Removing the C_INCLUDE_DIRS feature.
Technically there is some risk but I think the blast radius, if present, is extremely small.
C_INCLUDE_DIRS is not recognized by GCC.
If I use https://sourcegraph.com/search?q=context:global+%5CbC_INCLUDE_DIRS%3D+-f:clang/&patternType=regexp&case=yes&sm=1&groupBy=repo to find the use cases, one project has a use like add_opt C_INCLUDE_DIRS=$C_INCLUDES, but the search patch seems likely redundant.
So far nobody has popped up to say they want it.
@MaskRay I poked around a bit on sourcegraph.com and didn't see any statement about what it actually searches, other than vague "all your repositories" and "all your code." The "your" bit makes me wonder how broad it is really. The website doesn't say.
They index quite a lot: https://about.sourcegraph.com/blog/indexing-the-oss-universe-update-more-code-hosts
I also tried using my company's internal code search and I cannot find environment variables using C_INCLUDE_DIRS.
Yes, that is why I am a bit hesitant; as I know people are not always paying attention to mailing lists and maybe even notice something like this, even if in use. The kinds of changes
that even if they were sitting around for 6 month still come as a surprise.