[macro_util] Rename from derive_util, include more (#455)

Include macro utilities - namely, re-exports of core symbols used by
macro-generated code.

Release 0.7.7 to work around a cargo-semver-checks false positive; see
#455 (comment).

Author: joshlf

Cargo.toml

@@ -11,7 +11,7 @@
 [package]
 edition = "2021"
 name = "zerocopy"
-version = "0.7.6"
+version = "0.7.7"
 authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
 description = "Utilities for zero-copy parsing and serialization"
 license = "BSD-2-Clause"
@@ -41,7 +41,7 @@ simd-nightly = ["simd"]
 __internal_use_only_features_that_work_on_stable = ["alloc", "derive", "simd"]
 
 [dependencies]
-zerocopy-derive = { version = "=0.7.6", path = "zerocopy-derive", optional = true }
+zerocopy-derive = { version = "=0.7.7", path = "zerocopy-derive", optional = true }
 
 [dependencies.byteorder]
 version = "1.3"
@@ -52,7 +52,7 @@ optional = true
 # zerocopy-derive remain equal, even if the 'derive' feature isn't used.
 # See: https://github.com/matklad/macro-dep-test
 [target.'cfg(any())'.dependencies]
-zerocopy-derive = { version = "=0.7.6", path = "zerocopy-derive" }
+zerocopy-derive = { version = "=0.7.7", path = "zerocopy-derive" }
 
 [dev-dependencies]
 assert_matches = "1.5"
@@ -67,4 +67,4 @@ testutil = { path = "testutil" }
 # CI test failures.
 trybuild = "=1.0.80"
 # In tests, unlike in production, zerocopy-derive is not optional
-zerocopy-derive = { version = "=0.7.6", path = "zerocopy-derive" }
+zerocopy-derive = { version = "=0.7.7", path = "zerocopy-derive" }

src/lib.rs

@@ -170,9 +170,8 @@ mod macros;
 
 #[cfg(feature = "byteorder")]
 pub mod byteorder;
-#[cfg(any(feature = "derive", test))]
 #[doc(hidden)]
-pub mod derive_util;
+pub mod macro_util;
 mod util;
 // TODO(#252): If we make this pub, come up with a better name.
 mod wrappers;
@@ -1628,10 +1627,6 @@ mod simd {
     simd_arch_mod!(arm, int8x4_t, uint8x4_t);
 }
 
-// Used in `transmute!` below.
-#[doc(hidden)]
-pub use core::mem::transmute as __real_transmute;
-
 /// Safely transmutes a value of one type to a value of another type of the same
 /// size.
 ///
@@ -1666,14 +1661,15 @@ macro_rules! transmute {
             // We know this transmute is safe thanks to the `AsBytes` and
             // `FromBytes` bounds enforced by the `false` branch.
             //
-            // We use `$crate::__real_transmute` because we know it will always
-            // be available for crates which are using the 2015 edition of Rust.
-            // By contrast, if we were to use `std::mem::transmute`, this macro
-            // would not work for such crates in `no_std` contexts, and if we
-            // were to use `core::mem::transmute`, this macro would not work in
-            // `std` contexts in which `core` was not manually imported. This is
-            // not a problem for 2018 edition crates.
-            unsafe { $crate::__real_transmute(e) }
+            // We use this reexport of `core::mem::transmute` because we know it
+            // will always be available for crates which are using the 2015
+            // edition of Rust. By contrast, if we were to use
+            // `std::mem::transmute`, this macro would not work for such crates
+            // in `no_std` contexts, and if we were to use
+            // `core::mem::transmute`, this macro would not work in `std`
+            // contexts in which `core` was not manually imported. This is not a
+            // problem for 2018 edition crates.
+            unsafe { $crate::macro_util::core_reexport::mem::transmute(e) }
         }
     }}
 }

src/derive_util.rs renamed to src/macro_util.rs

@@ -2,14 +2,14 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-//! Utilities used by `zerocopy-derive`.
+//! Utilities used by macros and by `zerocopy-derive`.
 //!
-//! These are defined in `zerocopy` rather than in code generated by
-//! `zerocopy-derive` so that they can be compiled once rather than recompiled
-//! for every pair of type and trait (in other words, if they were defined in
-//! generated code, then deriving `AsBytes` and `FromBytes` on three different
-//! types would result in the code in question being emitted and compiled six
-//! different times).
+//! These are defined here `zerocopy` rather than in code generated by macros or
+//! by `zerocopy-derive` so that they can be compiled once rather than
+//! recompiled for every invocation (e.g., if they were defined in generated
+//! code, then deriving `AsBytes` and `FromBytes` on three different types would
+//! result in the code in question being emitted and compiled six different
+//! times).
 
 #![allow(missing_debug_implementations)]
 
@@ -63,6 +63,12 @@ macro_rules! union_has_padding {
     };
 }
 
+pub mod core_reexport {
+    pub mod mem {
+        pub use core::mem::transmute;
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use crate::util::testutil::*;

zerocopy-derive/Cargo.toml

@@ -5,7 +5,7 @@
 [package]
 edition = "2021"
 name = "zerocopy-derive"
-version = "0.7.6"
+version = "0.7.7"
 authors = ["Joshua Liebow-Feeser <joshlf@google.com>"]
 description = "Custom derive for traits from the zerocopy crate"
 license = "BSD-2-Clause"

zerocopy-derive/src/lib.rs

@@ -530,8 +530,8 @@ fn impl_block<D: DataExt>(
         let fields = field_types.iter();
         let validator_macro = check.validator_macro_ident();
         parse_quote!(
-            zerocopy::derive_util::HasPadding<#type_ident, {zerocopy::#validator_macro!(#type_ident, #(#fields),*)}>:
-                zerocopy::derive_util::ShouldBe<false>
+            zerocopy::macro_util::HasPadding<#type_ident, {zerocopy::#validator_macro!(#type_ident, #(#fields),*)}>:
+                zerocopy::macro_util::ShouldBe<false>
         )
     });