Escape original merge branch to compile regex

CHANGELOG.md

@@ -29,6 +29,7 @@
 - add pre-commit hook to keep uv.lock in sync ([#3933](https://github.com/nf-core/tools/pull/3933))
 - Fix quote handling in meta.yml ([#3948](https://github.com/nf-core/tools/pull/3948))
 - Add support for SVG files in bump-version command ([#3978](https://github.com/nf-core/tools/pull/3978))
+- Escape original merge branch to compile regex ([#3984](https://github.com/nf-core/tools/pull/3984))
 - handle type for val in topics correctly ([#3991](https://github.com/nf-core/tools/pull/3991))
 - Update docker/login-action digest to c94ce9f ([#3998](https://github.com/nf-core/tools/pull/3998))
 - fix wrong parsing when output values contain spaces ([#3999](https://github.com/nf-core/tools/pull/3999))

nf_core/pipelines/sync.py

@@ -371,7 +371,7 @@ def create_merge_base_branch(self):
         # Check if branch exists already
         branch_list = [b.name for b in self.repo.branches]
         if self.merge_branch in branch_list:
-            merge_branch_format = re.compile(rf"{self.original_merge_branch}-(\d+)")
+            merge_branch_format = re.compile(rf"{re.escape(self.original_merge_branch)}-(\d+)")
             max_branch = max(
                 [1]
                 + [

tests/pipelines/test_sync.py

@@ -396,6 +396,27 @@ def test_create_merge_base_branch_thrice(self):
         for branch_no in [2, 3]:
             assert f"{psync.original_merge_branch}-{branch_no}" in psync.repo.branches
 
+    def test_create_merge_base_branch_with_special_characters(self):
+        """Test that branch names with regex special characters (like +) are handled correctly.
+
+        This tests that the fix using re.escape() works properly when the version
+        contains characters that have special meaning in regex patterns (e.g., '+' in '3.6.0.dev0+local0').
+        Without re.escape(), the '+' would be interpreted as a regex quantifier instead of a literal character.
+        """
+        psync = nf_core.pipelines.sync.PipelineSync(self.pipeline_dir)
+        psync.inspect_sync_dir()
+        psync.get_wf_config()
+
+        psync.original_merge_branch = "nf-core-template-merge-3.6.0.dev0+local0"
+        psync.merge_branch = psync.original_merge_branch
+
+        for _ in range(3):
+            psync.create_merge_base_branch()
+
+        assert psync.merge_branch in psync.repo.branches
+        for branch_no in [2, 3]:
+            assert f"{psync.original_merge_branch}-{branch_no}" in psync.repo.branches
+
     def test_push_merge_branch(self):
         """Try pushing merge branch"""
         psync = nf_core.pipelines.sync.PipelineSync(self.pipeline_dir)