Add an Error and ResultOrError<T> type and tests

These types are meant to be used for computations that might but are not
expected to fail in backend/, such that the error case can be much
slower than the success case.

The NXT_TRY and NXT_TRY_RESULT macros are added to help write more
concise code that uses Error and ResultOrError.

src/backend/CMakeLists.txt

@@ -30,6 +30,7 @@ Generate(
 )
 target_link_libraries(backend_utils_autogen nxtcpp)
 target_include_directories(backend_utils_autogen PUBLIC ${GENERATED_DIR})
+target_include_directories(backend_utils_autogen PRIVATE ${SRC_DIR})
 
 function(GenerateProcTable backend)
     Generate(
@@ -342,6 +343,10 @@ list(APPEND BACKEND_SOURCES
     ${BACKEND_DIR}/CommandBufferStateTracker.h
     ${BACKEND_DIR}/Device.cpp
     ${BACKEND_DIR}/Device.h
+    ${BACKEND_DIR}/Error.cpp
+    ${BACKEND_DIR}/Error.h
+    ${BACKEND_DIR}/ErrorData.cpp
+    ${BACKEND_DIR}/ErrorData.h
     ${BACKEND_DIR}/Forward.h
     ${BACKEND_DIR}/InputState.cpp
     ${BACKEND_DIR}/InputState.h

src/backend/Error.cpp

@@ -0,0 +1,31 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "backend/Error.h"
+
+#include "backend/ErrorData.h"
+
+namespace backend {
+
+    ErrorData* MakeError(const char* message, const char* file, const char* function, int line) {
+        ErrorData* error = new ErrorData(message);
+        error->AppendBacktrace(file, function, line);
+        return error;
+    }
+
+    void AppendBacktrace(ErrorData* error, const char* file, const char* function, int line) {
+        error->AppendBacktrace(file, function, line);
+    }
+
+}  // namespace backend

src/backend/Error.h

@@ -0,0 +1,83 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef BACKEND_ERROR_H_
+#define BACKEND_ERROR_H_
+
+#include "common/Result.h"
+
+namespace backend {
+
+    // This is the content of an error value for MaybeError or ResultOrError, split off to its own
+    // file to avoid having all files including headers like <string> and <vector>
+    class ErrorData;
+
+    // MaybeError and ResultOrError are meant to be used as return value for function that are not
+    // expected to, but might fail. The handling of error is potentially much slower than successes.
+    using MaybeError = Result<void, ErrorData*>;
+
+    template <typename T>
+    using ResultOrError = Result<T, ErrorData*>;
+
+    // Returning a success is done like so:
+    //   return {}; // for Error
+    //   return SomethingOfTypeT; // for ResultOrError<T>
+    //
+    // Returning an error is done via:
+    //   NXT_RETURN_ERROR("My error message");
+#define NXT_RETURN_ERROR(EXPR) return MakeError(EXPR, __FILE__, __func__, __LINE__)
+
+#define NXT_CONCAT1(x, y) x##y
+#define NXT_CONCAT2(x, y) NXT_CONCAT1(x, y)
+#define NXT_LOCAL_VAR NXT_CONCAT2(_localVar, __LINE__)
+
+    // When Errors aren't handled explicitly, calls to functions returning errors should be
+    // wrapped in an NXT_TRY. It will return the error if any, otherwise keep executing
+    // the current function.
+#define NXT_TRY(EXPR)                                             \
+    {                                                             \
+        auto NXT_LOCAL_VAR = EXPR;                                \
+        if (NXT_UNLIKELY(NXT_LOCAL_VAR.IsError())) {              \
+            ErrorData* error = NXT_LOCAL_VAR.AcquireError();      \
+            AppendBacktrace(error, __FILE__, __func__, __LINE__); \
+            return {error};                                       \
+        }                                                         \
+    }                                                             \
+    for (;;)                                                      \
+    break
+
+    // NXT_TRY_ASSIGN is the same as NXT_TRY for ResultOrError and assigns the success value, if
+    // any, to VAR.
+#define NXT_TRY_ASSIGN(VAR, EXPR)                                 \
+    {                                                             \
+        auto NXT_LOCAL_VAR = EXPR;                                \
+        if (NXT_UNLIKELY(NXT_LOCAL_VAR.IsError())) {              \
+            ErrorData* error = NXT_LOCAL_VAR.AcquireError();      \
+            AppendBacktrace(error, __FILE__, __func__, __LINE__); \
+            return {error};                                       \
+        }                                                         \
+        VAR = NXT_LOCAL_VAR.AcquireSuccess();                     \
+    }                                                             \
+    for (;;)                                                      \
+    break
+
+    // Implementation detail of NXT_TRY and NXT_TRY_ASSIGN's adding to the Error's backtrace.
+    void AppendBacktrace(ErrorData* error, const char* file, const char* function, int line);
+
+    // Implementation detail of NXT_RETURN_ERROR
+    ErrorData* MakeError(const char* message, const char* file, const char* function, int line);
+
+}  // namespace backend
+
+#endif  // BACKEND_ERROR_H_

src/backend/ErrorData.cpp

@@ -0,0 +1,41 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "backend/ErrorData.h"
+
+namespace backend {
+
+    ErrorData::ErrorData() = default;
+
+    ErrorData::ErrorData(std::string message) : mMessage(std::move(message)) {
+    }
+
+    void ErrorData::AppendBacktrace(const char* file, const char* function, int line) {
+        BacktraceRecord record;
+        record.file = file;
+        record.function = function;
+        record.line = line;
+
+        mBacktrace.push_back(std::move(record));
+    }
+
+    const std::string& ErrorData::GetMessage() const {
+        return mMessage;
+    }
+
+    const std::vector<ErrorData::BacktraceRecord>& ErrorData::GetBacktrace() const {
+        return mBacktrace;
+    }
+
+}  // namespace backend

src/backend/ErrorData.h

@@ -0,0 +1,45 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#ifndef BACKEND_ERRORDATA_H_
+#define BACKEND_ERRORDATA_H_
+
+#include <string>
+#include <vector>
+
+namespace backend {
+
+    class ErrorData {
+      public:
+        ErrorData();
+        ErrorData(std::string message);
+
+        struct BacktraceRecord {
+            const char* file;
+            const char* function;
+            int line;
+        };
+        void AppendBacktrace(const char* file, const char* function, int line);
+
+        const std::string& GetMessage() const;
+        const std::vector<BacktraceRecord>& GetBacktrace() const;
+
+      private:
+        std::string mMessage;
+        std::vector<BacktraceRecord> mBacktrace;
+    };
+
+}  // namespace backend
+
+#endif  // BACKEND_ERRORDATA_H_

src/tests/CMakeLists.txt

@@ -33,6 +33,7 @@ list(APPEND UNITTEST_SOURCES
     ${UNITTESTS_DIR}/BitSetIteratorTests.cpp
     ${UNITTESTS_DIR}/CommandAllocatorTests.cpp
     ${UNITTESTS_DIR}/EnumClassBitmasksTests.cpp
+    ${UNITTESTS_DIR}/ErrorTests.cpp
     ${UNITTESTS_DIR}/MathTests.cpp
     ${UNITTESTS_DIR}/ObjectBaseTests.cpp
     ${UNITTESTS_DIR}/PerStageTests.cpp

src/tests/unittests/ErrorTests.cpp

@@ -0,0 +1,269 @@
+// Copyright 2018 The NXT Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include <gtest/gtest.h>
+
+#include "backend/Error.h"
+#include "backend/ErrorData.h"
+
+using namespace backend;
+
+namespace {
+
+int dummySuccess = 0xbeef;
+const char* dummyErrorMessage = "I am an error message :3";
+
+// Check returning a success MaybeError with {};
+TEST(ErrorTests, Error_Success) {
+    auto ReturnSuccess = []() -> MaybeError {
+        return {};
+    };
+
+    MaybeError result = ReturnSuccess();
+    ASSERT_TRUE(result.IsSuccess());
+}
+
+// Check returning an error MaybeError with NXT_RETURN_ERROR
+TEST(ErrorTests, Error_Error) {
+    auto ReturnError = []() -> MaybeError {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    MaybeError result = ReturnError();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+// Check returning a success ResultOrError with an implicit conversion
+TEST(ErrorTests, ResultOrError_Success) {
+    auto ReturnSuccess = []() -> ResultOrError<int*> {
+        return &dummySuccess;
+    };
+
+    ResultOrError<int*> result = ReturnSuccess();
+    ASSERT_TRUE(result.IsSuccess());
+    ASSERT_EQ(result.AcquireSuccess(), &dummySuccess);
+}
+
+// Check returning an error ResultOrError with NXT_RETURN_ERROR
+TEST(ErrorTests, ResultOrError_Error) {
+    auto ReturnError = []() -> ResultOrError<int*> {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    ResultOrError<int*> result = ReturnError();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+// Check NXT_TRY handles successes correctly.
+TEST(ErrorTests, TRY_Success) {
+    auto ReturnSuccess = []() -> MaybeError {
+        return {};
+    };
+
+    // We need to check that NXT_TRY doesn't return on successes
+    bool tryReturned = true;
+
+    auto Try = [ReturnSuccess, &tryReturned]() -> MaybeError {
+        NXT_TRY(ReturnSuccess());
+        tryReturned = false;
+        return {};
+    };
+
+    MaybeError result = Try();
+    ASSERT_TRUE(result.IsSuccess());
+    ASSERT_FALSE(tryReturned);
+}
+
+// Check NXT_TRY handles errors correctly.
+TEST(ErrorTests, TRY_Error) {
+    auto ReturnError = []() -> MaybeError {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto Try = [ReturnError]() -> MaybeError {
+        NXT_TRY(ReturnError());
+        // NXT_TRY should return before this point
+        EXPECT_FALSE(true);
+        return {};
+    };
+
+    MaybeError result = Try();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+// Check NXT_TRY adds to the backtrace.
+TEST(ErrorTests, TRY_AddsToBacktrace) {
+    auto ReturnError = []() -> MaybeError {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto SingleTry = [ReturnError]() -> MaybeError {
+        NXT_TRY(ReturnError());
+        return {};
+    };
+
+    auto DoubleTry = [SingleTry]() -> MaybeError {
+        NXT_TRY(SingleTry());
+        return {};
+    };
+
+    MaybeError singleResult = SingleTry();
+    ASSERT_TRUE(singleResult.IsError());
+
+    MaybeError doubleResult = DoubleTry();
+    ASSERT_TRUE(doubleResult.IsError());
+
+    ErrorData* singleData = singleResult.AcquireError();
+    ErrorData* doubleData = doubleResult.AcquireError();
+
+    ASSERT_EQ(singleData->GetBacktrace().size() + 1, doubleData->GetBacktrace().size());
+
+    delete singleData;
+    delete doubleData;
+}
+
+// Check NXT_TRY_ASSIGN handles successes correctly.
+TEST(ErrorTests, TRY_RESULT_Success) {
+    auto ReturnSuccess = []() -> ResultOrError<int*> {
+        return &dummySuccess;
+    };
+
+    // We need to check that NXT_TRY doesn't return on successes
+    bool tryReturned = true;
+
+    auto Try = [ReturnSuccess, &tryReturned]() -> ResultOrError<int*> {
+        int* result = nullptr;
+        NXT_TRY_ASSIGN(result, ReturnSuccess());
+        tryReturned = false;
+
+        EXPECT_EQ(result, &dummySuccess);
+        return result;
+    };
+
+    ResultOrError<int*> result = Try();
+    ASSERT_TRUE(result.IsSuccess());
+    ASSERT_FALSE(tryReturned);
+    ASSERT_EQ(result.AcquireSuccess(), &dummySuccess);
+}
+
+// Check NXT_TRY_ASSIGN handles errors correctly.
+TEST(ErrorTests, TRY_RESULT_Error) {
+    auto ReturnError = []() -> ResultOrError<int*> {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto Try = [ReturnError]() -> ResultOrError<int*> {
+        int* result = nullptr;
+        NXT_TRY_ASSIGN(result, ReturnError());
+        (void) result;
+
+        // NXT_TRY should return before this point
+        EXPECT_FALSE(true);
+        return &dummySuccess;
+    };
+
+    ResultOrError<int*> result = Try();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+// Check NXT_TRY_ASSIGN adds to the backtrace.
+TEST(ErrorTests, TRY_RESULT_AddsToBacktrace) {
+    auto ReturnError = []() -> ResultOrError<int*> {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto SingleTry = [ReturnError]() -> ResultOrError<int*> {
+        NXT_TRY(ReturnError());
+        return &dummySuccess;
+    };
+
+    auto DoubleTry = [SingleTry]() -> ResultOrError<int*> {
+        NXT_TRY(SingleTry());
+        return &dummySuccess;
+    };
+
+    ResultOrError<int*> singleResult = SingleTry();
+    ASSERT_TRUE(singleResult.IsError());
+
+    ResultOrError<int*> doubleResult = DoubleTry();
+    ASSERT_TRUE(doubleResult.IsError());
+
+    ErrorData* singleData = singleResult.AcquireError();
+    ErrorData* doubleData = doubleResult.AcquireError();
+
+    ASSERT_EQ(singleData->GetBacktrace().size() + 1, doubleData->GetBacktrace().size());
+
+    delete singleData;
+    delete doubleData;
+}
+
+// Check a ResultOrError can be NXT_TRY_ASSIGNED in a function that returns an Error
+TEST(ErrorTests, TRY_RESULT_ConversionToError) {
+    auto ReturnError = []() -> ResultOrError<int*> {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto Try = [ReturnError]() -> MaybeError {
+        int* result = nullptr;
+        NXT_TRY_ASSIGN(result, ReturnError());
+        (void) result;
+
+        return {};
+    };
+
+    MaybeError result = Try();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+// Check a MaybeError can be NXT_TRIED in a function that returns an ResultOrError
+// Check NXT_TRY handles errors correctly.
+TEST(ErrorTests, TRY_ConversionToErrorOrResult) {
+    auto ReturnError = []() -> MaybeError {
+        NXT_RETURN_ERROR(dummyErrorMessage);
+    };
+
+    auto Try = [ReturnError]() -> ResultOrError<int*>{
+        NXT_TRY(ReturnError());
+        return &dummySuccess;
+    };
+
+    ResultOrError<int*> result = Try();
+    ASSERT_TRUE(result.IsError());
+
+    ErrorData* errorData = result.AcquireError();
+    ASSERT_EQ(errorData->GetMessage(), dummyErrorMessage);
+    delete errorData;
+}
+
+}  // anonymous namespace