key tables: we now search the whole stack for match

This change causes key table activations to effectively layer
over prior key table activations.

This is necessary for the copy mode key assignment changes to
work.

refs: https://github.com/wez/wezterm/issues/993

docs/changelog.md

@@ -32,6 +32,7 @@ As features stabilize some brief notes about them will accumulate here.
 #### Changed
 * Debian packages now register wezterm as an alternative for `x-terminal-emulator`. Thanks to [@xpufx](https://github.com/xpufx)! [#1883](https://github.com/wez/wezterm/pull/1883)
 * Windows: wezterm will now read the default environment variables from the `HKLM\System\CurrentControlSet\Control\Session Manager\Environment` and `HKCU\Environment` and apply those to the base environment prior to applying `set_environment_variables`. [#1848](https://github.com/wez/wezterm/issues/1848)
+* [Key Table](config/key-tables.md) lookups will now keep searching the activation stack until a matching assignment is found, allowing for layered key tables. [#993](https://github.com/wez/wezterm/issues/993)
 
 #### Fixed
 * Flush after replying to XTGETTCAP and DECRQM. [#1850](https://github.com/wez/wezterm/issues/1850) [#1950](https://github.com/wez/wezterm/issues/1950)

docs/config/key-tables.md

@@ -119,5 +119,14 @@ The stack is also cleared when the configuration is reloaded, so if you're
 working on a complex key table setup and get stuck, you may be able to unstick
 yourself by re-saving your wezterm configuration to trigger a reload.
 
+*Since: nightly builds only*
 
+When resolving a key assignment, the top of stack is first searched for a match,
+and if one is not found, the next entry on the stack is searched and so on until a match is found.
+
+In previous releases, only a single lookup was performed on the top of the stack.
+
+The new behavior allows key table activations to effectively layer over the top
+of previously activated key assignments, making it a bit easier to compose key
+assignments.
 

wezterm-gui/src/termwindow/keyevent.rs

@@ -1,5 +1,7 @@
+use crate::termwindow::InputMap;
 use ::window::{DeadKeyStatus, KeyCode, KeyEvent, Modifiers, RawKeyEvent, WindowOps};
 use anyhow::Context;
+use config::keyassignment::KeyTableEntry;
 use mux::pane::Pane;
 use smol::Timer;
 use std::rc::Rc;
@@ -67,6 +69,24 @@ impl KeyTableState {
         self.stack.last().map(|entry| entry.name.as_str())
     }
 
+    pub fn lookup_key(
+        &mut self,
+        input_map: &InputMap,
+        key: &KeyCode,
+        mods: Modifiers,
+    ) -> Option<(KeyTableEntry, Option<&str>)> {
+        while self.process_expiration() {}
+        for entry in self.stack.iter().rev() {
+            let name = entry.name.as_str();
+            if let Some(entry) = input_map.lookup_key(key, mods, Some(name)) {
+                return Some((entry, Some(name)));
+            }
+        }
+        input_map
+            .lookup_key(key, mods, None)
+            .map(|entry| (entry, None))
+    }
+
     pub fn did_process_key(&mut self) {
         let should_pop = self
             .stack
@@ -160,15 +180,15 @@ impl super::TermWindow {
         }
 
         if is_down {
-            let current_table = self.key_table_state.current_table();
-            if let Some(entry) =
-                self.input_map
-                    .lookup_key(&keycode, raw_modifiers | leader_mod, current_table)
-            {
+            if let Some((entry, table_name)) = self.key_table_state.lookup_key(
+                &self.input_map,
+                &keycode,
+                raw_modifiers | leader_mod,
+            ) {
                 if self.config.debug_key_events {
                     log::info!(
                         "{}{:?} {:?} -> perform {:?}",
-                        match current_table {
+                        match table_name {
                             Some(name) => format!("table:{} ", name),
                             None => String::new(),
                         },