[LGTM - C++] Compiling with C++20

[php1ic]

My project uses C++20 so requires a newer compiler than is available on the version of ubuntu (Eoan/19.10) used by LGTM. Is it recommended to use the built-in CodeQL with GitHub actions in this scenario?

I tried adding a PPA but they aren't allowed.

The latest logs from my attempts at coverage are here if needed.
https://lgtm.com/logs/fc06a617fed09f06ab0f25c5459b7199ec3dd11a/lang:cpp

[edoardopirovano]

Greetings, thanks for getting in touch with us about this! We're actually in the process of updating the default version of Ubuntu used by LGTM to 20.04 and, unless any unforeseen problems arise in our testing, expect to have that rolled out later this week. It may well be that your project can be successfully built after we've completed that upgrade, so I would recommend trying again next week.

Having said that, I will note that support for C++20 in CodeQL is currently in beta (see https://help.semmle.com/QL/ql-support/language-support/), so while things should more-or-less work you may notice some issues, particularly when using new features of C++20. Do get in touch if you encounter any such issues.

[php1ic]

Thanks @edoardopirovano ! I'll try again next week.

Is there any plans to allow PPAs, or even just enable the ubuntu-toolchain by default to give access to newer versions of gcc?

[edoardopirovano]

There's no plans for that as far as I'm aware, no. We'll certainly take it into consideration for future work, though.

However, we've mostly shifted our focus off LGTM and towards code scanning on GitHub Actions, so it is unlikely we will be making major changes to LGTM at the moment.

[php1ic]

OK, good to know and thanks for the response.

[jbj]

The upgrade of the build environment to Ubuntu 20.04 was deployed on February 9. That upgrade allows you to have GCC 10 since Ubuntu has an official package for that. There is no GCC 11 package, so your use of C++20 on LGTM is limited to what's supported by GCC 10 (and by CodeQL).

I triggered a test run of your project with GCC 10, and the logs show compilation errors related to string_view. I don't know if there's any possible workaround you can apply.

[php1ic]

Thanks @jbj. I make heavy use of std::from_chars so need at least GCC 11. The project does compile with clang 12 on GitHub actions, however, it doesn't compile on the LGTM build environment.

The main difference seems to be the additional PPA which provides GCC 11 and what looks to be the necessary header(s).