server/tags: output tag usage count

API.md

@@ -1273,7 +1273,8 @@ A single tag. Tags are used to let users search for posts.
     "implications": <implications>,
     "suggestions":  <suggestions>,
     "creationTime": <creation-time>,
-    "lastEditTime": <last-edit-time>
+    "lastEditTime": <last-edit-time>,
+    "usages":       <usage-count>
 }
 ```
 
@@ -1288,6 +1289,7 @@ A single tag. Tags are used to let users search for posts.
   the user by the web client on usage.
 - `<creation-time>`: time the tag was created, formatted as per RFC 3339.
 - `<last-edit-time>`: time the tag was edited, formatted as per RFC 3339.
+- `<usage-count>`: the number of posts the tag was used in.
 
 ## Detailed tag
 **Description**

server/szurubooru/func/tags.py

@@ -36,6 +36,7 @@ def serialize_tag(tag):
             relation.names[0].name for relation in tag.implications],
         'creationTime': tag.creation_time,
         'lastEditTime': tag.last_edit_time,
+        'usages': tag.post_count,
     }
 
 def serialize_tag_with_details(tag):

server/szurubooru/tests/api/test_tag_creating.py

@@ -46,6 +46,7 @@ def test_creating_simple_tags(test_ctx, fake_datetime):
         'implications': [],
         'creationTime': datetime.datetime(1997, 12, 1),
         'lastEditTime': None,
+        'usages': 0,
     }
     assert len(result['snapshots']) == 1
     tag = tags.get_tag_by_name('tag1')

server/szurubooru/tests/api/test_tag_merging.py

@@ -41,6 +41,7 @@ def test_merging_without_usages(test_ctx, fake_datetime):
         'implications': [],
         'creationTime': datetime.datetime(1996, 1, 1),
         'lastEditTime': None,
+        'usages': 0,
     }
     assert 'snapshots' in result
     assert tags.try_get_tag_by_name('source') is None

server/szurubooru/tests/api/test_tag_retrieving.py

@@ -57,6 +57,7 @@ def test_retrieving_single(test_ctx):
             'lastEditTime': None,
             'suggestions': [],
             'implications': [],
+            'usages': 0,
         },
         'snapshots': [],
     }

server/szurubooru/tests/api/test_tag_updating.py

@@ -53,6 +53,7 @@ def test_simple_updating(test_ctx, fake_datetime):
         'implications': [],
         'creationTime': datetime.datetime(1996, 1, 1),
         'lastEditTime': datetime.datetime(1997, 12, 1),
+        'usages': 0,
     }
     assert len(result['snapshots']) == 1
     assert tags.try_get_tag_by_name('tag1') is None