Addresses #7279 : consistent formatting btw list serializers and list field errors

[p-r-a-v-i-n]

Fix #7279

This pr changes the formatting of list serializer errors.

• previously list serializer returing errors in list format.
• It was adding empty dict ("{}") for every valid item in the list
• this format was not consistent with the list field error format.
• this is previous sample format

{
    'list_serializer': [
        {},
        {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]},
        {},
        {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]}
    ],
    
    'list_field': {
        1: [ErrorDetail(string='This dictionary may not be empty.', code='empty')],
        3: [ErrorDetail(string='This dictionary may not be empty.', code='empty')]
    }
}

Changes:

• returning dict instead of the list bcs :

  • it is easier to handle dict compare to list for clients
  • if there 100 items in which 99 are valid then it would add 99 "{}" in the list.
  • both list field and list serializer errors are consistent.

• here is the updated sample format

{
    'list_serializer': {
        0: {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]},
        1: {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]}
    },
    
    'list_field': {
        1: [ErrorDetail(string='This dictionary may not be empty.', code='empty')],
        3: [ErrorDetail(string='This dictionary may not be empty.', code='empty')]
    }
}

for clarity I can add more example if needed.

[browniebroke]

here is the updated sample format

{
    'list_serializer': {
        0: {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]},
        1: {'num': [ErrorDetail(string='Must be a valid boolean.', code='invalid')]}
    },
    
    'list_field': {
        1: [ErrorDetail(string='This dictionary may not be empty.', code='empty')],
        3: [ErrorDetail(string='This dictionary may not be empty.', code='empty')]
    }
}

The top level structure is indeed a dict, but the values of this dict aren't consistent: in the list serializer case, they are dict[str, list[ErrorDetail]] while in the list field they are list[ErrorDetail].

Is that right or am I missing something?

EDIT: I think I got it, ignore this comment

[Copilot]

Pull request overview

This PR changes the error format for ListSerializer to use a dict-based structure (with indices as keys) instead of a list-based structure (with empty dicts for valid items). This improves consistency with how ListField handles errors and makes error handling easier for API clients.

• Changed error structure from list to dict format for ListSerializer
• Only invalid item indices are included in error dict (no empty placeholders for valid items)
• Ensures consistency between ListSerializer and ListField error formats

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
rest_framework/serializers.py	Modified to_internal_value to collect errors in a dict keyed by index instead of a list with empty dicts for valid items
tests/test_serializer_lists.py	Added comprehensive tests for dict-based error format and consistency between ListSerializer and ListField
tests/test_serializer_bulk_update.py	Updated expected error format in tests to use dict structure with indices as keys

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