Unable to reference a cdk.CfnParameter with Number type

[igilham]

I'm using parameters for commonly editable fields in my company's deployment infrastructure. I've found that some fields in the SDK can accept parameters but some seem not to work.

One such case is when the target property is of type Number. This triggers a type mismatch in the Typescript compiler.

const lambdaHandlerParam = new cdk.CfnParameter(this, 'LambdaHandler', {
    type: 'String',
    default: 'index.handler',
    description: 'The name of the function (within your source code) that Lambda calls to start running your code.'
});

const lambdaRuntimeParam = new cdk.CfnParameter(this, 'LambdaRuntime', {
    type: 'String',
    default: 'nodejs10.x',
    description: 'The name of the AWS Lambda runtime.'
});

const lambdaTimeoutParam = new cdk.CfnParameter(this, 'LambdaTimeout', {
    type: 'Number',
    default: 60,
    description: 'The function execution time (in seconds) after which Lambda terminates the function.'
});

const placeholderBucketNameParam = new cdk.CfnParameter(this, 'FunctionPlaceholderBucketName', {
    type: 'String',
    default: 'placeholder-assets',
    description: 'The name of the bucket that contains the default function code'
});

const placeholderKeyParam = new cdk.CfnParameter(this, 'FunctionPlaceholderKey', {
    type: 'String',
    default: 'placeholder.zip',
    description: 'The S3 key in the FunctionPlaceholderBucket containing the placeholder function.'
});

new lambda.Function(this, "Lambdahandler", {
    runtime: new lambda.Runtime(lambdaRuntimeParam.ref),
    code: lambda.Code.cfnParameters({
        bucketNameParam: placeholderBucketNameParam,
        objectKeyParam: placeholderKeyParam
    }),
    handler: lambdaHandlerParam.ref,
    timeout: lambdaTimeoutParam.ref, // type error
    role: new iam.Role(this, 'FunctionRole', {
        assumedBy: new iam.ServicePrincipal('lambda')
    })
});

Here's the error on the line defining the timeout property:

error TS2322: Type 'string' is not assignable to type 'number | undefined'.

I haven't found a way to make this work. It looks like hard-coding to a numerical value is the only way supported by the type system at this time.

[rix0rrr]

The right solution will be made more obvious in #2757, but for now what will work is lambdaTimoutParam.value.toNumber().

[github-actions]

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