Skip indexer properties in validation source generator

[adityamandaleeka]

Fixes #65424

The validation source generator crashes at runtime when encountering types with indexers (e.g. JsonElement, Dictionary<K,V>) used as minimal API endpoint parameters with AddValidation() enabled.

The source generator discovers validatable members by iterating typeSymbol.GetMembers().OfType<IPropertySymbol>(), but Roslyn exposes C# indexers (this[int index]) as IPropertySymbol with Name = "this[]". The generator emits these as ValidatablePropertyInfo entries. At runtime, ValidatablePropertyInfo.ValidateAsync calls DeclaringType.GetProperty("this[]"), which returns null because reflection names indexers "Item", causing:

System.InvalidOperationException: Property 'this[]' not found on type 'JsonElement'.

Confirmed this by decompiling the generated assembly, which showed:

new GeneratedValidatablePropertyInfo(
    typeof(JsonElement), typeof(JsonElement), "this[]", "this[]")

Fix

Added member.IsIndexer to the existing skip checks in ExtractValidatableMembers. Indexers represent parameterized access patterns, not data properties — they aren't meaningful targets for data annotation validation.

Testing

• Added SkipsIndexerPropertiesOnTypes test verifying JsonElement works as both a direct parameter and a property on another type, and that validation still runs on non-indexer properties of the containing type.
• Updated CanValidateParameters snapshot — Dictionary<string, TestService> was previously emitted solely due to its indexer, which would crash at runtime. It's now correctly excluded.
• All 27 generator tests pass.

[Copilot]

Pull request overview

This PR fixes a runtime crash in the minimal API validation source generator by ensuring C# indexer properties (e.g., this[int]) are not treated as validatable members, preventing invalid generated ValidatablePropertyInfo entries for types like JsonElement and Dictionary<TKey,TValue>.

Changes:

• Skip indexer properties during validatable member discovery (IPropertySymbol.IsIndexer).
• Add a generator test covering JsonElement as a parameter and as a property on another type.
• Update generator snapshot baselines to reflect the new exclusion behavior (notably removing the previously-generated Dictionary<,> entry driven by its indexer).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/Validation/gen/Parsers/ValidationsGenerator.TypesParser.cs	Filters out indexer properties during member extraction to avoid generating invalid property metadata.
src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/ValidationsGenerator.ComplexType.cs	Adds a regression test validating behavior with JsonElement and ensuring other properties still validate.
src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/snapshots/ValidationsGeneratorTests.SkipsIndexerPropertiesOnTypes#ValidatableInfoResolver.g.verified.cs	New snapshot verifying generated output excludes indexer-driven members and only includes meaningful properties.
src/Validation/test/Microsoft.Extensions.Validation.GeneratorTests/snapshots/ValidationsGeneratorTests.CanValidateParameters#ValidatableInfoResolver.g.verified.cs	Updates snapshot to remove previously-generated Dictionary<string, TestService> validatable info that came solely from an indexer.

[DeagleGross]

Nice fix!

[adityamandaleeka]

http2 CI failure is unrelated. Opened #65454 to fix that flakiness.