Fix ValidationsGenerator ITypeParameterSymbol handling by ANcpLua · Pull Request #65419 · dotnet/aspnetcore

ANcpLua · 2026-02-13T09:51:49Z

Summary

The ValidationsGenerator silently skips generic type parameters (ITypeParameterSymbol) and can emit invalid typeof(T) expressions when type parameters leak into ValidatableProperty.Type.

Changes

Single file: src/Validation/gen/Parsers/ValidationsGenerator.TypesParser.cs

ITypeParameterSymbol branch in TryExtractValidatableType — recognizes type parameters and walks their ConstraintTypes to discover concrete validatable types. Adds to visitedTypes before iterating constraints to prevent infinite recursion through circular constraints (e.g., where T : class, IEnumerable<T>).
ContainsTypeParameter guards — two guards (record property path + regular property path) that skip properties whose type contains an unresolved type parameter anywhere in the type tree. Without these, the emitter would generate typeof(TSelf) for CRTP patterns like RequestBase<TSelf>.
ContainsTypeParameter helper — recursively checks ITypeParameterSymbol, IArrayTypeSymbol, and INamedTypeSymbol.TypeArguments to catch T, T[], List<T>, Dictionary<string, T>, Nullable<T>, etc.

Why all four blocks are one fix

The ITypeParameterSymbol branch alone (without guards) causes a regression: constraint walking discovers types whose properties contain the type parameter, leading to typeof(TSelf) in emitted code.
The guards alone (without the branch) would silently drop the properties but never discover the validatable types through constraints.
The helper is required by the guards.

Test plan

CRTP pattern CommandBase<TSelf> where TSelf : CommandBase<TSelf> with concrete derived types validates correctly (class + record paths)
Base type properties ([Required]) and derived type properties ([Range]) discovered through CRTP inheritance
Runtime endpoint verification confirms validation errors are produced correctly
Existing validation tests continue to pass (CI)

…eters When endpoint handlers use generic extension methods (e.g., MapCommand<TRequest>()), the resolved method has ITypeParameterSymbol parameters. These have DeclaredAccessibility == NotApplicable, which fails the accessibility check in TryExtractValidatableType, causing the type to be silently skipped without any diagnostic. Handle ITypeParameterSymbol before the accessibility check by walking constraint types to discover validatable concrete types. Add the type parameter to visitedTypes before iterating constraints to prevent stack overflow with circular constraints. Add ContainsTypeParameter guard in ExtractValidatableMembers to prevent invalid typeof() expressions in generated code for properties whose types contain unresolved type parameters (e.g., CRTP patterns).

dotnet-policy-service · 2026-02-13T09:54:05Z

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

Copilot

Pull request overview

This PR fixes a critical bug in the ValidationsGenerator source generator where generic type parameters (like TRequest from a generic endpoint extension method) were either silently skipped or caused compilation errors when they leaked into generated typeof() expressions. The fix adds type parameter handling to discover validatable types through constraint types, while preventing type parameters from appearing in emitted code.

Changes:

Added ITypeParameterSymbol branch in TryExtractValidatableType to walk constraint types and discover validatable types
Added ContainsTypeParameter guards in both record and regular property extraction paths to prevent emitting typeof(T) expressions
Added ContainsTypeParameter helper method to recursively detect type parameters in type trees

Copilot · 2026-02-13T10:03:17Z

src/Validation/gen/Parsers/ValidationsGenerator.TypesParser.cs

+        // Type parameters (e.g., TRequest from a generic MapCommand<TRequest>() extension)
+        // have DeclaredAccessibility == NotApplicable. The concrete type is only known at
+        // call sites, not inside the generic method body where the endpoint delegate is
+        // defined. Walk constraint types to discover any validatable types reachable
+        // through type constraints.
+        if (typeSymbol is ITypeParameterSymbol typeParam)
+        {
+            // Add to visitedTypes BEFORE iterating constraints to prevent
+            // infinite recursion through circular constraints such as
+            // where T : class, IEnumerable<T> (SEC-001).
+            visitedTypes.Add(typeSymbol);
+            var foundValidatable = false;
+            foreach (var constraintType in typeParam.ConstraintTypes)
+            {
+                foundValidatable |= TryExtractValidatableType(constraintType, wellKnownTypes, ref validatableTypes, ref visitedTypes);
+            }
+            return foundValidatable;
+        }


This PR fixes a critical bug that would cause compilation errors when type parameters leak into generated code. However, there are no tests covering the scenarios described in the PR description and issue #65418:

Generic endpoint extension MapCommand<TRequest>() with constrained type parameter

CRTP pattern RequestBase<TSelf> where TSelf : RequestBase<TSelf>

Circular constraints where T : class, IEnumerable<T>

Edge cases like List<T>, T[], Dictionary<string, T>, Nullable<T>

The existing test files in src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/ show comprehensive test coverage for other features (records, polymorphism, IValidatableObject, etc.), but there's no test file for generic type parameters.

Without tests, there's a risk that:

Future changes could break this fix

The fix may not actually work in all the scenarios it's intended to handle

Edge cases may not be covered

Please add tests that verify:

Type parameters in endpoint handler signatures are discovered through constraints

CRTP patterns don't emit typeof(TSelf)

Circular constraints don't cause stack overflow

Properties with type parameter types are correctly skipped in both record and class code paths

Added tests in e20d0e4 — covers CRTP class and record patterns with runtime endpoint verification for Required and Range attributes.

Verifies that types using the Curiously Recurring Template Pattern (CommandBase<TSelf> where TSelf : CommandBase<TSelf>) are correctly discovered and validated through the inheritance hierarchy. Covers both class and record CRTP patterns with runtime endpoint verification for Required and Range validation attributes. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ANcpLua · 2026-02-13T10:44:32Z

@ANcpLua please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.
@dotnet-policy-service agree [company="{your company}"]
Options:

(default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.
@dotnet-policy-service agree
(when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.
@dotnet-policy-service agree company="Microsoft"
Contributor License Agreement

@dotnet-policy-service agree

ANcpLua · 2026-02-13T14:55:03Z

CI failures are pre-existing infrastructure flakes, unrelated to this change:

RestartAppShouldNotAffectOtherApps — 36.62% historical failure rate (IIS Express test)
Cannot create a file when that file already exists — tracked in Known Build Error: error : Cannot create a file when that file already exists. #61178

Happy to re-run if needed.

azure-pipelines · 2026-02-13T14:55:11Z

Commenter does not have sufficient privileges for PR 65419 in repo dotnet/aspnetcore

azure-pipelines · 2026-02-13T14:55:27Z

Commenter does not have sufficient privileges for PR 65419 in repo dotnet/aspnetcore

Copilot AI review requested due to automatic review settings February 13, 2026 09:51

github-actions bot added the needs-area-label Used by the dotnet-issue-labeler to label those issues which couldn't be triaged automatically label Feb 13, 2026

Copilot started reviewing on behalf of ANcpLua February 13, 2026 09:53 View session

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Feb 13, 2026

Copilot AI reviewed Feb 13, 2026

View reviewed changes

build-analysis bot mentioned this pull request Feb 13, 2026

Known Build Error: error : Cannot create a file when that file already exists. #61178

Open

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Fix ValidationsGenerator ITypeParameterSymbol handling#65419

Fix ValidationsGenerator ITypeParameterSymbol handling#65419
ANcpLua wants to merge 2 commits intodotnet:mainfrom
ANcpLua:fix/validations-generator-type-parameter-handling

ANcpLua commented Feb 13, 2026 •

edited

Loading

Uh oh!

dotnet-policy-service bot commented Feb 13, 2026

Uh oh!

Copilot AI left a comment

Uh oh!

Copilot AI Feb 13, 2026

Uh oh!

ANcpLua Feb 13, 2026

Uh oh!

ANcpLua commented Feb 13, 2026

Uh oh!

ANcpLua commented Feb 13, 2026 •

edited

Loading

Uh oh!

azure-pipelines bot commented Feb 13, 2026

Uh oh!

azure-pipelines bot commented Feb 13, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

Conversation

ANcpLua commented Feb 13, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Summary

Changes

Why all four blocks are one fix

Test plan

Uh oh!

dotnet-policy-service bot commented Feb 13, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Feb 13, 2026

Choose a reason for hiding this comment

Uh oh!

ANcpLua Feb 13, 2026

Choose a reason for hiding this comment

Uh oh!

ANcpLua commented Feb 13, 2026

Uh oh!

ANcpLua commented Feb 13, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

azure-pipelines bot commented Feb 13, 2026

Uh oh!

azure-pipelines bot commented Feb 13, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants

ANcpLua commented Feb 13, 2026 •

edited

Loading

ANcpLua commented Feb 13, 2026 •

edited

Loading