Add support for generic constraints to Actor source generator by oising · Pull Request #1535 · dapr/dotnet-sdk

oising · 2025-05-12T17:55:30Z

Description

The actor source generator will now correctly add any type constraints to the client class. Supported:

where T: class
where T: struct
where T: unmanaged
where T: <class or interface>
where T: new()
where T: notnull

...and any legal combinations thereof.

I've added tests for a single case (single type parameter and one constraint) and a complex case (multiple type parametes and constraints.)

Issue reference

We strive to have all PR being opened based on an issue, where the problem or feature have been discussed prior to implementation.

Please reference the issue this PR will close: #1534

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

Code compiles correctly
Created/updated tests
Extended the documentation

Signed-off-by: Oisin Grehan <oisin.grehan@ionodes.com>

Copilot

Pull Request Overview

This PR adds support for generic type constraints to the Actor source generator, enabling it to properly handle and generate constraint clauses for generic actor interfaces. The generator now correctly preserves constraints like where T: class, where T: struct, where T: unmanaged, interface constraints, where T: new(), and where T: notnull when creating actor client classes.

Implemented constraint clause generation for all supported generic constraint types
Added logic to iterate through type parameters and build appropriate constraint syntax
Added comprehensive test coverage for both single and multiple type parameter scenarios

Reviewed Changes

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

File	Description
src/Dapr.Actors.Generators/ActorClientGenerator.cs	Implements constraint clause generation logic for generic type parameters in the actor client generator
test/Dapr.Actors.Generators.Test/ActorClientGeneratorTests.cs	Adds test cases for single and multiple type parameter constraints to verify the generator works correctly

src/Dapr.Actors.Generators/ActorClientGenerator.cs

Copilot · 2025-08-07T16:37:26Z

src/Dapr.Actors.Generators/ActorClientGenerator.cs

+                    // Add unmanaged constraint
+                    if (typeParam.HasUnmanagedTypeConstraint)
+                    {
+                        constraints.Add(SyntaxFactory.TypeConstraint(SyntaxFactory.IdentifierName("unmanaged")));


The unmanaged constraint should be added before type constraints but after class/struct constraints. The current order may not follow C# constraint ordering requirements where 'unmanaged' should come before interface constraints.

@copilot Reevaluate this and suggest a fix using the information at https://learn.microsoft.com/en-us/dotnet/csharp/programming-guide/generics/constraints-on-type-parameters

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com> Signed-off-by: Oisin Grehan <oising@gmail.com>

Copilot

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 6 comments.

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Copilot · 2026-03-09T20:29:55Z

test/Dapr.Actors.Generators.Test/ActorClientGeneratorTests.cs

+    public sealed class TestActorClient<TTrait> : Test.ITestActor<TTrait> where TTrait : Test.ITrait
+    {


The expected generated code has inconsistent type parameter names: the class is declared as TestActorClient<TTrait> but the constraint clause refers to TTrait. These must match (and should likely use the same type parameter identifier as the source interface).

Copilot · 2026-03-09T20:29:55Z

test/Dapr.Actors.Generators.Test/ActorClientGeneratorTests.cs

+    [GenerateActorClient]
+    public interface ITestActor<TTrait, TValidator> 
+        where TTrait : ITrait, new() 
+        where TValidator : class, IValidator<TTrait>
+    {


This test input source has a typo in the constraint clause: the interface type parameter is TTrait, but the where clause uses TTrait. As written, the originalSource won’t compile, so the test won’t validate constraint copying.

Copilot · 2026-03-09T20:29:55Z

test/Dapr.Actors.Generators.Test/ActorClientGeneratorTests.cs

+        public System.Threading.Tasks.Task<TTrait> GetValidatedTrait(string name)
+        {
+            return this.actorProxy.InvokeMethodAsync<string, TTrait>(""GetValidatedTrait"", name);
+        }


The expected generated code uses InvokeMethodAsync<string, TTrait>(...), but TTrait isn’t a type parameter on the generated class (it’s TTrait). This mismatch will make the expected output invalid and fail the snapshot comparison once the generator is fixed.

Copilot · 2026-03-09T20:29:56Z

src/Dapr.Actors.Generators/ActorClientGenerator.cs

+                if (typeParam.HasReferenceTypeConstraint ||
+                    typeParam.HasValueTypeConstraint ||
+                    typeParam.HasUnmanagedTypeConstraint ||
+                    typeParam.HasNotNullConstraint ||


The condition deciding whether to emit a where ... clause doesn’t include HasConstructorConstraint. If a type parameter only has new() (no other constraints), no constraint clause will be generated, even though the PR claims new() is supported.

Suggested change

typeParam.HasNotNullConstraint ||

typeParam.HasNotNullConstraint ||

typeParam.HasConstructorConstraint ||

Copilot · 2026-03-09T20:29:56Z

src/Dapr.Actors.Generators/ActorClientGenerator.cs

+                    // Add type constraints (e.g., where T : IInterface)
+                    foreach (var constraintType in typeParam.ConstraintTypes)
+                    {
+                        constraints.Add(SyntaxFactory.TypeConstraint(
+                            SyntaxFactory.ParseTypeName(constraintType.ToString())));
+                    }
+
+                    // Add notnull constraint
+                    if (typeParam.HasNotNullConstraint)
+                    {
+                        constraints.Add(SyntaxFactory.TypeConstraint(SyntaxFactory.IdentifierName("notnull")));
+                    }


Constraint ordering here can produce invalid C#: notnull is appended after the type/interface constraints, but C# requires special constraints (class/struct/unmanaged/notnull) to come before any type constraints, with new() last. Reorder the list so notnull is emitted before ConstraintTypes (and keep new() last).

Copilot · 2026-03-09T20:29:56Z

test/Dapr.Actors.Generators.Test/ActorClientGeneratorTests.cs

+    public interface ITestActor<in TTrait> where TTrait : ITrait
+    {
+        Task<bool> SetTrait(TTrait trait);
+        Task<ITrait> GetTrait(string name);
+    }


The new test input source won’t compile: the type parameter is TTrait (ITestActor<in TTrait>), but SetTrait uses TTrait as the parameter type. This should reference the declared type parameter name consistently so the generator test is exercising constraint copying rather than failing to compile the input.

oising requested review from a team as code owners May 12, 2025 17:55

initial commit with tests

087f11b

Signed-off-by: Oisin Grehan <oisin.grehan@ionodes.com>

oising force-pushed the actor-srcgen-generic-constraints branch from aa000f9 to 087f11b Compare May 12, 2025 17:58

update actor generic if to use contravariant type arg

435933c

Signed-off-by: Oisin Grehan <oisin.grehan@ionodes.com>

oising force-pushed the actor-srcgen-generic-constraints branch from 1fb41e7 to 435933c Compare May 12, 2025 18:06

Merge branch 'master' into actor-srcgen-generic-constraints

4a4a338

WhitWaldo assigned oising Jun 27, 2025

WhitWaldo added the area/actor/client label Jun 27, 2025

Merge branch 'master' into actor-srcgen-generic-constraints

4658d9c

Copilot AI review requested due to automatic review settings August 7, 2025 16:36

Copilot AI reviewed Aug 7, 2025

View reviewed changes

oising and others added 3 commits August 7, 2025 14:37

Update src/Dapr.Actors.Generators/ActorClientGenerator.cs

95d92b3

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com> Signed-off-by: Oisin Grehan <oising@gmail.com>

Merge branch 'master' into actor-srcgen-generic-constraints

79f53f3

Merge branch 'master' into actor-srcgen-generic-constraints

67099be

oising requested a review from Copilot March 9, 2026 20:25

Copilot started reviewing on behalf of oising March 9, 2026 20:26 View session

Copilot AI reviewed Mar 9, 2026

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Add support for generic constraints to Actor source generator#1535

Add support for generic constraints to Actor source generator#1535
oising wants to merge 7 commits intodapr:masterfrom
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		public sealed class TestActorClient<TTrait> : Test.ITestActor<TTrait> where TTrait : Test.ITrait
		{

	typeParam.HasNotNullConstraint \|\|
	typeParam.HasNotNullConstraint \|\|
	typeParam.HasConstructorConstraint \|\|

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oising commented May 12, 2025 •

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