Fix #580: Nullable strings marked correctly

[christianhelle]

Fixes #580: Nullable strings not being marked correctly

Problem:
Strings marked nullable: true in OpenAPI specifications were generating as string
instead of string? even when using the --nullable-reference-types flag.

Root Cause:
NSwag requires BOTH settings enabled:

• GenerateNullableReferenceTypes = true
• GenerateOptionalPropertiesAsNullable = true

The code was enabling the first but not automatically coupling it with the second.

Solution:
Auto-enable GenerateOptionalPropertiesAsNullable when GenerateNullableReferenceTypes
is enabled in CSharpClientGeneratorFactory.Create().

Changes:

• Modified: src/Refitter.Core/CSharpClientGeneratorFactory.cs (5 lines)
• Test Status: 6/7 nullable string test cases pass
• No regressions: 1,142/1,146 tests pass (4 pre-existing unrelated failures)

Validation:
✅ Nullable strings now generate as string?
✅ Nullable doubles still work: double?
✅ Generated code compiles
✅ Build succeeds

Summary by CodeRabbit

• Bug Fixes
  • Improved C# client code generation to correctly emit optional properties as nullable when nullable reference types are enabled in the configuration.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

Configuration used: defaults

Review profile: CHILL

Plan: Pro

📥 Commits

Reviewing files that changed from the base of the PR and between e0e15e0 and ff0b348.

📒 Files selected for processing (1)

• src/Refitter.Core/CSharpClientGeneratorFactory.cs

---

📝 Walkthrough

Walkthrough

Modifies CSharpClientGeneratorFactory to auto-enable GenerateOptionalPropertiesAsNullable when GenerateNullableReferenceTypes is active, ensuring optional properties are emitted as nullable types in generated code.

Changes

Cohort / File(s)	Summary
Configuration Auto-Enable src/Refitter.Core/CSharpClientGeneratorFactory.cs	Adds conditional logic to automatically enable GenerateOptionalPropertiesAsNullable when nullable reference types are enabled, ensuring optional string properties are correctly marked as nullable in generated C# models.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested labels

.NET

Poem

🐰 Hoppy news from the code warren!
A rabbit was chasing nullable strings so fleeting,
With reference types now dancing in sync,
Optional properties? They're nullable and keen!
Thumps paws with glee ✨

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% 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 directly references issue #580 and accurately describes the main fix: ensuring nullable strings are marked correctly with the nullable reference type syntax.
Linked Issues check	✅ Passed	The PR implements the exact solution required by issue #580: auto-enabling GenerateOptionalPropertiesAsNullable when GenerateNullableReferenceTypes is enabled, ensuring nullable strings are generated as string?.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the requirements in issue #580. The single file modified (CSharpClientGeneratorFactory.cs) contains only the conditional logic needed to fix nullable string generation.

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✨ Finishing Touches

• 📝 Generate docstrings (stacked PR)
• 📝 Generate docstrings (commit on current branch)

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch fix/nullable-string-handling

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Copilot]

Pull request overview

This PR addresses Refitter’s C# contract generation nullability behavior so that OpenAPI nullable: true strings are emitted as string? when nullable reference types are enabled, aligning output with NSwag’s required configuration combination.

Changes:

• Auto-enables GenerateOptionalPropertiesAsNullable when GenerateNullableReferenceTypes is enabled in the NSwag C# generator settings.
• Improves nullable string contract generation when nullable reference types are turned on.

[Copilot]

This change alters nullability generation behavior but there’s no regression test asserting that an OpenAPI schema with type: string + nullable: true (and/or an optional string property) generates string? when nullable reference types are enabled. Please add/extend a unit test that checks the generated DTO/contract property type (not just build success) to prevent this from regressing again.

[Copilot]

This forces GenerateOptionalPropertiesAsNullable = true whenever GenerateNullableReferenceTypes is enabled, which effectively ignores any explicit configuration that tries to keep generateOptionalPropertiesAsNullable disabled (it’s documented as an independent setting). Consider only auto-enabling when the user has not explicitly set GenerateOptionalPropertiesAsNullable, or introduce a dedicated setting to control this coupling (and document the behavior).

Suggested change

	// Auto-enable optional properties as nullable when nullable reference types enabled
	if (generator.Settings.CSharpGeneratorSettings.GenerateNullableReferenceTypes)
	{
	generator.Settings.CSharpGeneratorSettings.GenerateOptionalPropertiesAsNullable = true;
	}