Update TRPL to add new Chapter 17: Async and Await

[chriskrycho]

• Add support to rustbook to pass through the -L/--library-path flag to mdbook so that references to the trpl crate
• Build the trpl crate as part of the book tests. Make it straightforward to add other such book dependencies in the future if needed by implementing that in a fairly general way.
• Update the submodule for the book to pull in the new chapter on async and await, as well as a number of other fixes. This will happen organically/automatically in a week, too, but this lets me group this change with the next one:
• Update the compiler messages which reference the existing chapters 17–20, which are now chapters 18-21. There are only two, both previously referencing chapter 18.
• Update the UI tests which reference the compiler message outputs.

[rustbot]

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[rustbot]

⚠️ Warning ⚠️

• These commits modify submodules.

[chriskrycho]

All right, this is going to be fun to sort out. 😂 In the book crate, the CI run explicitly handles making sure trpl is built and available; it looks like I’ll have to do the same here. However, trpl pulls in tokio (!) and I’m extremely confident (I was wrong! See below) we don’t want rust to depend on tokio. 😬 Much to sort out.

[Noratrieb]

However, trpl pulls in tokio (!) and I’m extremely confident we don’t want rust to depend on tokio

I'm not quite sure I understand, but I don't see a problem depending on tokio in this repo. It's in the lock file already:

rust/Cargo.lock

Line 5332 in d9c4b8d

[[package]]

[chriskrycho]

@Noratrieb Oh, well, that definitely simplifies things a bit then! I had missed that it was there. I just didn’t want to go adding it needlessly, given it is large! We do depend on a specific version in the book repo, but I think that will probably be Fine™ once I get the other bits around the build pipeline sorted out.

Long story short: For the new chapter on async, we built a small crate, trpl, which re-exports items from futures, tokio, and tokio-stream. Many of the examples in the book use those exports. So the rust build and tests need to support that!

I am currently digging into the spot we invoke rustbook to build the crate to figure out what I need to do to make this dance work. Unfortunately, mdbook does not really support external crates in a first-class way, but I think I’ll be able to get it working even so, along similar lines as what I did in the book repo.

(That said, if people have better suggestions on how to do this here, I am all ears!)

[ehuss]

Another thing we should probably include here is to add trpl as an unused dependency in rustbook/Cargo.toml. This will help ensure that the trpl dependencies are vendored.

Let me know if you run into any major roadblocks. I dropped the book update from #132007.

[rustbot]

The list of allowed third-party dependencies may have been modified! You must ensure that any new dependencies have compatible licenses before merging.

cc @davidtwco, @wesleywiser

[onur-ozkan]

Bootstrap side looks good to me, thanks!

[chriskrycho]

Thanks, @onur-ozkan! @cjgillot, I think this is ready for your eyes when you get a bit!