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_