Check we're on the right branch before tagging, and on the right tag before uploading

changelog.d/12556.misc

@@ -0,0 +1 @@
+Release script: confirm the commit to be tagged before tagging.

scripts-dev/release.py

@@ -167,9 +167,7 @@ def prepare():
     assert not parsed_new_version.is_devrelease
     assert not parsed_new_version.is_postrelease
 
-    release_branch_name = (
-        f"release-v{parsed_new_version.major}.{parsed_new_version.minor}"
-    )
+    release_branch_name = get_release_branch_name(parsed_new_version)
     release_branch = find_ref(repo, release_branch_name)
     if release_branch:
         if release_branch.is_remote():
@@ -288,6 +286,15 @@ def tag(gh_token: Optional[str]):
     if tag_name in repo.tags:
         raise click.ClickException(f"Tag {tag_name} already exists!\n")
 
+    # Check we're on the right release branch
+    release_branch = get_release_branch_name(current_version)
+    if repo.active_branch.name != release_branch:
+        click.echo(
+            f"Need to be on the release branch ({release_branch}) before tagging. "
+            f"Currently on ({repo.active_branch.name})."
+        )
+        click.get_current_context().abort()
+
     # Get the appropriate changelogs and tag.
     changes = get_changes_for_version(current_version)
 
@@ -459,6 +466,10 @@ def get_package_version() -> version.Version:
     return version.Version(version_string)
 
 
+def get_release_branch_name(version_number: version.Version) -> str:
+    return f"release-v{version_number.major}.{version_number.minor}"
+
+
 def find_ref(repo: git.Repo, ref_name: str) -> Optional[git.HEAD]:
     """Find the branch/ref, looking first locally then in the remote."""
     if ref_name in repo.refs: