3.9.0~alpha1

CHANGES:

• Validate file extension for $ dune ocaml top-module. (#8005, fixes #8004, @3Rafal)

• Include the time it takes to read/write state files when --trace-file is
  enabled (#7960, @rgrinberg)

• Add dune show command group which is an alias of dune describe. (#7946,
  @Alizter)

• Include source tree scans in the traces produced by --trace-file (#7937,
  @rgrinberg)

• Cinaps: The promotion rules for cinaps would only offer one file at a time no
  matter how many promotions were available. Now we offer all the promotions at
  once (#7901, @rgrinberg)

• Do not re-run OCaml syntax files on every iteration of the watch mode. This
  is too memory consuming. (#7894, fix #6900, @rgrinberg)

• Remove some compatibility code for old version of dune that generated
  .merlin files. Now dune will never remove .merlin files automatically
  (#7562)

• Add dune show env command and make dune printenv an alias of it. (#7985,
  @Alizter)

• Add additional metadata to the traces provided by --trace-file whenever
  --trace-extended is passed (#7778, @rleshchinskiy)

• Extensions used in (dialect) can contain periods (e.g., cppo.ml). (#7782,
  fixes #7777, @nojb)

• Allow (include_subdirs qualified) to be used when libraries define a
  (modules ...) field (#7797, fixes #7597, @anmonteiro)

• $ dune describe is now a command group, so arguments to subcommands must be
  passed after subcommand itself. (#7919, @Alizter)

• The interface and implementation fields of a (dialect) are now optional
  (#7757, @gpetiot)

• Add commands dune show targets and dune show aliases that display all the
  available targets and aliases in a given directory respectively. (#7770,
  grants #265, @Alizter)

• Allow multiple globs in library's (stdlib (internal_modules ..))
  (@anmonteiro, #7878)

• Attach melange rules to the default alias (#7926, @haochenx)

• In opam constraints, reject (and) and (or) with no arguments at parse
  time (#7730, @emillon)

• Compute digests and manage sandboxes in background threads (#7947,
  @rgrinberg)

• Add (build_if) to the (test) stanza. When it evaluates to false, the
  executable is not built. (#7899, fixes #6938, @emillon)

• Add necessary parentheses in generated opam constraints (#7682, fixes #3431,
  @Lucccyo)