Feature: Settings overrides are reported and shrunk 

Description 

Since the settings files are merged per entry, an override needs to name only what it changes - see Breaking: Settings files merge recursively. Two tools help turn an existing copy into that shape, and show what a copy inherits in the meantime.

The status report of EXT:reports lists, under Academic Persons, every package whose Configuration/AcademicPersons/Settings.yaml removes entries with ~ or leaves entries out of a map it copied, each as a dotted path such as contracts.fields.room. An entry a copy leaves out is inherited from the packages loaded before it, so it is back after the update; only the integrator knows whether the copy meant to remove it, and the entry is a notice until that is decided; a package that only removes is an info. A map counts as copied when the package restates at least two of its entries unchanged - in any key order, and also where upstream has added keys to them since - and so does every map inside a copy, because a copied map used to replace everything below it. A file that neither removes nor leaves anything out of a copy is not listed. The rule is a heuristic and errs both ways: a copy that restates at most one entry of a map unchanged, and sits in no other copy, is taken for a delta, and a delta that restates two unchanged keys next to its change is taken for a copy - the report then names more, never less.

The console command academic:persons:settings:migrate has a --delta option. It prints, for every package after the first one, the smallest file that has the same effect as the package's file, and the entries the package's copied maps leave out as comment lines:

vendor/bin/typo3 academic:persons:settings:migrate --delta

# my_site: Configuration/AcademicPersons/Settings.yaml
# Left out of a copied map, and inherited because the files are merged per entry.
# Add an entry with "~" where leaving it out was meant to remove it:
#   contracts.fields.room: ~
contracts:
  fields:
    validTo:
      validators:
        - required
        - date
    officeHours: ~

The printed file is exact: replacing the package's file with it changes nothing, the order of the entries included. A copy that names every entry of an upstream map decides the order of that map, so where leaving out its unchanged entries would change the order - the copy sorts them differently, or places a new entry among them - the map is printed with every entry it names. A field that gained a validators list between two of its shipped keys is therefore printed whole. A package whose file repeats upstream values only is named with a line saying the file can be dropped.

The option never writes a file and always exits with 0. Without it the command migrates the pre-3.0 keys and exits as before.

Impact 

Nothing changes for an installation that uses neither. To shrink an override:

1. Run the command with --delta.
2. For every commented entry, decide whether leaving it out was meant to remove it, and add it with ~ if so.
3. Replace the package's file with the result, and flush the TYPO3 caches.

The first package that ships the file is the base of the comparison and is never listed; on an installation that is academic_persons itself.