input: expand Mods size, convert everything to use it

src/Surface.zig

@@ -1149,8 +1149,8 @@ pub fn keyCallback(
             .set_other => if (!modify_other_keys) continue,
         }
 
-        const mods_int: u8 = @bitCast(binding_mods);
-        const entry_mods_int: u8 = @bitCast(entry.mods);
+        const mods_int = binding_mods.int();
+        const entry_mods_int = entry.mods.int();
         if (entry_mods_int == 0) {
             if (mods_int != 0 and !entry.mods_empty_is_any) continue;
             // mods are either empty, or empty means any so we allow it.
@@ -1186,8 +1186,8 @@ pub fn keyCallback(
 
     // Handle non-printables
     const char: u8 = char: {
-        const mods_int: u8 = @bitCast(unalt_mods);
-        const ctrl_only: u8 = @bitCast(input.Mods{ .ctrl = true });
+        const mods_int = unalt_mods.int();
+        const ctrl_only = (input.Mods{ .ctrl = true }).int();
 
         // If we're only pressing control, check if this is a character
         // we convert to a non-printable. The best table I've found for

src/apprt/embedded.zig

@@ -660,7 +660,10 @@ pub const CAPI = struct {
         surface.keyCallback(
             action,
             keycode,
-            @bitCast(@as(u8, @truncate(@as(c_uint, @bitCast(c_mods))))),
+            @bitCast(@as(
+                input.Mods.Backing,
+                @truncate(@as(c_uint, @bitCast(c_mods))),
+            )),
         ) catch |err| {
             log.err("error processing key event err={}", .{err});
             return;
@@ -684,7 +687,10 @@ pub const CAPI = struct {
         surface.mouseButtonCallback(
             action,
             button,
-            @bitCast(@as(u8, @truncate(@as(c_uint, @bitCast(mods))))),
+            @bitCast(@as(
+                input.Mods.Backing,
+                @truncate(@as(c_uint, @bitCast(mods))),
+            )),
         );
     }
 

src/apprt/glfw.zig

@@ -618,7 +618,12 @@ pub const Surface = struct {
         const core_win = window.getUserPointer(CoreSurface) orelse return;
 
         // Convert our glfw types into our input types
-        const mods: input.Mods = @bitCast(glfw_mods);
+        const mods: input.Mods = .{
+            .shift = glfw_mods.shift,
+            .ctrl = glfw_mods.control,
+            .alt = glfw_mods.alt,
+            .super = glfw_mods.super,
+        };
         const action: input.Action = switch (glfw_action) {
             .release => .release,
             .press => .press,
@@ -843,7 +848,12 @@ pub const Surface = struct {
         const core_win = window.getUserPointer(CoreSurface) orelse return;
 
         // Convert glfw button to input button
-        const mods: input.Mods = @bitCast(glfw_mods);
+        const mods: input.Mods = .{
+            .shift = glfw_mods.shift,
+            .ctrl = glfw_mods.control,
+            .alt = glfw_mods.alt,
+            .super = glfw_mods.super,
+        };
         const button: input.MouseButton = switch (glfw_button) {
             .left => .left,
             .right => .right,

src/input/key.zig

@@ -5,23 +5,45 @@ const Allocator = std.mem.Allocator;
 /// GLFW representation, but we use this generically.
 ///
 /// IMPORTANT: Any changes here update include/ghostty.h
-pub const Mods = packed struct(u8) {
+pub const Mods = packed struct(Mods.Backing) {
+    pub const Backing = u16;
+
     shift: bool = false,
     ctrl: bool = false,
     alt: bool = false,
     super: bool = false,
     caps_lock: bool = false,
     num_lock: bool = false,
-    _padding: u2 = 0,
+    sides: side = .{},
+    _padding: u6 = 0,
+
+    /// Tracks the side that is active for any given modifier. Note
+    /// that this doesn't confirm a modifier is pressed; you must check
+    /// the bool for that in addition to this.
+    ///
+    /// Not all platforms support this, check apprt for more info.
+    pub const side = packed struct(u4) {
+        shift: Side = .left,
+        ctrl: Side = .left,
+        alt: Side = .left,
+        super: Side = .left,
+    };
+
+    pub const Side = enum { left, right };
+
+    /// Integer value of this struct.
+    pub fn int(self: Mods) Backing {
+        return @bitCast(self);
+    }
 
     /// Returns true if no modifiers are set.
     pub fn empty(self: Mods) bool {
-        return @as(u8, @bitCast(self)) == 0;
+        return self.int() == 0;
     }
 
     /// Returns true if two mods are equal.
     pub fn equal(self: Mods, other: Mods) bool {
-        return @as(u8, @bitCast(self)) == @as(u8, @bitCast(other));
+        return self.int() == other.int();
     }
 
     /// Return mods that are only relevant for bindings.
@@ -45,10 +67,10 @@ pub const Mods = packed struct(u8) {
     // For our own understanding
     test {
         const testing = std.testing;
-        try testing.expectEqual(@as(u8, @bitCast(Mods{})), @as(u8, 0b0));
+        try testing.expectEqual(@as(Backing, @bitCast(Mods{})), @as(Backing, 0b0));
         try testing.expectEqual(
-            @as(u8, @bitCast(Mods{ .shift = true })),
-            @as(u8, 0b0000_0001),
+            @as(Backing, @bitCast(Mods{ .shift = true })),
+            @as(Backing, 0b0000_0001),
         );
     }
 };