Add unbind_default_keys config option (#1)

* Add `unbind_default_keys` config option

Based on helix-editor#2733

* Fix lint issues

book/src/remapping.md

@@ -75,5 +75,23 @@ Ctrl, Shift and Alt modifiers are encoded respectively with the prefixes
 
 Keys can be disabled by binding them to the `no_op` command.
 
+To remove all default bindings, `unbind-default-keys = true` can be added to the top level configuration.
+
+```toml
+unbind_default_keys = true
+
+# Only these normal mode bindings will be used
+[keys.normal]
+n = "normal_mode"
+t = "goto_definition"
+
+# remember to add bindings to return to normal mode
+[keys.select]
+esc = "normal_mode"
+
+[keys.insert]
+esc = "normal_mode"
+```
+
 A list of commands is available in the [Keymap](https://docs.helix-editor.com/keymap.html) documentation
  and in the source code at [`helix-term/src/commands.rs`](https://github.com/helix-editor/helix/blob/master/helix-term/src/commands.rs) at the invocation of `static_commands!` macro and the `TypableCommandList`.

helix-term/src/config.rs

@@ -20,6 +20,8 @@ pub struct Config {
 #[serde(deny_unknown_fields)]
 pub struct ConfigRaw {
     pub theme: Option<String>,
+    #[serde(default)]
+    pub unbind_default_keys: bool,
     pub keys: Option<HashMap<Mode, KeyTrie>>,
     pub editor: Option<toml::Value>,
 }
@@ -66,7 +68,11 @@ impl Config {
             local.and_then(|file| toml::from_str(&file).map_err(ConfigLoadError::BadConfig));
         let res = match (global_config, local_config) {
             (Ok(global), Ok(local)) => {
-                let mut keys = keymap::default();
+                let mut keys;
+                match local.unbind_default_keys {
+                    true => keys = HashMap::default(),
+                    false => keys = keymap::default(),
+                }
                 if let Some(global_keys) = global.keys {
                     merge_keys(&mut keys, global_keys)
                 }
@@ -96,7 +102,11 @@ impl Config {
                 return Err(ConfigLoadError::BadConfig(err))
             }
             (Ok(config), Err(_)) | (Err(_), Ok(config)) => {
-                let mut keys = keymap::default();
+                let mut keys;
+                match config.unbind_default_keys {
+                    true => keys = HashMap::default(),
+                    false => keys = keymap::default(),
+                }
                 if let Some(keymap) = config.keys {
                     merge_keys(&mut keys, keymap);
                 }

helix-term/src/keymap.rs

@@ -309,7 +309,10 @@ impl Keymaps {
     pub fn get(&mut self, mode: Mode, key: KeyEvent) -> KeymapResult {
         // TODO: remove the sticky part and look up manually
         let keymaps = &*self.map();
-        let keymap = &keymaps[&mode];
+        let keymap = match keymaps.get(&mode) {
+            Some(keymap) => keymap,
+            None => return KeymapResult::NotFound,
+        };
 
         if key!(Esc) == key {
             if !self.state.is_empty() {
@@ -364,14 +367,12 @@ impl Default for Keymaps {
     }
 }
 
-/// Merge default config keys with user overwritten keys for custom user config.
+/// Merge existing config keys with user overwritten keys.
 pub fn merge_keys(dst: &mut HashMap<Mode, KeyTrie>, mut delta: HashMap<Mode, KeyTrie>) {
-    for (mode, keys) in dst {
-        keys.merge_nodes(
-            delta
-                .remove(mode)
-                .unwrap_or_else(|| KeyTrie::Node(KeyTrieNode::default())),
-        )
+    for (mode, keys) in delta.drain() {
+        dst.entry(mode)
+            .or_insert(KeyTrie::Node(KeyTrieNode::default()))
+            .merge_nodes(keys)
     }
 }