[llvm-bugs] [Bug 51368] New: false positive with exclusive_locks_required in the presence of templates

[via llvm-bugs]

https://bugs.llvm.org/show_bug.cgi?id=51368

            Bug ID: 51368
           Summary: false positive with exclusive_locks_required in the
                    presence of templates
           Product: clang
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: enhancement
          Priority: P
         Component: Frontend
          Assignee: unassignedclangbugs at nondot.org
          Reporter: tamird at gmail.com
                CC: llvm-bugs at lists.llvm.org, neeilans at live.com,
                    richard-llvm at metafoo.co.uk

Reproduces with all clang versions tested (10, 11, 12, trunk):

```
class Status {
public:
  static Status OK;
};
namespace absl {
inline namespace a {
class __attribute__((lockable)) Mutex {};
class MutexLock {
public:
  MutexLock(Mutex *);
};
} // namespace a
} // namespace absl
class ServerContext;
template <class, class> class ServerReaderWriter;
namespace envoy {
namespace api {
namespace v2 {
class DiscoveryRequest;
class DiscoveryResponse;
} // namespace v2
} // namespace api
namespace service {
namespace discovery {
namespace v2 {
class AggregatedDiscoveryService {
public:
  class Service {
    virtual Status
    StreamAggregatedResources(ServerContext *,
                              ServerReaderWriter<api::v2::DiscoveryResponse,
                                                 api::v2::DiscoveryRequest> *);
  };
};
} // namespace v2
} // namespace discovery
} // namespace service
} // namespace envoy

namespace grpc {
namespace testing {
namespace {

class AdsServiceImpl {
public:
  AdsServiceImpl() : v2_rpc_service_(this) {}

  template <class RpcApi, class DiscoveryRequest, class DiscoveryResponse>
  class RpcService : public RpcApi::Service {
  public:
    using Stream = ServerReaderWriter<DiscoveryResponse, DiscoveryRequest>;

    RpcService(AdsServiceImpl *parent) : parent_(parent) {}

    Status StreamAggregatedResources(ServerContext *context,
                                     Stream *stream) override {
      (void)context;
      (void)stream;
      absl::MutexLock lock(&parent_->ads_mu_);
      ProcessRequest();
      return Status::OK;
    }

  private:
    void ProcessRequest()
        __attribute__((exclusive_locks_required(parent_->ads_mu_))) {
      parent_->ads_done_ = false;
    }

    AdsServiceImpl *parent_;
  };

  RpcService<::envoy::service::discovery::v2::AggregatedDiscoveryService,
             ::envoy::api::v2::DiscoveryRequest,
             ::envoy::api::v2::DiscoveryResponse>
      v2_rpc_service_;

  absl::Mutex ads_mu_;
  bool ads_done_ __attribute__((guarded_by(ads_mu_))) = false;
};
} // namespace
} // namespace testing
} // namespace grpc
```

produces the warning:

```
$ clang -Werror -Wthread-safety -c minimal.cc -o /dev/null
minimal.cc:67:16: error: writing variable 'ads_done_' requires holding mutex
'parent_->ads_mu_' exclusively [-Werror,-Wthread-safety-analysis]
      parent_->ads_done_ = false;
               ^
minimal.cc:60:7: note: in instantiation of member function
'grpc::testing::(anonymous
namespace)::AdsServiceImpl::RpcService<envoy::service::discovery::v2::AggregatedDiscoveryService,
envoy::api::v2::DiscoveryRequest,
envoy::api::v2::DiscoveryResponse>::ProcessRequest' requested here
      ProcessRequest();
      ^
minimal.cc:53:5: note: in instantiation of member function
'grpc::testing::(anonymous
namespace)::AdsServiceImpl::RpcService<envoy::service::discovery::v2::AggregatedDiscoveryService,
envoy::api::v2::DiscoveryRequest,
envoy::api::v2::DiscoveryResponse>::StreamAggregatedResources' requested here
    RpcService(AdsServiceImpl *parent) : parent_(parent) {}
    ^
minimal.cc:46:22: note: in instantiation of member function
'grpc::testing::(anonymous
namespace)::AdsServiceImpl::RpcService<envoy::service::discovery::v2::AggregatedDiscoveryService,
envoy::api::v2::DiscoveryRequest,
envoy::api::v2::DiscoveryResponse>::RpcService' requested here
  AdsServiceImpl() : v2_rpc_service_(this) {}
                     ^
1 error generated.
```

godbolt: https://godbolt.org/z/hG4h4dePG

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