glab-mr-line-comment

Line-attached MR comments on GitLab via glab

When to use

The user asks you to post review feedback as inline comments on specific lines of a GitLab MR diff. The deliverable is a DiffNote (rendered next to the changed line in the MR diff view), not a DiscussionNote (rendered in the MR-level activity feed).

The trap

The obvious approach is to use glab api with --field for each parameter, including nested position[*] keys:

# DO NOT DO THIS — silently degrades to a DiscussionNote
glab api projects/$PID/merge_requests/$IID/discussions -X POST \
  --field "body=$BODY" \
  --field "position[base_sha]=..." \
  --field "position[head_sha]=..." \
  --field "position[new_path]=path/to/file.ts" \
  --field "position[new_line]=42" \
  ...

GitLab's API accepts this request and returns 201, but the resulting note has type: DiscussionNote and no position field. The form-encoded position[*] keys are silently dropped on this endpoint. The comment appears on the MR but is not attached to any line of the diff.

This failure mode is invisible until you actually look at the MR in a browser or query the note back. glab mr note does not support diff positions at all — only glab api does, and only with a JSON body.

The fix

Send the request as a JSON body with --input and an explicit Content-Type header:

glab api projects/$PROJECT_ID/merge_requests/$MR_IID/discussions \
  -X POST \
  -H "Content-Type: application/json" \
  --input /tmp/comment.json

Where /tmp/comment.json is:

{
  "body": "...markdown...",
  "position": {
    "base_sha":     "...",
    "start_sha":    "...",
    "head_sha":     "...",
    "position_type": "text",
    "new_path":     "path/to/file.ts",
    "old_path":     "path/to/file.ts",
    "new_line":     42
  }
}

The response will have notes[0].type === 'DiffNote' and a populated position object. If type is DiscussionNote, the position was dropped — the comment is not line-attached.