Implement merge_label, fix computing of labels_to_merge

- Fix order of operations (merge, update, delete).

This implementation assumes that when an old label is merged to another
label, the old label should be deleted.

This should normally be what is intended, and avoids ambiguity (e.g.
people start adding the old label again by force of habit).

Author: jean

src/labels/cli.py

@@ -164,8 +164,9 @@ def sync_cmd(
     On success this will also update the local labels file, so that section
     names match the `name` parameter.
     """
-    labels_to_delete = {}
+    labels_to_merge = {}
     labels_to_update = {}
+    labels_to_delete = {}
     labels_to_create = {}
     labels_to_ignore = {}
 
@@ -187,7 +188,11 @@ def sync_cmd(
             if local_label.params_dict == remote_label.params_dict:
                 labels_to_ignore[remote_name] = local_label
             else:
-                labels_to_update[remote_name] = local_label
+                if (remote_name != local_label.name) and (local_label.name in remote_labels):
+                    # There is already a label with this name
+                    labels_to_merge[remote_name] = local_label.name
+                else:
+                    labels_to_update[remote_name] = local_label
         else:
             if remote_name == local_label.name:
                 labels_to_create[local_label.name] = local_label
@@ -212,18 +217,20 @@ def sync_cmd(
     if dryrun:
         # Do not modify remote labels, but only print info
         dryrun_echo(
-            labels_to_delete, labels_to_update, labels_to_create, labels_to_ignore
+            labels_to_merge, labels_to_update, labels_to_delete, labels_to_create, labels_to_ignore
         )
-        sys.exit(0)
+        # sys.exit(0)
+        return
 
     failures = []
 
-    for name in labels_to_delete.keys():
+    # Merge has to occur before update and delete
+    for old_label, new_label in labels_to_merge.items():
         try:
-            context.client.delete_label(repository, name=name)
+            context.client.merge_label(repository, old_label=old_label, new_label=new_label)
         except LabelsException as exc:
             click.echo(str(exc), err=True)
-            failures.append(name)
+            failures.append(old_label)
 
     for name, label in labels_to_update.items():
         try:
@@ -232,6 +239,13 @@ def sync_cmd(
             click.echo(str(exc), err=True)
             failures.append(name)
 
+    for name in labels_to_delete.keys():
+        try:
+            context.client.delete_label(repository, name=name)
+        except LabelsException as exc:
+            click.echo(str(exc), err=True)
+            failures.append(name)
+
     for name, label in labels_to_create.items():
         try:
             context.client.create_label(repository, label=label)
@@ -253,23 +267,29 @@ def sync_cmd(
 
 
 def dryrun_echo(
-    labels_to_delete: Labels_Dict,
+    labels_to_merge: dict,
     labels_to_update: Labels_Dict,
+    labels_to_delete: Labels_Dict,
     labels_to_create: Labels_Dict,
     labels_to_ignore: Labels_Dict,
 ) -> None:
     """Print information about how labels would be updated on sync."""
 
-    if labels_to_delete:
-        click.echo(f"This would delete the following labels:")
-        for name in labels_to_delete:
-            click.echo(f"  - {name}")
+    if labels_to_merge:
+        click.echo(f"This would merge the following labels:")
+        for name in labels_to_merge:
+            click.echo(f"  - {', '.join([' to '.join((old, new)) for old, new in labels_to_merge.items()])}")
 
     if labels_to_update:
         click.echo(f"This would update the following labels:")
         for name in labels_to_update:
             click.echo(f"  - {name}")
 
+    if labels_to_delete:
+        click.echo(f"This would delete the following labels:")
+        for name in labels_to_delete:
+            click.echo(f"  - {name}")
+
     if labels_to_create:
         click.echo(f"This would create the following labels:")
         for name in labels_to_create:

src/labels/github.py

@@ -170,6 +170,78 @@ def edit_label(self, repo: Repository, *, name: str, label: Label) -> Label:
 
         return Label(**response.json())
 
+    def merge_label(self, repo: Repository, *, old_label: str, new_label: str) -> None:
+        """Merge a GitHub issue label to an existing label.
+
+        - Add the target label to all issues with the old label.
+        - The old label will be deleted while processing labels to delete.
+        """
+        logger = logging.getLogger("labels")
+        logger.debug(f"Requesting issues for label {old_label} in {repo.owner}/{repo.name}")
+
+        response = self.session.get(
+                f"{self.base_url}/search/issues?q=label:{old_label}+repo:{repo.owner}/{repo.name}",
+            headers={"Accept": "application/vnd.github.symmetra-preview+json"},
+        )
+
+        if response.status_code != 200:
+            raise GitHubException(
+                f"Error retrieving issues for label {old_label} in {repo.owner}/{repo.name}: "
+                f"{response.status_code} - "
+                f"{response.reason}"
+            )
+
+        json = response.json()
+
+        next_page = response.links.get('next', None)
+        while next_page:
+            logger.debug(f"Requesting {next_page}")
+            response = self.session.get(
+                    next_page['url'],
+                    headers={"Accept": "application/vnd.github.symmetra-preview+json"},
+            )
+
+            if response.status_code != 200:
+                raise GitHubException(
+                    f"Error retrieving next page of issues for label {old_label}: "
+                    f"{response.status_code} - "
+                    f"{response.reason}"
+                )
+
+            json.extend(response.json())
+            next_page = response.links.get('next', None)
+
+        for issue in json['items']:
+            response = self.session.get(
+                    f"{self.base_url}/repos/{repo.owner}/{repo.name}/issues/{issue['number']}/labels",
+                headers={"Accept": "application/vnd.github.symmetra-preview+json"},
+            )
+
+            if response.status_code != 200:
+                raise GitHubException(
+                    f"Error retrieving labels for {repo.owner}/{repo.name}/issue/{issue['number']}: "
+                    f"{response.status_code} - "
+                    f"{response.reason}"
+                )
+
+            labels = [l['name'] for l in response.json()]
+
+            if new_label not in labels:
+                breakpoint()
+                response = self.session.post(
+                    f"{self.base_url}/repos/{repo.owner}/{repo.name}/issues/{issue['number']}/labels",
+                    headers={"Accept": "application/vnd.github.symmetra-preview+json"},
+                    json={'labels': [f"{new_label}"]},
+                )
+                if response.status_code != 200:
+                    raise GitHubException(
+                        f"Error adding '{new_label}' for issue {repo.owner}/{repo.name}/issues/{issue['number']}: "
+                        f"{response.status_code} - "
+                        f"{response.reason}"
+                )
+                logger.debug(f"Added label '{new_label}' to {repo.owner}/{repo.name}/issue/{issue['number']}")
+
+
     def delete_label(self, repo: Repository, *, name: str) -> None:
         """Delete a GitHub issue label.