,21 +51,47 @@ jobs:
     - name: Check
       run: cargo +${{ matrix.channel }} check --target ${{ matrix.target }} --features "${{ matrix.features }}" --verbose
 
+    - name: Check zerocopy-derive
+      run: cargo +${{ matrix.channel }} check --manifest-path ./zerocopy-derive/Cargo.toml --target ${{ matrix.target }} --verbose
+      # Don't bother to check `zerocopy-derive` multiple times; that's what
+      # would happen if we ran this step once for each set of `zerocopy`
+      # features.
+      if: ${{ matrix.features == '' }}
+
     - name: Build
       run: cargo +${{ matrix.channel }} build --target ${{ matrix.target }} --features "${{ matrix.features }}" --verbose
 
+    - name: Build zerocopy-derive
+      run: cargo +${{ matrix.channel }} build --manifest-path ./zerocopy-derive/Cargo.toml --target ${{ matrix.target }} --verbose
+      # Don't bother to build `zerocopy-derive` multiple times; that's what
+      # would happen if we ran this step once for each set of `zerocopy`
+      # features.
+      if: ${{ matrix.features == '' }}
+
     # When building tests for the i686 target, we need certain libraries which
     # are not installed by default; `gcc-multilib` includes these libraries.
     - name: Install gcc-multilib
       run: sudo apt-get install gcc-multilib
       if: ${{ contains(matrix.target, 'i686') }}
 
-    # Only run tests in the x86 architecture
     - name: Run tests
       # TODO(#21): Fix `test_new_error` on i686 and re-enable it here.
       run: cargo +${{ matrix.channel }} test --target ${{ matrix.target }} --features "${{ matrix.features }}" --verbose -- ${{ contains(matrix.target, 'i686') && '--skip test_new_error' || '' }}
+      # Only run tests when targetting x86 (32- or 64-bit) - we're executing on
+      # x86_64, so we can't run tests for any non-x86 target.
       if: ${{ contains(matrix.target, 'x86_64') || contains(matrix.target, 'i686') }}
-    
+
+    - name: Run zerocopy-derive tests
+      run: cargo +${{ matrix.channel }} test --manifest-path ./zerocopy-derive/Cargo.toml --target ${{ matrix.target }} --verbose
+      # Don't bother to test `zerocopy-derive` multiple times; that's what would
+      # happen if we ran this step once for each set of `zerocopy` features.
+      # Also, only run tests when targetting x86 (32- or 64-bit) - we're
+      # executing on x86_64, so we can't run tests for any non-x86 target.
+      #
+      # TODO(https://github.com/dtolnay/trybuild/issues/184#issuecomment-1269097742):
+      # Run compile tests when building for other targets.
+      if: ${{ matrix.features == '' && (contains(matrix.target, 'x86_64') || contains(matrix.target, 'i686')) }}
+
     - name: Run tests under Miri
       # Skip the `ui` test since it invokes the compiler, which we can't do from
       # Miri (and wouldn't want to do anyway).
diff --git a/INTERNAL.md b/INTERNAL.md
new file mode 100644
index 0000000000..aa6076d6b9
--- /dev/null
+++ b/INTERNAL.md
@@ -0,0 +1,22 @@
+# Internal details
+
+This file documents various internal details of zerocopy and its infrastructure
+that consumers don't need to be concerned about. It focuses on details that
+affect multiple files, and allows each affected code location to reference this
+document rather than requiring us to repeat the same explanation in multiple
+locations.
+
+## CI and toolchain versions
+
+In CI (`.github/workflows/ci.yml`), we pin to specific versions or dates of the
+stable and nightly toolchains. The reason is twofold: First, `zerocopy-derive`'s
+UI tests (see `zerocopy-derive/tests/trybuild.rs`) depend on the format of
+rustc's error messages, and that format can change between toolchain versions
+(we also maintain multiple copies of our UI tests - one for each toolchain
+version pinned in CI - for this reason). Second, not all nightlies have a
+working Miri, so we need to pin to one that does (see
+https://rust-lang.github.io/rustup-components-history/).
+
+Updating the versions pinned in CI may cause the UI tests to break. In order to
+fix UI tests after a version update, set the environment variable
+`TRYBUILD=overwrite` while running `cargo test`.
diff --git a/zerocopy-derive/Cargo.toml b/zerocopy-derive/Cargo.toml
index f75de49d98..0bbd20e1f2 100644
--- a/zerocopy-derive/Cargo.toml
+++ b/zerocopy-derive/Cargo.toml
@@ -24,5 +24,6 @@ quote = "1.0.10"
 syn = { version = "1.0.5", features = ["visit"] }
 
 [dev-dependencies]
+rustversion = "1.0"
 trybuild = "1.0"
 zerocopy = { path = "../" }
diff --git a/zerocopy-derive/tests/trybuild.rs b/zerocopy-derive/tests/trybuild.rs
index 8958cc2e28..b95a716455 100644
--- a/zerocopy-derive/tests/trybuild.rs
+++ b/zerocopy-derive/tests/trybuild.rs
@@ -2,8 +2,28 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// UI tests depend on the exact error messages emitted by rustc, but those error
+// messages are not stable, and sometimes change between Rust versions. Thus, we
+// maintain one set of UI tests for each Rust version that we test in CI, and we
+// pin to specific versions in CI (a specific stable version, a specific date of
+// the nightly compiler, and a specific MSRV). Updating those pinned versions
+// may also require updating these tests.
+// - `tests/ui` - Contains the source of truth for our UI test source files
+//   (`.rs`), and contains `.err` and `.out` files for nightly and beta
+// - `tests/ui-stable` - Contains symlinks to the `.rs` files in `tests/ui`, and
+//   contains `.err` and `.out` files for stable
+// - `tests/ui-msrv` - Contains symlinks to the `.rs` files in `tests/ui`, and
+//   contains `.err` and `.out` files for MSRV
+
+#[rustversion::any(nightly, beta)]
+const SOURCE_FILES_GLOB: &str = "tests/ui/*.rs";
+#[rustversion::all(stable, not(stable(1.56.1)))]
+const SOURCE_FILES_GLOB: &str = "tests/ui-stable/*.rs";
+#[rustversion::stable(1.56.1)]
+const SOURCE_FILES_GLOB: &str = "tests/ui-msrv/*.rs";
+
 #[test]
 fn ui() {
     let t = trybuild::TestCases::new();
-    t.compile_fail("tests/ui/*.rs");
+    t.compile_fail(SOURCE_FILES_GLOB);
 }
diff --git a/zerocopy-derive/tests/ui-msrv/enum.rs b/zerocopy-derive/tests/ui-msrv/enum.rs
new file mode 120000
index 0000000000..84502bdc2b
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/enum.rs
@@ -0,0 +1 @@
+../ui/enum.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-msrv/enum.stderr b/zerocopy-derive/tests/ui-msrv/enum.stderr
new file mode 100644
index 0000000000..14ddb0b4bb
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/enum.stderr
@@ -0,0 +1,173 @@
+error: unrecognized representation hint
+  --> tests/ui-msrv/enum.rs:15:8
+   |
+15 | #[repr("foo")]
+   |        ^^^^^
+
+error: unrecognized representation hint
+  --> tests/ui-msrv/enum.rs:21:8
+   |
+21 | #[repr(foo)]
+   |        ^^^
+
+error: unsupported representation for deriving FromBytes, AsBytes, or Unaligned on an enum
+  --> tests/ui-msrv/enum.rs:27:8
+   |
+27 | #[repr(transparent)]
+   |        ^^^^^^^^^^^
+
+error: conflicting representation hints
+  --> tests/ui-msrv/enum.rs:33:1
+   |
+33 | #[repr(u8, u16)]
+   | ^
+
+error: must have a non-align #[repr(...)] attribute in order to guarantee this type's memory layout
+  --> tests/ui-msrv/enum.rs:38:10
+   |
+38 | #[derive(FromBytes)]
+   |          ^^^^^^^^^
+   |
+   = note: this error originates in the derive macro `FromBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:48:8
+   |
+48 | #[repr(C)]
+   |        ^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:54:8
+   |
+54 | #[repr(usize)]
+   |        ^^^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:60:8
+   |
+60 | #[repr(isize)]
+   |        ^^^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:66:8
+   |
+66 | #[repr(u32)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:72:8
+   |
+72 | #[repr(i32)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:78:8
+   |
+78 | #[repr(u64)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-msrv/enum.rs:84:8
+   |
+84 | #[repr(i64)]
+   |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+  --> tests/ui-msrv/enum.rs:94:8
+   |
+94 | #[repr(C)]
+   |        ^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:100:8
+    |
+100 | #[repr(u16)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:106:8
+    |
+106 | #[repr(i16)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:112:8
+    |
+112 | #[repr(u32)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:118:8
+    |
+118 | #[repr(i32)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:124:8
+    |
+124 | #[repr(u64)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:130:8
+    |
+130 | #[repr(i64)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:136:8
+    |
+136 | #[repr(usize)]
+    |        ^^^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-msrv/enum.rs:142:8
+    |
+142 | #[repr(isize)]
+    |        ^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-msrv/enum.rs:148:12
+    |
+148 | #[repr(u8, align(2))]
+    |            ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-msrv/enum.rs:154:12
+    |
+154 | #[repr(i8, align(2))]
+    |            ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-msrv/enum.rs:160:18
+    |
+160 | #[repr(align(1), align(2))]
+    |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-msrv/enum.rs:166:8
+    |
+166 | #[repr(align(2), align(4))]
+    |        ^^^^^^^^
+
+error[E0565]: meta item in `repr` must be an identifier
+  --> tests/ui-msrv/enum.rs:15:8
+   |
+15 | #[repr("foo")]
+   |        ^^^^^
+
+error[E0552]: unrecognized representation hint
+  --> tests/ui-msrv/enum.rs:21:8
+   |
+21 | #[repr(foo)]
+   |        ^^^
+
+error[E0566]: conflicting representation hints
+  --> tests/ui-msrv/enum.rs:33:8
+   |
+33 | #[repr(u8, u16)]
+   |        ^^  ^^^
+   |
+   = note: `#[deny(conflicting_repr_hints)]` 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 #68585 <https://github.com/rust-lang/rust/issues/68585>
diff --git a/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.rs b/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.rs
new file mode 120000
index 0000000000..994bb5ebe4
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.rs
@@ -0,0 +1 @@
+../ui/enum_from_bytes_u8_too_few.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.stderr b/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.stderr
new file mode 100644
index 0000000000..c4e1bc6369
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/enum_from_bytes_u8_too_few.stderr
@@ -0,0 +1,11 @@
+error: FromBytes only supported on repr(u8) enum with 256 variants
+   --> tests/ui-msrv/enum_from_bytes_u8_too_few.rs:11:1
+    |
+11  | / #[repr(u8)]
+12  | | enum Foo {
+13  | |     Variant0,
+14  | |     Variant1,
+...   |
+267 | |     Variant254,
+268 | | }
+    | |_^
diff --git a/zerocopy-derive/tests/ui-msrv/late_compile_pass.rs b/zerocopy-derive/tests/ui-msrv/late_compile_pass.rs
new file mode 120000
index 0000000000..ce42bccc6a
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/late_compile_pass.rs
@@ -0,0 +1 @@
+../ui/late_compile_pass.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-msrv/late_compile_pass.stderr b/zerocopy-derive/tests/ui-msrv/late_compile_pass.stderr
new file mode 100644
index 0000000000..a692474f13
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/late_compile_pass.stderr
@@ -0,0 +1,66 @@
+error[E0277]: the trait bound `AsBytes1: HasPadding<false>` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:27:10
+   |
+27 | #[derive(AsBytes)]
+   |          ^^^^^^^ the trait `HasPadding<false>` is not implemented for `AsBytes1`
+   |
+   = help: the following implementations were found:
+             <AsBytes1 as HasPadding<true>>
+note: required by a bound in `assert_no_padding`
+  --> tests/ui-msrv/late_compile_pass.rs:27:10
+   |
+27 | #[derive(AsBytes)]
+   |          ^^^^^^^ required by this bound in `assert_no_padding`
+   = 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 `&'static str: FromBytes` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:18:10
+   |
+18 | #[derive(FromBytes)]
+   |          ^^^^^^^^^ the trait `FromBytes` is not implemented for `&'static str`
+   |
+note: required by a bound in `ImplementsFromBytes`
+  --> tests/ui-msrv/late_compile_pass.rs:18:10
+   |
+18 | #[derive(FromBytes)]
+   |          ^^^^^^^^^ required by this bound in `ImplementsFromBytes`
+   = 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 `u16: Unaligned` is not satisfied
+  --> tests/ui-msrv/late_compile_pass.rs:38:10
+   |
+38 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+note: required by a bound in `<Unaligned1 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-msrv/late_compile_pass.rs:38:10
+   |
+38 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned1 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = 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:46:10
+   |
+46 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+note: required by a bound in `<Unaligned2 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-msrv/late_compile_pass.rs:46:10
+   |
+46 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned2 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = 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:53:10
+   |
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+note: required by a bound in `<Unaligned3 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-msrv/late_compile_pass.rs:53:10
+   |
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned3 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/zerocopy-derive/tests/ui-msrv/struct.rs b/zerocopy-derive/tests/ui-msrv/struct.rs
new file mode 120000
index 0000000000..440d9d84c6
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/struct.rs
@@ -0,0 +1 @@
+../ui/struct.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-msrv/struct.stderr b/zerocopy-derive/tests/ui-msrv/struct.stderr
new file mode 100644
index 0000000000..c3e91d4390
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/struct.stderr
@@ -0,0 +1,49 @@
+error: unsupported on types with type parameters
+  --> tests/ui-msrv/struct.rs:14:10
+   |
+14 | #[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:23:11
+   |
+23 | #[repr(C, align(2))]
+   |           ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/struct.rs:27:21
+   |
+27 | #[repr(transparent, align(2))]
+   |                     ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/struct.rs:33:16
+   |
+33 | #[repr(packed, align(2))]
+   |                ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/struct.rs:37:18
+   |
+37 | #[repr(align(1), align(2))]
+   |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/struct.rs:41:8
+   |
+41 | #[repr(align(2), align(4))]
+   |        ^^^^^^^^
+
+error[E0692]: transparent struct cannot have other repr hints
+  --> tests/ui-msrv/struct.rs:27:8
+   |
+27 | #[repr(transparent, align(2))]
+   |        ^^^^^^^^^^^  ^^^^^^^^
+
+error[E0587]: type has conflicting packed and align representation hints
+  --> tests/ui-msrv/struct.rs:34:1
+   |
+34 | struct Unaligned3;
+   | ^^^^^^^^^^^^^^^^^^
diff --git a/zerocopy-derive/tests/ui-msrv/union.rs b/zerocopy-derive/tests/ui-msrv/union.rs
new file mode 120000
index 0000000000..b1faf84e5a
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/union.rs
@@ -0,0 +1 @@
+../ui/union.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-msrv/union.stderr b/zerocopy-derive/tests/ui-msrv/union.stderr
new file mode 100644
index 0000000000..56b72bebcf
--- /dev/null
+++ b/zerocopy-derive/tests/ui-msrv/union.stderr
@@ -0,0 +1,54 @@
+error: unsupported on types with type parameters
+  --> tests/ui-msrv/union.rs:16:10
+   |
+16 | #[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
+   |
+34 | #[repr(C, align(2))]
+   |           ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/union.rs:50:16
+   |
+50 | #[repr(packed, align(2))]
+   |                ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/union.rs:56:18
+   |
+56 | #[repr(align(1), align(2))]
+   |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-msrv/union.rs:62:8
+   |
+62 | #[repr(align(2), align(4))]
+   |        ^^^^^^^^
+
+error[E0277]: the trait bound `AsBytes: FieldsAreSameSize<true>` is not satisfied
+  --> tests/ui-msrv/union.rs:22:10
+   |
+22 | #[derive(AsBytes)]
+   |          ^^^^^^^ the trait `FieldsAreSameSize<true>` is not implemented for `AsBytes`
+   |
+   = help: the following implementations were found:
+             <AsBytes as FieldsAreSameSize<false>>
+note: required by a bound in `assert_fields_are_same_size`
+  --> tests/ui-msrv/union.rs:22:10
+   |
+22 | #[derive(AsBytes)]
+   |          ^^^^^^^ required by this bound in `assert_fields_are_same_size`
+   = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0587]: type has conflicting packed and align representation hints
+  --> tests/ui-msrv/union.rs:51:1
+   |
+51 | / union Unaligned3 {
+52 | |     foo: u8,
+53 | | }
+   | |_^
diff --git a/zerocopy-derive/tests/ui-stable/enum.rs b/zerocopy-derive/tests/ui-stable/enum.rs
new file mode 120000
index 0000000000..84502bdc2b
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/enum.rs
@@ -0,0 +1 @@
+../ui/enum.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-stable/enum.stderr b/zerocopy-derive/tests/ui-stable/enum.stderr
new file mode 100644
index 0000000000..a72d2884db
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/enum.stderr
@@ -0,0 +1,173 @@
+error: unrecognized representation hint
+  --> tests/ui-stable/enum.rs:15:8
+   |
+15 | #[repr("foo")]
+   |        ^^^^^
+
+error: unrecognized representation hint
+  --> tests/ui-stable/enum.rs:21:8
+   |
+21 | #[repr(foo)]
+   |        ^^^
+
+error: unsupported representation for deriving FromBytes, AsBytes, or Unaligned on an enum
+  --> tests/ui-stable/enum.rs:27:8
+   |
+27 | #[repr(transparent)]
+   |        ^^^^^^^^^^^
+
+error: conflicting representation hints
+  --> tests/ui-stable/enum.rs:33:1
+   |
+33 | #[repr(u8, u16)]
+   | ^
+
+error: must have a non-align #[repr(...)] attribute in order to guarantee this type's memory layout
+  --> tests/ui-stable/enum.rs:38:10
+   |
+38 | #[derive(FromBytes)]
+   |          ^^^^^^^^^
+   |
+   = note: this error originates in the derive macro `FromBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:48:8
+   |
+48 | #[repr(C)]
+   |        ^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:54:8
+   |
+54 | #[repr(usize)]
+   |        ^^^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:60:8
+   |
+60 | #[repr(isize)]
+   |        ^^^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:66:8
+   |
+66 | #[repr(u32)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:72:8
+   |
+72 | #[repr(i32)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:78:8
+   |
+78 | #[repr(u64)]
+   |        ^^^
+
+error: FromBytes requires repr of "u8", "u16", "i8", or "i16"
+  --> tests/ui-stable/enum.rs:84:8
+   |
+84 | #[repr(i64)]
+   |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+  --> tests/ui-stable/enum.rs:94:8
+   |
+94 | #[repr(C)]
+   |        ^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:100:8
+    |
+100 | #[repr(u16)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:106:8
+    |
+106 | #[repr(i16)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:112:8
+    |
+112 | #[repr(u32)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:118:8
+    |
+118 | #[repr(i32)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:124:8
+    |
+124 | #[repr(u64)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:130:8
+    |
+130 | #[repr(i64)]
+    |        ^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:136:8
+    |
+136 | #[repr(usize)]
+    |        ^^^^^
+
+error: Unaligned requires repr of "u8" or "i8", and no alignment (i.e., repr(align(N > 1)))
+   --> tests/ui-stable/enum.rs:142:8
+    |
+142 | #[repr(isize)]
+    |        ^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-stable/enum.rs:148:12
+    |
+148 | #[repr(u8, align(2))]
+    |            ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-stable/enum.rs:154:12
+    |
+154 | #[repr(i8, align(2))]
+    |            ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-stable/enum.rs:160:18
+    |
+160 | #[repr(align(1), align(2))]
+    |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+   --> tests/ui-stable/enum.rs:166:8
+    |
+166 | #[repr(align(2), align(4))]
+    |        ^^^^^^^^
+
+error[E0565]: meta item in `repr` must be an identifier
+  --> tests/ui-stable/enum.rs:15:8
+   |
+15 | #[repr("foo")]
+   |        ^^^^^
+
+error[E0552]: unrecognized representation hint
+  --> tests/ui-stable/enum.rs:21:8
+   |
+21 | #[repr(foo)]
+   |        ^^^
+
+error[E0566]: conflicting representation hints
+  --> tests/ui-stable/enum.rs:33:8
+   |
+33 | #[repr(u8, u16)]
+   |        ^^  ^^^
+   |
+   = note: `#[deny(conflicting_repr_hints)]` 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 #68585 <https://github.com/rust-lang/rust/issues/68585>
diff --git a/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.rs b/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.rs
new file mode 120000
index 0000000000..994bb5ebe4
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.rs
@@ -0,0 +1 @@
+../ui/enum_from_bytes_u8_too_few.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.stderr b/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.stderr
new file mode 100644
index 0000000000..5b604235df
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/enum_from_bytes_u8_too_few.stderr
@@ -0,0 +1,11 @@
+error: FromBytes only supported on repr(u8) enum with 256 variants
+   --> tests/ui-stable/enum_from_bytes_u8_too_few.rs:11:1
+    |
+11  | / #[repr(u8)]
+12  | | enum Foo {
+13  | |     Variant0,
+14  | |     Variant1,
+...   |
+267 | |     Variant254,
+268 | | }
+    | |_^
diff --git a/zerocopy-derive/tests/ui-stable/late_compile_pass.rs b/zerocopy-derive/tests/ui-stable/late_compile_pass.rs
new file mode 120000
index 0000000000..ce42bccc6a
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/late_compile_pass.rs
@@ -0,0 +1 @@
+../ui/late_compile_pass.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-stable/late_compile_pass.stderr b/zerocopy-derive/tests/ui-stable/late_compile_pass.stderr
new file mode 100644
index 0000000000..6f3bdbe6bf
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/late_compile_pass.stderr
@@ -0,0 +1,84 @@
+error[E0277]: the trait bound `AsBytes1: HasPadding<false>` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:27:10
+   |
+27 | #[derive(AsBytes)]
+   |          ^^^^^^^ the trait `HasPadding<false>` is not implemented for `AsBytes1`
+   |
+   = help: the trait `HasPadding<true>` is implemented for `AsBytes1`
+note: required by a bound in `assert_no_padding`
+  --> tests/ui-stable/late_compile_pass.rs:27:10
+   |
+27 | #[derive(AsBytes)]
+   |          ^^^^^^^ required by this bound in `assert_no_padding`
+   = 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 `&'static str: FromBytes` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:18:10
+   |
+18 | #[derive(FromBytes)]
+   |          ^^^^^^^^^ the trait `FromBytes` is not implemented for `&'static str`
+   |
+   = help: the following other types implement trait `FromBytes`:
+             ()
+             F32<O>
+             F64<O>
+             FromBytes1
+             I128<O>
+             I16<O>
+             I32<O>
+             I64<O>
+           and 36 others
+note: required by a bound in `ImplementsFromBytes`
+  --> tests/ui-stable/late_compile_pass.rs:18:10
+   |
+18 | #[derive(FromBytes)]
+   |          ^^^^^^^^^ required by this bound in `ImplementsFromBytes`
+   = 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 `u16: Unaligned` is not satisfied
+  --> tests/ui-stable/late_compile_pass.rs:38:10
+   |
+38 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+   = help: the following other types implement trait `Unaligned`:
+             i8
+             u8
+note: required by a bound in `<Unaligned1 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-stable/late_compile_pass.rs:38:10
+   |
+38 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned1 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = 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:46:10
+   |
+46 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+   = help: the following other types implement trait `Unaligned`:
+             i8
+             u8
+note: required by a bound in `<Unaligned2 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-stable/late_compile_pass.rs:46:10
+   |
+46 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned2 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = 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:53:10
+   |
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ the trait `Unaligned` is not implemented for `u16`
+   |
+   = help: the following other types implement trait `Unaligned`:
+             i8
+             u8
+note: required by a bound in `<Unaligned3 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+  --> tests/ui-stable/late_compile_pass.rs:53:10
+   |
+53 | #[derive(Unaligned)]
+   |          ^^^^^^^^^ required by this bound in `<Unaligned3 as Unaligned>::only_derive_is_allowed_to_implement_this_trait::ImplementsUnaligned`
+   = note: this error originates in the derive macro `Unaligned` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/zerocopy-derive/tests/ui-stable/struct.rs b/zerocopy-derive/tests/ui-stable/struct.rs
new file mode 120000
index 0000000000..440d9d84c6
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/struct.rs
@@ -0,0 +1 @@
+../ui/struct.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-stable/struct.stderr b/zerocopy-derive/tests/ui-stable/struct.stderr
new file mode 100644
index 0000000000..f3a5ccbb36
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/struct.stderr
@@ -0,0 +1,49 @@
+error: unsupported on types with type parameters
+  --> tests/ui-stable/struct.rs:14:10
+   |
+14 | #[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-stable/struct.rs:23:11
+   |
+23 | #[repr(C, align(2))]
+   |           ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/struct.rs:27:21
+   |
+27 | #[repr(transparent, align(2))]
+   |                     ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/struct.rs:33:16
+   |
+33 | #[repr(packed, align(2))]
+   |                ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/struct.rs:37:18
+   |
+37 | #[repr(align(1), align(2))]
+   |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/struct.rs:41:8
+   |
+41 | #[repr(align(2), align(4))]
+   |        ^^^^^^^^
+
+error[E0692]: transparent struct cannot have other repr hints
+  --> tests/ui-stable/struct.rs:27:8
+   |
+27 | #[repr(transparent, align(2))]
+   |        ^^^^^^^^^^^  ^^^^^^^^
+
+error[E0587]: type has conflicting packed and align representation hints
+  --> tests/ui-stable/struct.rs:34:1
+   |
+34 | struct Unaligned3;
+   | ^^^^^^^^^^^^^^^^^
diff --git a/zerocopy-derive/tests/ui-stable/union.rs b/zerocopy-derive/tests/ui-stable/union.rs
new file mode 120000
index 0000000000..b1faf84e5a
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/union.rs
@@ -0,0 +1 @@
+../ui/union.rs
\ No newline at end of file
diff --git a/zerocopy-derive/tests/ui-stable/union.stderr b/zerocopy-derive/tests/ui-stable/union.stderr
new file mode 100644
index 0000000000..5726d9933a
--- /dev/null
+++ b/zerocopy-derive/tests/ui-stable/union.stderr
@@ -0,0 +1,51 @@
+error: unsupported on types with type parameters
+  --> tests/ui-stable/union.rs:16:10
+   |
+16 | #[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-stable/union.rs:34:11
+   |
+34 | #[repr(C, align(2))]
+   |           ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/union.rs:50:16
+   |
+50 | #[repr(packed, align(2))]
+   |                ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/union.rs:56:18
+   |
+56 | #[repr(align(1), align(2))]
+   |                  ^^^^^^^^
+
+error: cannot derive Unaligned with repr(align(N > 1))
+  --> tests/ui-stable/union.rs:62:8
+   |
+62 | #[repr(align(2), align(4))]
+   |        ^^^^^^^^
+
+error[E0277]: the trait bound `AsBytes: FieldsAreSameSize<true>` is not satisfied
+  --> tests/ui-stable/union.rs:22:10
+   |
+22 | #[derive(AsBytes)]
+   |          ^^^^^^^ the trait `FieldsAreSameSize<true>` is not implemented for `AsBytes`
+   |
+   = help: the trait `FieldsAreSameSize<false>` is implemented for `AsBytes`
+note: required by a bound in `assert_fields_are_same_size`
+  --> tests/ui-stable/union.rs:22:10
+   |
+22 | #[derive(AsBytes)]
+   |          ^^^^^^^ required by this bound in `assert_fields_are_same_size`
+   = note: this error originates in the derive macro `AsBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
+
+error[E0587]: type has conflicting packed and align representation hints
+  --> tests/ui-stable/union.rs:51:1
+   |
+51 | union Unaligned3 {
+   | ^^^^^^^^^^^^^^^^