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/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