Fix Logitech mouse button chord handling

modules/common/home-manager.nix

@@ -1,19 +1,30 @@
-{ inputs, lib, os, ... }:
+{
+  inputs,
+  lib,
+  os,
+  ...
+}:
 let
   isDarwin = os == "darwin";
   isLinux = os == "linux";
-in {
+in
+{
   imports =
     lib.optional isDarwin inputs.home-manager.darwinModules.home-manager
     ++ lib.optional isLinux inputs.home-manager.nixosModules.home-manager;
 
   home-manager = {
-    useGlobalPkgs   = true;
+    useGlobalPkgs = true;
     useUserPackages = true;
     backupFileExtension = lib.mkDefault "home.bak";
   };
 
-  home-manager.sharedModules = [{
-    programs.home-manager.enable = true;
-  }];
+  home-manager.sharedModules = [
+    {
+      programs = {
+        home-manager.enable = true;
+        man.generateCaches = isLinux;
+      };
+    }
+  ];
 }

modules/darwin/karabiner.nix

@@ -86,7 +86,7 @@ let
     is_keyboard = true;
   };
 
-  # Swap the G213's Windows/Alt modifiers.
+  # Swap the G213's Windows/Alt modifiers and map Application to Fn.
   logitechG213SimpleModifications = [
     {
       from.key_code = "left_command";
@@ -96,6 +96,10 @@ let
       from.key_code = "left_option";
       to = [ { key_code = "left_command"; } ];
     }
+    {
+      from.key_code = "application";
+      to = [ { apple_vendor_top_case_key_code = "keyboard_fn"; } ];
+    }
   ];
 
   logitechMouseIdentifiers = {
@@ -104,12 +108,8 @@ let
     is_pointing_device = true;
   };
 
-  # Middle click sends Fn; side buttons navigate back and forward.
+  # Side buttons navigate back and forward.
   logitechMouseSimpleModifications = [
-    {
-      from.pointing_button = "button3";
-      to = [ { apple_vendor_top_case_key_code = "keyboard_fn"; } ];
-    }
     {
       from.pointing_button = "button4";
       to = [
@@ -133,6 +133,172 @@ let
   complex_modifications = {
     name = "Complex Modifications";
     rules = [
+      {
+        description = "Logitech mouse Button3 sends Fn, or middle click with Hyper, Shift, Button1, or Button2";
+        manipulators = [
+          # Keep the forwarded button as the only `to` event so Karabiner
+          # preserves its down state. A variable in the same `to` sequence
+          # either releases the button immediately or resets too early, so
+          # detect Button3 through `to_if_other_key_pressed` instead.
+          {
+            from.pointing_button = "button1";
+            to = [ { from_event = true; } ];
+            to_if_other_key_pressed = [
+              {
+                other_keys = [
+                  {
+                    pointing_button = "button3";
+                    modifiers.optional = [ "any" ];
+                  }
+                ];
+                to = [
+                  {
+                    set_variable = {
+                      name = "logitech_mouse_button1_held";
+                      value = 1;
+                    };
+                  }
+                ];
+              }
+            ];
+            to_after_key_up = [
+              {
+                set_variable = {
+                  name = "logitech_mouse_button1_held";
+                  value = 0;
+                };
+              }
+            ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from.pointing_button = "button2";
+            to = [ { from_event = true; } ];
+            to_if_other_key_pressed = [
+              {
+                other_keys = [
+                  {
+                    pointing_button = "button3";
+                    modifiers.optional = [ "any" ];
+                  }
+                ];
+                to = [
+                  {
+                    set_variable = {
+                      name = "logitech_mouse_button2_held";
+                      value = 1;
+                    };
+                  }
+                ];
+              }
+            ];
+            to_after_key_up = [
+              {
+                set_variable = {
+                  name = "logitech_mouse_button2_held";
+                  value = 0;
+                };
+              }
+            ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from = {
+              pointing_button = "button3";
+              modifiers.optional = [ "any" ];
+            };
+            to = [ { pointing_button = "button3"; } ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+              {
+                type = "variable_if";
+                name = "logitech_mouse_button1_held";
+                value = 1;
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from = {
+              pointing_button = "button3";
+              modifiers.mandatory = hyperModifiers;
+            };
+            to = [ { pointing_button = "button3"; } ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from = {
+              pointing_button = "button3";
+              modifiers = {
+                mandatory = [ "shift" ];
+                optional = [ "any" ];
+              };
+            };
+            to = [ { pointing_button = "button3"; } ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from = {
+              pointing_button = "button3";
+              modifiers.optional = [ "any" ];
+            };
+            to = [ { pointing_button = "button3"; } ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+              {
+                type = "variable_if";
+                name = "logitech_mouse_button2_held";
+                value = 1;
+              }
+            ];
+            type = "basic";
+          }
+          {
+            from = {
+              pointing_button = "button3";
+              modifiers.optional = [ "any" ];
+            };
+            to = [ { apple_vendor_top_case_key_code = "keyboard_fn"; } ];
+            conditions = [
+              {
+                type = "device_if";
+                identifiers = [ logitechMouseIdentifiers ];
+              }
+            ];
+            type = "basic";
+          }
+        ];
+      }
       # {
       #   description = "Change numbers to symbols and vice versa";
       #   manipulators = manipulators;
@@ -143,7 +309,9 @@ let
           {
             from = {
               key_code = "caps_lock";
-              modifiers = { optional = [ "any" ]; };
+              modifiers = {
+                optional = [ "any" ];
+              };
             };
             to = [
               {