Clarify AddValidation behavior vs nullability/binding semantics

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Clarify AddValidation behavior vs nullability/binding semantics

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Clarify AddValidation vs NRT binding effects

Description

This update addresses whether AddValidation behavior changes when endpoint parameters or JSON body properties move from nullable-oblivious to non-nullable reference types.
Conclusion: validation semantics from AddValidation are largely unchanged; behavior differences come from Minimal API binding optionality/requiredness decisions upstream.

• Scope

  • Clarifies the separation between:
    • Minimal API binding nullability behavior (RequestDelegateFactory)
    • Validation execution (ValidationEndpointFilterFactory + Validatable*Info)
  • No product code changes; this is an implementation-backed behavior clarification.

• Key behavior findings

  • AddValidation registers validation resolvers/filtering and does not introduce independent NRT-required semantics for reference types.
  • Runtime validation nullability checks are not NRT-sensitive for reference types.
  • Binding can change request outcomes (e.g., required parameter failures) when nullability annotations change, before validation filter execution.

• Relevant implementation points

  • ValidationServiceCollectionExtensions.AddValidation(...)
  • ValidationEndpointFilterFactory skips null arguments and validates bound values.
  • RequestDelegateFactory.IsOptionalParameter(...) uses nullability metadata to determine required/optional binding behavior.

// Binding semantics can differ with NRT:
app.MapGet("/{value}", (string value) => value);      // required binding
app.MapGet("/{value}", (string? value) => value ?? ""); // optional binding

// Validation semantics remain attribute/type driven:
builder.Services.AddValidation();
app.MapPost("/", ([Required] string name) => Results.Ok(name));

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