fix(examples): enable mplex feature for libp2p dep

[youngjoon-lee]

Description

Some rust-libp2p examples uses development_transport(...) that requires the mplex feature enabled. But, the Cargo.tomls of those examples don't enable the mplex.
This isn't an issue in this repo because those examples refer to the libp2p using path = "../../libp2p", but if you try to rewrite those examples from scratch by referring to libp2p = { version = "...", ...}, the following error will occur:

error[E0432]: unresolved import `libp2p::development_transport`

Notes & open questions

I just enable the mplex feature for those examples.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

[thomaseizinger]

mplex is deprecated and thus not active purposely.

If you are following examples, make sure you are looking at the correct source code, i.e. if you depend on 0.51.3, checkout that tag. The examples will work for that version.

[youngjoon-lee]

mplex is deprecated and thus not active purposely.

If you are following examples, make sure you are looking at the correct source code, i.e. if you depend on 0.51.3, checkout that tag. The examples will work for that version.

Thanks @thomaseizinger . I checked-out the tag libp2p-v0.51.3, but that is still not compiled because of the development_transport (which seems to require mplex).

git checkout libp2p-v0.51.3
cd examples/distributed-key-value-store
cargo build

error[E0432]: unresolved import `libp2p::development_transport`
  --> examples/distributed-key-value-store/src/main.rs:51:5
   |
51 |     development_transport, identity, mdns,
   |     ^^^^^^^^^^^^^^^^^^^^^ no `development_transport` in the root

For more information about this error, try `rustc --explain E0432`.
error: could not compile `distributed-key-value-store` due to previous error

[thomaseizinger]

Thanks for the report! That is strange. Let me investigate.

[thomaseizinger]

It seems that by running a full build on the workspace with --all-features, we mitigate the fact that we have to specify features for our examples. Dang.

Let me see if I can fix this with a new CI job.

[thomaseizinger]

It seems that by running a full build on the workspace with --all-features, we mitigate the fact that we have to specify features for our examples. Dang.

Let me see if I can fix this with a new CI job.

Submitted a PR here: #3811

[youngjoon-lee]

Submitted a PR here: #3811

Thank you!