Windows with `macos-titlebar-style = hidden` create new windows when the
new tab binding is pressed. This behavior has existed for a long time.
However, these windows did not cascade, meaning they'd appear overlapped
directly on top of the previous window, which is kind of nasty.
This commit changes it so that new windows created via new tab from a
hidden titlebar window will cascade.
When closing a window that contains multiple tabs, the undo operation
now properly restores all tabs as a single tabbed window rather than
just restoring the active tab.
The implementation:
- Collects undo states from all windows in the tab group before closing
- Sorts them by their original tab index to preserve order
- Clears tab group references to avoid referencing garbage collected objects
- Restores all windows and re-adds them as tabs to the first window
- Tracks and restores which tab was focused (or focuses the last tab if none were)
AI prompts that generated this commit are below.
Each separate prompt is separated by a blank line, so this session was
made up with many prompts in a back-and-forth conversation.
> We need to update the undo/redo implementation in
> @macos/Sources/Features/Terminal/TerminalController.swift `closeWindowImmediately`
> to handle the case that multiple windows in a tab group are closed all at once,
> and to restore them as a tabbed window. To do this, I think we should collect
> all the `undoStates`, sort them by `tabIndex` (null at the end), and then on j
> restore, restore them one at a time but add them back to the same tabGroup. We
> can't use the tab group in the `undoState` because it will be garbage collected
> by then. To be sure, we should just set it to nil.
I should note at this point that the feature already worked, but the
code quality and organization wasn't up to my standards. If someone
using AI were just trying to make something work, they might be done at
this point.
I do think this is the biggest gap I worry about with AI-assisted
development: bridging between the "it works" stage at a junior quality
and the "it works and is maintainable" stage at a senior quality. I
suspect this will be a balance of LLMs getting better but also senior
code reviewers remaining highly involved in the process.
> Let's extract all the work you just did into a dedicated private method
> called `registerUndoForCloseWindow`
Manual: made some tweaks to comments, moved some lines around, didn’t change
any logic.
> I think we can pull the tabIndex directly from the undoState instead of
> storing it in a tuple.
> Instead of `var undoStates`, I think we can create a `let undoStates` and
> build and filter and sort them all in a chain of functional mappings.
> Okay, looking at your logic for restoration, the `var firstController` and
> conditionals are littly messy. Can you make your own pass at cleaning those
> up and I'll review and provide more specific guidance after.
> Excellent. Perfect. The last thing we're missing is restoring the proper
> focused window of the tab group. We should store that and make sure the
> proper window is made key. If no windows were key, then we should make the
> last one key.
> Excellent. Any more cleanups or comments you'd recommend in the places you
> changed?
Notes on the last one: it gave me a bunch of suggestions, I rejected most but
did accept some.
> Can you write me a commit message summarizing the changes?
It wrote me a part of the commit message you're reading now, but I
always manually tweak the commit message and add my own flair.
This is a major rework of how we represent, handle, and render splits in
the macOS app.
This new PR moves the split structure into a dedicated, generic
(non-Ghostty-specific) value-type called `SplitTree<V>`. All logic
associated with splits (new split, close split, move split, etc.) is now
handled by notifications on `BaseTerminalController`. The view hierarchy
is still SwiftUI but it has no logic associated with it anymore and
purely renders a static tree of splits.
Previously, the split hierarchy was owned by AppKit in a type called
`SplitNode` (a recursive class that contained the tree structure). All
logic around creating, zooming, etc. splits was handled by notification
listeners directly within the SwiftUI hierarchy. SwiftUI managed a
significant amount of state and we heavily used bindings, publishers,
and more. The reasoning for this is mostly historical: splits date back
to when Ghostty tried to go all-in on SwiftUI. Since then, we've taken a
more balanced approach of SwiftUI for views and AppKit for data and
business logic, and this has proven a lot more maintainable.
## Spatial Navigation
Previously, focus moving was handled by traversing the tree structure.
This led to some awkward behaviors. See:
https://github.com/ghostty-org/ghostty/issues/524#issuecomment-2668396095
In this PR, we now handle focus moving spatially. This means that move
"left" means moving to the visually left split (from the top-left
corner, a future improvement would be to do it from the cursor
position).
Concretely, given the following split structure:
```
+----------+-----+
| | b |
| | |
| a +-----+
| | |
| | |
| | |
| | |
|----------| d |
| c | |
| | |
+----------+-----+
```
Moving "right" from `c` now moves to `d`. Previously, it would go to
`b`. On Linux, it still goes to `b`.
## Value Types
One of the major architectural shifts is moving **purely to immutable
value types.** Whenever a split property changes such as a new split,
the ratio between splits, zoomed state, etc. we _create an entirely new
`SplitTree` value_ and replace it along the entire view hierarchy. This
is in some ways wasteful, but split hierarchies are relatively small
(even the largest I've seen in practical use are dozens of splits, which
is small for a computer). And using value types lets us get rid of a ton
of change notification soup around the SwiftUI hierarchy. We can rely on
reference counting to properly clean up our closed views.
> [!NOTE]
>
> As an aside, I think value types are going to make it a lot easier in
the future to implement features like "undo close." We can just keep a
trailing list of surface tree states and just restore them. This PR
doesn't do anything like that, but it's now possible.
## SwiftUI Simplicity
Our SwiftUI view hierarchy is dramatically simplified. See the
difference in `TerminalSplitTreeView` (new) vs `TerminalSplit` (old).
There's so much less logic in our new views (almost none!). All of it is
in the AppKit layer which is just way nicer.
## AI Notes
This PR was heavily written by AI. I reviewed every line of code that
was rewritten, and I did manually rewrite at every step of the way in
minor ways. But it was very much written in concert. Each commit usually
started as an AI agent writing the whole commit, then nudging to get
cleaned up in the right way.
One thing I found in this task was that until the last commit, I kept
the entire previous implementation around and compiling. The agent
having access to a previous working version of code during a refactor
made the code it produced as follow up in the new architecture
significantly better, despite the new architecture having major
fundamental differences in how it works!
