From 8b3e2eab5afde62a4eb87b132b4196105c1cfaa6 Mon Sep 17 00:00:00 2001
From: nicm <nicm>
Date: Mon, 10 Jul 2023 09:24:53 +0000
Subject: Use a stack for last panes line windows, from Thomas Bertschinger in
 GitHub issue 3588.

---
 cmd-find.c        |  2 +-
 cmd-select-pane.c |  6 +++++-
 cmd-swap-pane.c   |  6 ++----
 format.c          |  2 +-
 spawn.c           |  1 +
 tmux.h            | 12 +++++++++---
 window.c          | 56 +++++++++++++++++++++++++++++++++++++++----------------
 7 files changed, 59 insertions(+), 26 deletions(-)

diff --git a/cmd-find.c b/cmd-find.c
index 2929bbc9..c651448d 100644
--- a/cmd-find.c
+++ b/cmd-find.c
@@ -583,7 +583,7 @@ cmd_find_get_pane_with_window(struct cmd_find_state *fs, const char *pane)
 
 	/* Try special characters. */
 	if (strcmp(pane, "!") == 0) {
-		fs->wp = fs->w->last;
+		fs->wp = TAILQ_FIRST(&fs->w->last_panes);
 		if (fs->wp == NULL)
 			return (-1);
 		return (0);
diff --git a/cmd-select-pane.c b/cmd-select-pane.c
index ae21d4ce..135729f5 100644
--- a/cmd-select-pane.c
+++ b/cmd-select-pane.c
@@ -98,7 +98,11 @@ cmd_select_pane_exec(struct cmd *self, struct cmdq_item *item)
 	struct options_entry	*o;
 
 	if (entry == &cmd_last_pane_entry || args_has(args, 'l')) {
-		lastwp = w->last;
+		/*
+		 * Check for no last pane found in case the other pane was
+		 * spawned without being visited (for example split-window -d).
+		 */
+		lastwp = TAILQ_FIRST(&w->last_panes);
 		if (lastwp == NULL && window_count_panes(w) == 2) {
 			lastwp = TAILQ_PREV(w->active, window_panes, entry);
 			if (lastwp == NULL)
diff --git a/cmd-swap-pane.c b/cmd-swap-pane.c
index 80c20c80..6931bd16 100644
--- a/cmd-swap-pane.c
+++ b/cmd-swap-pane.c
@@ -128,10 +128,8 @@ cmd_swap_pane_exec(struct cmd *self, struct cmdq_item *item)
 			window_set_active_pane(dst_w, src_wp, 1);
 	}
 	if (src_w != dst_w) {
-		if (src_w->last == src_wp)
-			src_w->last = NULL;
-		if (dst_w->last == dst_wp)
-			dst_w->last = NULL;
+		window_pane_stack_remove(&src_w->last_panes, src_wp);
+		window_pane_stack_remove(&dst_w->last_panes, dst_wp);
 		colour_palette_from_option(&src_wp->palette, src_wp->options);
 		colour_palette_from_option(&dst_wp->palette, dst_wp->options);
 	}
diff --git a/format.c b/format.c
index 3f745141..0c3bd3ba 100644
--- a/format.c
+++ b/format.c
@@ -1902,7 +1902,7 @@ static void *
 format_cb_pane_last(struct format_tree *ft)
 {
 	if (ft->wp != NULL) {
-		if (ft->wp == ft->wp->window->last)
+		if (ft->wp == TAILQ_FIRST(&ft->wp->window->last_panes))
 			return (xstrdup("1"));
 		return (xstrdup("0"));
 	}
diff --git a/spawn.c b/spawn.c
index dd3f6f50..7ae3f938 100644
--- a/spawn.c
+++ b/spawn.c
@@ -115,6 +115,7 @@ spawn_window(struct spawn_context *sc, char **cause)
 		window_pane_resize(sc->wp0, w->sx, w->sy);
 
 		layout_init(w, sc->wp0);
+		w->active = NULL;
 		window_set_active_pane(w, sc->wp0, 0);
 	}
 
diff --git a/tmux.h b/tmux.h
index d2a5671b..9588c285 100644
--- a/tmux.h
+++ b/tmux.h
@@ -1038,7 +1038,7 @@ struct window_pane {
 #define PANE_REDRAW 0x1
 #define PANE_DROP 0x2
 #define PANE_FOCUSED 0x4
-/* 0x8 unused */
+#define PANE_VISITED 0x8
 /* 0x10 unused */
 /* 0x20 unused */
 #define PANE_INPUTOFF 0x40
@@ -1093,7 +1093,8 @@ struct window_pane {
 	int		 border_gc_set;
 	struct grid_cell border_gc;
 
-	TAILQ_ENTRY(window_pane) entry;
+	TAILQ_ENTRY(window_pane) entry;  /* link in list of all panes */
+	TAILQ_ENTRY(window_pane) sentry; /* link in list of last visited */
 	RB_ENTRY(window_pane) tree_entry;
 };
 TAILQ_HEAD(window_panes, window_pane);
@@ -1114,7 +1115,7 @@ struct window {
 	struct timeval		 activity_time;
 
 	struct window_pane	*active;
-	struct window_pane	*last;
+	struct window_panes 	 last_panes;
 	struct window_panes	 panes;
 
 	int			 lastlayout;
@@ -1167,6 +1168,7 @@ struct winlink {
 #define WINLINK_ACTIVITY 0x2
 #define WINLINK_SILENCE 0x4
 #define WINLINK_ALERTFLAGS (WINLINK_BELL|WINLINK_ACTIVITY|WINLINK_SILENCE)
+#define WINLINK_VISITED 0x8
 
 	RB_ENTRY(winlink) entry;
 	TAILQ_ENTRY(winlink) wentry;
@@ -3041,6 +3043,10 @@ struct window_pane *window_pane_find_up(struct window_pane *);
 struct window_pane *window_pane_find_down(struct window_pane *);
 struct window_pane *window_pane_find_left(struct window_pane *);
 struct window_pane *window_pane_find_right(struct window_pane *);
+void		 window_pane_stack_push(struct window_panes *,
+		     struct window_pane *);
+void		 window_pane_stack_remove(struct window_panes *,
+		     struct window_pane *);
 void		 window_set_name(struct window *, const char *);
 void		 window_add_ref(struct window *, const char *);
 void		 window_remove_ref(struct window *, const char *);
diff --git a/window.c b/window.c
index 8f650a96..c1365993 100644
--- a/window.c
+++ b/window.c
@@ -248,21 +248,15 @@ winlink_stack_push(struct winlink_stack *stack, struct winlink *wl)
 
 	winlink_stack_remove(stack, wl);
 	TAILQ_INSERT_HEAD(stack, wl, sentry);
+	wl->flags |= WINLINK_VISITED;
 }
 
 void
 winlink_stack_remove(struct winlink_stack *stack, struct winlink *wl)
 {
-	struct winlink	*wl2;
-
-	if (wl == NULL)
-		return;
-
-	TAILQ_FOREACH(wl2, stack, sentry) {
-		if (wl2 == wl) {
-			TAILQ_REMOVE(stack, wl, sentry);
-			return;
-		}
+	if (wl != NULL && (wl->flags & WINLINK_VISITED)) {
+		TAILQ_REMOVE(stack, wl, sentry);
+		wl->flags &= ~WINLINK_VISITED;
 	}
 }
 
@@ -312,6 +306,7 @@ window_create(u_int sx, u_int sy, u_int xpixel, u_int ypixel)
 	w->flags = 0;
 
 	TAILQ_INIT(&w->panes);
+	TAILQ_INIT(&w->last_panes);
 	w->active = NULL;
 
 	w->lastlayout = -1;
@@ -512,18 +507,23 @@ window_pane_update_focus(struct window_pane *wp)
 int
 window_set_active_pane(struct window *w, struct window_pane *wp, int notify)
 {
+	struct window_pane *lastwp;
+
 	log_debug("%s: pane %%%u", __func__, wp->id);
 
 	if (wp == w->active)
 		return (0);
-	w->last = w->active;
+	lastwp = w->active;
+
+	window_pane_stack_remove(&w->last_panes, wp);
+	window_pane_stack_push(&w->last_panes, lastwp);
 
 	w->active = wp;
 	w->active->active_point = next_active_point++;
 	w->active->flags |= PANE_CHANGED;
 
 	if (options_get_number(global_options, "focus-events")) {
-		window_pane_update_focus(w->last);
+		window_pane_update_focus(lastwp);
 		window_pane_update_focus(w->active);
 	}
 
@@ -746,21 +746,21 @@ window_lost_pane(struct window *w, struct window_pane *wp)
 	if (wp == marked_pane.wp)
 		server_clear_marked();
 
+	window_pane_stack_remove(&w->last_panes, wp);
 	if (wp == w->active) {
-		w->active = w->last;
-		w->last = NULL;
+		w->active = TAILQ_FIRST(&w->last_panes);
 		if (w->active == NULL) {
 			w->active = TAILQ_PREV(wp, window_panes, entry);
 			if (w->active == NULL)
 				w->active = TAILQ_NEXT(wp, entry);
 		}
 		if (w->active != NULL) {
+			window_pane_stack_remove(&w->last_panes, w->active);
 			w->active->flags |= PANE_CHANGED;
 			notify_window("window-pane-changed", w);
 			window_update_focus(w);
 		}
-	} else if (wp == w->last)
-		w->last = NULL;
+	}
 }
 
 void
@@ -844,6 +844,11 @@ window_destroy_panes(struct window *w)
 {
 	struct window_pane	*wp;
 
+	while (!TAILQ_EMPTY(&w->last_panes)) {
+		wp = TAILQ_FIRST(&w->last_panes);
+		window_pane_stack_remove(&w->last_panes, wp);
+	}
+
 	while (!TAILQ_EMPTY(&w->panes)) {
 		wp = TAILQ_FIRST(&w->panes);
 		TAILQ_REMOVE(&w->panes, wp, entry);
@@ -1478,6 +1483,25 @@ window_pane_find_right(struct window_pane *wp)
 	return (best);
 }
 
+void
+window_pane_stack_push(struct window_panes *stack, struct window_pane *wp)
+{
+	if (wp != NULL) {
+		window_pane_stack_remove(stack, wp);
+		TAILQ_INSERT_HEAD(stack, wp, sentry);
+		wp->flags |= PANE_VISITED;
+	}
+}
+
+void
+window_pane_stack_remove(struct window_panes *stack, struct window_pane *wp)
+{
+	if (wp != NULL && (wp->flags & PANE_VISITED)) {
+		TAILQ_REMOVE(stack, wp, sentry);
+		wp->flags &= ~PANE_VISITED;
+	}
+}
+
 /* Clear alert flags for a winlink */
 void
 winlink_clear_flags(struct winlink *wl)
-- 
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