[cpp] Update clangd install snippet to clangd-10 in README.md

[jankeromnes]

Because that's what's in the 'llvm-toolchain-bionic' repository now: https://apt.llvm.org/

Thanks to @sylvestre for catching the outdated snippet!

What it does

Fixes the clangd install snippet in the default C++ extension's README.md.

How to test

Run the snippet in a fresh Ubuntu 18.04 Bionic install (e.g. using the ubuntu:bionic Docker image).

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[simark]

clang 9 has just been released, which means it's the current stable. clang 10 is the new development branch, not the stable one. So I believe we should drive people towards clang 9.

[sylvestre]

If you want to use the 9 branch, the repo should be llvm-toolchain-bionic-9 and not llvm-toolchain-bionic
llvm-toolchain-bionic only gets upstream master, so, 10 currently.

[jankeromnes]

@sylvestre Good point.

@simark According to https://apt.llvm.org/, clangd 8 is actually the "stable" branch, while clangd 9 is the "qualification" branch (and clangd 10 is the "development" branch).

We could install clangd-8 (stable EDIT: old stable) like so:

$ echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-8 main" | sudo tee /etc/apt/sources.list.d/llvm.list
$ sudo apt-get update && sudo apt-get install -y clang-tools-8
$ sudo ln -s /usr/bin/clangd-8 /usr/bin/clangd

Or clangd-9 (qualification EDIT: stable) like so:

$ echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-9 main" | sudo tee /etc/apt/sources.list.d/llvm.list
$ sudo apt-get update && sudo apt-get install -y clang-tools-9
$ sudo ln -s /usr/bin/clangd-9 /usr/bin/clangd

But these require version suffixes that will break after each LLVM release.

Alternatively, we can also install clangd-10 (development) as clangd (without any suffix anywhere), simply like so:

$ echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic main" | sudo tee /etc/apt/sources.list.d/llvm.list
$ sudo apt-get update && sudo apt-get install -y clang-tools

I believe that LLVM's development branch is considered "stable enough" by major actors and projects like Chromium and Firefox, so it's unlikely to break in catastrophic ways (or at least, it wouldn't remain broken for long).

Plus we could avoid having to switch suffixes when they become deprecated every few months. In any case, I'm happy to update this PR according to your preference.

[sylvestre]

@simark According to https://apt.llvm.org/, clangd 8 is actually the "stable" branch, while clangd 9 is
the "qualification" branch (and clangd 10 is the "development" branch).

Actually, 8 is old stable, 9 is stable quand 10 is dev.
I updated the webpage to reflect that.

[marcdumais-work]

@jankeromnes @sylvestre @simark thanks for this PR and thoughtful comments.

I notice that our clangd install instructions are quite fragile, needing update at every "crank of the clangd release wheel".

Maybe a better approach would be to make this section more generic by removing the mention of a specific Ubuntu version and pointing to instructions being updated by the clangd project. This one would be good, covering Windows and Mac too, except it instructs to install the the clangd version available in the Ubuntu 18.04 repo, which is quite old (8.x) and does not have the built-in clang-tidy.

Alternatively or additionally this page, mentioned above, would work, with a mention to add a symlink named clangd pointing to whatever version of the executable is installed.

We can still make a recommendation about which version to use; 9.x is potentially more stable than 10.x and has the built-in clang-tidy that we support, so it looks like a good one, until we find that 10.x or later has specific features we want.

WDYT?

[jankeromnes]

Thanks for your helpful thoughts @marcdumais-work!

I notice that our clangd install instructions are quite fragile, needing update at every "crank of the clangd release wheel".

That's true currently, but it's not the case with the latest suggestion:

$ echo "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic main" | sudo tee /etc/apt/sources.list.d/llvm.list
$ sudo apt-get update && sudo apt-get install -y clangd

This snippet will always pick the latest clangd version. There is no need to change anything when clangd makes a new release, nor to manually maintain a special symlink.

Also, as previously mentioned, using the latest clangd is considered "stable enough" by major projects that compile a lot of C++ code every day, like Chromium and Firefox. So I personally don't think we need to make efforts to recommend older versions of clangd.

Still, if you prefer recommending 9.x for now, we could indeed make the instructions more generic by pointing to https://clang.llvm.org/extra/clangd/Installation.html#installing-clangd and/or to https://apt.llvm.org/, and by explaining how to maintain the special symlink.

[marcdumais-work]

This snippet will always pick the latest clangd version. There is no need to change anything when clangd makes a new release, nor to manually maintain a special symlink.

👍 Perfect then, thanks for the clarification

So I personally don't think we need to make efforts to recommend older versions of clangd.

👍

Still, if you prefer recommending 9.x for now,

No, I think it's ok, as long as this documentation is "low maintenance" and we pick-up a version that has support for our integrations, which latest does.

[marcdumais-work]

I have tested by switching to the clangd package on my Ubuntu 18.04 machine (I had clangd-9 from same PPA before)

[akosyakov]

@marcdumais-work please merge @jankeromnes is not a committer