From 89d57ffb29577c99f0f5187b76bff369f19c5886 Mon Sep 17 00:00:00 2001
From: Waleed Khan <me@waleedkhan.name>
Date: Sat, 7 Dec 2024 23:02:11 +0200
Subject: [PATCH] build: add `rust-toolchain.toml`

Follow-up from discussion at https://discord.com/channels/968932220549103686/1288926971719323762

I don't think we achieved consensus in that thread. We could use `stable` or `nightly` here instead if we prefer. Note that user `rustup` overrides are still respected in the presence of a `rust-toolchain.toml`.
---
 Cargo.toml           |  2 +-
 docs/contributing.md | 14 ++++++++++++--
 rust-toolchain.toml  |  4 ++++
 3 files changed, 17 insertions(+), 3 deletions(-)
 create mode 100644 rust-toolchain.toml

diff --git a/Cargo.toml b/Cargo.toml
index a29e97cc1..e63a08291 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -7,7 +7,7 @@ members = ["cli", "lib", "lib/gen-protos", "lib/proc-macros", "lib/testutils"]
 [workspace.package]
 version = "0.24.0"
 license = "Apache-2.0"
-rust-version = "1.76" # NOTE: remember to update CI, contributing.md, changelog.md, install-and-setup.md, and flake.nix
+rust-version = "1.76" # NOTE: remember to update CI, rust-toolchain.toml, contributing.md, changelog.md, install-and-setup.md, and flake.nix
 edition = "2021"
 readme = "README.md"
 homepage = "https://github.com/martinvonz/jj"
diff --git a/docs/contributing.md b/docs/contributing.md
index f0a052f54..eee956578 100644
--- a/docs/contributing.md
+++ b/docs/contributing.md
@@ -133,7 +133,6 @@ recommended steps.
 One-time setup:
 
     rustup toolchain add nightly  # wanted for 'rustfmt'
-    rustup toolchain add 1.76     # also specified in Cargo.toml
     cargo install cargo-insta
     cargo install cargo-watch
     cargo install cargo-nextest
@@ -142,7 +141,7 @@ During development (adapt according to your preference):
 
     cargo watch --ignore '.jj/**' -s \
       'cargo clippy --workspace --all-targets \
-       && cargo +1.76 check --workspace --all-targets'
+       && cargo check --workspace --all-targets'
     cargo +nightly fmt # Occasionally
     cargo nextest run --workspace # Occasionally
     cargo insta test --workspace --test-runner nextest # Occasionally
@@ -189,6 +188,17 @@ These are listed roughly in order of decreasing importance.
    On Linux, you may be able to speed up `nextest` even further by using
    the `mold` linker, as explained below.
 
+### Using an alternative Rust compiler version
+
+To use a different version of the Rust compiler/toolchain for development, you
+can run:
+
+    rustup override set 1.80  # or any other version
+
+Or manually set it in individual `cargo` commands:
+
+    cargo +1.80 clippy --workspace --all-targets  # or any other version
+
 ### Using `mold` for faster tests on Linux
 
 On a machine with a multi-core CPU, one way to speed up
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 000000000..876b6bdf3
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,4 @@
+[toolchain]
+channel = "1.76"
+profile = "default"
+components = ["rust-analyzer"]