Modify config merging of non-'clickhouse' rooted configs.

[yakov-olkhovskiy]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

When merging into non-'clickhouse' rooted configuration, configs with different root node name just bypassed without exception.

Closes #50289
Closes #47485

Rationale:
Sometimes we want to assemble configs which have different than 'clickhouse' root node name - for example UDF configuration. According to logic besides immediate config file, we also traverse directories with '<file_name>.d' and 'conf.d' where merging file resides. Also we want to have the same root node name for merging configs. As a result, if we assemble non-'clickhouse' rooted configuration and 'conf.d' in the same directory contains differently rooted config, next exception will be produced:

Processing configuration file 'function.xml'.
Merging configuration file 'conf.d/graphite_rollup.xml'.
2023.07.29 19:25:14.079309 [ 3806116 ] {} <Error> ExternalUserDefinedExecutableFunctionsLoader: Failed to load config file 'function.xml': Poco::Exception. Code: 1000, e.code() = 0, Exception: Failed to merge config with 'conf.d/gr
aphite_rollup.xml': Exception: Root element doesn't have the corresponding root element as the config file. It must be <functions>, Stack trace (when copying this message, always include the lines below):

0. ./build_docker/./src/Common/Config/ConfigProcessor.cpp:0: DB::ConfigProcessor::processConfig(bool*, zkutil::ZooKeeperNodeCache*, std::shared_ptr<Poco::Event> const&) @ 0x00000000157e78d2 in /home/ubuntu/ClickHouse/clickhouse
1. ./build_docker/./contrib/llvm-project/libcxx/include/__memory/shared_ptr.h:701: DB::ConfigProcessor::loadConfig(bool) @ 0x00000000157e7bb4 in /home/ubuntu/ClickHouse/clickhouse
2. ./build_docker/./contrib/llvm-project/libcxx/include/string:1499: DB::ExternalLoaderXMLConfigRepository::load(String const&) @ 0x0000000013be2745 in /home/ubuntu/ClickHouse/clickhouse
3. ./build_docker/./src/Interpreters/ExternalLoader.cpp:284: DB::ExternalLoader::LoadablesConfigReader::readFileInfo(DB::ExternalLoader::LoadablesConfigReader::FileInfo&, DB::IExternalLoaderConfigRepository&, String const&) const @
 0x0000000013bd96b2 in /home/ubuntu/ClickHouse/clickhouse
4. ./build_docker/./src/Interpreters/ExternalLoader.cpp:223: DB::ExternalLoader::LoadablesConfigReader::readRepositories(std::optional<String> const&, std::optional<String> const&) @ 0x0000000013bd58aa in /home/ubuntu/ClickHouse/cl
ickhouse
5. ./build_docker/./contrib/llvm-project/libcxx/include/optional:260: DB::ExternalLoader::LoadablesConfigReader::read(String const&) @ 0x0000000013bcb920 in /home/ubuntu/ClickHouse/clickhouse
6. ./build_docker/./src/Interpreters/ExternalLoader.cpp:1510: DB::ExternalLoader::addConfigRepository(std::unique_ptr<DB::IExternalLoaderConfigRepository, std::default_delete<DB::IExternalLoaderConfigRepository>>) const @ 0x0000000
013bca1a7 in /home/ubuntu/ClickHouse/clickhouse
7. ./build_docker/./src/Interpreters/Context.cpp:2188: DB::Context::loadOrReloadUserDefinedExecutableFunctions(Poco::Util::AbstractConfiguration const&) @ 0x000000001370f353 in /home/ubuntu/ClickHouse/clickhouse
8. ./build_docker/./programs/server/Server.cpp:1812: DB::Server::main(std::vector<String, std::allocator<String>> const&) @ 0x000000000e9487c3 in /home/ubuntu/ClickHouse/clickhouse
9. ./build_docker/./base/poco/Util/src/Application.cpp:0: Poco::Util::Application::run() @ 0x00000000181dea46 in /home/ubuntu/ClickHouse/clickhouse
10. ./build_docker/./programs/server/Server.cpp:396: DB::Server::run() @ 0x000000000e93669e in /home/ubuntu/ClickHouse/clickhouse
11. ./build_docker/./base/poco/Util/src/ServerApplication.cpp:132: Poco::Util::ServerApplication::run(int, char**) @ 0x00000000181f2179 in /home/ubuntu/ClickHouse/clickhouse
12. ./build_docker/./programs/server/Server.cpp:0: mainEntryClickHouseServer(int, char**) @ 0x000000000e93336a in /home/ubuntu/ClickHouse/clickhouse
13. ./build_docker/./programs/main.cpp:0: main @ 0x0000000008f0e50f in /home/ubuntu/ClickHouse/clickhouse
14. ? @ 0x00007f21e4429d90 in ?
15. __libc_start_main @ 0x00007f21e4429e40 in ?
16. _start @ 0x000000000828b3ae in /home/ubuntu/ClickHouse/clickhouse
 (version 23.7.1.2471 (official build))

This PR resolves this problem by bypassing all non-'clickhouse' rooted configs for non-'clickhouse' assemblies.

[robot-ch-test-poll2]

This is an automated comment for commit 63b155a with description of existing statuses. It's updated for the latest CI running
The full report is available here
The overall status of the commit is 🟢 success

Check name	Description	Status
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SQLancer	Fuzzing tests that detect logical bugs with SQLancer tool	🟢 success
Sqllogic	Run clickhouse on the sqllogic test set against sqlite and checks that all statements are passed	🟢 success
Stateful tests	Runs stateful functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	🟢 success
Stateless tests	Runs stateless functional tests for ClickHouse binaries built in various configurations -- release, debug, with sanitizers, etc	🟢 success
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Upgrade check	Runs stress tests on server version from last release and then tries to upgrade it to the version from the PR. It checks if the new server can successfully startup without any errors, crashes or sanitizer asserts	🟢 success

[cangyin]

It seems the PR is just changing an exception into a implicit debug message, this may confuse users if they use same way as #50289, #47485, and may raise another issue like "why my configuration not loaded, even after restarting server"

[yakov-olkhovskiy]

@cangyin unfortunately it's the only option to resolve this issue. This solution is limited for non-'clickhouse' rooted configs - for clickhouse assembly it will still produce a proper exception.