[RFC] Add GitHub PR update delta comments

eden/scm/sapling/ext/github/consts/query.py

@@ -81,6 +81,18 @@
 }
 """
 
+GRAPHQL_ADD_COMMENT = """
+mutation ($subjectId: ID!, $body: String!) {
+  addComment(input: {subjectId: $subjectId, body: $body}) {
+    commentEdge {
+      node {
+        id
+      }
+    }
+  }
+}
+"""
+
 GRAPHQL_CREATE_BRANCH = """
 mutation ($repositoryId: ID!, $name: String!, $oid: GitObjectID!) {
   createRef(input: {repositoryId: $repositoryId, name: $name, oid: $oid}) {

eden/scm/sapling/ext/github/gh_submit.py

@@ -355,6 +355,20 @@ async def update_pull_request(
         return Ok(result.unwrap()["data"]["updatePullRequest"]["pullRequest"]["id"])
 
 
+async def add_comment(hostname: str, subject_id: str, body: str) -> Result[str, str]:
+    """Adds a comment to an issue or pull request, returning the comment node ID."""
+    params: Dict[str, _Params] = {
+        "query": query.GRAPHQL_ADD_COMMENT,
+        "subjectId": subject_id,
+        "body": body,
+    }
+    result = await gh_cli.make_request(params, hostname=hostname)
+    if result.is_err():
+        return Err(result.unwrap_err())
+    else:
+        return Ok(result.unwrap()["data"]["addComment"]["commentEdge"]["node"]["id"])
+
+
 async def create_branch(
     *, hostname: str, repo_id: str, branch_name: str, oid: str
 ) -> Result[str, str]:

eden/scm/sapling/ext/github/mock_utils.py

@@ -286,7 +286,7 @@ def expect_update_pr_request(
     ) -> "UpdatePrRequest":
         if not stack_pr_ids:
             stack_pr_ids = [pr_number]
-        stack_pr_ids = list(reversed(sorted(stack_pr_ids)))
+        stack_pr_ids = sorted(stack_pr_ids, reverse=True)
 
         if len(stack_pr_ids) > 1:
             pr_list = [
@@ -313,6 +313,19 @@ def expect_update_pr_request(
         self._add_request(key, request)
         return request
 
+    def expect_add_comment_request(
+        self, pr_id: str, body: str
+    ) -> "AddCommentRequest":
+        params: ParamsType = {
+            "query": query.GRAPHQL_ADD_COMMENT,
+            "subjectId": pr_id,
+            "body": body,
+        }
+        key = create_request_key(params, self.hostname)
+        request = AddCommentRequest(key, pr_id)
+        self._add_request(key, request)
+        return request
+
     def expect_get_username_request(
         self,
     ) -> "GetUsernameRequest":
@@ -545,6 +558,29 @@ def get_response(self) -> Result[JsonDict, str]:
         return self._response
 
 
+class AddCommentRequest(MockRequest):
+    def __init__(self, key: str, pr_id: str) -> None:
+        self._key = key
+        self._response: Optional[Result[JsonDict, str]] = None
+
+        self._pr_id = pr_id
+
+    def and_respond(self):
+        data = {
+            "data": {
+                "addComment": {
+                    "commentEdge": {"node": {"id": f"comment_{self._pr_id}"}}
+                }
+            }
+        }
+        self._response = Ok(data)
+
+    def get_response(self) -> Result[JsonDict, str]:
+        if self._response is None:
+            raise MockResponseNotSet(self._key)
+        return self._response
+
+
 class GetUsernameRequest(MockRequest):
     def __init__(self, key: str) -> None:
         self._key = key