Fix compilation in --dev mode with 4.08

[ghost]

A few things that we use are deprecated in 4.08:

• Pervasives
• the tag functions of the Format module

Since we are currently keeping compatibility with OCaml >= 4.02, i simply disabled warning 3 for these. I also disabled the new warning 66 in dev mode, since it is causing a lot of code in Dune, and I expect in many projects to break. This warning is for unused open!, which we often use to keep open Stdune or similar even when they are not used.

BTW, testing 4.08 in the CI is going to be annoying as a lot of compiler messages changed in 4.08. I.e. the captured output will be different between < 4.08 and >= 4.08 :(

[ghost]

The compiler now complains if the comment is before the constructor, so I moved them all after

[ejgallego]

Sorry folks I hickjack this to mention that for a while dune has also been broken in OCaml master [we witness in Coq's CI]

Do you see value in adding a trunk job to Dune's CI? We could mark it allow_failure, so the biggest downside would be an increase on CI time.

I am almost done with other stuff so I shall shortly have time to see / debug the trunk problem more in-depth.

[rgrinberg]

Yeah, it's fine to have it I think. It would be useful to know when dune starts failing on trunk as soon as possible.

[ejgallego]

Ok I will take care of #2298 next week if still open.

[bobot]

BTW, testing 4.08 in the CI is going to be annoying as a lot of compiler messages changed in 4.08. I.e. the captured output will be different between < 4.08 and >= 4.08 :(

We should deactivate output of ocaml command printing for our tests. The message of error is never, I believe, useful.

[ghost]

Makes sense. I didn't know it was possible at the time.

[bobot]

I was thinking something directly inside dune, to always hide the output of ocaml commands in our test. I don't know if ocaml has a toggle for the printing of the source.

[bobot]

But, you are right, -error-style short exists. However I believe that the message could also change, so we should remove all the output.