🔧 Refactor populate_field_type to use type-directed schema walking

[chrisjsewell]

This PR simplifies the populate_field_type function by replacing runtime keyword detection with type-directed traversal of the SchemasRootType structure.

Changes

Refactored populate_field_type (~190 → ~130 lines)

Before: Generic recursive function operating on Any, detecting JSON schema keywords (properties, items, contains, etc.) at runtime to infer structure, with special-case handling for network context.

After: Type-directed implementation that surgically walks the known typed structure:

• SchemasRootType → select / validate
• ValidateSchemaType → local / network
• NeedFieldsSchemaType → properties / allOf
• ResolvedLinkSchemaType → recursive items / contains

Key improvements

1. Clearer structure — 5 focused helper functions with single responsibilities:

   • _process_validate_schema
   • _process_resolved_link
   • _process_need_fields_schema
   • _inject_field_type
   • _inject_type_and_item_type

2. Eliminated ambiguity — No more is_inside_network path checks; the type structure dictates context

3. Defensive handling — All field accesses guarded with isinstance() checks; blanket exception handler wraps unexpected errors with context

4. Unified field lookup — Single pattern for extra/link/core fields with fallback to NeedsCoreFields

Added tests

New test file tests/schema/test_populate_field_type.py with 32 tests covering:

• Type injection for extra fields, link fields, and core fields
• Array type injection with items/contains
• Recursive processing of network and allOf
• Error handling for unknown fields, type mismatches, and malformed schemas
• Defensive behavior for missing/invalid structure

Breaking changes

None. All existing tests pass. Error messages for malformed schemas may differ slightly in wording but still provide equivalent information.

[codecov]

Codecov Report

❌ Patch coverage is 97.64706% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.80%. Comparing base (4e10030) to head (fae627e).
⚠️ Report is 234 commits behind head on master.

Files with missing lines	Patch %	Lines
sphinx_needs/schema/config_utils.py	97.64%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1639      +/-   ##
==========================================
+ Coverage   86.87%   88.80%   +1.92%     
==========================================
  Files          56       70      +14     
  Lines        6532     9972    +3440     
==========================================
+ Hits         5675     8856    +3181     
- Misses        857     1116     +259     

Flag	Coverage Δ
pytests	88.80% <97.64%> (+1.92%)	⬆️

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[ubmarco]

2 minor comments, good for merge