zig/test/behavior/bugs/3367.zig

const builtin = @import("builtin");
const Foo = struct {
    usingnamespace Mixin;
};

const Mixin = struct {
    pub fn two(self: Foo) void {
        _ = self;
    }
};

test "container member access usingnamespace decls" {
    var foo = Foo{};
    foo.two();
}