Dune runtime failure Regression building reason master branch.

[jordwalke]

Passes:
#847bc67b2f02ab51c6ea524b34dbbfa8cc221a32
Passes:
#081e1011c5d28b609a0e189c8ea121e6076cd337
Passes:
#0fccd3792294a76ed5c89637d449898a988e2bae
Fails:
#cd213cd4953e66f5927ed0c4838f56700973c15d
Fails:
#528ed3abf592382e294816c1766e189e27a05e0b
Fails:
#cfeb84a08be48e93040d047f90d99fa0be25308a
Fails:
#723e17baf1d74ac7c47a9dbc69a00c1b9d7d2ecb

Reason master branch started failing with the following:

Error: exception Invalid_argument("Option.value_exn")
Backtrace:
Raised at file "src/build_system.ml", line 1361, characters 9-14
Called from file "src/fiber/fiber.ml", line 91, characters 8-15

And then after building it prints a really confusing error message about segfaulting and uncertainty and mindkilling and little-death which I'm not sure is relevant to this observed error.

I'll post more details as I find them but this looks like it's a problem with the Dune implementation so I thought I'd flag it before your next release.

It looks like the commit cd213cd caused the regression:
cc @bobot

[avsm]

minor edit to original report to link the regressing commit id

[rgrinberg]

We should just add a mandatory message:string argument to Option.value_exn. The error messages are not useful at all otherwise.

[rgrinberg]

I can't reproduce this on reason#master btw. @jordwalke any other details that could help reproduce?

[rgrinberg]

@jordwalke Could you try running this again with this patch

[jordwalke]

Sure, I'll try with the patch, but on reason master, you just add:

  "resolutions": {
    "@opam/dune": "ocaml/dune:dune.opam#cd213cd4"
  },

To the esy.json, then run esy from the root directory.

[jordwalke]

Running esy after adding this to esy.json: to test your patch:

"resolutions": { "@opam/dune": "rgrinberg/jbuilder:dune.opam#179dbd78"},

I still get the error:

Error: exception Invalid_argument("Option.value_exn")
Backtrace:
Raised at file "src/build_system.ml", line 1361, characters 9-14
Called from file "src/fiber/fiber.ml", line 91, characters 8-15

[rgrinberg]

I tried doing $ esy with your resolutions and could not reproduce. Perhaps this is a windows issue? I'll try and prepare something that will make this easier to debug.

[jordwalke]

This was not on Windows, it was on Mac.

[andreypopp]

The offending Option.value_exn is at

dune/src/obj_dir.ml

Line 99 in c2c9bf1

|> Option.value_exn

which unwraps result of Path.descendant which doesn't work with non local paths (in case of esy we set DUNE_BUILD_DIR to an absolute path outside of dune workspace).

[ghost]

Hmm, it should still work for path in the build directory, it seems that it is Path.descendant that's wrong. I'm having a look.

[jordwalke]

Thanks for the fix @diml and thanks for debugging @andreypopp .