[PATCH] D79400: [CMAKE] Fix build failure when source directory is read only

Tue May 26 03:12:19 PDT 2020

pdhaliwal added a comment.

Hi,

Sorry for late reply.

> If that is not feasible for some reason, I would lean towards your option (2), but I think more is needed in this patch to ensure the generation script is always run, right?

I think you are right. As of now, just removing the dependency on `.git/logs/HEAD` is not triggering the cmake script for even when branch is changed. One way I tried to solve this was to retain the dependency on `.git/logs/HEAD` if it is present and fallback to `.git/HEAD` if it is missing. Basically, `.git/HEAD` will ensure the retrigger on every branch-to-branch change or headless checkouts but will not retrigger in case of changes on same branch. Not sure if it is a good idea.

Another solution that I found was to use the logic mentioned here: https://stackoverflow.com/questions/13920072/how-to-always-run-command-when-building-regardless-of-any-dependency. This requires a bit more code, but ensures all the required cases are handled. I think this should be used only in case of branchless checkouts and keep the old behaviour if `.git/logs/HEAD` is present. I will test this and update here if it is able to solve the problem.

> We also don't need to check Clang or LLD source tree separately from LLVM now that everything is in one repo, but the logic for determining Git revision should be still correct.

I will submit this as a separate patch once this gets resolved.

Let me know if your thoughts.

Thanks,
Dhaliwal

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D79400/new/

https://reviews.llvm.org/D79400