Check whether ROOTSYS is defined in rootcling_stage1.

[chilikink]

This Pull request:

Changes or fixes:

It is not checked in the existing code whether getenv("ROOTSYS") returns NULL. It does so if the environment variable is not defined; it is exactly what happens during building here. Then std::string gets initialized from the C string from address 0, which may result in a segmentation fault.

Checklist:

• [ x ] tested changes locally
• updated the docs (if necessary)

This PR fixes #

[phsft-bot]

Can one of the admins verify this patch?

[Axel-Naumann]

That's a symptom of another issue that we also need to understand. rootcling_stage1 is supposed to putenv ROOTSYS itself (in SetRootSys() in core/dictgen/src/rootcling_impl.cxx); it should not need to be set from the "outside". Do you know why SetRootSys() fails to do what it's supposed to?

[chilikink]

Yes, this happened because I was trying to compile on an officially unsupported system. The function GetExePath() is not implemented and returns an empty string. It the new commit, an error message is printed in SetRootSys() in case of unknown executable path, and the missing implementation of GetExePath() is added. The program rootcling_stage1 now determines its ROOTSYS (build directory) successfully as confirmed by printing rootsys in GetIncludeDir(), although it then still fails reporting circular dependencies in the headers, but it is a separate issue.

[Axel-Naumann]

Should we instead assert that ROOTSYS is set at this point? This is rootcling_stage1.cxx - ROOTSYS must have been set by rootcling itself.

[chilikink]

Yes, I agree that it is a better idea since the variable should always be defined. As requested, the assertion is added together with a comment pointing to the place of definition.

[guitargeek]

Hi @chilikink, what's the status of this PR? Is this tweak still needed, and so you still want to get it merged? If yes, please let us know and resolve the conflicts by re-basing the commits on master.

[guitargeek]

Superseded by #12996. Thanks for the initial effort, I'm sure it was helpful for the authors of the linked PR!