Jenkinsfile: Switch to declarative syntax

* Switch to declarative syntax
* Test parallel Windows/Linux build
* Remove some hard drive restrictions as now I have more HDD space on the server

Jenkinsfile

@@ -1,20 +1,25 @@
 #!/usr/bin/env groovy
-if (env.BRANCH_NAME.startsWith('PR-')) {
-    properties([[$class: 'BuildDiscarderProperty', strategy: [$class: 'LogRotator', artifactNumToKeepStr: '1']]])
-} else {
-    properties([[$class: 'BuildDiscarderProperty', strategy: [$class: 'LogRotator', artifactDaysToKeepStr: '30', artifactNumToKeepStr: '20']]])
-}
 
+pipeline {
+    agent { label 'colobot-build' }
+    options {
+        buildDiscarder(logRotator(artifactDaysToKeepStr: '30', artifactNumToKeepStr: '20'))
+    }
+    stages {
+        stage('Check pull request target') {
+            when { changeRequest() }
+            steps {
+                script {
                     if (env.CHANGE_TARGET == 'master') {
-    error("This pull request targets the wrong branch. Please reopen the pull request targetting the dev branch.")
+                        throw "This pull request targets the wrong branch. Please reopen the pull request targetting the dev branch."
                     }
-
-node('master') {
-    stage('Pull changes') {
-        checkout scm
                 }
-
+            }
+        }
+        stage('Build') {
+            parallel {
                 stage('Build Windows') {
+                    steps {
                         sh 'mkdir -p build/windows'
                         dir('build/windows') {
                             sh '''
@@ -27,11 +32,17 @@ node('master') {
                                 DESTDIR=. make install
                             '''
                         }
+                    }
+                    post {
+                        success {
                             sh 'rm -f windows-debug.zip'
                             zip zipFile: 'windows-debug.zip', archive: true, dir: 'build/windows/install'
                         }
+                    }
+                }
                 
                 stage('Build Linux') {
+                    steps {
                         sh 'mkdir -p build/linux'
                         dir('build/linux') {
                             sh '''
@@ -45,27 +56,40 @@ node('master') {
                                 patchelf --set-rpath '.' install/colobot
                             '''
                         }
+                    }
+                    post {
+                        success {
                             sh 'rm -f linux-debug.zip'
                             zip zipFile: 'linux-debug.zip', archive: true, dir: 'build/linux/install'
                         }
+                    }
+                }
                 
-    stage('Doxygen') {
+                // TODO: Run colobot-lint
+            }
+        }
+
+        stage('Generate docs') {
+            steps {
                 dir('build/linux') {
                     sh 'make doc'
                 }
+            }
+            post {
+                success {
                     publishHTML target: [$class: 'HtmlPublisherTarget', reportName: 'Doxygen', reportDir: 'build/linux/doc/html', reportFiles: 'index.html']
                 }
+            }
+        }
 
         stage('Run tests') {
+            steps {
                 dir('build/linux') {
                     sh './colobot_ut --gtest_output=xml:gtestresults.xml || true'
                 }
                 step([$class: 'XUnitBuilder', testTimeMargin: '3000', thresholdMode: 1, thresholds: [[$class: 'FailedThreshold', failureNewThreshold: '', failureThreshold: '', unstableNewThreshold: '', unstableThreshold: '0'], [$class: 'SkippedThreshold', failureNewThreshold: '', failureThreshold: '', unstableNewThreshold: '', unstableThreshold: '']], tools: [[$class: 'GoogleTestType', deleteOutputFiles: true, failIfNotNew: true, pattern: 'build/linux/gtestresults.xml', skipNoTestFiles: false, stopProcessingIfError: true]]])
             }
-
-    // Clean workspace after building pull requests
-    // to save disk space on the Jenkins host
-    if (env.BRANCH_NAME.startsWith('PR-')) {
-        cleanWs()
+            // TODO: Maybe run Windows tests using wine as well?
+        }
     }
 }