Groovy multiline string interpolation whitespace - jenkins

Question

I am trying to generate some generic Groovy code for Jenkins but I seem to have trouble with multi line strings and extra white space. I've tried everything I could find by Googling but I can't seem to get it working.
My issue isn't related to simple multi line strings. I managed to trim white space by using the stripIndent() and stripMargin() methods for simple cases. My issue is caused by having interpolated methods inside my strings.
Groovy info: Groovy Version: 3.0.2 JVM: 13.0.2 Vendor: Oracle Corporation OS: Mac OS X
String method2(String tier, String jobName) {
return """
Map downstreamJobs = [:]
stage ("${jobName}-${tier}-\${region}_${jobName}") {
test
}
""".stripIndent().stripMargin()
}
static String simpleLog() {
return """
script {
def user = env.BUILD_USER_ID
}
""".stripIndent().stripMargin()
}
static String method1() {
return """\
import jenkins.model.Jenkins
currentBuild.displayName = "name"
${simpleLog()}
""".stripIndent().stripMargin()
}
String generateFullDeploymentPipelineCode() {
return """Text here
${method1()}
${method2("test1", "test2")}
""".stripIndent().stripMargin()
}
println(generateFullDeploymentPipelineCode())
This is what it prints(or writes to disk):
Text here
import jenkins.model.Jenkins
currentBuild.displayName = "name"
script {
def user = env.BUILD_USER_ID
}
Map downstreamJobs = [:]
stage ("test2-test1-${region}_test2") {
test
}
Why the extra space around the import lines? I know the indentation method is supposed to trim all white space according to the least number of leading spaces, so that's why we use backslash (example here https://stackoverflow.com/a/19882917/7569335).
That works for simple strings, but it breaks down once use start using interpolation. Not with regular variables, just when you interpolate an entire method.

Answer 1

as variant - use just stripMargin() and only once on a final string
String method2(String tier, String jobName) {
return """\
|Map downstreamJobs = [:]
|stage ("${jobName}-${tier}-\${region}_${jobName}") {
| test
|}
"""
}
static String simpleLog() {
return """\
|script {
| def user = env.BUILD_USER_ID
|}
"""
}
static String method1() {
return """\
|import jenkins.model.Jenkins
|currentBuild.displayName = "name"
${simpleLog()}
"""
}
String generateFullDeploymentPipelineCode() {
return """\
|Text here
${method1()}
${method2("test1", "test2")}
""".stripIndent().stripMargin()
}
println(generateFullDeploymentPipelineCode())
result:
Text here
import jenkins.model.Jenkins
currentBuild.displayName = "name"
script {
def user = env.BUILD_USER_ID
}
Map downstreamJobs = [:]
stage ("test2-test1-${region}_test2") {
test
}
another variant with trim() and stripIndent()
def method2(String tier, String jobName) {
return """
Map downstreamJobs = [:]
stage ("${jobName}-${tier}-\${region}_${jobName}") {
test
}
""".trim()
}
def simpleLog() {
return """
script {
def user = env.BUILD_USER_ID
}
""".trim()
}
def method1() {
return """
import jenkins.model.Jenkins
currentBuild.displayName = "name"
${simpleLog()}
""".trim()
}
def generateFullDeploymentPipelineCode() {
return """\
Text here
${method1()}
${method2("test1", "test2")}
""".stripIndent()
}
println(generateFullDeploymentPipelineCode())

Answer 2

When you insert a string through interpolation you only indent the first line of it. The following lines of the inserted string will be indented differently, which messes everything up.
Using some lesser-known members of GString (namely .strings[] and .values[]), we can align the indentation of all lines of each interpolated value.
String method2(String tier, String jobName) {
indented """
Map downstreamJobs = [:]
stage ("${jobName}-${tier}-\${region}_${jobName}") {
test
}
"""
}
String simpleLog() {
indented """\
script {
def user = env.BUILD_USER_ID
}
"""
}
String method1() {
indented """\
import jenkins.model.Jenkins
currentBuild.displayName = "name"
${simpleLog()}
"""
}
String generateFullDeploymentPipelineCode() {
indented """\
Text here
${method1()}
${method2("test1", "test2")}
"""
}
println generateFullDeploymentPipelineCode()
//---------- Move the following code into its own script ----------
// Function to adjust the indentation of interpolated values so that all lines
// of a value match the indentation of the first line.
// Finally stripIndent() will be called before returning the string.
String indented( GString templ ) {
// Iterate over the interpolated values of the GString template.
templ.values.eachWithIndex{ value, i ->
// Get the string preceding the current value. Always defined, even
// when the value is at the beginning of the template.
def beforeValue = templ.strings[ i ]
// RegEx to match any indent substring before the value.
// Special case for the first string, which doesn't necessarily contain '\n'.
def regexIndent = i == 0
? /(?:^|\n)([ \t]+)$/
: /\n([ \t]+)$/
def matchIndent = ( beforeValue =~ regexIndent )
if( matchIndent ) {
def indent = matchIndent[ 0 ][ 1 ]
def lines = value.readLines()
def linesNew = [ lines.head() ] // The 1st line is already indented.
// Insert the indentation from the 1st line into all subsequent lines.
linesNew += lines.tail().collect{ indent + it }
// Finally replace the value with the reformatted lines.
templ.values[ i ] = linesNew.join('\n')
}
}
return templ.stripIndent()
}
// Fallback in case the input string is not a GString (when it doesn't contain expressions)
String indented( String templ ) {
return templ.stripIndent()
}
Live Demo at codingground
Output:
Text here
import jenkins.model.Jenkins
currentBuild.displayName = "name"
script {
def user = env.BUILD_USER_ID
}
Map downstreamJobs = [:]
stage ("test2-test1-${region}_test2") {
test
}
Conclusion:
Using the indented function, a clean Groovy syntax for generating code from GString templates has been achieved.
This was quite a learning experience. I first tried to do it completely different using the evaluate function, which turned out to be too complicated and not so flexible. Then I randomly browsed through some posts from mrhaki blog (always a good read!) until I discovered "Groovy Goodness: Get to Know More About a GString". This was the key to implementing this solution.