Per-perspective lazy-load for perspective.el on Emacs daemon

perspective-lazy-load.el

;; ── Per-perspective state files for Emacs daemon mode ──────────────
;; Requires: perspective, eglot
;;
;; Saves each perspective as var/perspectives/<name>.el.
;; Buffers open lazily — only the perspective you switch into loads files.
;; Unloaded perspectives appear dimmed in dashboard and load on click.
;; Works around perspectives not supporting daemon mode (issues #41, #194).
;; Tested on Emacs 30.2 + daemon + vtsls LSP.
;;
;; ── Key design decisions ────────────────────────────────────────────
;;
;; 1. Save on switch-away (:before advice on persp-switch)
;;    Saves the outgoing perspective while it's still current.
;;
;; 2. Load switches first, then opens files
;;    find-file must run AFTER persp-switch so buffers enter the right
;;    perspective.  Otherwise they leak into whatever perspective was
;;    current before the switch.
;;
;; 3. my-persp-saving guard prevents double-saves
;;    with-perspective calls persp-switch internally, which would
;;    re-trigger the :before advice.  Bind my-persp-saving to t
;;    during save-all and load to suppress recursive saves.
;;
;; 4. Non-current perspectives read struct data directly
;;    my-persp-save-all cannot use with-perspective (it imports buffers
;;    into wrong perspective on switch-back).  Read persp-buffers and
;;    persp-point-marker from the struct directly.
;;
;; 5. (windows nil) for non-current perspectives
;;    persp-window-configuration returns #<window-configuration>, which
;;    prin1 cannot serialize.  Current perspective uses window-state-get
;;    instead (produces a readable list).
;;
;; 6. Terminal frame hash stripped on init
;;    Daemon creates two frames (terminal + GUI).  persp--state-frame-data
;;    saves both.  On load, Frame-1 (terminal data) overwrites the GUI
;;    frame.  Strip persp--hash from non-GUI frames in after-init-hook.
;;
;; ── Dashboard integration ──────────────────────────────────────────
;;
;; Add a perspectives section to dashboard that:
;;   - Lists all perspectives (live + unloaded from disk)
;;   - Dims unloaded perspectives with the 'shadow face
;;   - Opens unloaded perspectives with my-persp-switch (lazy-load)
;;   - Opens loaded perspectives with persp-switch (direct)
;;
;; Register a generator in dashboard-item-generators and a shortcut in
;; dashboard-item-shortcuts.

;; ── Directory and helper ────────────────────────────────────────

(defvar my-persp-dir
  (expand-file-name "var/perspectives" user-emacs-directory))

(defun my-persp-file (name)
  "State file path for perspective NAME."
  (expand-file-name (concat name ".el") my-persp-dir))

;; ── Save (per-switch + per-perspective) ─────────────────────────

(defvar my-persp-saving nil
  "Guard flag to prevent recursive saves.")

(defun my-persp-save (&optional name)
  "Save perspective NAME to var/perspectives/<name>.el.
Assumes caller is already in the target perspective (the :before
advice fires before persp-switch changes context)."
  (let* ((name (or name (persp-current-name)))
         (file (my-persp-file name))
         (persp (gethash name (perspectives-hash))))
    (when (and persp (not (persp-killed-p persp)))
      (persp-save)
      (make-directory my-persp-dir t)
      (let ((data `(persp-state
                     (buffers
                      ,(cl-loop for b in (persp-current-buffers)
                                when (buffer-file-name b)
                                collect (buffer-file-name b)))
                     (windows
                      ,(window-state-get (frame-root-window) t))
                     (point ,(point)))))
        (with-temp-file file
          (prin1 data (current-buffer)))))))

;; ── Load (lazy, one perspective at a time) ──────────────────────

(defun my-persp-load (name)
  "Load perspective NAME from its state file into the current frame."
  (let ((file (my-persp-file name)))
    (when (file-exists-p file)
      (let* ((data (with-temp-buffer
                     (insert-file-contents file)
                     (read (current-buffer))))
             (buffers (cadr (assq 'buffers data)))
             (windows (cadr (assq 'windows data)))
             (point-pos (cadr (assq 'point data)))
             (eglot-server-programs nil)
             (my-eglot-suppressed t))
        ;; Switch to perspective FIRST so files open into it
        (unless (gethash name (perspectives-hash))
          (persp-switch name))
        ;; Open files — they go into the target perspective
        (dolist (f buffers)
          (when (file-exists-p f)
            (find-file f)))
        ;; Ensure all opened buffers are in the perspective
        (dolist (b buffers)
          (when-let ((buf (get-file-buffer b)))
            (unless (persp-is-current-buffer buf)
              (persp-add-buffer buf))))
        ;; Restore window layout
        (when windows
          (ignore-errors
            (window-state-put windows (frame-root-window) 'safe)))
        ;; Restore point
        (ignore-errors
          (goto-char point-pos))))
    t)))

;; ── Save-all (kill-emacs hook) ──────────────────────────────────

(defun my-persp-save-all ()
  "Save all live perspectives to their per-perspective files."
  (let ((my-persp-saving t))
    (dolist (name (hash-table-keys (perspectives-hash)))
      (if (equal name (persp-current-name))
          (ignore-errors (my-persp-save name))
        ;; Non-current: read struct directly — no context switch
        (let* ((persp (gethash name (perspectives-hash)))
               (file (my-persp-file name)))
          (when (and persp (not (persp-killed-p persp)))
            (make-directory my-persp-dir t)
            (let* ((buffers (cl-loop for b in (persp-buffers persp)
                                     when (and (buffer-live-p b)
                                               (buffer-file-name b))
                                     collect (buffer-file-name b)))
                   (point (when-let ((m (persp-point-marker persp)))
                            (and (marker-position m)
                                 (marker-position m))))
                   (data `(persp-state (buffers ,buffers)
                           (windows nil)    ;; non-current: can't serialize
                           (point ,point))))
              (with-temp-file file
                (prin1 data (current-buffer))))))))))

;; ── Lazy switch (loads from disk if not yet in hash) ────────────

(defun my-persp-switch (name)
  "Switch to perspective NAME, loading from disk if not yet loaded."
  (interactive
   (list (completing-read "Perspective: " (my-persp-names) nil nil)))
  (unless (my-persp-loaded-p name)
    (message "Loading perspective %s..." name)
    (let ((my-persp-saving t))
      (my-persp-load name)))
  (persp-switch name))

;; ── Name listing (live hash + disk files) ───────────────────────

(defun my-persp-names ()
  "Return all known perspective names (live + on-disk)."
  (delete-dups
   (append (hash-table-keys (perspectives-hash))
           (when (file-directory-p my-persp-dir)
             (mapcar (lambda (f) (file-name-base f))
                     (directory-files my-persp-dir nil "\\.el\\'"))))))

(defun my-persp-loaded-p (name)
  "Return t if perspective NAME is currently loaded."
  (and (gethash name (perspectives-hash)) t))

;; ── Hooks ───────────────────────────────────────────────────────

;; Save outgoing perspective before every switch
(advice-add 'persp-switch :before
            (lambda (name &rest _)
              (unless my-persp-saving
                (when-let ((old-name (persp-current-name)))
                  (unless (equal old-name name)
                    (let ((my-persp-saving t))
                      (ignore-errors (my-persp-save old-name))))))))

;; Save all perspectives on kill-emacs
(add-hook 'kill-emacs-hook #'my-persp-save-all)

;; Delete state file when perspective is killed
(add-hook 'persp-killed-hook
          (lambda ()
            (ignore-errors
              (delete-file (my-persp-file (persp-current-name))))))

;; Don't import buffers when switching perspectives
(setq persp-switch-to-buffer-behavior nil)

;; ── Daemon: strip terminal frame hash ───────────────────────────

(add-hook 'after-init-hook
          (lambda ()
            (dolist (frame (frame-list))
              (unless (display-graphic-p frame)
                (set-frame-parameter frame 'persp--hash nil)
                (set-frame-parameter frame 'persp--curr nil)))))