Merge #259: ci: unify nightly versions in Cargo.toml

b8a32c9 ci: unify nightly embedded version on Cargo.toml (satsfy (Renato Britto))
a924cdc ci: migrate nightly update to rbmt on Cargo.toml (satsfy (Renato Britto))

Pull request description:

  Follow up from #254 (comment)
  
  After the rbmt CI migration, most jobs were already consuming nightly from `[package.metadata.rbmt.toolchains]` in `Cargo.toml`, but the weekly updater still wrote `nightly-version`. This change makes `Cargo.toml` the single nightly source of truth across the updater and CI jobs.
  
  Changes:
  - update weekly nightly cron to use `cargo rbmt toolchains --update-nightly.` Replicates rust-bitcoin CI closely.
  - `nightly-version` removed.
  - migrate Embedded CI job to read nightly from `Cargo.toml` instead of `nightly-version.`
  
  Validated in personal fork CI: 
  - The CI run (didn't create the PR because it wasn't allowed): https://github.com/satsfy/rust-bech32/actions/runs/24799694669/job/72578713007
  - PR produced: https://github.com/satsfy/rust-bech32/compare/master...satsfy:rust-bech32:create-pull-request/weekly-nightly-update?expand=1


ACKs for top commit:
  apoelstra:
    ACK b8a32c9; successfully ran local tests


Tree-SHA512: f2381f1c13eaebcb6e256bf82ee110dab9bf1fe2615a0075b9953e0fd808d4b8f94f1f49568522dc99193f6e1a5ae9619a60cf3b77c084027d9236a8fa206bf1

Author: apoelstra

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

@@ -3,39 +3,33 @@ on:
   schedule:
     - cron: "5 0 * * 6" # Saturday at 00:05
   workflow_dispatch: # allows manual triggering
+permissions: {}
 jobs:
   format:
     name: Update nightly rustc
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-24.04
+    permissions:
+      contents: write
+      id-token: write
+      pull-requests: write
     steps:
-      - uses: actions/checkout@v4
-      - uses: dtolnay/rust-toolchain@nightly
-      - name: Update rust.yml to use latest nightly
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+        with:
+          persist-credentials: false
+      - name: Install cargo-rbmt
+        run: cargo install --git https://github.com/rust-bitcoin/rust-bitcoin-maintainer-tools.git --rev $(cat rbmt-version) cargo-rbmt
+      - name: Update nightly toolchain in Cargo.toml
         run: |
-          set -x
-          # Not every night has a nightly, so extract the date from whatever
-          # version of the compiler dtolnay/rust-toolchain gives us.
-          NIGHTLY_DATE=$(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" >> $GITHUB_ENV
-          fi
+          cargo rbmt toolchains --update-nightly
+          echo "nightly_version=$RBMT_NIGHTLY" >> $GITHUB_ENV
       - name: Create Pull Request
-        if: env.changes_made == 'true'
-        uses: peter-evans/create-pull-request@v7
+        uses: peter-evans/create-pull-request@271a8d0340265f705b14b6d32b9829c1cb33d45e # v7.0.8
         with:
           token: ${{ secrets.APOELSTRA_RUST_BITCOIN_ORG_CREATE_PR }}
           author: Update Nightly Rustc Bot <bot@example.com>
           committer: Update Nightly Rustc Bot <bot@example.com>
-          title: Automated update to nightly-version (to nightly-${{ env.nightly_date }})
+          title: Automated daily update to rustc (to ${{ env.nightly_version }})
           body: |
-           Automated update to Github CI workflow `rust.yml` by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action
-          commit-message: Automated update to Github CI to rustc nightly-${{ env.nightly_date }}
-          branch: create-pull-request/weekly-nightly-update
+           Automated update to Cargo.toml workspace metadata by [create-pull-request](https://github.com/peter-evans/create-pull-request) GitHub action
+          commit-message: Automated update to rustc ${{ env.nightly_version }}
+          branch: create-pull-request/daily-nightly-update

.github/workflows/rust.yml

@@ -99,9 +99,9 @@ jobs:
         uses: actions/checkout@v4
       - name: Set up QEMU
         run: sudo apt-get update -y && sudo apt-get install -y qemu-system-arm gcc-arm-none-eabi
-      - name: Read nightly version
+      - name: Read nightly version from Cargo.toml
         id: nightly
-        run: echo "version=$(cat nightly-version)" >> $GITHUB_OUTPUT
+        run: echo "version=$(cargo metadata --format-version 1 --no-deps | jq -r '.packages[0].metadata.rbmt.toolchains.nightly')" >> "$GITHUB_OUTPUT"
       - name: Checkout Toolchain
         uses: dtolnay/rust-toolchain@v1
         with: