ci: simplify extension check - always require version bump (#2380)

Previous check could not cope with releases off-main.
This simpler form just means sometimes versions need to be
bumped unnecessarily (have already been bumped since last release)
but that is not a problem.

See
https://github.com/CQCL/hugr/actions/runs/15928196052/job/44930533975

Author: ss2165

.github/workflows/ci-py.yml

@@ -200,14 +200,13 @@ jobs:
             # Check against latest tag on the target branch
             # When not on a pull request, base_ref should be empty so we default to HEAD
             if [ -z "$TARGET_REF" ]; then
-              BASE_SHA=""
+              BASE_SHA="HEAD~1"
             else
               BASE_SHA=$(git rev-parse origin/$TARGET_REF)
             fi
-            LAST_TAG=$(git describe --abbrev=0 --match="hugr-*" $BASE_SHA)
-            echo "Latest tag on target: $LAST_TAG"
+            echo "Comparing to ref: $BASE_SHA"
 
-            python ./scripts/check_extension_versions.py $LAST_TAG
+            python ./scripts/check_extension_versions.py $BASE_SHA
         env:
           TARGET_REF: ${{ github.base_ref }}
 

scripts/check_extension_versions.py

@@ -48,8 +48,13 @@ def check_version_changes(changed_files: list[Path], target: str) -> list[str]:
 
                 if current_version == target_version:
                     errors.append(
-                        f"Error: {file_path} was modified but version was not updated. "
-                        f"Current: {current_version}, base: {target_version}"
+                        f"Error: {file_path} was modified but version {current_version}"
+                        " was not updated."
+                    )
+                else:
+                    print(
+                        f"Version updated in {file_path}: {target_version}"
+                        f" -> {current_version}"
                     )
 
             else:
@@ -59,7 +64,6 @@ def check_version_changes(changed_files: list[Path], target: str) -> list[str]:
         except json.JSONDecodeError:
             # File is new or not valid JSON in target
             pass
-
     return errors
 
 
@@ -75,7 +79,7 @@ def main() -> int:
     errors = check_version_changes(changed_files, target)
     if errors:
         for error in errors:
-            print(error)
+            sys.stderr.write(error)
         return 1
 
     print("All changed extension files have updated versions.")