[achatham]

At Waymo we use c++ modules via clang and got the demanded 5x speedup.

As the article mentions, you need a close relationship between the compiler and build system, which Google already has. The google build tooling team got modules to mostly work but only turned them on in limited situations. But we but the bullet and turned them on everywhere, which has sped up compilation of individual files by more than 5x (I forget the exact number).

The remaining problem is that sometimes we get weird compilation errors and have to disable modules for that compilation unit. It's always around templates, and Eigen has been gnarly to get working.