Feature request: merge labels

[jean]

Given input like the following, I'd like all issues with the mergeme label to get the bug label, and for the mergeme label to be deleted.

[bug]
color = "d73a4a"
name = "bug"
description = "Something isn't working"

[mergeme]
color = "f9d0c4"
name = "bug"
description = "To be merged with 'bug' label"

This requires the issue labelling functionality requested in #6

[jean]

Here's some WIP, it doesn't actually do anything yet.

diff --git a/src/labels/cli.py b/src/labels/cli.py
index b904c82..cbc1e46 100644
--- a/src/labels/cli.py
+++ b/src/labels/cli.py
@@ -166,6 +166,7 @@ def sync_cmd(
     """
     labels_to_delete = {}
     labels_to_update = {}
+    labels_to_merge = {}
     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] = remote_label
+                else:
+                    labels_to_update[remote_name] = local_label
         else:
             if remote_name == local_label.name:
                 labels_to_create[local_label.name] = local_label
@@ -212,7 +217,7 @@ 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_delete, labels_to_update, labels_to_merge, labels_to_create, labels_to_ignore
         )
         sys.exit(0)
 
@@ -232,6 +237,13 @@ def sync_cmd(
             click.echo(str(exc), err=True)
             failures.append(name)
 
+    for name, label in labels_to_merge.items():
+        try:
+            context.client.merge_label(repository, name=name, label=label)
+        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)
@@ -255,6 +267,7 @@ def sync_cmd(
 def dryrun_echo(
     labels_to_delete: Labels_Dict,
     labels_to_update: Labels_Dict,
+    labels_to_merge: Labels_Dict,
     labels_to_create: Labels_Dict,
     labels_to_ignore: Labels_Dict,
 ) -> None:
@@ -270,6 +283,11 @@ def dryrun_echo(
         for name in labels_to_update:
             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"  - {name} to {labels_to_merge.params_dict['name']}")
+
     if labels_to_create:
         click.echo(f"This would create the following labels:")
         for name in labels_to_create:
diff --git a/src/labels/github.py b/src/labels/github.py
index c4209d6..aa644d1 100644
--- a/src/labels/github.py
+++ b/src/labels/github.py
@@ -170,6 +170,15 @@ class Client:
 
         return Label(**response.json())
 
+    def merge_label(self, repo: Repository, *, name: str, label: Label) -> Label:
+        """Merge a GitHub issue label to an existing label.
+
+        - Add the target label to all issues with the old label.
+        - Remove the old label from all issues.
+        - Delete the source label.
+        """
+        raise NotImplementedError
+
     def delete_label(self, repo: Repository, *, name: str) -> None:
         """Delete a GitHub issue label.

[jean]

My current implementation does this:

This would merge the following labels:

• 'High priority' to 'P2'
  This would delete the following labels:
• High priority

So all labels that had 'High priority' before, will now have only the 'P2' label.

Is there a case for adding the 'P2' label and leaving the 'High priority' label hanging around?

[jean]

Superseded by #19