Build Definitions

A build definition is the central class of an Atom build. It declares which targets exist, what parameters are available, and how the build host is configured.

The `[BuildDefinition]` Attribute

Every build definition class must be:

Decorated with [BuildDefinition]
Marked partial (so source generators can augment it)
Derived from BuildDefinition (or WorkflowBuildDefinition)

[BuildDefinition]
[GenerateEntryPoint]
internal partial class Build : BuildDefinition
{
    // targets, parameters, etc.
}

What the Source Generator Does

When you apply [BuildDefinition], the Atom source generator automatically:

Discovers all Target properties (including those from implemented interfaces) and populates the TargetDefinitions dictionary.
Discovers all [ParamDefinition] / [SecretDefinition] properties and populates the ParamDefinitions dictionary.
Generates the AccessParam method so the framework can inspect parameter values.

This means you never need to manually register targets or parameters — just declare them and the generator wires everything up.

`[GenerateEntryPoint]`

Adding this attribute causes the source generator to emit a Program.cs with a Main method:

// Auto-generated
AtomHost.Run<Build>(args);

If you need custom host configuration, omit [GenerateEntryPoint] and write your own entry point:

var builder = AtomHost.CreateAtomBuilder<Build>(args);
// customise builder.Services, builder.Configuration, etc.
builder.Build().UseAtom().Run();

Composing with Interfaces

Targets and parameters are typically defined in interfaces so they can be shared across builds or published in module packages:

public interface IMyTargets : IBuildAccessor
{
    [ParamDefinition("greeting", "The greeting message")]
    string Greeting => GetParam(() => Greeting, "Hello");

    Target SayGreeting => t => t
        .DescribedAs("Says a greeting")
        .Executes(() => Logger.LogInformation(Greeting));
}

[BuildDefinition]
[GenerateEntryPoint]
internal partial class Build : BuildDefinition, IMyTargets { }

The source generator discovers SayGreeting and Greeting from IMyTargets and includes them in the build model.

`[GenerateSolutionModel]`

When applied alongside [BuildDefinition], this attribute generates a typed model of your solution's projects, giving you compile-time access to project paths.

`ConfigureDefinitionHost`

Override ConfigureDefinitionHost on your build class to register additional services before the build runs:

public override void ConfigureDefinitionHost(IHostApplicationBuilder builder)
{
    base.ConfigureDefinitionHost(builder);
    builder.Services.AddSingleton<IMyService, MyService>();
}

Next Steps

→ Targets

Table of Contents

Build Definitions

The [BuildDefinition] Attribute