csi: implement CSI 22t and CSI 23t

22;0|1|2t pushes the current window title/icon to the stack, while 23
pops it.

The second parameter, 0|1|2 has the following meaning:

0 - push/pop icon+title
1 - push/pop icon
2 - push/pop title

csi.c

@@ -546,11 +546,39 @@ csi_dispatch(struct terminal *term, uint8_t final)
             break;
         }
 
-        case 't':
+        case 't': {
-            /* 22 - save window title */
+            unsigned param = vt_param_get(term, 0, 0);
-            /* 23 - restore window title */
+
-            LOG_WARN("ignoring %s", csi_as_string(term, final));
+            switch (param) {
+            case 22: { /* push window title */
+                /* 0 - icon + title, 1 - icon, 2 - title */
+                unsigned what = vt_param_get(term, 1, 0);
+                if (what == 0 || what == 2) {
+                    tll_push_back(
+                        term->window_title_stack, strdup(term->window_title));
+                }
+                break;
+            }
+
+            case 23: { /* pop window title */
+                /* 0 - icon + title, 1 - icon, 2 - title */
+                unsigned what = vt_param_get(term, 1, 0);
+                if (what == 0 || what == 2) {
+                    if (tll_length(term->window_title_stack) > 0) {
+                        char *title = tll_pop_back(term->window_title_stack);
+                        term_set_window_title(term, title);
+                        free(title);
+                    }
+                }
+                break;
+            }
+
+            default:
+                LOG_WARN("ignoring %s", csi_as_string(term, final));
+                break;
+            }
             break;
+        }
 
         case 'n': {
             if (term->vt.params.idx > 0) {

foot.info

@@ -156,7 +156,7 @@ foot+base|foot base fragment,
     ritm=\E[23m,
     rmacs=\E(B,
     rmam=\E[?7l,
-    rmcup=\E[?1049l,
+    rmcup=\E[?1049l\E[23;0t,
     rmir=\E[4l,
     rmkx=\E[?1l\E>,
     rmso=\E[27m,
@@ -169,7 +169,7 @@ foot+base|foot base fragment,
     sitm=\E[3m,
     smacs=\E(0,
     smam=\E[?7h,
-    smcup=\E[?1049h,
+    smcup=\E[?1049h\E[22;0t,
     smir=\E[4h,
     smkx=\E[?1h\E=,
     smso=\E[7m,

main.c

@@ -324,6 +324,7 @@ main(int argc, char *const *argv)
         .cursor_keys_mode = CURSOR_KEYS_NORMAL,
         .keypad_keys_mode = KEYPAD_NUMERICAL,
         .auto_margin = true,
+        .window_title_stack = tll_init(),
         .vt = {
             .state = 1,  /* STATE_GROUND */
             .attrs = {
@@ -848,7 +849,9 @@ out:
     for (int row = 0; row < term.alt.num_rows; row++)
         grid_row_free(term.alt.rows[row]);
     free(term.alt.rows);
+
     free(term.window_title);
+    tll_free_and_free(term.window_title_stack, free);
 
     for (size_t i = 0; i < sizeof(term.fonts) / sizeof(term.fonts[0]); i++) {
         struct font *f = &term.fonts[i];

terminal.h

@@ -246,6 +246,7 @@ struct terminal {
     int selected_charset;
     enum charset charset[4]; /* G0-G3 */
     char *window_title;
+    tll(char *) window_title_stack;
 
     struct vt vt;
     struct kbd kbd;