Problem

It's tough to understand where a dune build spends most of its time. In particular, it's not clear which external commands are the most time consuming.

Solution

Dune could have a profiling mode where it would emit events for the start and termination of external commands. Eventually, dune could even emit events for other actions/events, but I think starting with external commands is fine.

Dune should emit these events according to chrome's tracing view [1]. If we do that, then we'll be able to explore this information using chrome's neat visualizations [2]. This practice is quite common and is available in build systems such as buck and shake

[1] https://docs.google.com/document/d/1CvAClvFfyA5R-PhYUmn5OOQtYMH4h6I0nSsKchNAySU/edit

[2] https://www.gamasutra.com/view/news/176420/Indepth_Using_Chrometracing_to_view_your_inline_profiling_data.php