refactor: add shader pass and backend variants

tests/Resources/Shader/test_shader_loader.cpp

@@ -3,6 +3,10 @@
 #include <XCEngine/Core/Asset/ResourceTypes.h>
 #include <XCEngine/Core/Containers/Array.h>
 
+#include <cstdio>
+#include <filesystem>
+#include <fstream>
+
 using namespace XCEngine::Resources;
 using namespace XCEngine::Containers;
 
@@ -35,4 +39,35 @@ TEST(ShaderLoader, LoadInvalidPath) {
     EXPECT_FALSE(result);
 }
 
+TEST(ShaderLoader, LoadLegacySingleStageShaderBuildsDefaultPassVariant) {
+    namespace fs = std::filesystem;
+
+    const fs::path shaderPath = fs::temp_directory_path() / "xc_shader_loader_stage.vert";
+    {
+        std::ofstream shaderFile(shaderPath);
+        ASSERT_TRUE(shaderFile.is_open());
+        shaderFile << "#version 430\nvoid main() {}";
+    }
+
+    ShaderLoader loader;
+    LoadResult result = loader.Load(shaderPath.string().c_str());
+    ASSERT_TRUE(result);
+    ASSERT_NE(result.resource, nullptr);
+
+    Shader* shader = static_cast<Shader*>(result.resource);
+    ASSERT_NE(shader, nullptr);
+    EXPECT_EQ(shader->GetShaderType(), ShaderType::Vertex);
+    ASSERT_EQ(shader->GetPassCount(), 1u);
+
+    const ShaderPass* pass = shader->FindPass("Default");
+    ASSERT_NE(pass, nullptr);
+    ASSERT_EQ(pass->variants.Size(), 1u);
+    EXPECT_EQ(pass->variants[0].stage, ShaderType::Vertex);
+    EXPECT_EQ(pass->variants[0].backend, ShaderBackend::Generic);
+    EXPECT_EQ(pass->variants[0].sourceCode, shader->GetSourceCode());
+
+    delete shader;
+    std::remove(shaderPath.string().c_str());
+}
+
 } // namespace