错误[E0277]：特征绑定`std::result::Result&lt;_, Box<archivebzip2error> &gt;: std::error::Error` 不满足</archivebzip2error>

Question

When I use this map statement:

                        .map(|mut entry| -> Result<Box<&str>, Box<dyn Error>> {
                            Ok(Box::new(entry.path().or_else(|e| Err(e))?
                                .file_name().ok_or(Err(Box::new(ArchiveBzip2Error::InvalidArchive)))?
                                .to_str()?
                            ))
                        })

I get this error:

error[E0277]: the trait bound `std::result::Result<_, Box<ArchiveBzip2Error>>: std::error::Error` is not satisfied
  --> src/archive/bzip2file.rs:58:101
   |
58 | ...                   .file_name().ok_or(Err(Box::new(ArchiveBzip2Error::InvalidArchive)))?
   |                                                                                           ^ the trait `std::error::Error` is not implemented for `std::result::Result<_, Box<ArchiveBzip2Error>>`
   |
   = note: required because of the requirements on the impl of `From<std::result::Result<_, Box<ArchiveBzip2Error>>>` for `Box<dyn std::error::Error>`
   = note: required by `from`

Why can I not use the ? operator for what appears to be a regular Result instance?

Here is the full code segment:

        match self.archive {
            Some(a) => match a {
                InnerArchive::ThingArchive(mut ta) =>
                    Ok(Box::new(ta.entries()?
                        .filter_map(|e| e.ok())
                        .map(|mut entry| -> Result<Box<&str>, Box<dyn Error>> {
                            Ok(Box::new(entry.path().or_else(|e| Err(e))?
                                .file_name().ok_or(Err(Box::new(ArchiveBzip2Error::InvalidArchive)))?
                                .to_str()?
                            ))
                        })
                    )),
                InnerArchive::ThingGzDecoder(tgd) =>
                    match tgd.header() {
                        Some(h) => match h.filename() {
                            Some(s) => Ok(Box::new(vec![&std::str::from_utf8(s)].iter())),
                            None => Err(Box::new(ArchiveBzip2Error::InvalidArchive)),
                        },
                        None => Err(Box::new(ArchiveBzip2Error::InvalidArchive)),
                    },
            }
            None => Err(Box::new(ArchiveBzip2Error::FailedInstantiationError))
        }

Here is the full context from the IDE, with type hints:

Answer 1

The signature of ok_or is

pub fn ok_or<E>(self, err: E) -> Result<T, E>

So the argument to ok_or is the error itself, not a Result<T, E> value. Rather than

.file_name().ok_or(Err(Box::new(ArchiveBzip2Error::InvalidArchive)))?

Consider

.file_name().ok_or(Box::new(ArchiveBzip2Error::InvalidArchive))?