Add basic translation of NSExceptions to Status (#8010)

When the Swift API is misused from within a callback from core a NSException
may escape, which we want to propagate. Since this is always a fatal error that
cannot be programmatically handled by the user, we can always translate this to
UnknownError rather than trying to preserve the original error code.

CHANGELOG.md

@@ -11,6 +11,7 @@
 * Fix crash during client app shutdown when Logger log level is set higher than Info. ([#7969](https://github.com/realm/realm-core/issues/7969), since v13.23.3)
 * If File::rw_lock() fails to open a file the exception message does not contain the filename ([#7999](https://github.com/realm/realm-core/issues/7999), since v6.0.21)
 * Fallback to hashed filename will fail if length of basename is between 240 and 250 ([#8007](https://github.com/realm/realm-core/issues/8007), since v10.0.0)
+* Swift API misuse within a callback from core would result in an internal unreachable error rather than the exception being propagated properly ([#7836](https://github.com/realm/realm-core/issues/7836)).
 
 ### Breaking changes
 * None.

Package.swift

@@ -73,6 +73,7 @@ let notSyncServerSources: [String] = [
     "realm/disable_sync_to_disk.cpp",
     "realm/error_codes.cpp",
     "realm/exceptions.cpp",
+    "realm/exceptions.mm",
     "realm/geospatial.cpp",
     "realm/global_key.cpp",
     "realm/group.cpp",

src/realm/CMakeLists.txt

@@ -291,6 +291,10 @@ if(NOT MSVC)
     list(APPEND REALM_SOURCES util/interprocess_mutex.cpp)
 endif()
 
+if(APPLE)
+    list(APPEND REALM_SOURCES exceptions.mm)
+endif()
+
 if (REALM_ENABLE_GEOSPATIAL)
     list(APPEND REALM_SOURCES geospatial.cpp)
     list(APPEND REALM_INSTALL_HEADERS geospatial.hpp)

src/realm/exceptions.cpp

@@ -64,6 +64,8 @@ Exception::Exception(Status status)
 {
 }
 
+// Apple implementation in exceptions.mm
+#if !REALM_PLATFORM_APPLE
 Status exception_to_status() noexcept
 {
     try {
@@ -80,6 +82,7 @@ Status exception_to_status() noexcept
         REALM_UNREACHABLE();
     }
 }
+#endif // !REALM_PLATFORM_APPLE
 
 UnsupportedFileFormatVersion::UnsupportedFileFormatVersion(int version)
     : Exception(ErrorCodes::UnsupportedFileFormatVersion,

src/realm/exceptions.mm

@@ -0,0 +1,45 @@
+/*************************************************************************
+ *
+ * Copyright 2024 Realm Inc.
+ *
+ * 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 <realm/exceptions.hpp>
+
+#include <realm/util/demangle.hpp>
+
+#include <Foundation/Foundation.h>
+
+namespace realm {
+Status exception_to_status() noexcept
+{
+    try {
+        throw;
+    }
+    catch (NSException* e) {
+        return Status(ErrorCodes::UnknownError, e.reason.UTF8String);
+    }
+    catch (const Exception& e) {
+        return e.to_status();
+    }
+    catch (const std::exception& e) {
+        return Status(ErrorCodes::UnknownError,
+                      util::format("Caught std::exception of type %1: %2", util::get_type_name(e), e.what()));
+    }
+    catch (...) {
+        REALM_UNREACHABLE();
+    }
+}
+} // namespace realm

test/CMakeLists.txt

@@ -113,6 +113,10 @@ if (REALM_ENABLE_GEOSPATIAL)
     list(APPEND CORE_TEST_SOURCES test_query_geo.cpp)
 endif()
 
+if (APPLE)
+    list(APPEND CORE_TEST_SOURCES test_nsexception.mm)
+endif()
+
 set(LARGE_TEST_SOURCES
     large_tests/test_column_large.cpp
     large_tests/test_strings.cpp)

test/test_nsexception.mm

@@ -0,0 +1,39 @@
+/*************************************************************************
+ *
+ * Copyright 2024 Realm Inc.
+ *
+ * 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 "test.hpp"
+
+#include "realm/status.hpp"
+
+#include <Foundation/Foundation.h>
+
+namespace realm {
+namespace {
+TEST(Status_NSException)
+{
+    try {
+        @throw [NSException exceptionWithName:@"Exception Name" reason:@"Expected reason" userInfo:nil];
+    }
+    catch (...) {
+        auto status = exception_to_status();
+        CHECK_EQUAL(status.code(), ErrorCodes::UnknownError);
+        CHECK_EQUAL(status.reason(), "Expected reason");
+    }
+}
+} // namespace
+} // namespace realm