mux: propagate User Vars across to the client

user vars were stubbed out.  This commit adds storage for them
in the mux client and adds a new notification that publishes each
var as it is changed.  That differential stream is applied to the
storage in the mux client when it is received.

```lua
local wezterm = require 'wezterm'

wezterm.on("update-right-status", function(window, pane)
  local woot = pane:get_user_vars().woot
  window:set_right_status(tostring(woot))
end);

return {
  unix_domains = {
    {name="unix"},
  },
}
```

then running:

* `wezterm connect unix`
* in that session: `printf "\033]1337;SetUserVar=%s=%s\007" woot `echo -n nice | base64``

causes `nice` to show in the status area.

refs: #1528

codec/src/lib.rs

@@ -406,7 +406,7 @@ macro_rules! pdu {
 /// The overall version of the codec.
 /// This must be bumped when backwards incompatible changes
 /// are made to the types and protocol.
-pub const CODEC_VERSION: usize = 12;
+pub const CODEC_VERSION: usize = 13;
 
 // Defines the Pdu enum.
 // Each struct has an explicit identifying number.

docs/changelog.md

@@ -42,6 +42,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Kitty Image Protocol: didn't respect `c` and `r` parameters to scale images
 * Cursor location on the primary screen wasn't updated correctly if the window was resized while the alternate screen was active [#1512](https://github.com/wez/wezterm/issues/1512)
 * Windows: latency issue with AltSnap and other window-managery things [#1013](https://github.com/wez/wezterm/issues/1013) [#1398](https://github.com/wez/wezterm/issues/1398) [#1075](https://github.com/wez/wezterm/issues/1075) [#1099](https://github.com/wez/wezterm/issues/1099)
+* Multiplexer sessions now propagate user vars [#1528](https://github.com/wez/wezterm/issues/1528)
 
 ### 20220101-133340-7edc5b5a
 

term/src/terminal.rs

@@ -50,6 +50,11 @@ pub enum Alert {
     TitleMaybeChanged,
     /// When the color palette has been updated
     PaletteChanged,
+    /// A UserVar has changed value
+    SetUserVar {
+        name: String,
+        value: String,
+    },
 }
 
 pub trait AlertHandler {

term/src/terminalstate/performer.rs

@@ -603,9 +603,9 @@ impl<'a> Performer<'a> {
             OperatingSystemCommand::ITermProprietary(iterm) => match iterm {
                 ITermProprietary::File(image) => self.set_image(*image),
                 ITermProprietary::SetUserVar { name, value } => {
-                    self.user_vars.insert(name, value);
+                    self.user_vars.insert(name.clone(), value.clone());
                     if let Some(handler) = self.alert_handler.as_mut() {
-                        handler.alert(Alert::TitleMaybeChanged);
+                        handler.alert(Alert::SetUserVar { name, value });
                     }
                 }
                 ITermProprietary::UnicodeVersion(ITermUnicodeVersionOp::Set(n)) => {

wezterm-client/src/pane/clientpane.rs

@@ -15,6 +15,7 @@ use rangeset::RangeSet;
 use ratelim::RateLimiter;
 use std::cell::RefCell;
 use std::cell::RefMut;
+use std::collections::HashMap;
 use std::ops::Range;
 use std::rc::Rc;
 use std::sync::Arc;
@@ -36,6 +37,7 @@ pub struct ClientPane {
     clipboard: RefCell<Option<Arc<dyn Clipboard>>>,
     mouse_grabbed: RefCell<bool>,
     ignore_next_kill: RefCell<bool>,
+    user_vars: RefCell<HashMap<String, String>>,
 }
 
 impl ClientPane {
@@ -92,6 +94,7 @@ impl ClientPane {
             clipboard: RefCell::new(None),
             mouse_grabbed: RefCell::new(false),
             ignore_next_kill: RefCell::new(false),
+            user_vars: RefCell::new(HashMap::new()),
         }
     }
 
@@ -134,6 +137,14 @@ impl ClientPane {
             }
             Pdu::NotifyAlert(NotifyAlert { alert, .. }) => {
                 let mux = Mux::get().unwrap();
+                match &alert {
+                    Alert::SetUserVar { name, value } => {
+                        self.user_vars
+                            .borrow_mut()
+                            .insert(name.clone(), value.clone());
+                    }
+                    _ => {}
+                }
                 mux.notify(MuxNotification::Alert {
                     pane_id: self.local_pane_id,
                     alert,
@@ -418,6 +429,10 @@ impl Pane for ClientPane {
             CloseReason::Pane => false,
         }
     }
+
+    fn copy_user_vars(&self) -> HashMap<String, String> {
+        self.user_vars.borrow().clone()
+    }
 }
 
 struct PaneWriter {

wezterm-gui/src/frontend.rs

@@ -65,13 +65,9 @@ impl GuiFrontEnd {
                     } => {
                         // Handled via TermWindowNotif; NOP it here.
                     }
-                    MuxNotification::Alert {
-                        pane_id: _,
-                        alert: Alert::PaletteChanged,
-                    }
                     | MuxNotification::Alert {
                         pane_id: _,
-                        alert: Alert::TitleMaybeChanged,
+                        alert: Alert::PaletteChanged | Alert::TitleMaybeChanged | Alert::SetUserVar{..},
                     } => {}
                     MuxNotification::Empty => {
                         if mux::activity::Activity::count() == 0 {

wezterm-gui/src/termwindow/mod.rs

@@ -921,7 +921,7 @@ impl TermWindow {
             }
             TermWindowNotif::MuxNotification(n) => match n {
                 MuxNotification::Alert {
-                    alert: Alert::TitleMaybeChanged,
+                    alert: Alert::TitleMaybeChanged | Alert::SetUserVar { .. },
                     ..
                 } => {
                     self.update_title();

wezterm-mux-server-impl/src/dispatch.rs

@@ -92,7 +92,7 @@ where
                 {
                     let per_pane = handler.per_pane(pane_id);
                     let mut per_pane = per_pane.lock().unwrap();
-                    per_pane.notifications.push(alert);
+                    per_pane.notifications.push(dbg!(alert));
                 }
                 handler.schedule_pane_push(pane_id);
             }