I'm now wondering what languages and projects the author has worked on if they expect compilation to take less than 20 seconds. Maybe small-ish golang projects? I don't remember the last time I worked on something interesting where recompilation was always under a minute...
IIRC, C family compilers suffer from some problem with headers that makes compile time much longer than it should.
Edit: oh, and that was rebuilding the whole program from scratch, including all libraries. A little change in the current file was les than one sec. Native code, in case you're wondering.
Thinking about proper modularization, runtime code (hot-re)loading, and eliminating single-point-of-recompilation for header files goes a long way.
The gamedev industry figured this out a long time ago, see Handmade Hero's Hot reloading[0].
Also, an interactive shell (we use IPython) with all of the compiling and debugging utilities you need is easily a 5x efficiency boost, e.g. I can run `./devshell.py <NAME_OF_TARGET>`, then `run('foo', 'bar')` and the script will compile, upload, and re-execute the `foo` and `bar` modules. Makes onboarding much easier too.
At an old job, we had files that were slow enough that we'd have them in a separate compilation unit (automatic derivation of typelcasses with multiple serialization schemes) , so if you didn't change them, you'd just be picking up the binary. And if you were changing them, you weren't changing anything else, so ultimately a very slow compilation step was never a thing.
But yes, it's a matter of investment that few companies are willing to make
So you either worked on the biggest codebases in the world
Or youre doing CPP :)