Rust 1.29: What's New, Release History & Support Lifecycle

What Is New in Rust 1.29

How can cargo fix automatically resolve compiler warnings?

cargo fix can apply compiler-suggested fixes to your code without manual edits.

In practice you run the command and Cargo rewrites the source files where a safe fix exists.

$ cargo fix
    Checking mycrate v0.1.0
      Fixing src/main.rs (1 fix)
    Finished dev [unoptimized + debuginfo] target(s)

After the run the warning disappears because the unused variable was renamed to _i.

What is cargo clippy and why should I run it?

cargo clippy runs an extensive set of lints that catch subtle bugs and style issues.

This matters if you want early detection of patterns that the compiler does not flag, such as dead-locks caused by dropping a reference.

$ rustup component add clippy-preview
$ cargo clippy
error: calls to `std::mem::drop` with a reference instead of an owned value. Dropping a reference does nothing.

The output points to the drop_ref lint and suggests correcting the call.

How do I generate documentation for private items with cargo doc?

Use cargo doc --document-private-items to include non-public symbols in the generated docs.

This is useful for internal teams that need full API visibility while working on a crate.

$ cargo doc --document-private-items
   Compiling mycrate v0.1.0
   Finished dev [unoptimized + debuginfo] target(s) in 0.45s
   Documenting mycrate v0.1.0

The resulting HTML contains pages for private functions, structs, and modules.

Which standard library APIs became stable in Rust 1.29?

Three APIs were stabilized, giving you more ergonomic primitives out of the box.

• Comparison between &str and OsString is now stable.
• Two additional APIs (not named in the release notes) were marked stable for general use.
• These stabilizations reduce the need for external crates for common string handling tasks.