Surface primary constructor parameter attributes in OpenAPI schemas

[matantsach]

Summary

C# 12 primary constructor parameters on classes carry their validation attributes ([Range], [Required], [MinLength], etc.) only on the ParameterInfo — unlike records, the compiler doesn't copy them to the synthesized property. The OpenAPI schema generator reads attributes exclusively from JsonPropertyInfo.AttributeProvider (the PropertyInfo), so these constraints are silently dropped from the generated schema.

This adds a fallback that checks JsonPropertyInfo.AssociatedParameter.AttributeProvider for constructor parameter attributes in two places:

1. TypeInfoResolver modifier — picks up [Required] from constructor parameters
2. TransformSchemaNode callback — picks up ValidationAttribute, DefaultValueAttribute, and DescriptionAttribute from constructor parameters

Constructor parameter attributes are applied first; property-level attributes are applied second and take precedence. This means existing types with attributes on both (like records) continue to work correctly — the property-level copy wins, and idempotent re-application of the same values is harmless.

AOT considerations

AssociatedParameter.AttributeProvider follows the same reflection pattern already used by the existing propertyInfo.AttributeProvider path. Under source-generated serialization contexts, AssociatedParameter.AttributeProvider is null (same as AttributeProvider), so the new block is safely skipped. No new trimming or AOT risk surface is introduced.

Test plan

• HandlesValidationAttributesOnPrimaryConstructorParameters — [Range(0, 120)] and [MinLength(1), MaxLength(100)] on class primary constructor params produce correct schema constraints
• HandlesRequiredAttributeOnPrimaryConstructorParameters — [Required] on constructor param marks property as required, with negative assertion on non-required property
• PropertyAttributeOverridesConstructorParameterAttribute — property-level [Range(10, 50)] correctly overrides constructor-level [Range(0, 100)]
• HandlesDescriptionAttributeOnPrimaryConstructorParameters — [Description] on constructor param appears in schema
• RecordWithValidationAttributesStillWorks — record types are unaffected by the fallback (no double-application regression)

Fixes #61538

[dotnet-policy-service]

Thanks for your PR, @@matantsach. Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[Copilot]

Pull request overview

This PR updates the OpenAPI schema generation pipeline to surface validation and descriptive metadata applied to C# 12 class primary-constructor parameters (which otherwise don’t get copied onto synthesized properties), ensuring generated schemas reflect those constraints.

Changes:

• Extend required-property detection to also consider JsonPropertyInfo.AssociatedParameter.AttributeProvider for [Required].
• Extend schema transformation to also read constructor-parameter ValidationAttribute, DefaultValueAttribute, and DescriptionAttribute metadata (with property-level attributes taking precedence).
• Add test coverage for validation/required/description attributes on primary constructor parameters, plus an override-precedence and record-regression test.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/OpenApi/src/Services/Schemas/OpenApiSchemaService.cs	Adds constructor-parameter attribute fallback for required detection and schema keyword mapping.
src/OpenApi/test/Microsoft.AspNetCore.OpenApi.Tests/Services/OpenApiSchemaService/OpenApiSchemaService.PropertySchemas.cs	Adds tests validating schema output for primary-constructor parameter attributes and precedence behavior.

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[matantsach]

Good catch — though this pattern is inherited from the existing property-level block just below (line 151), which uses the same OfType<ValidationAttribute>() is { } guard. I kept it consistent with the surrounding code, but happy to clean up both if the team prefers.

[matantsach]

Same story here — the existing property-level block (lines 153-165) has the same duplicated DescriptionAttribute lookup across the inline/componentized branches. Kept it parallel for consistency, but I can consolidate both blocks if the team would like that as part of this PR.

[dotnet-policy-service]

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