Add offsetAllocator package (#6150)

packages/o/offsetallocator/xmake.lua

@@ -0,0 +1,41 @@
+package("offsetallocator")
+    set_homepage("https://github.com/sebbbi/OffsetAllocator")
+    set_description("Fast O(1) offset allocator with minimal fragmentation")
+    set_license("MIT")
+
+    add_urls("https://github.com/sebbbi/OffsetAllocator.git")
+    add_versions("2023.03.27", "3610a7377088b1e8c8f1525f458c96038a4e6fc0")
+
+    on_install(function (package)
+        if package:is_plat("windows") and package:config("shared") then
+            io.replace("offsetAllocator.hpp", "namespace OffsetAllocator", [[
+                #define LIBRARY_API __declspec(dllexport)
+                namespace OffsetAllocator
+            ]], {plain = true})
+            io.replace("offsetAllocator.hpp", "struct Allocation", "struct LIBRARY_API Allocation", {plain = true})
+            io.replace("offsetAllocator.hpp", "struct Region", "struct LIBRARY_API Region", {plain = true})
+            io.replace("offsetAllocator.hpp", "struct StorageReport", "struct LIBRARY_API StorageReport", {plain = true})
+            io.replace("offsetAllocator.hpp", "class Allocator", "class LIBRARY_API Allocator", {plain = true})
+            io.replace("offsetAllocator.hpp", "struct Node", "struct LIBRARY_API Node", {plain = true})
+        end
+        io.writefile("xmake.lua", [[
+            add_rules("mode.release", "mode.debug")
+            target("OffsetAllocator")
+                set_kind("$(kind)")
+                set_languages("c++20")
+                add_files("offsetAllocator.cpp")
+                add_headerfiles("offsetAllocator.hpp")
+        ]])
+        import("package.tools.xmake").install(package)
+    end)
+
+    on_test(function (package)
+        assert(package:check_cxxsnippets({test = [[
+            void test() {
+                using namespace OffsetAllocator;
+                Allocator allocator(12345);
+                Allocation a = allocator.allocate(1337);
+                uint32 offset_a = a.offset;
+            }
+        ]]}, {configs = {languages = "c++20"}, includes = {"offsetAllocator.hpp"}}))
+    end)