ci: pin rustc nightly version

Author: apoelstra

.github/workflows/rust.yml

@@ -9,6 +9,17 @@ on:   # yamllint disable-line rule:truthy
 name: Continuous integration
 
 jobs:
+  Prepare:
+    runs-on: ubuntu-24.04
+    outputs:
+      nightly_version: ${{ steps.read_toolchain.outputs.nightly_version }}
+    steps:
+      - name: "Checkout repo"
+        uses: actions/checkout@v4
+      - name: "Read nightly version"
+        id: read_toolchain
+        run: echo "nightly_version=$(cat nightly-version)" >> $GITHUB_OUTPUT
+
   Stable:                       # 2 jobs, one per lock file.
     name: Test - stable toolchain
     runs-on: ubuntu-latest
@@ -34,6 +45,7 @@ jobs:
 
   Nightly:                      # 2 jobs, one per lock file.
     name: Test - nightly toolchain
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -49,7 +61,9 @@ jobs:
           ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: "Set dependencies"
         run: cp Cargo-${{ matrix.dep }}.lock Cargo.lock
       - name: "Run test script"
@@ -82,6 +96,7 @@ jobs:
 
   Lint:
     name: Lint - nightly toolchain
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -97,7 +112,9 @@ jobs:
           ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: "Install clippy"
         run: rustup component add clippy
       - name: "Set dependencies"
@@ -130,6 +147,7 @@ jobs:
 
   Docsrs:
     name: Docs - nightly toolchain
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -145,14 +163,17 @@ jobs:
           ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: "Set dependencies"
         run: cp Cargo-${{ matrix.dep }}.lock Cargo.lock
       - name: "Run test script"
         run: ./maintainer-tools/ci/run_task.sh docsrs
 
   Bench:
     name: Bench - nightly toolchain
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
@@ -168,26 +189,31 @@ jobs:
           ref: c3324024ced9bb1eb854397686919c3ff7d97e1e
           path: maintainer-tools
       - name: "Select toolchain"
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: "Set dependencies"
         run: cp Cargo-${{ matrix.dep }}.lock Cargo.lock
       - name: "Run test script"
         run: ./maintainer-tools/ci/run_task.sh bench
 
   Format:                       #  1 job, run cargo fmt directly.
     name: Format - nightly toolchain
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
     steps:
       - name: "Checkout repo"
         uses: actions/checkout@v4
       - name: "Select toolchain"
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: "Install rustfmt"
         run: rustup component add rustfmt
       - name: "Check formatting"
-        run: cargo +nightly fmt --all -- --check
+        run: cargo fmt --all -- --check
 
   Integration:                  # 1 job for each bitcoind version we support.
     name: Integration tests - stable toolchain

nightly-version

@@ -0,0 +1 @@
+nightly-2025-03-21