fix: move UnionMode import outside TYPE_CHECKING for Pydantic runtime…

[phil65]

… access

The UnionMode type is used in GenerateConfig.union_mode field annotation. Pydantic needs to access this type at runtime for model validation, but it was only imported inside TYPE_CHECKING block, causing:

PydanticUserError: GenerateConfig is not fully defined; you should define UnionMode, then call GenerateConfig.model_rebuild().

This follows the same pattern as other runtime-required imports in this file (Path, DataModel, DataModelFieldBase, etc.) which have noqa: TC001 comments.

Summary by CodeRabbit

• Refactor
  • A previously internal type is now publicly available for import from the library.

_{✏️ Tip: You can customize this high-level summary in your review settings.}

[coderabbitai]

📝 Walkthrough

Walkthrough

UnionMode is now imported at module scope from datamodel_code_generator.model.pydantic_v2 in src/datamodel_code_generator/config.py, replacing a TYPE_CHECKING-guarded import. This makes UnionMode directly importable at runtime for both typing and runtime usage.

Changes

Cohort / File(s)	Summary
Import Structure Changes src/datamodel_code_generator/config.py	Moved UnionMode import from TYPE_CHECKING block to module-scope import, making it available for runtime usage and direct importation

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

Poem

🐰 A hop, a skip, an import so bright,
UnionMode now shines in runtime light!
No TYPE_CHECKING chains to bind,
Free at last—what peace to find! ✨

Pre-merge checks and finishing touches

✅ Passed checks (3 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and accurately summarizes the main change: moving the UnionMode import outside the TYPE_CHECKING block for Pydantic runtime access.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing touches

• 📝 Generate docstrings

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📥 Commits

Reviewing files that changed from the base of the PR and between 4decf36 and fa175a7.

📒 Files selected for processing (1)

• src/datamodel_code_generator/config.py

🧰 Additional context used

🧠 Learnings (2)

📓 Common learnings

Learnt from: koxudaxi
Repo: koxudaxi/datamodel-code-generator PR: 2799
File: src/datamodel_code_generator/model/pydantic/__init__.py:43-43
Timestamp: 2025-12-25T09:22:22.481Z
Learning: In datamodel-code-generator project, defensive `# noqa: PLC0415` directives should be kept on lazy imports (imports inside functions/methods) even when Ruff reports them as unused via RUF100, to prepare for potential future Ruff configuration changes that might enable the import-outside-top-level rule.

📚 Learning: 2025-12-25T09:23:08.506Z

Learnt from: koxudaxi
Repo: koxudaxi/datamodel-code-generator PR: 2799
File: src/datamodel_code_generator/util.py:49-66
Timestamp: 2025-12-25T09:23:08.506Z
Learning: In datamodel-code-generator, the is_pydantic_v2() and is_pydantic_v2_11() functions in src/datamodel_code_generator/util.py intentionally use global variable caching (_is_v2, _is_v2_11) on top of lru_cache for performance optimization. This dual-layer caching eliminates function call overhead and cache lookup overhead for frequently-called version checks. The PLW0603 linter warnings should be suppressed with # noqa: PLW0603 as this is a deliberate design choice.

Applied to files:

• src/datamodel_code_generator/config.py

🧬 Code graph analysis (1)

src/datamodel_code_generator/config.py (1)

src/datamodel_code_generator/enums.py (1)

• UnionMode (212-216)

🪛 Ruff (0.14.10)

src/datamodel_code_generator/config.py

47-47: Unused noqa directive (non-enabled: TC001)

Remove unused noqa directive

(RUF100)

⏰ Context from checks skipped due to timeout of 90000ms. You can increase the timeout in your CodeRabbit configuration to a maximum of 15 minutes (900000ms). (2)

• GitHub Check: Agent
• GitHub Check: CodeQL analysis (python)

🔇 Additional comments (2)

src/datamodel_code_generator/config.py (2)

47-47: Regarding the RUF100 static analysis hint: Keep the noqa directive.

Ruff reports the noqa: TC001 directive as unused, but this should be retained. The project follows a defensive pattern of keeping noqa directives even when not currently triggered, to prepare for potential future linter configuration changes. This aligns with existing runtime imports in this file (lines 7, 43, 51, 53) that all use the same noqa: TC001 pattern.

Based on learnings.

---

47-47: Import path is correct and follows project conventions.

The import of UnionMode from datamodel_code_generator.model.pydantic_v2 is correct. The pydantic_v2/__init__.py module explicitly re-exports UnionMode from datamodel_code_generator.enums, making this the intended public API import path. The noqa: TC001 directive is appropriate because it correctly suppresses the type-checking-only import check while documenting the runtime requirement for Pydantic validation.

The change properly moves UnionMode outside the TYPE_CHECKING block to fix the PydanticUserError, and the import path and suppression directive are correct.

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[Copilot]

Pull request overview

This PR fixes a Pydantic runtime validation error by moving the UnionMode import outside the TYPE_CHECKING block. The type annotation is used in the GenerateConfig.union_mode field and must be accessible at runtime for Pydantic model validation.

Key changes:

• Moved UnionMode import from TYPE_CHECKING block to runtime imports
• Added noqa: TC001 comment to suppress type-checking linter warning, consistent with other runtime-required imports

---

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[phil65]

Alternatively this here in pyproject :)

[tool.ruff.lint.flake8-type-checking]
runtime-evaluated-base-classes = ["pydantic.BaseModel"]

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will degrade performance by 15.48%

_{Comparing phil65:fix/unionmode-type-checking-import (fa175a7) with main (4decf36)}

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

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

Summary

❌ 11 regressed benchmarks
⏩ 98 skipped benchmarks¹

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	WallTime	test_perf_duplicate_names	842.7 ms	988.2 ms	-14.73%
❌	WallTime	test_perf_deep_nested	5.2 s	5.9 s	-12.83%
❌	WallTime	test_perf_kubernetes_style_pydantic_v2	2.2 s	2.6 s	-15.32%
❌	WallTime	test_perf_aws_style_openapi_pydantic_v2	1.7 s	1.9 s	-12.54%
❌	WallTime	test_perf_graphql_style_pydantic_v2	705 ms	809.8 ms	-12.94%
❌	WallTime	test_perf_complex_refs	1.8 s	2 s	-12.07%
❌	WallTime	test_perf_multiple_files_input	3.2 s	3.8 s	-15.48%
❌	WallTime	test_perf_stripe_style_pydantic_v2	1.7 s	1.9 s	-14%
❌	WallTime	test_perf_all_options_enabled	5.8 s	6.7 s	-13.55%
❌	WallTime	test_perf_openapi_large	2.5 s	2.9 s	-14.3%
❌	WallTime	test_perf_large_models_pydantic_v2	3.1 s	3.6 s	-15.14%

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 (4decf36) to head (fa175a7).

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2950   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           94        94           
  Lines        17716     17717    +1     
  Branches      2037      2037           
=========================================
+ Hits         17716     17717    +1     

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

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