rumqttd doesn't build

[qwandor]

A clean checkout of rumqttd fails to build:

$ cargo build
    Updating crates.io index
   Compiling prost-derive v0.7.0
   Compiling which v4.0.2
   Compiling prost-build v0.7.0
   Compiling prost v0.7.0
   Compiling prost-types v0.7.0
   Compiling pprof v0.3.21
   Compiling rumqttd v0.2.0 (/home/andrew/src/rumqtt/rumqttd)
error[E0599]: no method named `encode` found for struct `Profile` in the current scope
  --> rumqttd/src/bin.rs:52:17
   |
52 |         profile.encode(&mut content).unwrap();
   |                 ^^^^^^ method not found in `Profile`
   | 
  ::: /home/andrew/.cargo/registry/src/github.com-1ecc6299db9ec823/prost-0.7.0/src/message.rs:47:8
   |
47 |     fn encode<B>(&self, buf: &mut B) -> Result<(), EncodeError>
   |        ------ the method is available for `Box<Profile>` here
   |
   = help: items from traits can only be used if the trait is in scope
help: the following trait is implemented but not in scope; perhaps add a `use` for it:
   |
1  | use pprof::protos::Message;
   |

warning: unused import: `prost::Message`
 --> rumqttd/src/bin.rs:7:5
  |
7 | use prost::Message;
  |     ^^^^^^^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` on by default

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0599`.
error: could not compile `rumqttd`

To learn more, run the command again with --verbose.

This appears to be due to a non-backwards-compatible change in pprof 0.3.21. Pinning pprof to 0.3.20 works around the issue. Probably this version of pprof should be yanked and re-released as 0.4.

[jplatte]

Why is this an issue here rather than on the pprof repo? I don't see an issue about this there (https://github.com/tikv/pprof-rs/issues).

[tekjar]

@qwandor Thanks for the follow up with pprof. I'll trigger CI again