Fix incorrect relative imports with --use-exact-imports and --collapse-root-models

[koxudaxi]

Fixes: #2979

Summary by CodeRabbit

• New Features

  • Import resolution now supports an explicit "exact imports" mode when collapsing root models, improving import accuracy and aliasing.

• Generated Output

  • Generated model files and package initializers updated to reflect exact-imports behavior; ensures a top-level init.py when outputs span multiple top-level directories.

• Tests

  • Added test coverage for exact-imports combined with root-model collapse and name-collision scenarios.

[coderabbitai]

📝 Walkthrough

Walkthrough

Apply exact import path computation when imports.use_exact is enabled for root-type and non-BaseClass imports, and create a top-level __init__.py when multiple top-level directories are produced during module finalization.

Changes

Cohort / File(s)	Summary
Parser core src/datamodel_code_generator/parser/base.py	When imports.use_exact is true, use exact_import to compute exact from_/import_ pairs in __collapse_root_models and __change_from_import; add guard to emit a top-level __init__.py if multiple top-level dirs exist.
Generated fixtures (expected) tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/__init__.py, tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/data/__init__.py, tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/data/ReflectionSetData.py, tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/datatypes/__init__.py, tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/datatypes/FooStats.py, tests/data/expected/main/jsonschema/exact_imports_collapse_root_models/datatypes/BarStats.py	Add expected generated model modules and package __init__.py files reflecting exact-import paths and collapsed root-model outputs.
Tests tests/main/jsonschema/test_main_jsonschema.py	Add test_main_exact_imports_collapse_root_models_module_class_collision to verify generation with --use-exact-imports + --collapse-root-models (guarded with PYDANTIC_V2_SKIP).

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

• Fix exact imports with module/class name collision #2998: Modifies src/datamodel_code_generator/parser/base.py import computation logic; directly related to exact-import handling.
• Add --collapse-root-models-name-strategy option #2791: Alters __collapse_root_models behavior and import/name resolution; overlaps with collision and collapse logic.

Suggested labels

breaking-change-analyzed

Poem

🐰 Hopping through code with a twitch and a wink,
Exact paths now chosen — imports no longer stink.
Roots collapsed tidy, top-level files in sight,
I nibble through collisions and hop off tonight. 🥕

🚥 Pre-merge checks | ✅ 5 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 75.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately describes the main fix: addressing incorrect relative imports when using --use-exact-imports with --collapse-root-models flags.
Linked Issues check	✅ Passed	The PR directly addresses issue #2979 by fixing the generation of correct relative import paths (from ..datatypes.FooStats import FooStats) instead of duplicated/incorrect imports when using --use-exact-imports and --collapse-root-models together.
Out of Scope Changes check	✅ Passed	All changes are in scope: core parser fix in base.py, expected test output files for the new test case, and a new integration test verifying the fix for the exact collision scenario.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into main

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/exact-imports-collapse-root-models-collision

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[github-actions]

📚 Docs Preview: https://pr-2996.datamodel-code-generator.pages.dev

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (34b7d29) to head (ea6e8dd).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main     #2996   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           94        94           
  Lines        18120     18130   +10     
  Branches      2096      2099    +3     
=========================================
+ Hits         18120     18130   +10     

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

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[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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.

✅ 11 untouched benchmarks
⏩ 98 skipped benchmarks¹

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_{Comparing fix/exact-imports-collapse-root-models-collision (ea6e8dd) with main (34b7d29)}

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. ↩

[github-actions]

Breaking Change Analysis

Result: No breaking changes detected

Reasoning: This PR is a bug fix that corrects two issues: (1) When using --use-exact-imports with --collapse-root-models, relative imports were not being transformed to exact imports, producing incorrect/broken code. The fix applies exact_import() in this code path. (2) When output spans multiple top-level directories, a root __init__.py is now generated to ensure a valid Python package structure. Both changes fix incorrect behavior rather than modifying correct behavior, so they are not breaking changes. Users who were encountering the bug will see different (working) output, but this is the expected outcome of a bug fix.

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This analysis was performed by Claude Code Action

[github-actions]

🎉 Released in 0.54.0

This PR is now available in the latest release. See the release notes for details.