This adds a new formatter that can be used with standard Zig `{f}`
formatting that emits any portion of the terminal screen as VT
sequences. In addition to simply styling, this can emit the entire
terminal/screen state such as cursor positions, active style, terminal
modes, etc.
To do this, I've extracted all formatting to a dedicated `formatter`
package within `terminal`. This handles all formatting types (currently
plaintext and VT formatting, but can imagine things like HTML in the
future). Presently, we have "formatting" split out across a variety of
places in Terminal, Screen, PageList, and Page. I didn't remove this
code yet but I intend to unify it all on formatter in the future.
This also doesn't expose this functionality in any user-facing way yet.
This PR just adds it to the ghostty-vt Zig module and unit tests it.
Ghostty app changes will come later.
**This also improves the readonly stream** to handle OSC color
operations for _setting_ but it doesn't emit any responses of course,
since its readonly.
This adds a new stream handler implementation that updates terminal
state in reaction to VT sequences, but doesn't perform any of the
actions that would require responses (e.g. queries).
This is exposed in two ways: first, as a standalone `ReadonlyStream` and
`ReadonlyHandler` type that contains all the implementation. Second, as
a convenience func on `Terminal` as `vtStream` and `vtHandler` which
return their respective types preconfigured to update the calling
terminal state.
This dramatically simplifies libghostty-vt usage from Zig (and will
eventually be exposed to C, too) since a Terminal on its own is ready to
go as a full VT parser and state machine without needing to build any
custom types!
There's a second big bonus here which is that our `stream_readonly.zig`
tests are true end-to-end tests for raw bytes to terminal state. This
will let us test a wider variety of situations more broadly. To start,
there are only a handful of tests implemented here.
**AI disclosure:** Amp wrote basically this whole thing, but I reviewed
it. https://ampcode.com/threads/T-3490efd2-1137-4112-96f6-4bf8a0141ff5
Mitchell Hashimoto