chore: make just release open a pull request

justfile

@@ -22,7 +22,8 @@ status:
     echo "newest tag   : $tag"
     echo "on npm       : $published"
 
-# Publish a new version. LEVEL is patch, minor, or major.
+# Step 1 of 2. Bump the version and open the release pull request.
+# LEVEL is patch, minor, or major. This tags nothing.
 release level="patch":
     #!/usr/bin/env bash
     set -euo pipefail
@@ -32,8 +33,13 @@ release level="patch":
       *) echo "error: level must be patch, minor, or major"; exit 1 ;;
     esac
 
-    # A tag is only correct if it points at code that is already on GitHub.
-    # Everything below refuses to tag until that is true.
+    if ! command -v gh >/dev/null 2>&1; then
+      echo "error: the GitHub CLI is missing. Install it from https://cli.github.com"
+      exit 1
+    fi
+
+    # main is protected: it only takes commits through a pull request. So the
+    # bump is made on its own branch and merged the normal way.
     branch="$(git rev-parse --abbrev-ref HEAD)"
     if [ "$branch" != "main" ]; then
       echo "error: you are on '$branch'. Switch to main first."
@@ -52,15 +58,82 @@ release level="patch":
       exit 1
     fi
 
-    # Never tag code that does not build. A bad tag cannot be unpublished.
+    # Never open a release pull request for code that does not build.
     just check
 
-    # npm version bumps package.json, commits, and tags -- in that order,
-    # on the newest commit. Do not do these steps by hand.
-    new="$(npm version {{level}} -m 'chore: release %s')"
+    # --no-git-tag-version: bump package.json and the lockfile, nothing else,
+    # and print the new version. The tag is made later by `just release-tag`,
+    # once the merged commit exists. A tag made now would point at a commit
+    # that a squash or rebase merge throws away, and a wrong tag cannot be
+    # unpublished.
+    tag="$(npm version {{level}} --no-git-tag-version)"
+    version="${tag#v}"
+    release_branch="chore/release-$version"
+
+    if git rev-parse -q --verify "refs/heads/$release_branch" >/dev/null; then
+      git checkout -- package.json package-lock.json
+      echo "error: branch $release_branch already exists. Finish or delete it first."
+      exit 1
+    fi
+
+    # The bumped files are uncommitted, so they follow us onto the new branch
+    # and main is left exactly as it was.
+    git switch --create "$release_branch"
+    git commit --all --message "chore: release $version"
+    git push --set-upstream origin "$release_branch"
+
+    body="$(printf '%s\n\n%s\n' \
+      "Version bump to $version, made by \`just release {{level}}\`." \
+      "Merging this does not publish anything. After it merges, run \`git switch main && just release-tag\` to tag $tag, which is what starts the npm publish.")"
+
+    gh pr create --base main --title "chore: release $version" --body "$body"
+
+    echo ""
+    echo "opened the pull request for $version. Merging it does NOT publish."
+    echo "next: merge it, then run  git switch main && just release-tag"
+
+# Step 2 of 2. Tag the merged release and start the npm publish.
+release-tag:
+    #!/usr/bin/env bash
+    set -euo pipefail
+
+    branch="$(git rev-parse --abbrev-ref HEAD)"
+    if [ "$branch" != "main" ]; then
+      echo "error: you are on '$branch'. Run: git switch main"
+      exit 1
+    fi
+
+    if [ -n "$(git status --porcelain)" ]; then
+      echo "error: you have uncommitted changes. Commit or stash them first."
+      git status --short
+      exit 1
+    fi
+
+    git fetch origin --prune --tags
+    git merge --ff-only origin/main
+
+    version="$(node -p "require('./package.json').version")"
+    tag="v$version"
+
+    if git rev-parse -q --verify "refs/tags/$tag" >/dev/null; then
+      # A tag left over from an earlier run. It is only correct if the code it
+      # points at is the code that is now on main.
+      if ! git merge-base --is-ancestor "$tag" origin/main; then
+        echo "error: tag $tag exists but its commit is not on main."
+        echo "delete it and run this again:  git tag --delete $tag"
+        exit 1
+      fi
+      echo "reusing the existing tag $tag."
+    else
+      git tag --annotate "$tag" --message "chore: release $version"
+    fi
+
+    if git ls-remote --exit-code --tags origin "$tag" >/dev/null 2>&1; then
+      echo "error: $tag is already on GitHub. This release is already done."
+      exit 1
+    fi
 
-    git push origin main
-    git push origin "$new"
+    git push origin "$tag"
 
     echo ""
-    echo "pushed $new. GitHub Actions is publishing it now."
+    echo "pushed $tag. GitHub Actions is publishing it now."