Crash with (bisect_ppx) and (lang dune 2.5)

[aantron]

Expected Behavior

If one accidentally does not use (lang dune 2.6), Dune should print a neat error message that (bisect_ppx) requires 2.6.

Actual Behavior

Internal error, please report upstream including the contents of _build/log.

Reproduction

1. git clone https://github.com/aantron/lambdasoup.git
2. cd lambdasoup
3. git checkout dune+bisect
4. Edit dune-project to have (lang dune 2.5)
5. dune runtest

Specifications

• Version of dune (output of dune --version): 2.5.1-99-gf6ef0be5
• Version of ocaml (output of ocamlc --version): 4.08.0
• Operating system (distribution and version): WSL

Additional information

• Link to gist with verbose output (run dune with the --verbose flag): https://gist.github.com/aantron/8d8c13ddde1e6b7f70f33d3d7536c14a

[ghost]

Agreed

[ghost]

Adding to the 2.6 milestone because that should be easy to fix and it seems like something we should fix before releasing support for bisect_ppx.