build: use fixed nightly, add scheduled workflow with latest nightly

.github/workflows/ci.yaml

@@ -6,10 +6,15 @@ on:
       - main
     tags-ignore:
       - v*
-
   pull_request:
     branches:
       - main
+  workflow_dispatch:
+  schedule:
+    - cron: 0 6/18 * * *
+
+env:
+  IS_SCHEDULE: ${{ github.event_name == 'schedule' && 'true' || '' }}
 
 jobs:
   ci:
@@ -18,12 +23,19 @@ jobs:
       - name: Check out
         uses: actions/checkout@v3
 
+      - name: Determine toolchain
+        run: |
+          if [ -z $IS_SCHEDULE ]; then
+            toolchain = grep channel rust-toolchain.toml | sed -r 's/channel = "(.*)"/\1/'
+          else
+            toolchain = 'nightly'
+          fi
+          echo "setting RUSTUP_TOOLCHAIN to $toolchain"
+          echo "RUSTUP_TOOLCHAIN=$toolchain" >> "$GITHUB_ENV"
+
       - name: Install Rust toolchain
         run: |
-          rustup update
-          rustup toolchain install nightly --profile minimal
-          rustup component add rustfmt --toolchain nightly
-          rustup component add clippy --toolchain nightly
+          rustup toolchain install $RUSTUP_TOOLCHAIN
 
       - name: Install just
         uses: taiki-e/install-action@v2

justfile

@@ -1,24 +1,31 @@
 set shell := ["bash", "-uc"]
 
 check:
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
 	cargo check --tests --all-features
 
 fmt:
-	cargo +nightly fmt
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
+	cargo fmt
 
 fmt_check:
-	cargo +nightly fmt --check
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
+	cargo check
 
 lint:
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
 	cargo clippy --no-deps --all-features -- -D warnings
 
 test:
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
 	cargo test --all-features
 
 fix:
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
 	cargo fix --allow-dirty --allow-staged --all-features
 
 doc:
+	@echo "using toolchain $RUSTUP_TOOLCHAIN"
 	RUSTDOCFLAGS="-D warnings" cargo doc --no-deps --all-features
 
 all: fmt check lint test doc

rust-toolchain.toml

@@ -1,2 +1,2 @@
 [toolchain]
-channel = "nightly"
+channel = "nightly-2023-10-21"