dev meeting 2024 08 07

Present: @Leonidas-from-XIV @leostera @nojb @maxRN Lucas M.

Flags for non-standard behavior @Leonidas-from-XIV

• We plan to introduce some mechanisms that are opt-in because they're not compatible with opam workflows
• For this we want to have extra configuration flags
• The idea is that they use the existing Dune Config mechanism but the defaults would be changed at build-time
• Draft PR: #10724
• @nojb: Can't this be configured by Dune Workspace?
• @leostera: The idea is that this would prepare for an opam-less workflow where users download a Dune binary and that will have all the configuration out of the box.

Package Coverage @Leonidas-from-XIV

• We are running a tool that checks how many projects we can currently build out of the box without OPAM
• Initial run was 19% though by fixing the two most common failure reasons (seq and either) we are at about 53% at time of writing
• Lucas M: Will Dune support building projects not using Dune?
• @Leonidas-from-XIV: Not directly, but other projects that don't use Dune are supposed to be usable. Checking that we can depend on every OPAM package is a slightly different question but the idea is that users should be able to depend on any opam package.

dune-project formatting @maxRN

• @maxRN started working on this, the dune formatter currently only autoformats dune files not dune-project files. Formatting the latter is a bit trickier since long strings (description, synopsis) get messed up
• @maxRN is currently adding support for the parser to know whether the input was a long-string or not
• @Leonidas-from-XIV: Another option would be to have the pretty-printer decide how to format a string on some rules (length, newlines etc)
• @Leonidas-from-XIV: This will come in very handy if we want to programmatically write to dune-project as then it can get reformatted nicely!

Q&A

• Lucas M: Will we deprecate opam file generation, now that Dune is not depending on OPAM much?
  • @Leonidas-from-XIV: We currently can read dependencies from dune-project and opam files so that will not go away any time soon, removing it would be a major release bump
  • @leostera: OPAM files and the opam-repository are still underpinning everything, we are mostly just making an alternative to opam the binary
• Lucas M: Is there a way to have build --watch and exec work?
  • @Leonidas-from-XIV: Not at the moment, its not quite trivial to have two dune processes run at the same time. In theory they could communicate through RPC but its not quite simple
  • @maxRN: There is #9290 for tracking this
  • @Leonidas-from-XIV (somewhat later): It is possible to run exec in watch mode however, as a workaround
• @nojb: Will Dune Pkg Mgmt support injecting external libraries into the dependencies via OCAMLPATH
  • @Leonidas-from-XIV: Technically it should be doable, we just haven't tested it
  • @leostera: This is not something we focus on at the moment, to prioritize doing everything though Dune
  • @Leonidas-from-XIV: In any case I believe you can write an opam file and .install script to let Dune Pkg Mgmt know about the files, then these would work as any other opam package and should be supported
• @nojb: Is supporting environment supplied compilers possible in Dune Pkg Mgmt? Or how do compilers work?
  • @Leonidas-from-XIV: Dune Pkg Mgmt selects a fitting compiler and builds it as any other opam dependency, but external compilers work if using the ocaml-system package