We leverage many third party C++ libraries with complex templates, concepts, and constexpr expressions that seem to require lots of CPU to compile. We've found unity builds to be almost 3X faster, so we make it the default for both developer and CI jobs.
But we keep a separate CI job that checks the non-unity build, so developers have to add the right #include statements and can't accidentally reference file-scoped functions from other files. While working on a given library or project, developers often disable the unity build for just that project to reduce incremental build times. It seems to offer the benefits of both approaches.
Precompiled headers don't give nearly the same speedup. We're excited for C++ modules of course, but we're trying to temper any expectations that modules will improve build speed.
But we keep a separate CI job that checks the non-unity build, so developers have to add the right #include statements and can't accidentally reference file-scoped functions from other files. While working on a given library or project, developers often disable the unity build for just that project to reduce incremental build times. It seems to offer the benefits of both approaches.
Precompiled headers don't give nearly the same speedup. We're excited for C++ modules of course, but we're trying to temper any expectations that modules will improve build speed.