Inconsistent ppx reporting in `dune describe workspace`

[sim642]

Expected Behavior

dune describe workspace includes ppx-s, both the compile time and runtime libraries.

Actual Behavior

In some cases dune describe workspace output only includes runtime libraries, but not the compile time ones.

Reproduction

1. Checkout https://github.com/sim642/ocaml-depgraph/tree/f12c7fbe48c819334fa6b1b4500cc733b09da61a.
2. dune describe workspace --with-deps > old.txt
3. Checkout an immediately following commit sim642/odep@310ecab.
4. dune describe workspace --with-deps > new.txt
5. diff old.txt new.txt shows a large amount of libraries related to compile time components of ppx-s now present that weren't for some reason before, even though the same ppx-s were used before and after that commit (only slightly modifying dune project structure). For example ppx_deriving.std, ppx_sexp_conv, ppxlib, etc.

I haven't yet tried to minimize the reproduction, but can try if necessary.

Specifications

• Version of dune (output of dune --version): 3.5.0
• Version of ocaml (output of ocamlc --version): 4.14.0
• Operating system (distribution and version): Ubuntu 22.04.1

[esope]

I can reproduce the bug. This is surprising. I will take a look. Thanks for reporting.

[esope]

Note for myself: ppx_deriving.std is added to the list of libraries, although no library or executable requires it.

[esope]

Fixed by #6727