ci: pin nightly compiler version

.github/workflows/cron-weekly-update-nightly.yml

@@ -0,0 +1,41 @@
+name: Update Nightly rustc
+on:
+  schedule:
+    - cron: "5 0 * * 6" # Saturday at 00:05
+  workflow_dispatch: # allows manual triggering
+jobs:
+  format:
+    name: Update nightly rustc
+    runs-on: ubuntu-24.04
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@nightly
+      - name: Update rust.yml to use latest nightly
+        run: |
+          set -x
+          # Not every night has a nightly, so extract the date from whatever
+          # version of the compiler dtolnay/rust-toolchain gives us.
+          NIGHTLY_DATE=$(rustc +nightly --verbose --version | sed -ne 's/^commit-date: //p')
+          # Update the nightly version in the reference file.
+          echo "nightly-${NIGHTLY_DATE}" > nightly-version
+          echo "nightly_date=${NIGHTLY_DATE}" >> $GITHUB_ENV
+          # Some days there is no new nightly. In this case don't make an empty PR.
+          if ! git diff --exit-code > /dev/null; then
+              echo "Updated nightly. Opening PR."
+              echo "changes_made=true" >> $GITHUB_ENV
+          else
+              echo "Attempted to update nightly but the latest-nightly date did not change. Not opening any PR."
+              echo "changes_made=false" >> $GITHUB_ENV
+          fi
+      - name: Create Pull Request
+        if: env.changes_made == 'true'
+        uses: peter-evans/create-pull-request@v7
+        with:
+          token: ${{ secrets.APOELSTRA_CREATE_PR_TOKEN }}
+          author: Update Nightly Rustc Bot <bot@example.com>
+          committer: Update Nightly Rustc Bot <bot@example.com>
+          title: Automated daily update to rustc (to nightly-${{ env.nightly_date }})
+          body: |
+           Automated update to Github CI workflow `rust.yml` by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action
+          commit-message: Automated update to Github CI to rustc nightly-${{ env.nightly_date }}
+          branch: create-pull-request/daily-nightly-update

.github/workflows/main.yml

@@ -3,6 +3,17 @@ on: [push, pull_request]
 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
+
   fmt:
     name: Rustfmt
     runs-on: ubuntu-latest
@@ -46,14 +57,15 @@ jobs:
 
   test:
     name: Tests
+    needs: Prepare
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
         rust:
           - stable
           - beta
-          - nightly
+          - ${{ needs.Prepare.outputs.nightly_version }}
           - 1.78.0
     steps:
       - name: Checkout Crate
@@ -122,12 +134,15 @@ jobs:
 
   docs:
     name: Docs
+    needs: Prepare
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Crate
         uses: actions/checkout@v4
       - name: Checkout Toolchain
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@v1
+        with:
+          toolchain: ${{ needs.Prepare.outputs.nightly_version }}
       - name: Check that documentation builds without errors
         env:
           RUSTDOCFLAGS: "--cfg docsrs -D warnings -D rustdoc::broken-intra-doc-links"

nightly-version

@@ -0,0 +1 @@
+nightly-2025-04-11