Changes to default build targets on docs.rs

This post announces two changes to the list of default targets used to build documentation on docs.rs.

Crate authors can specify a custom list of targets using docs.rs metadata in Cargo.toml. If this metadata is not provided, docs.rs falls back to a default list. We are updating this list to better reflect the current state of the Rust ecosystem.

Apple silicon (ARM64) replaces x86_64

Reflecting Apple's transition from x86_64 to its own ARM64 silicon, the Rust project has updated its platform support tiers. The aarch64-apple-darwin target is now Tier 1, while x86_64-apple-darwin has moved to Tier 2. You can read more about this in RFC 3671 and RFC 3841.

To align with this, docs.rs will now use aarch64-apple-darwin as the default target for Apple platforms instead of x86_64-apple-darwin.

Linux ARM64 replaces 32-bit x86

Support for 32-bit i686 architectures is declining, and major Linux distributions have begun to phase it out.

Consequently, we are replacing the i686-unknown-linux-gnu target with aarch64-unknown-linux-gnu in our default set.

New default target list

The updated list of default targets is:

x86_64-unknown-linux-gnu
aarch64-apple-darwin (replaces x86_64-apple-darwin)
x86_64-pc-windows-msvc
aarch64-unknown-linux-gnu (replaces i686-unknown-linux-gnu)
i686-pc-windows-msvc

Opting out

If your crate requires the previous default target list, you can explicitly define it in your Cargo.toml:

[package.metadata.docs.rs]
targets = [
    "x86_64-unknown-linux-gnu",
    "x86_64-apple-darwin",
    "x86_64-pc-windows-msvc",
    "i686-unknown-linux-gnu",
    "i686-pc-windows-msvc"
]

Note that docs.rs continues to support any target available in the Rust toolchain; only the default list has changed.