Is cached_digest doing extra work on cmt files? #4273
Description
Dear dune devs,
I have been observing some re-hashing of files on what should be a no-op rebuild, example from the Coq sources after doing dune build coq.install after a previous full build:
[dirty / mtime] _build/install/default/lib/coq/vernac/vernacextend.cmt {old: 1613989865.805196/ new: 1613990621.966763}
[dirty / perm ] _build/install/default/lib/coq/vernac/vernacextend.cmt {old: 292/ new: 511}
[dirty / size ] _build/install/default/lib/coq/vernac/vernacextend.cmt {old: 112027/ new: 64}
[dirty / mtime] _build/install/default/lib/coq/vernac/vernacextend.cmti {old: 1613989865.479193/ new: 1613990621.967763}
[dirty / perm ] _build/install/default/lib/coq/vernac/vernacextend.cmti {old: 292/ new: 511}
[dirty / size ] _build/install/default/lib/coq/vernac/vernacextend.cmti {old: 40355/ new: 65}
so indeed, all .cmt{,i} files in the source tree seem to be re-digested, however it seems to me they should not. After the digest, nothing is rebuilt, I guess the digest matches the stored one, tho cmt tend to be leaves themselves.
- dune version: master
- OCaml version: 4.12.0-rc1