The change of compiler in 1.7.4 is breaking situations where one of g++/clang++ isn't installed

[mmiller-max]

Hi, in our pipelines we install gcc and use PackageCompiler to build sysimages. This change with 1.7.4 makes it look for g++ rather than gcc which has now broken all of our pipelines.

Should this have been a breaking version change?

[KristofferC]

Well, it is a bugfix since using gcc was a bug and caused linking error in certain cases (https://discourse.julialang.org/t/packagecompiler-create-app-function-failing-on-slurm-cluster-error-undefined-reference-to-ceil/69344). Is it difficult for you to also get g++? You can also set the environment variable JULIA_CC to gcc if you want the old behavior.

Also, for work that is very important to be reproducible, I would check in a Manifest.toml file to lock all the package versions to a known working set and only upgrade after checking that things work ok with the new versions.

[mmiller-max]

Well, it is a bugfix since using gcc was a bug and caused linking error in certain cases

This makes sense, but for it not to be breaking it assumes that the system on which people are compiling packages has g++ installed. E.g. this template which is commonly used for microservices won't work now without changing the compiler being installed in the dockerfile.

Clearly switching to g++ is better as it solves some issues, but perhaps letting it fall back to the old compilers when g++/clang++ are not installed along with a warning could stop it breaking?

Is it difficult for you to also get g++?

No, I just need to update several dockerfiles accordingly

Also, for work that is very important to be reproducible, I would check in a Manifest.toml

We are careful to use compat entries so that (in theory) no breaking changes can be introduced. Yes checking in the Manifest.toml would ensure this completely, but feels like with semantic versioning this is overkill. I guess its a trade-off between stability and maintenance overhead (for example we'd need a manifest for just the application and one for the build pipeline separately)

[KristofferC]

but perhaps letting it fall back to the old compilers when g++/clang++ are not installed along with a warning could stop it breaking?

Yeah, I think that is an ok trade-off. I can make that happen.

[mmiller-max]

That's great, thanks very much for your help and quick response

[KristofferC]

@mmiller-max, can you try out #608?

[mmiller-max]

Yep that works well, thanks. Just one comment on the PR about the error message