> maintaining a complicated build process in-tree

For what it's worth, if you have any sort of "in a perfect world" vision for what the upstream BLAKE3 project could do to make it trivially easy for you to integrate, I'd be very interested in getting that done. Making integration easy would benefit all callers. We have some issues on the backburner about committing CMake build files, but I assume those would be useless for us here. Is there anything that would be more useful? If we provided autotools build files, could you call into them?

Fundamentally, BLAKE3 wants to build some code on x86 and some other code on ARM, and also some code on Unix and some other code on Windows. Currently we just ask the caller to do that for us, for lack of a common standard. (And if we're building intrinsics rather than assembly, we also need the compiler flags that enable our intrinsics.) But maybe we could handle more of that upstream, using the preprocessor? If the build instructions said "compile this one giant file on all platforms and don't worry about what it does", would that be better? Or would that be gross? Is a header-only library the gold standard? Or too C++-ish? Has anyone ever done a really good job of this?