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Chapter 5. Changes in Rust Toolset in Red Hat Developer Tools 2018.4

This chapter lists some notable changes in Rust Toolset since its previous release.

5.1. Rust
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Rust has been updated from version 1.26.2 to 1.29.2. Notable changes include:

  • Explicit SIMD: While Rust’s code generator will automatically try to use SIMD when possible, developers can now exercise more control over this. Using #[cfg(target_feature = "avx2")] will detect if that feature is globally enabled, and the #[target_feature = "avx2"] attribute will enable that feature for the codegen of a particular function. The std::arch module provides explicit SIMD intrinsics for different targets.
  • dyn Trait is the new preferred syntax for trait objects that dynamically dispatch method calls. For example, Box<Debug> is now Box<dyn Debug>. This is intended to provide better contrast to impl Trait, which always statically dispatches method calls since its concrete type is known.
  • The #[must_use] attribute can be applied to functions, raising a compiler warning if the return value is not used by the caller. This was previously only available on type definitions.
  • New library stabilizations like Iterator::try_fold and Option::filter.
  • Global allocators are now supported to override the default allocator configured by the compiler (by default, glibc malloc in rust-toolset). For instance, the jemallocator crate lets one choose jemalloc instead.
  • The compiler has improved diagnostics for format strings, indicating more specific reasons why a format is invalid.
  • New library stabilizations such as NonZeroU<n> wrappers. These enable size optimizations for numbers that will never be zero, like using zero to mean None in an Option<NonZeroU32>.
  • #[test] functions can now return Result values, similar to the prior change allowing this on main().

5.2. cargo
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The cargo tool has been updated from version 0.26.0 to 1.29.0. Notable changes include:

  • The new --target-dir option may be used to set the build output path.
  • cargo will now automatically discover tests, examples, and binaries.
  • Published crates are not allowed to modify their src directory.

5.3. cargo-vendor
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The cargo-vendor tool has been updated from version 0.1.13 to 0.1.17.

5.4. Rust Language Server
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The Rust Language Server (RLS) version 0.130.0 has been added to Red Hat Developer Tools. This tool enables integration of Rust with Integrated development environments. RLS is provided by the rust-toolset-8-rls-preview package.

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