clang-tidy `detach_promise`: dereference of a null pointer

[Łukasz Kurowski]

Hello,

I am running clang-tidy on smf and I'm encountering this warning from clang-tidy which warns about possible nullptr dereference in future.hh `detach_promise` and I'm not sure if it's a false positive or an issue with my code and it will take me some time to understand.

https://gist.github.com/crackcomm/f8b05ad60b6fffe7f7236a4cc9eb2483

It seems like a super edge case but it might be right, I don't know. Any help would be appreciated.

Thank you.

[Avi Kivity]

The trace shows code that is not part of Seastar. Could it be that the code that calls out.close() does so despite it being already closed?

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[Łukasz Kurowski]

The gist has two separate log files, the first line contains a link to source code.

The trace in log2.log is from https://github.com/smfrpc/smf/blob/master/src/core/rpc_server.cc#L271 (line/position is different only because of clang-format).

It doesn't seem like there is any call to close in this case.

The fist trace - https://github.com/smfrpc/smf/blob/master/src/core/histogram_seastar_utils.cc#L33 - I suspected the issue is likely to be in this code - it uses `with_file_close_on_failure` and `out.close()` but only in `then` case so it shouldn't be called twice. I've rewritten this code using coroutines to make it easier to read. I still have no idea if there really was an issue in this code.

[Łukasz Kurowski]

Here is a result of running clang-tidy on future.cc: https://gist.github.com/crackcomm/9b4bfff59a3c6eecc4390ff1b218ba6c

[Łukasz Kurowski]

I added clang-tidy to seastar_bazel because I'm not sure how easy it is to run from seastar/CMake:

```

wget -O/tmp/bazel https://github.com/bazelbuild/bazelisk/releases/download/v1.25.0/bazelisk-linux-amd64

chmod +x /tmp/bazel

alias bazel=/tmp/bazel

git clone https://github.com/crackcomm/seastar_bazel.git

bazel build --config=clang-tidy --keep_going @seastar//:core

```