Strip Field None defaults with metadata

[koxudaxi]

Fixes: #1816

Summary by CodeRabbit

• Bug Fixes

  • Improved --strip-default-none behavior for Pydantic v1/v2 generation by omitting Field(None, ...) defaults only when the default is an actual None and the field type is not optional, resulting in more accurate required/default semantics in generated OpenAPI/Pydantic code.

• Tests

  • Added a regression test covering Pydantic v2 stripping behavior and updated OpenAPI/Pydantic expected outputs to match the revised Field(...) declarations.

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📝 Walkthrough

Walkthrough

DataModelField in pydantic_base.py gains a _should_strip_default_none_from_field helper that returns True when strip_default_none is set, the rendered default is "None", and the field type is not optional. __str__ now uses this helper to conditionally omit the None positional argument from Field(...) output. Related expected output fixtures are updated and a new Pydantic v2 test case is added.

Changes

strip_default_none Field rendering fix

Layer / File(s)	Summary
DataModelField helper and __str__ wiring src/datamodel_code_generator/model/pydantic_base.py	Adds _should_strip_default_none_from_field(default_repr) that returns True when strip_default_none is enabled, default_repr == "None", and the field type is not optional. __str__ now conditionally omits the None default from field_arguments based on this helper.
Updated and new expected output fixtures tests/data/expected/main/jsonschema/root_in_enum.py, tests/data/expected/main/openapi/pyproject.py, tests/data/expected/main/openapi/with_strip_default_none.py, tests/data/expected/main/openapi/strip_default_none_pydantic_v2.py	Removes explicit None defaults from Field(...) in root_in_enum, with_strip_default_none, and pyproject fixtures. Adds strip_default_none_pydantic_v2.py defining Issue1816Model with metadata-only, explicit non-None default, and plain optional fields.
New Pydantic v2 strip_default_none test tests/main/openapi/test_main_openapi.py	Adds test_main_openapi_pydantic_v2_strip_default_none_field_metadata that generates from strip_default_none_pydantic_v2.yaml with --output-model-type pydantic_v2.BaseModel and asserts output matches the new fixture.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Possibly related PRs

• koxudaxi/datamodel-code-generator#2520: Adjusts Pydantic v2 field default rendering under strip_default_none, overlapping with the same feature area.
• koxudaxi/datamodel-code-generator#3166: Modifies DataModelField.__str__ and helper methods for Field(...) argument construction in the same code path.
• koxudaxi/datamodel-code-generator#3289: Changes default/constraint representation in DataModelField string rendering, directly overlapping with this diff's code path.

Suggested labels

safe-to-fix

Suggested reviewers

• ilovelinux

Poem

🐇 Hop hop, no more None where it shouldn't be,
The field strips its default and runs free!
Optional stays optional, required stays true,
A helper decides what the Field args should do.
Fixtures updated, tests pass with a cheer —
The rabbit approves: the schema is clear! 🌿

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 71.43% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'Strip Field None defaults with metadata' directly describes the main change: removing None defaults from Field definitions that contain metadata, which is the core fix for issue #1816.
Linked Issues check	✅ Passed	The PR successfully addresses issue #1816 by implementing the strip-default-none functionality for fields with metadata. The changes demonstrate removal of Field(None, ...) defaults across multiple test files while preserving optional type annotations.
Out of Scope Changes check	✅ Passed	All changes are directly related to implementing the strip-default-none feature for fields with metadata. The modifications to the core logic, test fixtures, and test cases are all aligned with the stated objective.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix/strip-default-none-field

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[github-actions]

📚 Docs Preview: https://pr-3476.datamodel-code-generator.pages.dev

[codspeed-hq]

Merging this PR will improve performance by 11.53%

⚠️ Unknown Walltime execution environment detected

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For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚠️ Different runtime environments detected

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Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 10 untouched benchmarks
⏩ 98 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	test_perf_stripe_style_pydantic_v2	1.8 s	1.6 s	+11.53%

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---

_{Comparing fix/strip-default-none-field (347f6f1) with main (48335d0)}

Footnotes

1. 98 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (00cf006) to head (347f6f1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #3476   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          151       151           
  Lines        32484     32494   +10     
  Branches      3780      3783    +3     
=========================================
+ Hits         32484     32494   +10     

Flag	Coverage Δ
unittests	100.00% <100.00%> (ø)

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[github-actions]

🎉 Released in 0.65.1

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