Fix empty keybind setting (#5977)

Fixes https://github.com/ghostty-org/ghostty/issues/5936.

Extracts the default keybind setting to an `init` function. Add logic to
call `init` in `parseIntoField` if it is defined for the type.

src/cli/args.zig

@@ -247,16 +247,6 @@ pub fn parseIntoField(
 
     inline for (info.Struct.fields) |field| {
         if (field.name[0] != '_' and mem.eql(u8, field.name, key)) {
-            // If the value is empty string (set but empty string),
-            // then we reset the value to the default.
-            if (value) |v| default: {
-                if (v.len != 0) break :default;
-                const raw = field.default_value orelse break :default;
-                const ptr: *const field.type = @alignCast(@ptrCast(raw));
-                @field(dst, field.name) = ptr.*;
-                return;
-            }
-
             // For optional fields, we just treat it as the child type.
             // This lets optional fields default to null but get set by
             // the CLI.
@@ -264,11 +254,27 @@ pub fn parseIntoField(
                 .Optional => |opt| opt.child,
                 else => field.type,
             };
+            const fieldInfo = @typeInfo(Field);
+            const canHaveDecls = fieldInfo == .Struct or fieldInfo == .Union or fieldInfo == .Enum;
+
+            // If the value is empty string (set but empty string),
+            // then we reset the value to the default.
+            if (value) |v| default: {
+                if (v.len != 0) break :default;
+                // Set default value if possible.
+                if (canHaveDecls and @hasDecl(Field, "init")) {
+                    try @field(dst, field.name).init(alloc);
+                    return;
+                }
+                const raw = field.default_value orelse break :default;
+                const ptr: *const field.type = @alignCast(@ptrCast(raw));
+                @field(dst, field.name) = ptr.*;
+                return;
+            }
 
             // If we are a type that can have decls and have a parseCLI decl,
             // we call that and use that to set the value.
-            const fieldInfo = @typeInfo(Field);
-            if (fieldInfo == .Struct or fieldInfo == .Union or fieldInfo == .Enum) {
+            if (canHaveDecls) {
                 if (@hasDecl(Field, "parseCLI")) {
                     const fnInfo = @typeInfo(@TypeOf(Field.parseCLI)).Fn;
                     switch (fnInfo.params.len) {
@@ -761,6 +767,29 @@ test "parseIntoField: ignore underscore-prefixed fields" {
     try testing.expectEqualStrings("12", data._a);
 }
 
+test "parseIntoField: struct with init func" {
+    const testing = std.testing;
+    var arena = ArenaAllocator.init(testing.allocator);
+    defer arena.deinit();
+    const alloc = arena.allocator();
+
+    var data: struct {
+        a: struct {
+            const Self = @This();
+
+            v: []const u8,
+
+            pub fn init(self: *Self, _alloc: Allocator) !void {
+                _ = _alloc;
+                self.* = .{ .v = "HELLO!" };
+            }
+        },
+    } = undefined;
+
+    try parseIntoField(@TypeOf(data), alloc, &data, "a", "");
+    try testing.expectEqual(@as([]const u8, "HELLO!"), data.a.v);
+}
+
 test "parseIntoField: string" {
     const testing = std.testing;
     var arena = ArenaAllocator.init(testing.allocator);