Publish a GitHub release from the changelog section

.github/workflows/nuget.release.yml

@@ -5,7 +5,7 @@ on:
     branches: [ release ]
 
 permissions:
-  contents: read
+  contents: write
   packages: write
   id-token: write
 
@@ -16,6 +16,72 @@ jobs:
     steps:
     - uses: actions/checkout@v4
 
+    # Deliberately before the build. A CHANGES.md section that is missing or
+    # still titled "Unreleased" fails the run here, while nothing has been
+    # published yet - rather than after the push to nuget.org, which cannot be
+    # taken back and whose version number cannot be reused.
+    - name: Resolve version and release notes
+      id: notes
+      run: |
+        set -euo pipefail
+
+        # No pipe into head: under `set -o pipefail` that only holds while the
+        # file has a single <PackageVersion>, and would start failing the day a
+        # second one appears. awk takes the first match and exits.
+        version=$(awk 'match($0, /<PackageVersion>[^<]+<\/PackageVersion>/) {
+                         s = substr($0, RSTART, RLENGTH)
+                         sub(/<PackageVersion>/, "", s)
+                         sub(/<\/PackageVersion>/, "", s)
+                         print s
+                         exit
+                       }' Xrpl/Xrpl.csproj)
+        if [ -z "$version" ]; then
+          echo "::error file=Xrpl/Xrpl.csproj::No <PackageVersion> found."
+          exit 1
+        fi
+
+        # Tags follow NuGet's own normalisation: 11.0.0.0 is published as
+        # 11.0.0, and v10.9.0 / v10.8.0 were tagged that way by hand. A
+        # non-zero fourth component is kept, because then it means something.
+        if [[ "$version" =~ ^([0-9]+\.[0-9]+\.[0-9]+)\.0$ ]]; then
+          tag="v${BASH_REMATCH[1]}"
+        else
+          tag="v${version}"
+        fi
+
+        # From the "## <version> <date>" heading to the next "## " heading.
+        awk -v v="$version" '
+          $0 ~ "^## " v "( |$)" { found = 1; next }
+          found && /^## / { exit }
+          found { print }
+        ' CHANGES.md > release-notes.md
+
+        if [ ! -s release-notes.md ]; then
+          echo "::error file=CHANGES.md::No section headed '## $version' - the release heading is not stamped, or the version does not match."
+          exit 1
+        fi
+
+        # GitHub caps release bodies at 125000 characters and this changelog runs
+        # long - 11.0.0.0 came to 98638 - so truncate rather than fail, and say
+        # so. By whole lines, not bytes: these notes carry non-ASCII characters
+        # and a byte cut would split one, handing the API a body that is not
+        # valid UTF-8. LC_ALL=C makes awk's length() count bytes, which is the
+        # unit the cap is expressed in.
+        limit=120000
+        if [ "$(wc -c < release-notes.md)" -gt "$limit" ]; then
+          LC_ALL=C awk -v limit="$limit" '
+            { n += length($0) + 1; if (n > limit) exit; print }
+          ' release-notes.md > release-notes.trimmed
+          printf '\n\n---\n\n*Truncated at %s characters. The full entry is in [CHANGES.md](https://github.com/%s/blob/release/CHANGES.md).*\n' \
+            "$limit" "$GITHUB_REPOSITORY" >> release-notes.trimmed
+          mv release-notes.trimmed release-notes.md
+          echo "::warning::Release notes truncated to $limit characters."
+        fi
+
+        echo "version=$version" >> "$GITHUB_OUTPUT"
+        echo "tag=$tag" >> "$GITHUB_OUTPUT"
+        echo "Release $tag from version $version, $(wc -c < release-notes.md) characters of notes."
+
     - name: Setup .NET
       uses: actions/setup-dotnet@v4
       with:
@@ -53,3 +119,26 @@ jobs:
 
     - name: Publish to NuGet.org
       run: dotnet nuget push "**/*.nupkg" --skip-duplicate -s https://api.nuget.org/v3/index.json -k ${{ steps.nuget-login.outputs.NUGET_API_KEY }}
+
+    # Last, so a release only ever appears for packages that actually shipped.
+    # Skips an existing tag rather than failing: a re-run of this workflow
+    # should be able to finish, and --skip-duplicate above means the pushes
+    # are already idempotent.
+    - name: Publish GitHub release
+      env:
+        GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        TAG: ${{ steps.notes.outputs.tag }}
+      run: |
+        set -euo pipefail
+
+        if gh release view "$TAG" >/dev/null 2>&1; then
+          echo "Release $TAG already exists - nothing to do."
+          exit 0
+        fi
+
+        gh release create "$TAG" \
+          --target "$GITHUB_SHA" \
+          --title "$TAG" \
+          --notes-file release-notes.md
+
+        echo "Created release $TAG."