Add dump/restore commands to save and recreate session layouts - #5585

Thanks - this is a reasonable start but I think:

• It should contain a lot more and the intent is for this to use JSON now that we have a parser.
• Output and input should go via the file.c API like load-buffer/save-buffer.
• The commands should have more tmux-typical names.

Also can you please put your real name in the copyright header.

I don't think you got the point...

I think this should be entirely driven by JSON, it should not generate tmux commands.

Could you maybe write up how you see this working? All the stuff that would be saved, restored, how the JSON would look, etc. So we can agree the design before writing the code.

Thanks for the pointer - I think I understand now. Here's how I'd like this to work, before I write any more code:

Scope (v1): for every session - name, base-index, current window; for every window - index, name, layout tree (splits/sizes/active pane, the same JSON the new layout format already produces); for every pane - index, live working directory. Not included: window/pane options, session environment, pane titles, zoomed state, or relaunching whatever was running in each pane. I'd rather ship this minimal version first and add any of that afterwards if you want it - let me know if you'd rather see more of that up front.

JSON shape:

{
  "version": 1,
  "sessions": [
    {
      "name": "work",
      "base_index": 0,
      "current_window": 1,
      "windows": [
        {
          "index": 0,
          "name": "zsh",
          "active_pane": 0,
          "layout": { "V": 2, "L": { "t": "p", "w": 80, "h": 24, "x": 0, "y": 0, "a": true, "i": 0, "I": "%0" } },
          "panes": [ { "index": 0, "cwd": "/home/user" } ]
        }
      ]
    }
  ]
}

layout is exactly what layout_dump() already emits for a window, embedded directly rather than escaped into a string.

save-layout: unchanged from the current code - walks the live session/window/pane trees and writes the JSON above via file_write().

load-layout: this is what I'll rework. Right now it parses the JSON and then generates a script of tmux commands (new-session, new-window, select-layout, ...) and runs that through load_cfg_from_buffer(). I understand now that's not what you want - instead it should read the file via file_read(), parse it with json_parse(), and for each session/window/pane call the internal creation functions directly: session_create() for the session, spawn_window() (the same primitive new-session/new-window already use internally, with sc.idx set to the recorded index so each window lands at the right place without needing any base-index tricks) for each window's first pane, and layout_parse() on the embedded layout JSON to build out the rest of that window's panes and geometry. No cmd_parse/load_cfg_from_buffer anywhere in the restore path.

Let me know if this matches what you had in mind, or if I'm still off - happy to adjust before writing the code.

OK I think this is fine but I'm not sure about base_index, what do you need it for? If you are saving the options you should save them all probably (or at least the selection you want to save for now) in an options section - but mostly a session will use the global option here, and I assume we are not saving that.

Pushed an update addressing this. load-layout no longer generates any tmux commands - it walks the parsed JSON directly and calls session_create(), spawn_window() (with sc.idx set to the recorded index, so windows land correctly with no base-index tricks needed), layout_split_pane()/spawn_pane() for the remaining panes, and layout_parse() on the embedded layout JSON for the exact geometry and active pane.

On base_index specifically: it's gone from the saved JSON. It was only ever needed to place a session's first window correctly when generating new-session text - since spawn_window() can place any window (including the first) at an explicit recorded index directly, it's not needed at all anymore. I also dropped active_pane from the per-window JSON since it was redundant with the "a":true flag already inside the layout tree, which layout_parse() applies on its own.

Verified end to end, including restoring a layout saved under base-index 0 into a session whose config sets base-index 1 - windows still land at their recorded indexes.