Native AOT

Generated validators work in trimmed and Native AOT applications. They read properties directly and the registration uses closed generic types, so there is nothing for the trimmer to remove and nothing to compile at run time.

How this is checked

• ValidationModules.Runtime, ValidationModules.AspNetCore and ValidationModules.Options are built with IsAotCompatible set. Their builds treat the main trim and AOT analysis warnings as errors, so none of their code can use reflection that the trimmer cannot follow. In continuous integration every warning is an error.
• Every build of the repository publishes test applications with PublishAot and runs them. They exercise generated validators, the registration method, runners, list validation, and an ASP.NET Core application that uses the endpoint filter and the exception handler. A publish that produces any trim or AOT warning fails the build.

What to do in your application

Most models need nothing. Four areas need attention.

Regular expressions

Declare patterns with [GeneratedRegex] and point [Pattern] at them. The inline form, [Pattern("...")], needs the regular expression parser and interpreter at run time, which adds about 360 KB to the binary however many inline patterns it has. Options or a match timeout on an inline pattern adds about 490 KB more.

By default, a project that sets PublishAot or IsAotCompatible to true treats an inline pattern as an error, VM1301. The message shows the referenced form to use instead. ValidationModules_PatternPolicy changes this. Patterns describes both forms and the policy.

A class library that AOT applications consume should set IsAotCompatible. Its inline patterns then fail in the library's own build rather than in an application's publish.

The DataAnnotations [RegularExpression] attribute always compiles to an inline pattern, so the policy applies to it too. VM1301 then prints the [Pattern] and [GeneratedRegex] to use in its place. The attribute has a 2000 millisecond match timeout unless MatchTimeoutInMilliseconds is -1, so by default it adds about 840 KB.

JSON in ASP.NET Core

A minimal API published with Native AOT needs a JsonSerializerContext for its request and response types. The problem details body that ValidationModules.AspNetCore writes carries its own metadata, so the application's context lists only the application's types. ASP.NET Core shows the setup.

DataAnnotations resource messages

A custom ValidationAttribute that sets ErrorMessageResourceType formats its message through DataAnnotations, which looks up the resource property with reflection. The trimmer can remove that property. The generator reports VM2009. Set ErrorMessage instead, or keep the resource type from being trimmed. The built-in DataAnnotations attributes read resources without reflection.

Language packs and invariant globalization

Language packs choose their text by CultureInfo.CurrentUICulture. An application published with InvariantGlobalization set to true has only the invariant culture, so it cannot switch to another culture and the packs are never used. Leave globalization on in an application that shows translated messages.

Smaller validators

Two properties remove code that a size-sensitive application may not need:

Property	Removes
ValidationModules_FailFast set to false	The early return after each check. A StopOnFirstError pass then runs every check, though it still records one error.
ValidationModules_CaptureValues set to false	The capture of the failed value into ValidationError.Value.

The MSBuild reference lists every property.