feat(diff): Enable commenting on expanded lines in PR diffs

[brymut]

Fixes #32257
/claim #32257

Implemented commenting on unchanged lines in Pull Request diffs, lines are accessed by expanding the diff preview. Comments also appear in the "Files Changed" tab on the unchanged lines where they were placed.

Screenshots

• Comment form on expanded lines not in diff

• Comments available to view on Files Changed tab, with badge indicating that there are hidden comments available to view.

Screen.Recording.2025-10-16.at.17.34.43.mov

• Comments available to view on Conversation tab, with line context preview to show where they are located.

• Full commenting process

Screen.Recording.2025-10-18.at.14.33.43.mp4

• Shared link expands to hidden comment

Screen.Recording.2025-10-18.at.06.08.55.mov

[brymut]

Hi @techknowlogick / @lunny, could you please have a look

[lunny]

One concern is how users can tell there are comments on lines that aren’t currently expanded. It would be helpful to display an icon or marker to indicate the presence of comments when those lines cannot be automatically expanded. I believe this is also one of the main challenges of this issue.

[brymut]

One concern is how users can tell there are comments on lines that aren’t currently expanded

Thanks, will look into a suitable way to address this.

[brymut]

Hi @lunny, I added badges on the code expanding buttons to indicate that there are hidden comments outside of the diff. I think this should cover it, in combination of the code context preview in the conversations tab to show where the comments are in context as well at a glance.

Screen.Recording.2025-10-15.at.15.02.42.mov

[lunny]

This floating counter looks great, but there’s a small issue: if the comments are part of the content loaded the second time, then after the first load, the floating box doesn’t appear.

[brymut]

then after the first load, the floating box doesn’t appear.

Hadn't noticed, updated to include updated count of hidden comments if not revealed yet after code expansion.

Screen.Recording.2025-10-16.at.17.34.43.mov

[brymut]

Hi @lunny, thanks for the feedback. Addressed them in comments/changes & updated screen recording with fixes. Please have a look.

[wxiaoguang]

Oh wait, a new bug:

Expand, there is only one comment (at the first line of that section)

(ps: the right side has more "deleted lines", so left 54 ---- right 42 )

[wxiaoguang]

The root problem is that FillHiddenCommentIDsForDiffLine logic is not right.

• Line < 0: use Left to calculate
• Line > 0: use Right to calculate

[brymut]

I can see the issue, even just adding the comment on the line 51, with no comment on the unchanged lines before, we're still getting a badge count of 1

Edit, you were right, FillHiddenCommentIDsForDiffLine was problematic. Left-side comments were being counted as hidden comments in the right-side expand button badge.
Fixed:

• before expansion

• after expansion

[wxiaoguang]

Oh wait, a new problem.

When using Split diff, then if the comment is added by "left" side, then the assumption if commentLineNum < 0 // Skip left-side, unchanged lines always use "right (proposed)" side for comments is wrong .....

Update: made a quick fix. af864c2

[brymut]

When using Split diff, the if the comment is added by "left" side, then the assumption if commentLineNum < 0 // Skip left-side, unchanged lines always use "right (proposed)" side for comments is wrong .....

Thanks, the semantics here have really got into the weeds for me. But I think I see what you mean