sl0ppty: the pane title is a name — double-click it to rename

The top row was both the frame's drag handle and its top edge: resting on it
armed the split guide, and a click that never moved split upward. That is
right for a border and wrong for the cells the title sits on, because it left
no gesture free for naming a pane — a double-click there split twice.

So the title text carves its own hit region out of the top row. It is
registered after the row's handle and after the title is painted, which is
what makes it correct: hit_test scans backwards, so the region that wins is
the one whose glyphs the user can actually see, and its width comes from
screen_text's return so a title of wide characters claims the cells it drew.
Resting there arms nothing (draw_split_guide matches "title:" exactly), and a
press takes no side, so the click-splits path — now guarded on a side being
set — does nothing. Dragging still moves the pane: that reads as grabbing it
by its name. Everything else on the top row still splits upward.

Renaming happens in the title cell itself. There is no dialog to place,
nothing to dismiss, and the pane it belongs to cannot be in doubt. It is the
finder's shape: state on app_t, a key handler that owns the keyboard while it
is open, drawn by the pass that draws the frame. Enter keeps the name, Escape
abandons it, clicking away keeps it the way leaving a field does.

A typed name shadows the program's title rather than overwriting it. The
program's OSC 2 keeps arriving underneath, so a shell that rewrites its title
cannot undo a rename, and clearing the name gives the pane back to what the
program calls itself *now* rather than to whatever it happened to say when the
rename began. That is the whole reason pane_t grew a second string instead of
a flag.

Backspace deletes a character rather than a byte — a title is whatever a
program could set, and half a UTF-8 sequence is not a name — and a name too
long for the frame scrolls its head off, because the caret is the one thing
that has to stay visible. double_click_ms (400) joins hover_delay_ms in the
config.

The tests keep a control beside each behaviour, since most of these could pass
by breaking something else: two slow clicks must open no editor, the top edge
must still split, keystrokes must not reach the shell, and a pane closing
mid-rename must give the keyboard back.

5 files changed, 187 insertions, 16 deletions

diff --git a/src/app.c b/src/app.c
index 7f4f089..9d3bc1c 100644
--- a/src/app.c
+++ b/src/app.c
@@ -159,6 +159,17 @@ struct app {
   bool finder;
   char query[64];
   size_t sel;
+
+  /* Renaming a pane in place: the title cell becomes the editor, so the name
+   * is typed where it will live rather than in a dialog somewhere else. */
+  bool renaming;
+  uint32_t rename_id;
+  /* As wide as a pane title, so seeding the editor never truncates one (and so
+   * never truncates one mid-UTF-8). */
+  char rename_buf[256];
+  /* The first click of a candidate double-click on a title. */
+  int64_t name_click_ms;
+  uint32_t name_click_id;
   const char *const *argv;
   /* the screen we last composed into: its hit list is what a click resolves
    * against, so routing can never consult geometry the user never saw */
@@ -1325,20 +1336,57 @@ static void draw_frame(app_t *a, screen_t *s, node_t *leaf) {
   }
 
   const char *title = pane_title(leaf->pane);
-  if (title && *title && avail >= 3) {
-    char buf[256];
-    int len = snprintf(buf, sizeof buf, " %s ", title);
+  bool editing = a->renaming && a->rename_id == leaf->id;
+  if ((editing || (title && *title)) && avail >= 3) {
+    char buf[320]; /* a full-length name, plus the caret and its spaces */
+    int len = editing ? snprintf(buf, sizeof buf, " %s\u2588 ", a->rename_buf)
+                      : snprintf(buf, sizeof buf, " %s ", title);
+    /* snprintf reports what it *would* have written; clamp to what it did, or
+     * the scroll below would move bytes that are not there. */
+    if (len < 0) len = 0;
+    if ((size_t)len >= sizeof buf) len = (int)strlen(buf);
     if (len > (int)avail) {
-      len = (int)avail;
-      buf[len] = 0;
+      if (editing) {
+        /* Scroll the head off, not the tail: the cursor is the one thing that
+         * must stay on screen while typing. Whole characters only. */
+        size_t off = (size_t)(len - (int)avail);
+        while (off < (size_t)len && ((unsigned char)buf[off] & 0xC0) == 0x80)
+          off++;
+        memmove(buf, buf + off, (size_t)len - off + 1);
+        len = (int)((size_t)len - off);
+      } else {
+        len = (int)avail;
+        buf[len] = 0;
+      }
     }
     uint16_t tx = (uint16_t)(r.x + 1);
     if (CFG.title_align == ALIGN_CENTER)
       tx = (uint16_t)(r.x + 1 + (avail - len) / 2);
     else if (CFG.title_align == ALIGN_RIGHT)
       tx = (uint16_t)(r.x + 1 + avail - len);
-    screen_text(s, tx, r.y, buf, focused ? TITLE_FOCUS : fg, NO_COLOR,
-                focused ? ATTR_BOLD : 0);
+    /* An editor announces itself: the name sits in the button colours while it
+     * is being typed, so a half-finished rename can never be mistaken for what
+     * the pane is actually called. */
+    uint16_t drawn =
+        screen_text(s, tx, r.y, buf, editing ? BTN_FG : (focused ? TITLE_FOCUS : fg),
+                    editing ? BTN_BG : NO_COLOR,
+                    editing || focused ? ATTR_BOLD : 0);
+
+    /* The title names the pane; it is not an edge. It carves its own cells out
+     * of the top row's handle so that resting there arms no split guide and
+     * clicking there splits nothing, which leaves the gesture free for a
+     * double-click rename — otherwise a rename would split twice on its way.
+     * Dragging still moves the pane: that reads as grabbing it by its name.
+     *
+     * Registered last, because hit_test() scans backwards and the title is
+     * painted last too. Hit-testing therefore agrees with what is on screen,
+     * and the width comes from screen_text() so a title of wide characters
+     * claims the cells it actually drew. */
+    if (drawn) {
+      char action[48];
+      snprintf(action, sizeof action, "panetitle:%u", leaf->id);
+      hit_add(&s->hits, tx, r.y, drawn, 1, action);
+    }
   }
 }
 
@@ -1626,6 +1674,70 @@ static bool finder_key(app_t *a, const input_event_t *ev) {
   return true;
 }
 
+/* ---- renaming a pane ---------------------------------------------------- */
+
+/* The editor lives in the title cell itself (drawn by draw_frame), so the name
+ * is typed where it is going to live. There is no dialog to place, nothing to
+ * dismiss, and the pane it belongs to cannot be in doubt. */
+static void rename_begin(app_t *a, uint32_t id) {
+  node_t *n = pane_by_id(a, id);
+  if (!n) return;
+  a->renaming = true;
+  a->rename_id = id;
+  /* Seed with what is on screen: a rename is usually an edit, not a retype. */
+  const char *shown = pane_title(n->pane);
+  snprintf(a->rename_buf, sizeof a->rename_buf, "%s", shown ? shown : "");
+  a->name_click_ms = 0;
+  a->name_click_id = 0;
+  app_focus_pane(a, id);
+}
+
+static void rename_end(app_t *a, bool keep) {
+  if (!a->renaming) return;
+  node_t *n = pane_by_id(a, a->rename_id);
+  if (keep && n) {
+    pane_set_name(n->pane, a->rename_buf);
+    app_toast(a, a->rename_buf[0] ? "renamed" : "name cleared");
+  }
+  a->renaming = false;
+  a->rename_id = 0;
+  a->rename_buf[0] = 0;
+}
+
+/* Returns true when the rename editor consumed the event. */
+static bool rename_key(app_t *a, const input_event_t *ev) {
+  if (!a->renaming) return false;
+  if (ev->kind != EV_KEY || ev->action == KEY_RELEASE) return true;
+
+  switch (ev->key) {
+    case GHOSTTY_KEY_ESCAPE:
+      rename_end(a, false);
+      return true;
+    case GHOSTTY_KEY_ENTER:
+      rename_end(a, true);
+      return true;
+    case GHOSTTY_KEY_BACKSPACE: {
+      /* A character, not a byte: a title is whatever the program could set,
+       * and half a UTF-8 sequence is not a name. */
+      size_t l = strlen(a->rename_buf);
+      while (l && ((unsigned char)a->rename_buf[l - 1] & 0xC0) == 0x80) l--;
+      if (l) l--;
+      a->rename_buf[l] = 0;
+      return true;
+    }
+    default:
+      break;
+  }
+  if (ev->text_len && (unsigned char)ev->text[0] >= 0x20) {
+    size_t l = strlen(a->rename_buf);
+    if (l + ev->text_len < sizeof a->rename_buf) {
+      memcpy(a->rename_buf + l, ev->text, ev->text_len);
+      a->rename_buf[l + ev->text_len] = 0;
+    }
+  }
+  return true;
+}
+
 void app_compose(app_t *a, screen_t *s) {
   screen_clear(s); /* every frame starts blank: no ghosts in the gap ring */
   hit_reset(&s->hits);
@@ -1766,27 +1878,43 @@ static void drag_edge(app_t *a, node_t *sp, size_t i, int cells) {
  * pointer crossed its header — which is why only `pane:` and `title:` targets
  * count, and the frame rect's `focus:` does not. */
 static bool hover_focus_allowed(const app_t *a) {
-  return CFG.focus_follows_mouse && !a->prefix && !a->finder &&
+  return CFG.focus_follows_mouse && !a->prefix && !a->finder && !a->renaming &&
          a->drag.kind == DRAG_NONE;
 }
 
 static void do_action(app_t *a, const char *action, const input_event_t *ev) {
-  if (strncmp(action, "title:", 6) == 0) {
-    uint32_t id = (uint32_t)strtoul(action + 6, NULL, 10);
+  bool on_name = strncmp(action, "panetitle:", 10) == 0;
+  if (on_name || strncmp(action, "title:", 6) == 0) {
+    uint32_t id = (uint32_t)strtoul(action + (on_name ? 10 : 6), NULL, 10);
     if (ev->maction == MOUSE_MOTION && hover_focus_allowed(a)) {
       app_focus_pane(a, id);
       return;
     }
     if (ev->maction == MOUSE_PRESS) {
+      /* Two clicks on the name, close together, rename the pane. This is why
+       * the name is not an edge: the first click must not have split, or the
+       * second would be renaming a pane that had already moved. */
+      if (on_name) {
+        int64_t now = now_ms_();
+        if (a->name_click_id == id &&
+            now - a->name_click_ms <= (int64_t)CFG.double_click_ms) {
+          rename_begin(a, id);
+          return; /* a rename, not a grab: start no drag */
+        }
+        a->name_click_ms = now;
+        a->name_click_id = id;
+      }
       /* The top border is both a drag handle and an edge: whether this is a
-       * move or a split-upward is decided by whether the pointer moves. */
+       * move or a split-upward is decided by whether the pointer moves. The
+       * title text is only a handle, so it takes no side: a click that never
+       * moved does nothing there instead of splitting upward. */
       a->drag.kind = DRAG_TITLE;
       a->drag.src = id;
       a->drag.target = id;
       a->drag.x = ev->mx;
       a->drag.y = ev->my;
       a->drag.moved = false;
-      a->drag.side = 't';
+      a->drag.side = on_name ? 0 : 't';
       app_focus_pane(a, id);
     }
     return;
@@ -1965,8 +2093,16 @@ static bool prefix_command(app_t *a, const input_event_t *ev) {
 void app_event(app_t *a, const input_event_t *ev) {
   if (!a->ntabs || !cur(a)->focus) return;
 
-  /* The finder owns the keyboard while it is open; the mouse still routes
-   * through the hit list, whose topmost entries are the finder's own rows. */
+  /* A rename whose pane went away must not keep the keyboard. */
+  if (a->renaming && !pane_by_id(a, a->rename_id)) rename_end(a, false);
+
+  /* The rename editor and the finder each own the keyboard while open; the
+   * mouse still routes through the hit list, whose topmost entries are the
+   * finder's own rows. */
+  if (a->renaming && ev->kind == EV_KEY) {
+    rename_key(a, ev);
+    return;
+  }
   if (a->finder && ev->kind == EV_KEY) {
     finder_key(a, ev);
     return;
@@ -2021,6 +2157,15 @@ void app_event(app_t *a, const input_event_t *ev) {
       if (!a->painted) break;
       const char *action = hit_test(&a->painted->hits, ev->mx, ev->my);
 
+      /* Clicking away keeps the name, the way leaving a field commits it.
+       * Clicking the pane's own name again does not, so a stray second
+       * double-click lands in the editor instead of closing it. */
+      if (a->renaming && ev->maction == MOUSE_PRESS) {
+        char own[48];
+        snprintf(own, sizeof own, "panetitle:%u", a->rename_id);
+        if (!action || strcmp(action, own) != 0) rename_end(a, true);
+      }
+
       if (!a->ptr_valid || ev->mx != a->ptr_x || ev->my != a->ptr_y)
         a->ptr_still_since = now_ms_();
       a->ptr_x = ev->mx;
@@ -2043,6 +2188,9 @@ void app_event(app_t *a, const input_event_t *ev) {
             drag_edge(a, sp, a->drag.edge, cells);
           } else if (action && strncmp(action, "title:", 6) == 0) {
             a->drag.target = (uint32_t)strtoul(action + 6, NULL, 10);
+          } else if (action && strncmp(action, "panetitle:", 10) == 0) {
+            /* Dropping onto a pane's name is dropping onto that pane. */
+            a->drag.target = (uint32_t)strtoul(action + 10, NULL, 10);
           } else if (action && strncmp(action, "pane:", 5) == 0) {
             a->drag.target = (uint32_t)strtoul(action + 5, NULL, 10);
           }
@@ -2051,7 +2199,7 @@ void app_event(app_t *a, const input_event_t *ev) {
         } else if (ev->maction == MOUSE_RELEASE) {
           /* A press that never moved is a click, and a click on an edge
            * splits toward it. */
-          if (!a->drag.moved &&
+          if (!a->drag.moved && a->drag.side &&
               (a->drag.kind == DRAG_BORDER || a->drag.kind == DRAG_TITLE)) {
             node_t *n = pane_by_id(a, a->drag.src);
             if (n) {
diff --git a/src/config.c b/src/config.c
index 09d6e09..a55969a 100644
--- a/src/config.c
+++ b/src/config.c
@@ -128,6 +128,7 @@ void config_defaults(config_t *c) {
   c->scroll_lines = 3;
   c->toast_ms = 2500;
   c->hover_delay_ms = 250;
+  c->double_click_ms = 400;
   c->status_bar = true;
   c->focus_follows_mouse = true;
 
@@ -248,6 +249,8 @@ bool config_load(config_t *c, const char *path, char *err, size_t errcap) {
   c->toast_ms = (uint16_t)kdl_arg_int(kdl_child(root, "toast_ms"), 0, c->toast_ms);
   c->hover_delay_ms = (uint16_t)kdl_arg_int(kdl_child(root, "hover_delay_ms"), 0,
                                             c->hover_delay_ms);
+  c->double_click_ms = (uint16_t)kdl_arg_int(kdl_child(root, "double_click_ms"),
+                                             0, c->double_click_ms);
 
   const char *sh = kdl_arg(kdl_child(root, "shell"), 0, NULL);
   if (sh) {
diff --git a/src/config.h b/src/config.h
index cee2203..8482116 100644
--- a/src/config.h
+++ b/src/config.h
@@ -60,6 +60,7 @@ typedef struct {
   uint16_t scroll_lines;
   uint16_t toast_ms;
   uint16_t hover_delay_ms; /* how long the pointer must rest to arm a guide */ /* how long an announcement stays up */ /* rows per wheel notch */
+  uint16_t double_click_ms; /* how close two clicks must be to be a double */
   bool status_bar;
   bool focus_follows_mouse;
 
diff --git a/src/pane.c b/src/pane.c
index 8969065..51c3970 100644
--- a/src/pane.c
+++ b/src/pane.c
@@ -27,6 +27,11 @@ struct pane {
   bool alive;
   bool dirty;
   char title[256];
+  /* A name the user typed. It shadows `title` rather than overwriting it, so
+   * the program's own title keeps arriving underneath and clearing the name
+   * (renaming to nothing) falls back to whatever the program calls itself
+   * now — not to whatever it happened to say when the rename began. */
+  char name[256];
 
   /* OSC 5577 state: what this pane asked us to draw in its frame */
   /* A suspended pane is real, sized and laid out, but has not run anything:
@@ -312,7 +317,17 @@ void pane_free(pane_t *p) {
 int pane_fd(const pane_t *p) { return p->pty.fd; }
 bool pane_alive(const pane_t *p) { return p->alive; }
 bool pane_dirty(pane_t *p) { return p->dirty; }
-const char *pane_title(const pane_t *p) { return p->title; }
+const char *pane_title(const pane_t *p) {
+  return p->name[0] ? p->name : p->title;
+}
+
+const char *pane_name(const pane_t *p) { return p->name; }
+
+void pane_set_name(pane_t *p, const char *name) {
+  if (!name) name = "";
+  snprintf(p->name, sizeof p->name, "%s", name);
+  p->dirty = true;
+}
 
 ssize_t pane_pump(pane_t *p) {
   if (p->pty.fd < 0) return 0;
diff --git a/src/sl0ppty.h b/src/sl0ppty.h
index 955185c..b7a1de2 100644
--- a/src/sl0ppty.h
+++ b/src/sl0ppty.h
@@ -156,6 +156,10 @@ void pane_scroll_pos(const pane_t *p, uint32_t *above, uint32_t *total);
 bool pane_alt_screen(const pane_t *p);
 bool pane_wants_mouse(const pane_t *p);
 const char *pane_title(const pane_t *p);
+/* The user-assigned name, "" when the program's title is showing through. */
+const char *pane_name(const pane_t *p);
+/* "" clears the name and gives the pane back to the program's title. */
+void pane_set_name(pane_t *p, const char *name);
 const char *pane_status(const pane_t *p);
 size_t pane_buttons(const pane_t *p, const pane_button_t **out);
 void pane_click_button(pane_t *p, const char *id);