Add [DynamoDBEvent] annotation attribute and source generator support

[GarrettBeatty]

Summary

Adds [DynamoDBEvent] annotation attribute support to the Lambda Annotations framework, enabling developers to declaratively configure DynamoDB stream-triggered Lambda functions directly in C# code. The source generator automatically produces the corresponding SAM/CloudFormation template configuration at build time.

User Experience

With this change, developers can write DynamoDB stream-triggered Lambda functions like this:

[LambdaFunction]
[DynamoDBEvent("@MyTable")]
public async Task ProcessRecords(DynamoDBEvent evnt)
{
    foreach (var record in evnt.Records)
    {
        // Handle stream records
    }
}

The source generator will automatically generate the SAM template entry:

ProcessRecords:
  Type: AWS::Serverless::Function
  Properties:
    Events:
      MyTable:
        Type: DynamoDB
        Properties:
          Stream: !GetAtt MyTable.StreamArn
          StartingPosition: LATEST
          BatchSize: 100

Attribute Properties

Property	Required	Description	Default
Stream	Yes	DynamoDB stream reference (@TableName for CloudFormation Ref, or stream ARN)	-
ResourceName	No	CloudFormation event resource name	Derived from stream/table name
BatchSize	No	Max records per batch (1-10000)	100
StartingPosition	No	LATEST or TRIM_HORIZON	LATEST
MaximumBatchingWindowInSeconds	No	Max time to gather records (0-300)	Not set
Filters	No	Semicolon-separated filter patterns	Not set
Enabled	No	Whether the event source is enabled	true

Compile-Time Validation

The source generator validates at build time:

• Stream reference: Must start with @ (CloudFormation resource) or be a valid DynamoDB stream ARN
• Method signature: First parameter must be DynamoDBEvent, optional second parameter must be ILambdaContext
• Return type: Must be void or Task
• Dependencies: Project must reference Amazon.Lambda.DynamoDBEvents NuGet package
• BatchSize: Must be between 1 and 10000
• MaximumBatchingWindowInSeconds: Must be between 0 and 300
• StartingPosition: Must be LATEST or TRIM_HORIZON
• Resource name: Must be alphanumeric if explicitly set

Example with all properties

[LambdaFunction]
[DynamoDBEvent("@MyTable",
    ResourceName = "TableStreamEvent",
    BatchSize = 50,
    StartingPosition = "TRIM_HORIZON",
    MaximumBatchingWindowInSeconds = 60,
    Filters = "{\"eventName\": [\"INSERT\"]}",
    Enabled = true)]
public async Task ProcessRecords(DynamoDBEvent evnt, ILambdaContext context)
{
    context.Logger.LogLine($"Processing {evnt.Records.Count} records");
}

What Changed

Annotation Attribute (Amazon.Lambda.Annotations)

• New DynamoDBEventAttribute class in Amazon.Lambda.Annotations.DynamoDB namespace with configurable properties and built-in validation

Source Generator (Amazon.Lambda.Annotations.SourceGenerator)

• DynamoDBEventAttributeBuilder — extracts attribute data from Roslyn syntax tree
• AttributeModelBuilder — recognizes and routes DynamoDBEvent attributes
• EventTypeBuilder — maps to EventType.DynamoDB
• SyntaxReceiver — registers DynamoDBEvent as a recognized attribute
• TypeFullNames — adds DynamoDB type constants
• LambdaFunctionValidator — validates method signatures, return types, dependencies, and attribute properties
• CloudFormationWriter.ProcessDynamoDBAttribute() — generates SAM template with Stream (GetAtt StreamArn or ARN), StartingPosition, BatchSize, MaximumBatchingWindowInSeconds, FilterCriteria, and Enabled
• New diagnostic AWSLambda0132 for invalid DynamoDBEventAttribute errors

Tests

• Attribute unit tests covering constructor, defaults, property tracking, and validation
• CloudFormation writer tests covering attribute configurations and template formats
• E2E source generator snapshot tests (sync + async)
• Integration test deploying a real DynamoDB stream-triggered Lambda and verifying event source mapping

Related: DOTNET-8571

[Copilot]

Pull request overview

Adds DynamoDB Streams trigger support to Lambda Annotations via a new [DynamoDBEvent] attribute and extends the source generator to validate usage and emit the corresponding SAM/CloudFormation DynamoDB event configuration.

Changes:

• Introduces DynamoDBEventAttribute (including validation and derived resource naming) in Amazon.Lambda.Annotations.DynamoDB.
• Extends the source generator to recognize/build/validate DynamoDB events and write the SAM template event mapping.
• Adds unit, snapshot, and integration tests plus a test serverless app DynamoDB table and handler.

Reviewed changes

Copilot reviewed 27 out of 27 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
Libraries/test/TestServerlessApp/serverless.template	Adds a DynamoDB table with Streams enabled for integration testing.
Libraries/test/TestServerlessApp/TestServerlessApp.csproj	References Amazon.Lambda.DynamoDBEvents for the test app.
Libraries/test/TestServerlessApp/DynamoDbStreamProcessing.cs	Adds a sample DynamoDB stream Lambda handler using the new attribute.
Libraries/test/TestServerlessApp/DynamoDBEventExamples/ValidDynamoDBEvents.cs.txt	Adds valid attribute usage inputs for source generator snapshot tests.
Libraries/test/TestServerlessApp.IntegrationTests/TestServerlessApp.IntegrationTests.csproj	Adds DynamoDB SDK dependency for integration validation.
Libraries/test/TestServerlessApp.IntegrationTests/IntegrationTestContextFixture.cs	Fetches DynamoDB Stream ARN from the deployed test table; updates expected function count.
Libraries/test/TestServerlessApp.IntegrationTests/DynamoDBEventSourceMapping.cs	New integration test validating the deployed event source mapping config.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/WriterTests/DynamoDBEventsTests.cs	Adds CloudFormation writer tests for DynamoDB event rendering and sync behavior.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/SourceGeneratorTests.cs	Adds snapshot-based source generator test coverage for DynamoDB events.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/ServerlessTemplates/dynamoDBEvents.template	Snapshot of generated template containing DynamoDB events.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/DynamoDB/ValidDynamoDBEvents_ProcessMessages_Generated.g.cs	Snapshot of generated handler for sync DynamoDB event usage.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/DynamoDB/ValidDynamoDBEvents_ProcessMessagesAsync_Generated.g.cs	Snapshot of generated handler for async DynamoDB event usage.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/DynamoDBEventAttributeTests.cs	Adds unit tests for attribute defaults, tracking, and validation.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/CSharpSourceGeneratorVerifier.cs	Adds DynamoDBEvents assembly reference to generator test harness.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Amazon.Lambda.Annotations.SourceGenerators.Tests.csproj	Adds project reference to Amazon.Lambda.DynamoDBEvents for tests.
Libraries/src/Amazon.Lambda.Annotations/README.md	Documents the new DynamoDB event attribute and usage.
Libraries/src/Amazon.Lambda.Annotations/DynamoDB/DynamoDBEventAttribute.cs	Implements the new [DynamoDBEvent] attribute and validation logic.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Writers/CloudFormationWriter.cs	Emits DynamoDB event definitions into the generated template.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Validation/LambdaFunctionValidator.cs	Adds dependency + signature + attribute-property validation for DynamoDB events.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/TypeFullNames.cs	Adds DynamoDB type/attribute full-name constants and recognized attribute list entry.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/SyntaxReceiver.cs	Registers DynamoDBEventAttribute as a recognized annotation.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/EventTypeBuilder.cs	Adds mapping from DynamoDBEventAttribute to EventType.DynamoDB.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/Attributes/DynamoDBEventAttributeBuilder.cs	Builds DynamoDBEventAttribute model from Roslyn AttributeData.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/Attributes/AttributeModelBuilder.cs	Routes DynamoDBEventAttribute to the new builder/model.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Diagnostics/DiagnosticDescriptors.cs	Adds a new diagnostic descriptor for invalid DynamoDBEventAttribute.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Diagnostics/AnalyzerReleases.Unshipped.md	Records the newly added diagnostic in analyzer release notes.
.autover/changes/add-dynamodbevent-annotation.json	Adds an autover change entry for the new feature.

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[Copilot]

Validate() treats a stream ARN as valid if it contains either ":dynamodb:" or "/stream/" because the condition uses &&. This will let invalid ARNs through (e.g., missing /stream/). Update validation to require both parts (or parse the ARN structure similarly to SQSEventAttribute.Validate()).

Suggested change

	if (!Stream.Contains(":dynamodb:") && !Stream.Contains("/stream/"))
	if (!Stream.Contains(":dynamodb:") || !Stream.Contains("/stream/"))