Support logical modifiers

README.md

@@ -153,7 +153,12 @@ is supported only in `modmap` since `keymap` handles modifier keys differently.
 modmap:
   - name: Name # Optional
     remap: # Required
+      # Replace a key with another
       KEY_XXX: KEY_YYY # Required
+      # Make it a logical modifier key
+      KEY_XXX:
+        modifier: true # Required
+      # Dispatch different keys depending on whether you hold it or press it alone
       KEY_XXX:
         held: KEY_YYY # Required
         alone: KEY_ZZZ # Required
@@ -226,6 +231,8 @@ You can use multiple prefixes like `C-M-Shift-a`.
 You may also suffix them with `_L` or `_R` (case-insensitive) so that
 remapping is triggered only on a left or right modifier, e.g. `Ctrl_L-a`.
 
+If you set `modifier: true` in `modmap`, you can use it in the `MOD1-` part too.
+
 ### application
 
 `application` can be used for both `modmap` and `keymap`, which allows you to specify application-specific remapping.

src/config/key_action.rs

@@ -12,10 +12,16 @@ use super::action::{Action, Actions};
 pub enum KeyAction {
     #[serde(deserialize_with = "deserialize_key")]
     Key(Key),
+    ModifierKey(ModifierKey),
     MultiPurposeKey(MultiPurposeKey),
     PressReleaseKey(PressReleaseKey),
 }
 
+#[derive(Clone, Debug, Deserialize)]
+pub struct ModifierKey {
+    pub modifier: bool,
+}
+
 #[serde_as]
 #[derive(Clone, Debug, Deserialize)]
 pub struct MultiPurposeKey {
@@ -28,7 +34,6 @@ pub struct MultiPurposeKey {
     pub alone_timeout: Duration,
 }
 
-#[serde_as]
 #[derive(Clone, Debug, Deserialize)]
 pub struct PressReleaseKey {
     #[serde(deserialize_with = "deserialize_actions")]

src/event_handler.rs

@@ -1,7 +1,7 @@
 use crate::client::{build_client, WMClient};
 use crate::config::action::Action;
 use crate::config::application::Application;
-use crate::config::key_action::{KeyAction, MultiPurposeKey, PressReleaseKey};
+use crate::config::key_action::{KeyAction, ModifierKey, MultiPurposeKey, PressReleaseKey};
 use crate::config::key_press::{KeyPress, Modifier};
 use crate::config::keymap::{build_override_table, OverrideEntry};
 use crate::config::remap::Remap;
@@ -162,6 +162,17 @@ impl EventHandler {
     ) -> Result<Vec<(Key, i32)>, Box<dyn Error>> {
         let keys = match key_action {
             KeyAction::Key(modmap_key) => vec![(modmap_key, value)],
+            KeyAction::ModifierKey(ModifierKey { modifier }) => {
+                if modifier {
+                    if value == PRESS {
+                        self.modifiers.insert(key);
+                    } else if value == RELEASE {
+                        self.modifiers.remove(&key);
+                    }
+                }
+                // Process this key only in xremap
+                vec![]
+            }
             KeyAction::MultiPurposeKey(MultiPurposeKey {
                 held,
                 alone,