keys: add prevent_fallback option for ActivateKeyTable

The behavior is to prevent falling back to a later key table
if no key matched.

refs: https://github.com/wez/wezterm/issues/2702

config/src/keyassignment.rs

@@ -520,6 +520,8 @@ pub enum KeyAssignment {
         one_shot: bool,
         #[dynamic(default)]
         until_unknown: bool,
+        #[dynamic(default)]
+        prevent_fallback: bool,
     },
     PopKeyTable,
     ClearKeyTableStack,

wezterm-gui/src/termwindow/keyevent.rs

@@ -1,7 +1,7 @@
 use crate::termwindow::InputMap;
 use ::window::{DeadKeyStatus, KeyCode, KeyEvent, Modifiers, RawKeyEvent, WindowOps};
 use anyhow::Context;
-use config::keyassignment::KeyTableEntry;
+use config::keyassignment::{KeyAssignment, KeyTableEntry};
 use mux::pane::{Pane, PerformAssignmentResult};
 use smol::Timer;
 use std::rc::Rc;
@@ -16,6 +16,7 @@ pub struct KeyTableStateEntry {
     /// Whether this activation pops itself after recognizing a key press
     one_shot: bool,
     until_unknown: bool,
+    prevent_fallback: bool,
     /// The timeout duration; used when updating the expiration
     timeout_milliseconds: Option<u64>,
 }
@@ -27,6 +28,7 @@ pub struct KeyTableArgs<'a> {
     pub replace_current: bool,
     pub one_shot: bool,
     pub until_unknown: bool,
+    pub prevent_fallback: bool,
 }
 
 #[derive(Debug, Default, Clone)]
@@ -46,6 +48,7 @@ impl KeyTableState {
                 .map(|ms| Instant::now() + Duration::from_millis(ms)),
             one_shot: args.one_shot,
             until_unknown: args.until_unknown,
+            prevent_fallback: args.prevent_fallback,
             timeout_milliseconds: args.timeout_milliseconds,
         });
     }
@@ -116,6 +119,19 @@ impl KeyTableState {
             if stack_entry.until_unknown {
                 pop_count += 1;
             }
+
+            if stack_entry.prevent_fallback {
+                // We can't simply return None for this case, as there
+                // may be later phases of key lookup.
+                // Instead, we synthesize a Nop and return that.
+                result = Some((
+                    KeyTableEntry {
+                        action: KeyAssignment::Nop,
+                    },
+                    Some(name.to_string()),
+                ));
+                break;
+            }
         }
 
         // This is a little bit tricky: until_unknown needs to

wezterm-gui/src/termwindow/mod.rs

@@ -2215,6 +2215,7 @@ impl TermWindow {
                 replace_current,
                 one_shot,
                 until_unknown,
+                prevent_fallback,
             } => {
                 anyhow::ensure!(
                     self.input_map.has_table(name),
@@ -2227,6 +2228,7 @@ impl TermWindow {
                     replace_current: *replace_current,
                     one_shot: *one_shot,
                     until_unknown: *until_unknown,
+                    prevent_fallback: *prevent_fallback,
                 });
                 self.update_title();
             }
@@ -2469,6 +2471,7 @@ impl TermWindow {
                                 replace_current,
                                 one_shot: false,
                                 until_unknown: false,
+                                prevent_fallback: false,
                             });
                         });
                 }
@@ -2518,6 +2521,7 @@ impl TermWindow {
                                 replace_current,
                                 one_shot: false,
                                 until_unknown: false,
+                                prevent_fallback: false,
                             });
                         });
                 }