rust-toolchain.toml

# rust-toolchain.toml -- the Rust toolchain this crate is built and linted with.
#
# ONE DECLARATION, THREE READERS, and that is the whole reason this file exists
# rather than a fourth manifest entry. rustup reads it on every cargo
# invocation in this tree; GitHub Actions' Rust setup reads it; and mise reads
# it as an idiomatic version file. Before it, the same two facts were written
# out in three places that nothing compared:
#
#   .github/workflows/test.yml   dtolnay/rust-toolchain@stable
#   toolchain.toml [[setup]]     rustup default stable; rustup component add rustfmt clippy
#   toolchain.toml [[tool]]      rustc want = ">=1.90"
#
# The first two are the same instruction typed twice, and the third is a
# restatement of Cargo.toml `rust-version`. A developer's box was configured by
# the setup step, the runner by the workflow, and nothing checked that the two
# agreed about either the channel or the component list.
#
# `stable`, NOT A PINNED VERSION. The pinned form is a version a dependency bot
# cannot see, which is what `unmanaged-pins` refuses elsewhere in this fleet.
# The floor this crate refuses to build below is a different claim and stays
# where it was: Cargo.toml `rust-version`, declared once, which cargo itself
# enforces at resolution.
#
# COMPONENTS ARE THE POINT. They are rustup's vocabulary and no version manager
# owns them, so this is the only file that can carry `rustfmt` and `clippy`
# beside the channel. A fresh checkout now has them after the first cargo
# command, rather than after remembering to run an install step.

[toolchain]
channel = "stable"
components = ["rustfmt", "clippy"]