Add ActivateLastTab command

This replicates `last-window` in tmux. To pull this off, I
deliberately store the last tab whenever I'm activating a new one or
spawning a new one. I had to do this explicitly rather than hooking
set_active, because we end up setting the active tab briefly for some
common operations like moving a tab.

config/src/keyassignment.rs

@@ -164,6 +164,7 @@ pub enum KeyAssignment {
     ResetFontSize,
     ResetFontAndWindowSize,
     ActivateTab(isize),
+    ActivateLastTab,
     SendString(String),
     Nop,
     DisableDefaultAssignment,

docs/config/lua/keyassignment/ActivateLastTab.md

@@ -0,0 +1,14 @@
+# ActivateLastTab
+
+Activate the last active tab. If there is none, it will do nothing.
+
+
+```lua
+return {
+  keys = {
+    {key="o", mods="LEADER|CTRL", action="ActivateLastTab"},
+  }
+}
+```
+
+

mux/src/window.rs

@@ -10,6 +10,7 @@ pub struct Window {
     id: WindowId,
     tabs: Vec<Rc<Tab>>,
     active: usize,
+    last_active: Option<TabId>,
     clipboard: Option<Arc<dyn Clipboard>>,
     invalidated: bool,
 }
@@ -20,6 +21,7 @@ impl Window {
             id: WIN_ID.fetch_add(1, ::std::sync::atomic::Ordering::Relaxed),
             tabs: vec![],
             active: 0,
+            last_active: None,
             clipboard: None,
             invalidated: false,
         }
@@ -124,6 +126,19 @@ impl Window {
         self.active
     }
 
+    pub fn save_last_active(&mut self) {
+        self.last_active = self.get_by_idx(self.active).map(|tab| tab.tab_id());
+    }
+
+    #[inline]
+    pub fn get_last_active_idx(&self) -> Option<usize> {
+        if let Some(tab_id) = self.last_active {
+            self.idx_by_id(tab_id)
+        } else {
+            None
+        }
+    }
+
     pub fn set_active(&mut self, idx: usize) {
         assert!(idx < self.tabs.len());
         self.invalidated = true;

wezterm-gui/src/termwindow/mod.rs

@@ -1098,6 +1098,9 @@ impl TermWindow {
         };
 
         if tab_idx < max {
+            if tab_idx != window.get_active_idx() {
+                window.save_last_active();
+            }
             window.set_active(tab_idx);
 
             drop(window);
@@ -1128,6 +1131,20 @@ impl TermWindow {
         self.activate_tab((tab as usize % max) as isize)
     }
 
+    fn activate_last_tab(&mut self) -> anyhow::Result<()> {
+        let mux = Mux::get().unwrap();
+        let window = mux
+            .get_window(self.mux_window_id)
+            .ok_or_else(|| anyhow!("no such window"))?;
+
+        let last_idx = window.get_last_active_idx();
+        drop(window);
+        match last_idx {
+            Some(idx) => self.activate_tab(idx as isize),
+            None => Ok(()),
+        }
+    }
+
     fn move_tab(&mut self, tab_idx: usize) -> anyhow::Result<()> {
         let mux = Mux::get().unwrap();
         let mut window = mux
@@ -1387,6 +1404,7 @@ impl TermWindow {
             ActivateTabRelative(n) => {
                 self.activate_tab_relative(*n)?;
             }
+            ActivateLastTab => self.activate_last_tab()?,
             DecreaseFontSize => self.decrease_font_size(),
             IncreaseFontSize => self.increase_font_size(),
             ResetFontSize => self.reset_font_size(),

wezterm-gui/src/termwindow/spawn.rs

@@ -186,6 +186,7 @@ impl super::TermWindow {
                     let mut window = mux
                         .get_window_mut(target_window_id)
                         .ok_or_else(|| anyhow!("no such window!?"))?;
+                    window.save_last_active();
                     if let Some(idx) = window.idx_by_id(tab_id) {
                         window.set_active(idx);
                     }