Share the compilation/installation of ocaml compilers between aliases

[samoht]

Currently, we download/compile/install a fresh OCaml compiler for each alias (when the compiler is different of system).

A very good optimization would be to do that once for compiler, and add the right path in $PATH for each alias.

[avsm]

would be good if the compiler files could be cached too. right now a fresh switch requires a net connection.

[avsm]

(can you tell I'm working on trains quite a lot :-)

[samoht]

wrong issue number in the commit previous commit ...

[rgrinberg]

Is this issue on the cards for 2.0? This recompilation thing is very annoying.

Is there anything particularly hard about this or it's just low priority? I would very much like to have this so I wouldn't putting in some elbow grease if this feature is feasible.

[yomimono]

I'd also really like this, although I can't commit to putting in any time on it.

[AltGr]

This not getting updates is mostly because of issues with relocating the ocaml compiler itself.

Otherwise, with the 2.0 layout of compilers as packages, we could imagine having opam switch install <new-switch> --copy-from <existing-switch> that would create a new switch, and copy the compiler packages and their files from an existing switch to it. It would be possible (assuming that files installed by the compiler haven't changed in the origin switch) now that opam registers owning packages of each installed files.

If this works, we could even detect on opam switch install foo --alias-of bar that a switch based on bar already exists and propose to copy from it instead of recompile.

I don't know where exactly we stand on OCaml relocation. Setting always the proper environment variables in the ocaml packages, to make sure the right paths are used, may help, but note that on unix, the bytecode compilers, e.g. ocamlc, will still start with #!/absolute_path/to/original/ocamlrun. This can be patched with ocp-reloc, but I don't see a clean and generic way of doing this.

Another option could be to compile different versions of OCaml in separate directories and keep them isolated from the actual switches, that would use them like is done for "system" compilers. This sounds a bit tedious to maintain though.

[hcarty]

Would it be possible to treat an opam installed switch as a system switch? This could at least allow sharing the compiler itself across switches without requiring an external-to-opam compiler installation.

[AltGr]

Superseded by #629