where does RollingFileAppender implement MakeWriterExt?

[keepsimple1]

tracing/examples/examples/appender-multifile.rs

Line 17 in 6f23c12

let all_files = debug_file.and(warn_file);

From the above example code, RollingFileAppender implements MakeWriterExt trait and can use and. Does that mean any type that implement std::io::Write also implements MakeWriterExt when using tracing-subscriber?

I tried a different 3rd-party RollingFileAppender that implements std::io::Write but seems not have MakeWriterExt implemented. I'm confused and wondering where tracing_appender::rolling::RollingFileAppender implements MakeWriterExt trait.

[davidbarsky]

From the above example code, RollingFileAppender implements MakeWriterExt trait and can use and. Does that mean any type that implement std::io::Write also implements MakeWriterExt when using tracing-subscriber?

Not quite. MakeWriter is implemented on anything that implements std::io::Write and is wrapped by a std::sync::Arc or std::sync::Mutex. The documentation on MakeWriter notes:

This trait is already implemented for function pointers and immutably-borrowing closures that return an instance of io::Write, such as io::stdout and io::stderr. Additionally, it is implemented for std::sync::Mutex when the type inside the mutex implements io::Write.

Transitively, MakeWriterExt is implemented on types implementing MakeWriter. However, the use .and doesn't come from a blanket implementation; it comes from this MakeWriter implementation.