🚚 Use an actual error type for LoaderData issues

Author: fredemmott

src/LoaderData.hpp

@@ -5,11 +5,39 @@
 #include <openxr/openxr.h>
 
 #include <string>
+#include <system_error>
 #include <unordered_set>
+#include <variant>
 
 namespace FredEmmott::OpenXRLayers {
 
 struct LoaderData {
+  struct PipeCreationError {
+    std::error_code mError;
+  };
+  struct PipeAttributeError {
+    std::error_code mError;
+  };
+  struct CanNotFindExecutableError {
+    std::error_code mError;
+  };
+  struct CanNotSpawnError {
+    std::error_code mError;
+  };
+  struct BadExitCodeError {
+    uint32_t mExitCode;
+  };
+  struct InvalidJSONError {
+    std::string mExplanation;
+  };
+  using Error = std::variant<
+    PipeCreationError,
+    PipeAttributeError,
+    CanNotFindExecutableError,
+    CanNotSpawnError,
+    BadExitCodeError,
+    InvalidJSONError>;
+
   XrResult mQueryExtensionsResult {XR_RESULT_MAX_ENUM};
   XrResult mQueryLayersResult {XR_RESULT_MAX_ENUM};
 

src/Platform.hpp

@@ -10,11 +10,11 @@
 #include <imgui.h>
 
 #include "APILayerSignature.hpp"
+#include "LoaderData.hpp"
 
 namespace FredEmmott::OpenXRLayers {
 class APILayerStore;
 class ReadWriteAPILayerStore;
-struct LoaderData;
 
 struct DPIChangeInfo {
   float mDPIScaling {};
@@ -70,7 +70,7 @@ class Platform {
 
   virtual std::expected<APILayerSignature, APILayerSignature::Error>
   GetAPILayerSignature(const std::filesystem::path&) = 0;
-  virtual std::expected<LoaderData, std::string> GetLoaderData() = 0;
+  virtual std::expected<LoaderData, LoaderData::Error> GetLoaderData() = 0;
   virtual std::vector<std::filesystem::path> GetNewAPILayerJSONPaths() = 0;
   virtual std::optional<std::filesystem::path> GetExportFilePath() = 0;
   virtual std::unordered_set<std::string> GetEnvironmentVariableNames() = 0;

src/windows/WindowsPlatform.cpp

@@ -574,14 +574,26 @@ std::vector<std::filesystem::path> WindowsPlatform::GetNewAPILayerJSONPaths() {
   return ret;
 }
 
-std::expected<LoaderData, std::string> WindowsPlatform::GetLoaderData() {
+template <class T>
+static std::unexpected<T> UnexpectedHRESULT(HRESULT value) {
+  return std::unexpected {
+    T {{value, std::system_category()}},
+  };
+}
+
+template <class T>
+static std::unexpected<T> UnexpectedGetLastError() {
+  return UnexpectedHRESULT<T>(HRESULT_FROM_WIN32(GetLastError()));
+}
+
+std::expected<LoaderData, LoaderData::Error> WindowsPlatform::GetLoaderData() {
   if (!mLoaderData) {
     mLoaderData = GetLoaderDataWithoutCache();
   }
   return mLoaderData.value();
 }
 
-std::expected<LoaderData, std::string>
+std::expected<LoaderData, LoaderData::Error>
 WindowsPlatform::GetLoaderDataWithoutCache() {
   SECURITY_ATTRIBUTES saAttr {
     .nLength = sizeof(SECURITY_ATTRIBUTES),
@@ -591,15 +603,16 @@ WindowsPlatform::GetLoaderDataWithoutCache() {
   wil::unique_handle stdoutRead;
   wil::unique_handle stdoutWrite;
   if (!CreatePipe(stdoutRead.put(), stdoutWrite.put(), &saAttr, 0)) {
-    return std::unexpected("Failed to create pipe");
+    return UnexpectedGetLastError<LoaderData::PipeCreationError>();
   }
   if (!SetHandleInformation(stdoutRead.get(), HANDLE_FLAG_INHERIT, 0)) {
-    return std::unexpected("Failed to set pipe properties");
+    return UnexpectedGetLastError<LoaderData::PipeAttributeError>();
   }
 
-  wchar_t modulePath[MAX_PATH];
-  if (!GetModuleFileNameW(nullptr, modulePath, MAX_PATH)) {
-    return std::unexpected("Failed to get executable path");
+  constexpr auto MaxPathExtended = 32768;
+  wchar_t modulePath[MaxPathExtended];
+  if (!GetModuleFileNameW(nullptr, modulePath, MaxPathExtended)) {
+    return UnexpectedGetLastError<LoaderData::CanNotFindExecutableError>();
   }
 
   STARTUPINFOW si {
@@ -623,7 +636,7 @@ WindowsPlatform::GetLoaderDataWithoutCache() {
         nullptr,
         &si,
         &pi)) {
-    return std::unexpected("Failed to create process");
+    return UnexpectedGetLastError<LoaderData::CanNotSpawnError>();
   }
 
   wil::unique_handle process {pi.hProcess};
@@ -643,14 +656,13 @@ WindowsPlatform::GetLoaderDataWithoutCache() {
 
   DWORD exitCode;
   if (!GetExitCodeProcess(process.get(), &exitCode) || exitCode != 0) {
-    return std::unexpected(
-      std::format("Subprocess failed with exit code {}", exitCode));
+    return std::unexpected {LoaderData::BadExitCodeError {exitCode}};
   }
 
   try {
     return static_cast<LoaderData>(nlohmann::json::parse(output));
   } catch (const nlohmann::json::exception& e) {
-    return std::unexpected(e.what());
+    return std::unexpected {LoaderData::InvalidJSONError {e.what()}};
   }
 }
 

src/windows/WindowsPlatform.hpp

@@ -20,7 +20,7 @@ class WindowsPlatform final : public Platform {
 
   std::optional<std::filesystem::path> GetExportFilePath() override;
   std::vector<std::filesystem::path> GetNewAPILayerJSONPaths() override;
-  std::expected<LoaderData, std::string> GetLoaderData() override;
+  std::expected<LoaderData, LoaderData::Error> GetLoaderData() override;
 
   float GetDPIScaling() override {
     return mDPIScaling;
@@ -58,7 +58,7 @@ class WindowsPlatform final : public Platform {
     Config::MINIMUM_WINDOW_WIDTH,
     Config::MINIMUM_WINDOW_HEIGHT,
   };
-  std::optional<std::expected<LoaderData, std::string>> mLoaderData;
+  std::optional<std::expected<LoaderData, LoaderData::Error>> mLoaderData;
 
   HWND CreateAppWindow();
   void InitializeFonts(ImGuiIO* io);
@@ -71,7 +71,8 @@ class WindowsPlatform final : public Platform {
   void MainLoop(const std::function<void()>& drawFrame);
   void Shutdown();
 
-  static std::expected<LoaderData, std::string> GetLoaderDataWithoutCache();
+  static std::expected<LoaderData, LoaderData::Error>
+  GetLoaderDataWithoutCache();
   static LRESULT WindowProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam);
 
   LRESULT