From 01ebdac5b727fc7226023f9ed9f1581fe07de230 Mon Sep 17 00:00:00 2001
From: Kevin Reid <kpreid@switchb.org>
Date: Tue, 19 Sep 2023 10:13:05 -0700
Subject: [PATCH] Use `rust-toolchain.toml` to specify target and component
 requirements.

This way, the requirements are automatically available to all users,
not just specifically the GitHub Actions CI.

A caveat is that `rustup override set` ignores the file entirely, so
in order to change toolchains we have to patch the file instead of
using the override command. Still seems better overall.
---
 .github/workflows/ci.yml          | 11 ++++++-----
 .github/workflows/unstable-ci.yml | 12 ++++--------
 rust-toolchain.toml               |  5 +++++
 3 files changed, 15 insertions(+), 13 deletions(-)
 create mode 100644 rust-toolchain.toml

diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 430155721..5cc26612c 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -92,12 +92,13 @@ jobs:
 
     - run: df -h .
 
-    - name: Install Rust toolchain
-      # Install exactly what we need: compiler, Cargo, clippy, rustfmt
+    - name: Set Rust toolchain
+      # The rust-toolchain.toml file specifies the targets and components we need,
+      # but we may want to override the toolchain.
+      if: ${{ matrix.toolchain != 'stable' }}
       run: |
-          rustup toolchain install "${{ matrix.toolchain }}" --profile=minimal --component=clippy --component=rustfmt
-          rustup target add --toolchain="${{ matrix.toolchain }}" wasm32-unknown-unknown
-          rustup override set "${{ matrix.toolchain }}"
+          sed -i "s/stable/${{ matrix.toolchain }}/" rust-toolchain.toml
+          rustup show  # triggers installation of selected toolchain
 
     - name: Install nightly for -Z direct-minimal-versions
       if: ${{ matrix.depversions == 'minimal' }}
diff --git a/.github/workflows/unstable-ci.yml b/.github/workflows/unstable-ci.yml
index 9cfcd5e07..49cd1e0b4 100644
--- a/.github/workflows/unstable-ci.yml
+++ b/.github/workflows/unstable-ci.yml
@@ -63,16 +63,12 @@ jobs:
       with:
         ref: unstable-rust
 
-    - name: Install Rust toolchain
-      # Install exactly what we need: compiler, Cargo, clippy, rustfmt
+    - name: Set Rust toolchain
+      # The rust-toolchain.toml file specifies the targets and components we need.
+      # Therefore, CI only needs to set the toolchain override.
       run: |
-          rustup toolchain install "${{ matrix.toolchain }}" --profile=minimal --component=clippy --component=rustfmt
-          rustup target add --toolchain="${{ matrix.toolchain }}" wasm32-unknown-unknown
           rustup override set "${{ matrix.toolchain }}"
-
-    - name: Install nightly too
-      if: ${{ matrix.depversions == 'minimal' }}
-      run: rustup toolchain install nightly --profile=minimal 
+          rustup show  # triggers installation of selected toolchain
 
     - name: Install native libraries
       if: ${{ runner.os == 'Linux' }}
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 000000000..a01bbcd6c
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,5 @@
+[toolchain]
+channel = "stable"
+targets = ["wasm32-unknown-unknown"]
+profile = "minimal"
+components = ["clippy", "rustfmt"]