Jenkins Declarative Pipeline: How to read choice from input step?

Using the Input Step in the following form works for multiparameters:

script {
       def params = input message: 'Message',
                          parameters: [choice(name: 'param1', choices: ['1', '2', '3', '4', '5'],description: 'description'),
                                       booleanParam(name: 'param2', defaultValue: true, description: 'description')]
echo params['param1']
echo params['param2']

Since you are using declarative pipelines we will need to do some tricks. Normally you save the return value from the input stage, like this

def returnValue = input message: 'Need some input', parameters: [string(defaultValue: '', description: '', name: 'Give me a value')]

However this is not allowed directly in declarative pipeline steps. Instead, what you need to do is wrap the input step in a script step and then propagate the value into approprierte place (env seems to work good, beware that the variable is exposed to the rest of the pipeline though).

pipeline {
    agent any
    stages {
        stage("foo") {
            steps {
                script {
                    env.RELEASE_SCOPE = input message: 'User input required', ok: 'Release!',
                            parameters: [choice(name: 'RELEASE_SCOPE', choices: 'patch\nminor\nmajor', description: 'What is the release scope?')]
                echo "${env.RELEASE_SCOPE}"

Note that if you have multiple parameters in the input step, then input will return a map and you need to use map references to get the entry that you want. From the snippet generator in Jenkins:

If just one parameter is listed, its value will become the value of the input step. If multiple parameters are listed, the return value will be a map keyed by the parameter names. If parameters are not requested, the step returns nothing if approved.