[7.x] Only run xpack siem cypress in PRs when there are siem changes (#60661)

Jenkinsfile

@@ -40,7 +40,12 @@ kibanaPipeline(timeoutMinutes: 135, checkPrChanges: true) {
           'xpack-ciGroup9': kibanaPipeline.xpackCiGroupProcess(9),
           'xpack-ciGroup10': kibanaPipeline.xpackCiGroupProcess(10),
           'xpack-accessibility': kibanaPipeline.functionalTestProcess('xpack-accessibility', './test/scripts/jenkins_xpack_accessibility.sh'),
-          'xpack-siemCypress': kibanaPipeline.functionalTestProcess('xpack-siemCypress', './test/scripts/jenkins_siem_cypress.sh'),
+          'xpack-siemCypress': { processNumber ->
+            whenChanged(['x-pack/legacy/plugins/siem/', 'x-pack/test/siem_cypress/']) {
+              kibanaPipeline.functionalTestProcess('xpack-siemCypress', './test/scripts/jenkins_siem_cypress.sh')(processNumber)
+            }
+          },
+
           // 'xpack-visualRegression': kibanaPipeline.functionalTestProcess('xpack-visualRegression', './test/scripts/jenkins_xpack_visual_regression.sh'),
         ]),
       ])

vars/prChanges.groovy

@@ -1,3 +1,6 @@
+import groovy.transform.Field
+
+public static @Field PR_CHANGES_CACHE = null
 
 def getSkippablePaths() {
   return [
@@ -36,9 +39,13 @@ def areChangesSkippable() {
 }
 
 def getChanges() {
-  withGithubCredentials {
-    return githubPrs.getChanges(env.ghprbPullId)
+  if (!PR_CHANGES_CACHE && env.ghprbPullId) {
+    withGithubCredentials {
+      PR_CHANGES_CACHE = githubPrs.getChanges(env.ghprbPullId)
+    }
   }
+
+  return PR_CHANGES_CACHE
 }
 
 def getChangedFiles() {

vars/whenChanged.groovy

@@ -0,0 +1,57 @@
+/*
+  whenChanged('some/path') { yourCode() } can be used to execute pipeline code in PRs only when changes are detected on paths that you specify.
+  The specified code blocks will also always be executed during the non-PR jobs for tracked branches.
+
+  You have the option of passing in path prefixes, or regexes. Single or multiple.
+  Path specifications are NOT globby, they are only prefixes.
+  Specifying multiple will treat them as ORs.
+
+  Example Usages:
+    whenChanged('a/path/prefix/') { someCode() }
+    whenChanged(startsWith: 'a/path/prefix/') { someCode() } // Same as above
+    whenChanged(['prefix1/', 'prefix2/']) { someCode() }
+    whenChanged(regex: /\.test\.js$/) { someCode() }
+    whenChanged(regex: [/abc/, /xyz/]) { someCode() }
+*/
+
+def call(String startsWithString, Closure closure) {
+  return whenChanged([ startsWith: startsWithString ], closure)
+}
+
+def call(List<String> startsWithStrings, Closure closure) {
+  return whenChanged([ startsWith: startsWithStrings ], closure)
+}
+
+def call(Map params, Closure closure) {
+  if (!githubPr.isPr()) {
+    return closure()
+  }
+
+  def files = prChanges.getChangedFiles()
+  def hasMatch = false
+
+  if (params.regex) {
+    params.regex = [] + params.regex
+    print "Checking PR for changes that match: ${params.regex.join(', ')}"
+    hasMatch = !!files.find { file ->
+      params.regex.find { regex -> file =~ regex }
+    }
+  }
+
+  if (!hasMatch && params.startsWith) {
+    params.startsWith = [] + params.startsWith
+    print "Checking PR for changes that start with: ${params.startsWith.join(', ')}"
+    hasMatch = !!files.find { file ->
+      params.startsWith.find { str -> file.startsWith(str) }
+    }
+  }
+
+  if (hasMatch) {
+    print "Changes found, executing pipeline."
+    closure()
+  } else {
+    print "No changes found, skipping."
+  }
+}
+
+return this