Feature request: show submodule changes in git diff view

[yangyao]

Problem

git diff view does not work well for monorepos/workspaces that use Git submodules.

In this setup, it is not enough to only show that the superproject has a submodule pointer change. I also need to see what changed inside each submodule.

Request

Please add support in git diff view for repositories built with Git submodules, so the UI can surface changes for each submodule.

Ideally this would include:

• detecting modified submodules in the current workspace
• showing each submodule as its own changed unit in the diff view
• allowing users to inspect the actual changes inside each submodule, not just the top-level pointer update

Why this matters

For submodule-based monorepos, the current diff is incomplete from a review/workflow perspective.

If the UI only shows that a submodule SHA changed, users still need to manually enter each submodule and inspect changes separately. That breaks the review flow and makes the built-in diff view much less useful.

A proper diff experience should make submodule changes visible directly in the app.

Thanks.

[CyntaxDotDev]

Strong +1. This is the single thing keeping me out of the diff view on my two largest projects, and honestly it's the one thing standing between me and moving over to T3 Code for real.

The layout, which I suspect is common enough: a thin superproject that owns nothing but .gitmodules, compose.yaml, a Makefile and the docs, with every line of real code living in a submodule. One of mine has 18 submodules, the other 5. They hold a backend API, several frontend apps, and a set of shared packages (design system, generated API client, tsconfig) that the apps consume. The superproject is orchestration; the submodules are the product.

The consequence is that the diff tree is empty almost all of the time. A normal turn touches a shared package, the app that consumes it, and the API behind it. That's three submodules and three real diffs, and T3 Code shows me either nothing at all or a single pointer bump with a SHA on it. To review the turn I just watched an agent produce, I have to leave the app and run git -C <submodule> diff three times. The per-turn diff is the feature I want most from this app, and on these repos it's the one feature I can't use.

That's why this matters more to me than a nice-to-have: I currently run PhpStorm/Rider plus Ghostty alongside T3 Code, and the only reason the JetBrains window stays open is that it's where I can actually see and stage what changed across the submodules. Until the diff view understands this layout I can't properly judge T3 Code on its merits, because the part I'd judge it on is dark. Fix this and the IDE becomes optional for me; leave it and I stay on a split workflow no matter how good the rest gets.

What would cover it:

1. Treat each checked-out submodule as its own root when collecting changes, grouped per submodule in the diff tree. git submodule foreach --recursive git status --porcelain enumerates them; git diff --submodule=diff on the superproject already emits the nested hunks if that's the cheaper route.
2. The same grouping in Source Control and commit, because a change spanning three submodules is three commits plus a pointer bump, not one commit.

Worth flagging the overlap with #7041 (multi-repo workspaces), because I think submodules are the cheap corner of that problem rather than a separate feature. The repo boundaries are already declared in-tree by .gitmodules, so there's no new project file, no .code-workspace to agree on, and no user configuration. git hands you the list. If the per-repo-root plumbing from that thread ever lands, submodule roots should fall out of it nearly free.

One thing I have not verified and would want to know before trusting it: what checkpoint restore currently does with submodules. If checkpoints only track the superproject, then "go back" silently leaves every submodule working tree untouched while claiming the turn was reverted. That's a considerably worse failure mode than an incomplete diff, and it has the same root cause.