Summary:
With profiles and `(env ...)` stanza it's possible to consolidate
various ocamlc/ocamlopt/etc setups in a single place.
Where previously we needed to append `dune.common` to every dune file
and specify `flags` and `ocamlopt_flags` now the flags are specified
in `env` and applied accross the board.
This allows to
1. simplify build definitions,
2. avoid the need to generate dune files,
3. use plain sexps instead of OCaml and JBuilder plugin in build
files.
(I'll try to address 2 and 3 in the followup patches).
Existing `make` targets should continue working as before. Also, we
can use dune CLI like so:
```
infer/src$ dune printenv --profile opt # <- very useful for introspection
infer/src$ dune build check
infer/src$ dune build check --profile test
infer/src$ dune build infer.exe --profile dev
infer/src$ dune build infer.exe --profile opt
```
Also, with just 1 context something like `dune runtest` will run unit
tests only once instead of N times, where N is the number of contexts.
Now, there's one difference compared to the previous setup with
contexts:
- Previously, each context had its own build folder, and building infer
in opt context didn't invalidate any of the build artifacts in default
context. Therefore, alternating between `make` and `make opt` had low
overhead at the expense of having N copies of all build artifacts (1
for every context).
- Now, there's just 1 build folder and switching between profiles does
invalidate some artifacts (but not all) and rebuild takes a bit more
time.
So, if you're alternating like crazy between profiles your experience
may get worse (but not necessarily, more on that below). If you want
to trigger an opt build occasionally, you shouldn't notice much
difference.
For those who are concerned about slower build times when alternating
between different build profiles, there's a solution: [dune
cache](https://dune.readthedocs.io/en/stable/caching.html).
You can enable it by creating a file `~/.config/dune/config` with the
following contents:
```
(lang dune 2.0)
(cache enabled)
```
With cache enabled switching between different build profiles (but
also branches and commits) has ~0 overhead.
Dune cache works fine on Linux, but unfortunately there are [certain
problems with
MacOS](https://github.com/ocaml/dune/issues/3233) (hopefully, those
will be fixed soon and then there will be no downsides to using
profiles compared to contexts for our case).
Reviewed By: jvillard
Differential Revision: D20247864
fbshipit-source-id: 5f8afa0db
Artem Pianykh
fcce3c0659