requirements: no longer drop `generaldelta` requirement with revlogv2

A repository could use a mix of revlogv1 and revlogv2, making the requirements
still necessary. Overall we should move away from the "requirements" file being
used a way to configure the repository and stick to it "what do you need to
access this repository". However this is a wider work for another time.

In addition the logic we just dropped was confusing the `hg debugformat`
command, breaking the upgrade code and inconsistent (eg: `sparse-revlog` is also
implied by `revlogv2`).

Finally, multiple other config option would imply the use of the `revlogv2`
requirements, without drop the `generaldelta` one, leading to more
inconsistency.

Differential Revision: https://phab.mercurial-scm.org/D10612

mercurial/localrepo.py

@@ -3531,8 +3531,6 b' def newreporequirements(ui, createopts):'
     revlogv2 = ui.config(b'experimental', b'revlogv2')
     if revlogv2 == b'enable-unstable-format-and-corrupt-my-data':
         requirements.discard(requirementsmod.REVLOGV1_REQUIREMENT)
-        # generaldelta is implied by revlogv2.
-        requirements.discard(requirementsmod.GENERALDELTA_REQUIREMENT)
         requirements.add(requirementsmod.REVLOGV2_REQUIREMENT)
     # experimental config: format.internal-phase
     if ui.configbool(b'format', b'internal-phase'):

tests/test-revlog-v2.t

@@ -24,6 +24,7 b' Can create and open repo with revlog v2 '
   dotencode
   exp-revlogv2.2
   fncache
+  generaldelta
   persistent-nodemap (rust !)
   revlog-compression-zstd (zstd !)
   sparserevlog