persp-current-buffers*: read frame-global buffers without switching perspectives

[aiba]

Problem

persp-current-buffers* with INCLUDE-GLOBAL reads the frame global perspective's buffer list via with-perspective, which runs persp-switch twice (there and back). Each switch restores a window configuration. Callers of persp-current-buffers* / persp-is-current-buffer / persp-buffer-filter reasonably treat them as pure predicates, so this side effect is surprising — and it turns out to be fatal in one realistic scenario:

Emacs evaluates menu-bar :enable forms during redisplay (update_menu_bar → menu_item_eval_property). If such a form reaches a perspective buffer predicate (in my case: CIDER's menu :enable (cider-connected-p) → sesman session lookup → a sesman-to-perspective filter → persp-is-current-buffer buf t), the with-perspective round-trip executes delete-other-windows mid-redisplay, which calls adjust_frame_glyphs and reallocates the window's glyph matrices while display_line holds pointers into them. Emacs 31.0.90 segfaults 100% reproducibly (set_cursor_from_row computes a garbage w->cursor.vpos from a stale row pointer; the next display_line indexes ~340 GB out of bounds). I debugged this under lldb down to the exact instructions, and caught the persp-switch → delete-other-windows → adjust_glyph_matrix chain live with a breakpoint while redisplay_internal was on the stack. A hardening report to bug-gnu-emacs is in flight, but the crash is trivially avoided by not switching perspectives here at all.

Fix

Read the frame global perspective's buffer list directly from perspectives-hash. persp-get-scratch-buffer already accepts the perspective name, so the scratch-buffer exclusion behaves identically. This follows the same approach as #226 (persp-maybe-kill-buffer: avoid switching perspectives).

Bonus fix: the previous code returned the global perspective's live buffer list as the shared tail of append, exposing it to the destructive delete-dups; copy-sequence now protects it.

Testing

make test: 32/33 pass, matching pristine HEAD on the same Emacs — the one failure (basic-persp-window-prev-buffers) pre-exists on master under Emacs 31.0.90 batch mode and is unrelated (verified by running the suite on an unpatched checkout). Byte-compiles with no new warnings. The equivalent change applied at the configuration level (checking persp-buffers membership directly, bypassing the with-perspective round-trip) eliminates the segfault in the originally crashing CIDER + perspective session.

🤖 Generated with Claude Code

https://claude.ai/code/session_01F3SLHGSnQuGu2QukBqs1wd

[gcv]

Looks solid. That’s some impressive lldb work by Claude. Merged.