Add head-filter-regex to gerrit_scm

This makes it possible to filter branches with regular expressions
also when using the gerrit_scm.

Change-Id: Ie43674cccf942420d42e1ee4fd194db30b09d19f

jenkins_jobs/modules/project_multibranch.py

@@ -653,6 +653,9 @@ def gerrit_scm(xml_parent, data):
         (default '*')
     :arg str excludes: Comma-separated list of branches to be excluded.
         (default '')
+    :arg str head-filter-regex: A regular expression for filtering
+        discovered source branches. Requires the :jenkins-plugins:`SCM API
+        Plugin <scm-api>`.
     :arg list build-strategies: Provides control over whether to build a branch
         (or branch like things such as change requests and tags) whenever it is
         discovered initially or a change from the previous revision has been
@@ -786,6 +789,10 @@ def gerrit_scm(xml_parent, data):
     if data.get("build-strategies", None):
         build_strategies(xml_parent, data)
 
+    if data.get("head-filter-regex", None):
+        rshf = XML.SubElement(traits, "jenkins.scm.impl.trait.RegexSCMHeadFilterTrait")
+        XML.SubElement(rshf, "regex").text = data.get("head-filter-regex")
+
     # FilterChecks Trait
     checks = data.get("filter-checks", None)
     if checks:

tests/multibranch/fixtures/scm_gerrit_full.xml

@@ -47,6 +47,9 @@
                 </jenkins.plugins.git.traits.RefSpecsSCMSourceTrait_-RefSpecTemplate>
               </templates>
             </jenkins.plugins.git.traits.RefSpecsSCMSourceTrait>
+            <jenkins.scm.impl.trait.RegexSCMHeadFilterTrait>
+              <regex>(.*/master|.*/release/.*)</regex>
+            </jenkins.scm.impl.trait.RegexSCMHeadFilterTrait>
             <jenkins.plugins.gerrit.traits.FilterChecksTrait>
               <queryOperator>SCHEME</queryOperator>
               <queryString>jenkins</queryString>

tests/multibranch/fixtures/scm_gerrit_full.yaml

@@ -46,6 +46,7 @@ scm:
                 - exact-name: {}
                 - regex-name: {}
                 - wildcards-name: {}
+        head-filter-regex: "(.*/master|.*/release/.*)"
         clean:
             after: true
             before: true