How does make bootstrap work?

[unfode]

When I run make bootstrap, the first thing that is executed seems to be ocamlc ..., but I don't see it in the Makefile.

[Alizter]

This recently changed. The target you are looking for in the makefile is $(BIN). Which is _boot/dune.exe.

[Alizter]

What you are really doing when you do make bootstrap is recalling the makefile in -B mode (which will always rebuild for reasons I'll explain later). The target _boot/dune.exe is the bootstrapped version of Dune which is put together by running the script boot/bootstrap.ml.

The reason we pass -B is so that you can run make bootstrap anytime you like without make rejecting the request since _boot/dune.exe will be "up-to-date". You don't need to bootstrap manually in many cases since the other targets in the makefile will ask for the bootstrapped version and then proceed to use it to build whatever.

[Alizter]

The @ in front of ocaml in the makefile hides the output. If you remove the @ from the _boot/dune.exe target you will see the order of execution. First the bootstrap.ml script it run, then ocamlc within that script and then finally _boot/dune.exe is built. You can run it from ./dune.exe which points to _boot/dune.exe.

[unfode]

So

bootstrap:
	$(MAKE) -B _boot/dune.exe

is equivalent to

bootstrap:
	$(MAKE) -B $(BIN)

?

Why not use the latter? It's clearer. The former causes a misconception in me that _boot/dune.exe is a file rather than a target.

[Alizter]

Good point, this was changed earlier this week. I simply copied the command I did for manually bootstrapping.

[unfode]

Thank you! I'll create a pull request for this.