Support left/right-specific modifiers

README.md

@@ -167,7 +167,9 @@ For the `MOD1-` part, the following prefixes can be used (also case-insensitive)
 * Alt: `M-`, `ALT-`
 * Windows: `SUPER-`, `WIN-`, `WINDOWS-`
 
-You may use multiple prefixes like `C-M-Shift-a`.
+You can use multiple prefixes like `C-M-Shift-a`.
+You may also prefix them with `L` or `R` (case-insensitive) so that
+remapping is triggered only on a left or right modifier, e.g. `LCtrl-a`.
 
 ### application
 

src/config/key_press.rs

@@ -70,21 +70,37 @@ fn parse_key_press(input: &str) -> Result<KeyPress, Box<dyn error::Error>> {
 
 fn parse_modifier(modifier: &str) -> Option<(Modifier, ModifierState)> {
     // Everything is case-insensitive
-    match &modifier.to_uppercase()[..] {
+    let mut modifier = &modifier.to_uppercase()[..];
+    let mut modifier_state = ModifierState::Either;
+    if modifier.starts_with("L") {
+        modifier = remove_first_char(modifier);
+        modifier_state = ModifierState::Left;
+    } else if modifier.starts_with("R") {
+        modifier = remove_first_char(modifier);
+        modifier_state = ModifierState::Right;
+    }
+
+    match modifier {
         // Shift
-        "SHIFT" => Some((Modifier::Shift, ModifierState::Either)),
+        "SHIFT" => Some((Modifier::Shift, modifier_state)),
         // Control
-        "C" => Some((Modifier::Control, ModifierState::Either)),
-        "CTRL" => Some((Modifier::Control, ModifierState::Either)),
-        "CONTROL" => Some((Modifier::Control, ModifierState::Either)),
+        "C" => Some((Modifier::Control, modifier_state)),
+        "CTRL" => Some((Modifier::Control, modifier_state)),
+        "CONTROL" => Some((Modifier::Control, modifier_state)),
         // Alt
-        "M" => Some((Modifier::Alt, ModifierState::Either)),
-        "ALT" => Some((Modifier::Alt, ModifierState::Either)),
+        "M" => Some((Modifier::Alt, modifier_state)),
+        "ALT" => Some((Modifier::Alt, modifier_state)),
         // Windows
-        "SUPER" => Some((Modifier::Windows, ModifierState::Either)),
-        "WIN" => Some((Modifier::Windows, ModifierState::Either)),
-        "WINDOWS" => Some((Modifier::Windows, ModifierState::Either)),
+        "SUPER" => Some((Modifier::Windows, modifier_state)),
+        "WIN" => Some((Modifier::Windows, modifier_state)),
+        "WINDOWS" => Some((Modifier::Windows, modifier_state)),
         // else
         _ => None,
     }
 }
+
+fn remove_first_char(string: &str) -> &str {
+    let mut chars = string.chars();
+    chars.next();
+    chars.as_str()
+}

src/config/tests.rs

@@ -56,7 +56,19 @@ fn test_keymap_basic() {
         remap:
           Alt-Enter: Ctrl-Enter
       - remap:
-          Alt-S: Ctrl-S
+          M-S: C-S
+    "})
+}
+
+#[test]
+fn test_keymap_lr_modifiers() {
+    assert_parse(indoc! {"
+    keymap:
+      - name: Global
+        remap:
+          LAlt-Enter: RCtrl-Enter
+      - remap:
+          RM-S: LC-S
     "})
 }