[Abhiroop3917]

Type of changes

• Bug fix
• New feature
• Documentation / docstrings
• Tests
• Other

AI?

• AI was used to generate this PR

Checklist

• I've run the latest black with default args on new code.
• I've updated CHANGELOG.md and CONTRIBUTORS.md where appropriate.
• I've added tests for new code.
• I accept that @pytest-dev/pytest may be pedantic in the code review.

Description

Python 3.15 added frozendict as a built-in type (PEP 814). When an assertion comparing two lists of frozendicts fails with -vv, the "Full diff" prints each frozendict on a single line because _pytest/_io/pprint.py has no dispatch handler for it, falling through to repr().

A dict with the same contents gets one key per line, making the changed value easy to spot. With frozendict the change is buried mid-line.

Root cause: PrettyPrinter._dispatch has handlers for dict, OrderedDict, defaultdict, MappingProxyType, etc., but not frozendict.

Fix: Add _pprint_frozendict, mirroring _pprint_ordered_dict, and register it only when builtins.frozendict exists (Python 3.15+). Older Python versions are completely unaffected.

Before:

Full diff:
  [
      frozendict({'name': 'alice', 'age': 30, 'city': 'Lagos'}),
-     frozendict({'name': 'bob', 'age': 26, 'city': 'Abuja'}),
+     frozendict({'name': 'bob', 'age': 25, 'city': 'Abuja'}),
  ]

After:

Full diff:
  [
      frozendict({
          'name': 'alice',
          'age': 30,
          'city': 'Lagos',
      }),
      frozendict({
          'name': 'bob',
-         'age': 26,
+         'age': 25,
          'city': 'Abuja',
      }),
  ]

closes #15172

[bluetech]

Thanks, but there is already a PR open for this.