@mrgrain/jsii-struct-builder

Build jsii structs with ease.

Jsii doesn't support TypeScript Utility Types like Partial or Omit, making it difficult to re-use existing struct interfaces. With this package, you can work around that limitation and create brand new struct interfaces based on the jsii specification of any existing structs, their parents, and your custom specification.

From jsii's perspective, these structs are completely new types. From a maintainer's perspective, they require the same minimal effort as utility types do. Everybody wins!

Usage

Install with:

npm install --save-dev @mrgrain/jsii-struct-builder

Then add a new ProjenStruct in your .projenrc.ts file, passing a TypeScript project as the first parameter. See the sections below for more usage details.

If you're not using projen, see Use without projen.

Requirements

Node.js >= 18
projen >= 0.65.0

Create from an existing Struct

Use the jsii FQN to mix in an existing struct. Use omit() to remove any properties you are not interested in.

new ProjenStruct(project, { name: 'MyProjectOptions' })
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))
  .omit('sampleCode', 'projenrcTs', 'projenrcTsOptions');

Adding new Properties

New properties can be added with a @jsii/spec definition. Complex types can be used and will be imported using their FQN. Any existing properties of the same name will be replaced.

new ProjenStruct(project, { name: 'MyProjectOptions' })
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))
  .add(
    {
      name: 'booleanSetting',
      type: { primitive: jsii.PrimitiveType.Boolean },
    },
    {
      name: 'complexSetting',
      type: { fqn: 'my_project.SomeEnum' },
    }
  );

Updating existing Properties

Existing properties can be updated. The provided partial @jsii/spec definition will be deep merged with the existing spec.

A convenience rename() method is provided. An update() of the name field has the same effect and can be combined with other updates.

new ProjenStruct(project, { name: 'MyProjectOptions'})
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))

  // Update a property
  .update('typescriptVersion', { optional: false })
  // Nested values can be updated
  .update('sampleCode', {
    docs: {
        summary: 'New summary',
        default: 'false',
      }
    }
  )

  // Rename a property
  .rename('homepage', 'website'})
  // ...this also does a rename
  .update('eslint', {
    name: 'lint',
    optional: false,
  });

Updating multiple properties

A callback function can be passed to updateEvery() to update multiple properties at a time.

Use updateAll() to uniformly update all properties. A convenience allOptional() method is provided to make all properties optional.

new ProjenStruct(project, { name: 'MyProjectOptions'})
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))

  // Use a callback to make conditional updates
  .updateEvery((property) => {
    if (!property.optional) {
      return {
        docs: {
          remarks: 'This property is required.',
        },
      };
    }
    return {};
  })

  // Apply an update to all properties
  .updateAll({
    immutable: true,
  })

  // Mark all properties as optional
  .allOptional();

Replacing properties

Existing properties can be replaced with a new @jsii/spec definition. If a different name is provided, the property is also renamed.

A callback function can be passed to map() to map every property to a new @jsii/spec definition.

new ProjenStruct(project, { name: 'MyProjectOptions' })
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))

  // Replace a property with an entirely new definition
  .replace('autoApproveOptions', {
    name: 'autoApproveOptions',
    type: { fqn: 'my_project.AutoApproveOptions' },
    docs: {
      summary: 'Configure the auto-approval workflow.'
    }
  })

  // Passing a new name, will also rename the property
  .replace('autoMergeOptions', {
    name: 'mergeFlowOptions',
    type: { fqn: 'my_project.MergeFlowOptions' },
  })

  // Use a callback to map every property to a new definition
  .map((property) => {
    if (property.protected) {
      return {
        ...property,
        protected: false,
        docs: {
          custom: {
            'internal': 'true',
          }
        }
      }
    }
    return property;
  });

Filter properties

Arbitrary predicate functions can be used to filter properties. Only properties that meet the condition are kept.

Use omit() and only() for easy name based filtering. A convenience withoutDeprecated() method is also provided.

new ProjenStruct(project, { name: 'MyProjectOptions' })
  .mixin(Struct.fromFqn('projen.typescript.TypeScriptProjectOptions'))

  // Keep properties using arbitrary filters
  .filter((prop) => !prop.optional)

  // Keep or omit properties by name
  .only('projenrcTs', 'projenrcTsOptions')
  .omit('sampleCode')

  // Remove all deprecated properties
  .withoutDeprecated();

AWS CDK properties

A common use-case of this project is to expose arbitrary overrides in CDK constructs. For example, you may want to provide common AWS Lambda configuration, but allow a consuming user to override any arbitrary property.

To accomplish this, first create the new struct in your .projenrc.ts file.

import { ProjenStruct, Struct } from '@mrgrain/jsii-struct-builder';
import { awscdk } from 'projen';

const project = new awscdk.AwsCdkConstructLibrary({
  // your config - see https://projen.io/awscdk-construct.html
});

new ProjenStruct(project, { name: 'MyFunctionProps' })
  .mixin(Struct.fromFqn('aws-cdk-lib.aws_lambda.FunctionProps'))
  .withoutDeprecated()
  .allOptional()
  .omit('code'); // our construct always provides the code

Then use the new struct in your CDK construct.

// lib/MyFunction.ts
import { Code, Function, Runtime } from 'aws-cdk-lib/aws-lambda';
import { Construct } from 'constructs';
import { join } from 'path';
import { MyFunctionProps } from './MyFunctionProps';

export class MyFunction extends Construct {
  constructor(scope: Construct, id: string, props: MyFunctionProps = {}) {
    super(scope, id);

    new Function(this, 'Function', {
      // sensible defaults
      runtime: Runtime.NODEJS_18_X,
      handler: 'index.handler',
      // user provided props
      ...props,
      // always force `code` from our construct
      code: Code.fromAsset(join(__dirname, 'lambda-handler')),
    });
  }
}

Use without projen

It is not required to use projen with this package. You can use a renderer directly to create files:

const myProps = Struct.empty('@my-scope/my-pkg.MyFunctionProps')
  .mixin(Struct.fromFqn('aws-cdk-lib.aws_lambda.FunctionProps'))
  .withoutDeprecated();

const renderer = new TypeScriptRenderer();
fs.writeFileSync('my-props.ts', renderer.renderStruct(myProps));

Advanced usage

Struct and ProjenStruct both share the same interface. This allows some advanced applications.

For example you can manipulate the source for re-use:

const base = Struct.fromFqn('projen.typescript.TypeScriptProjectOptions');
base.omit('sampleCode', 'projenrcTs', 'projenrcTsOptions');

Or you can mix in a ProjenStruct with another:

const foo = new ProjenStruct(project, { name: 'Foo' });
const bar = new ProjenStruct(project, { name: 'Bar' });

bar.mixin(foo);

You can also use Struct and ProjenStruct as type of a property:

const foo = new ProjenStruct(project, { name: 'Foo' });
const bar = new ProjenStruct(project, { name: 'Bar' });

foo.add({
  name: 'barSettings',
  type: bar,
});

The default configuration makes assumptions about the new interface that are usually okay. For more complex scenarios fqn, filePath and importLocations can be used to influence the rendered output.

new JsiiInterface(project, {
  name: 'MyProjectOptions',
  fqn: 'my_project.nested.location.MyProjectOptions',
  filePath: 'src/nested/my-project-options.ts',
  importLocations: {
    my_project: '../enums',
  },
}).add({
  name: 'complexSetting',
  type: { fqn: 'my_project.SomeEnum' },
});