Add [ScheduleEvent] annotation attribute and source generator support

[GarrettBeatty]

Summary

Adds [ScheduleEvent] annotation attribute support to the Lambda Annotations framework, enabling developers to declaratively configure schedule-triggered Lambda functions directly in C# code using rate or cron expressions. The source generator automatically produces the corresponding SAM/CloudFormation template configuration at build time.

User Experience

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

[LambdaFunction]
[ScheduleEvent("rate(5 minutes)")]
public async Task ProcessScheduledEvent(ScheduledEvent evnt)
{
    // Handle scheduled invocation
}

The source generator will automatically generate the SAM template entry:

ProcessScheduledEvent:
  Type: AWS::Serverless::Function
  Properties:
    Events:
      rate5minutes:
        Type: Schedule
        Properties:
          Schedule: rate(5 minutes)

Attribute Properties

Property	Required	Description	Default
Schedule	Yes	Schedule expression (rate(...) or cron(...))	-
ResourceName	No	CloudFormation event resource name	Derived from schedule expression
Description	No	Description for the schedule rule	Not set
Input	No	JSON string to pass as input to the Lambda function	Not set
Enabled	No	Whether the event source is enabled	true

Compile-Time Validation

The source generator validates at build time:

• Schedule expression: Must start with rate( or cron(
• Method signature: First parameter must be ScheduledEvent, optional second parameter must be ILambdaContext
• Return type: Must be void or Task
• Dependencies: Project must reference Amazon.Lambda.CloudWatchEvents NuGet package
• Resource name: Must be alphanumeric if explicitly set

Example with all properties

[LambdaFunction]
[ScheduleEvent("cron(0 12 * * ? *)",
    ResourceName = "DailyCleanup",
    Description = "Runs daily at noon UTC",
    Input = "{\"action\": \"cleanup\"}",
    Enabled = true)]
public async Task ProcessScheduledEvent(ScheduledEvent evnt, ILambdaContext context)
{
    context.Logger.LogLine("Running scheduled cleanup");
}

What Changed

Annotation Attribute (Amazon.Lambda.Annotations)

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

Source Generator (Amazon.Lambda.Annotations.SourceGenerator)

• ScheduleEventAttributeBuilder — extracts attribute data from Roslyn syntax tree
• AttributeModelBuilder — recognizes and routes ScheduleEvent attributes
• EventTypeBuilder — maps to EventType.Schedule
• SyntaxReceiver — registers ScheduleEvent as a recognized attribute
• TypeFullNames — adds Schedule type constants
• LambdaFunctionValidator — validates method signatures, return types, dependencies, and attribute properties
• CloudFormationWriter.ProcessScheduleAttribute() — generates SAM template with Schedule expression, Description, Input, and Enabled
• New diagnostic AWSLambda0132 for invalid ScheduleEventAttribute 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 schedule-triggered Lambda and verifying EventBridge rule

Manual Testing

• I played around with the integration test app/deleted the annotation/changed some things and it updated the template as expected

Related: DOTNET-8574

[Copilot]

Pull request overview

Adds first-class [ScheduleEvent] support to the Lambda Annotations framework so schedule-triggered Lambdas (rate/cron) can be declared in C# and emitted into the generated SAM/CloudFormation template.

Changes:

• Introduces ScheduleEventAttribute (schedule expression + optional ResourceName/Description/Input/Enabled).
• Extends the source generator to recognize/validate schedule events and emit Type: Schedule event configuration in the template.
• Adds unit, snapshot, and integration tests plus docs/examples for schedule events.

Reviewed changes

Copilot reviewed 26 out of 26 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
Libraries/test/TestServerlessApp/TestServerlessApp.csproj	Adds CloudWatchEvents project reference for schedule event sample app.
Libraries/test/TestServerlessApp/ScheduledProcessing.cs	Adds an example scheduled handler Lambda using [ScheduleEvent].
Libraries/test/TestServerlessApp/ScheduleEventExamples/ValidScheduleEvents.cs.txt	Adds valid schedule event usages for generator snapshot tests (kept as .txt).
Libraries/test/TestServerlessApp.IntegrationTests/TestServerlessApp.IntegrationTests.csproj	Adds AWSSDK.CloudWatchEvents dependency for schedule integration testing.
Libraries/test/TestServerlessApp.IntegrationTests/ScheduleEventRule.cs	Adds integration test to validate the deployed EventBridge rule configuration.
Libraries/test/TestServerlessApp.IntegrationTests/IntegrationTestContextFixture.cs	Updates expected Lambda function count to include the new scheduled handler.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/WriterTests/ScheduleEventsTests.cs	Adds CloudFormation writer tests for schedule event emission and property syncing.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/SourceGeneratorTests.cs	Adds snapshot-based source generator test for valid schedule events.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/ServerlessTemplates/scheduleEvents.template	Adds expected generated serverless template snapshot for schedule events.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/Schedule/ValidScheduleEvents_ProcessScheduledEvent_Generated.g.cs	Adds expected generated handler snapshot (sync).
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Snapshots/Schedule/ValidScheduleEvents_ProcessScheduledEventAsync_Generated.g.cs	Adds expected generated handler snapshot (async).
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/ScheduleEventAttributeTests.cs	Adds unit tests for ScheduleEventAttribute defaults/derivations/validation.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/CSharpSourceGeneratorVerifier.cs	Adds metadata reference for ScheduledEvent type in the Roslyn test harness.
Libraries/test/Amazon.Lambda.Annotations.SourceGenerators.Tests/Amazon.Lambda.Annotations.SourceGenerators.Tests.csproj	Adds CloudWatchEvents project reference for tests.
Libraries/src/Amazon.Lambda.Annotations/Schedule/ScheduleEventAttribute.cs	Introduces the new ScheduleEventAttribute implementation + validation.
Libraries/src/Amazon.Lambda.Annotations/README.md	Documents ScheduleEvent usage and updates supported-attributes list.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Writers/CloudFormationWriter.cs	Emits Schedule SAM event entries for [ScheduleEvent].
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Validation/LambdaFunctionValidator.cs	Adds dependency checks + signature/return/attribute validation for schedule handlers.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/TypeFullNames.cs	Adds full-name constants for ScheduleEventAttribute and ScheduledEvent.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/SyntaxReceiver.cs	Recognizes ScheduleEventAttribute during syntax collection.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/EventTypeBuilder.cs	Maps ScheduleEventAttribute to EventType.Schedule.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/Attributes/ScheduleEventAttributeBuilder.cs	Builds ScheduleEventAttribute models from Roslyn attribute data.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Models/Attributes/AttributeModelBuilder.cs	Routes ScheduleEventAttribute to the new builder/model type.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Diagnostics/DiagnosticDescriptors.cs	Adds a new diagnostic descriptor for invalid ScheduleEventAttribute usage.
Libraries/src/Amazon.Lambda.Annotations.SourceGenerator/Diagnostics/AnalyzerReleases.Unshipped.md	Records the new diagnostic ID in analyzer release notes.
.autover/changes/add-scheduleevent-annotation.json	Adds versioning/changelog entry for the new feature.

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[Copilot]

Pull request overview

Copilot reviewed 30 out of 30 changed files in this pull request and generated 3 comments.

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[normj]

Approved with a small feature request. I'll let you decide if you want to add it.

[normj]

Feature suggestion: I doubt too many people want to put large JSON documents in this attribute. You could make the logic look to see if this is a file path, relative or absolute, and if it is read the file and put that in the template. If you do think this is worth adding be sure the comment block for Input calls out this can be a file path.