diff --git a/.zuul.yaml b/.zuul.yaml
index 041681a..a87c196 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -36,6 +36,8 @@
             irrelevant-files:
               - zuul/cmd/migrate.py
               - playbooks/zuul-migrate/.*
+            vars:
+              sphinx_python: python3
         - tox-cover:
             irrelevant-files:
               - zuul/cmd/migrate.py
@@ -53,6 +55,8 @@
             irrelevant-files:
               - zuul/cmd/migrate.py
               - playbooks/zuul-migrate/.*
+            vars:
+              sphinx_python: python3
         - tox-pep8
         - tox-py35:
             irrelevant-files:
@@ -61,5 +65,7 @@
         - zuul-stream-functional
     post:
       jobs:
-        - publish-openstack-sphinx-docs-infra
+        - publish-openstack-sphinx-docs-infra:
+            vars:
+              sphinx_python: python3
         - publish-openstack-python-branch-tarball
diff --git a/doc/source/user/config.rst b/doc/source/user/config.rst
index 173e615..916e66a 100644
--- a/doc/source/user/config.rst
+++ b/doc/source/user/config.rst
@@ -1097,6 +1097,14 @@
          changes which break the others.  This is a free-form string;
          just set the same value for each group of projects.
 
+      .. attr:: debug
+
+         If this is set to `true`, Zuul will include debugging
+         information in reports it makes about items in the pipeline.
+         This should not normally be set, but in situations were it is
+         difficult to determine why Zuul did or did not run a certain
+         job, the additional information this provides may help.
+
 .. _project-template:
 
 Project Template
@@ -1318,7 +1326,7 @@
 
 .. attr:: pragma
 
-   The pragma item currently only supports one attribute:
+   The pragma item currently supports the following attributes:
 
    .. attr:: implied-branch-matchers
 
@@ -1333,3 +1341,43 @@
 
       Note that if a job contains an explicit branch matcher, it will
       be used regardless of the value supplied here.
+
+   .. attr:: implied-branches
+
+      This is a list of regular expressions, just as
+      :attr:`job.branches`, which may be used to supply the value of
+      the implied branch matcher for all jobs in a file.
+
+      This may be useful if two projects share jobs but have
+      dissimilar branch names.  If, for example, two projects have
+      stable maintenance branches with dissimilar names, but both
+      should use the same job variants, this directive may be used to
+      indicate that all of the jobs defined in the stable branch of
+      the first project may also be used for the stable branch of the
+      other.  For example:
+
+      .. code-block:: yaml
+
+         - pragma:
+             implied-branches:
+               - stable/foo
+               - stable/bar
+
+      The above code, when added to the ``stable/foo`` branch of a
+      project would indicate that the job variants described in that
+      file should not only be used for changes to ``stable/foo``, but
+      also on changes to ``stable/bar``, which may be in another
+      project.
+
+      Note that if a job contains an explicit branch matcher, it will
+      be used regardless of the value supplied here.
+
+      Note also that the presence of `implied-branches` does not
+      automatically set `implied-branch-matchers`.  Zuul will still
+      decide if implied branch matchers are warranted at all, using
+      the heuristics described in :attr:`job.branches`, and only use
+      the value supplied here if that is the case.  If you want to
+      declare specific implied branches on, for example, a
+      :term:`config-project` project (which normally would not use
+      implied branches), you must set `implied-branch-matchers` as
+      well.
diff --git a/tests/fixtures/config/pragma-multibranch/git/common-config/zuul.yaml b/tests/fixtures/config/pragma-multibranch/git/common-config/zuul.yaml
new file mode 100644
index 0000000..dc83f9d
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/common-config/zuul.yaml
@@ -0,0 +1,61 @@
+- pipeline:
+    name: check
+    manager: independent
+    trigger:
+      gerrit:
+        - event: patchset-created
+    success:
+      gerrit:
+        Verified: 1
+    failure:
+      gerrit:
+        Verified: -1
+
+- pipeline:
+    name: gate
+    manager: dependent
+    post-review: True
+    trigger:
+      gerrit:
+        - event: comment-added
+          approval:
+            - Approved: 1
+    success:
+      gerrit:
+        Verified: 2
+        submit: true
+    failure:
+      gerrit:
+        Verified: -2
+    start:
+      gerrit:
+        Verified: 0
+    precedence: high
+
+- job:
+    name: base
+    parent: null
+
+- project:
+    name: common-config
+    check:
+      jobs: []
+    gate:
+      jobs:
+        - noop
+
+- project:
+    name: org/project1
+    check:
+      jobs: []
+    gate:
+      jobs:
+        - noop
+
+- project:
+    name: org/project2
+    check:
+      jobs: []
+    gate:
+      jobs:
+        - noop
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project1/README b/tests/fixtures/config/pragma-multibranch/git/org_project1/README
new file mode 100644
index 0000000..9daeafb
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project1/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job1.yaml b/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job1.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job1.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job2.yaml b/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job2.yaml
new file mode 100644
index 0000000..f679dce
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project1/playbooks/test-job2.yaml
@@ -0,0 +1,2 @@
+- hosts: all
+  tasks: []
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project1/zuul.yaml b/tests/fixtures/config/pragma-multibranch/git/org_project1/zuul.yaml
new file mode 100644
index 0000000..6c8352a
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project1/zuul.yaml
@@ -0,0 +1,13 @@
+- job:
+    name: test-job1
+    run: playbooks/test-job1.yaml
+
+- job:
+    name: test-job2
+    run: playbooks/test-job2.yaml
+
+- project-template:
+    name: test-template
+    check:
+      jobs:
+        - test-job1
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project2/README b/tests/fixtures/config/pragma-multibranch/git/org_project2/README
new file mode 100644
index 0000000..9daeafb
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project2/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/pragma-multibranch/git/org_project2/zuul.yaml b/tests/fixtures/config/pragma-multibranch/git/org_project2/zuul.yaml
new file mode 100644
index 0000000..748cab2
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/git/org_project2/zuul.yaml
@@ -0,0 +1,7 @@
+- project:
+    name: org/project2
+    templates:
+      - test-template
+    check:
+      jobs:
+        - test-job2
diff --git a/tests/fixtures/config/pragma-multibranch/main.yaml b/tests/fixtures/config/pragma-multibranch/main.yaml
new file mode 100644
index 0000000..950b117
--- /dev/null
+++ b/tests/fixtures/config/pragma-multibranch/main.yaml
@@ -0,0 +1,9 @@
+- tenant:
+    name: tenant-one
+    source:
+      gerrit:
+        config-projects:
+          - common-config
+        untrusted-projects:
+          - org/project1
+          - org/project2
diff --git a/tests/unit/test_v3.py b/tests/unit/test_v3.py
index 1f401d0..44aa966 100755
--- a/tests/unit/test_v3.py
+++ b/tests/unit/test_v3.py
@@ -1552,6 +1552,32 @@
                       C.messages[0],
                       "C should have an error reported")
 
+    def test_pipeline_debug(self):
+        in_repo_conf = textwrap.dedent(
+            """
+            - job:
+                name: project-test1
+                run: playbooks/project-test1.yaml
+            - project:
+                name: org/project
+                check:
+                  debug: True
+                  jobs:
+                    - project-test1
+            """)
+
+        file_dict = {'.zuul.yaml': in_repo_conf}
+        A = self.fake_gerrit.addFakeChange('org/project', 'master', 'A',
+                                           files=file_dict)
+        self.fake_gerrit.addEvent(A.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+
+        self.assertEqual(A.data['status'], 'NEW')
+        self.assertEqual(A.reported, 1,
+                         "A should report success")
+        self.assertIn('Debug information:',
+                      A.messages[0], "A should have debug info")
+
 
 class TestInRepoJoin(ZuulTestCase):
     # In this config, org/project is not a member of any pipelines, so
@@ -2232,6 +2258,115 @@
             self.assertIsNone(job.branch_matcher)
 
 
+class TestPragmaMultibranch(ZuulTestCase):
+    tenant_config_file = 'config/pragma-multibranch/main.yaml'
+
+    def test_no_branch_matchers(self):
+        self.create_branch('org/project1', 'stable/pike')
+        self.create_branch('org/project2', 'stable/jewel')
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project1', 'stable/pike'))
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project2', 'stable/jewel'))
+        self.waitUntilSettled()
+        # We want the jobs defined on the stable/pike branch of
+        # project1 to apply to the stable/jewel branch of project2.
+
+        # First, without the pragma line, the jobs should not run
+        # because in project1 they have branch matchers for pike, so
+        # they will not match a jewel change.
+        B = self.fake_gerrit.addFakeChange('org/project2', 'stable/jewel', 'B')
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertHistory([])
+
+        # Add a pragma line to disable implied branch matchers in
+        # project1, so that the jobs and templates apply to both
+        # branches.
+        with open(os.path.join(FIXTURE_DIR,
+                               'config/pragma-multibranch/git/',
+                               'org_project1/zuul.yaml')) as f:
+            config = f.read()
+        extra_conf = textwrap.dedent(
+            """
+            - pragma:
+                implied-branch-matchers: False
+            """)
+        config = extra_conf + config
+        file_dict = {'zuul.yaml': config}
+        A = self.fake_gerrit.addFakeChange('org/project1', 'stable/pike', 'A',
+                                           files=file_dict)
+        A.addApproval('Code-Review', 2)
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+        self.fake_gerrit.addEvent(A.getChangeMergedEvent())
+        self.waitUntilSettled()
+
+        # Now verify that when we propose a change to jewel, we get
+        # the pike/jewel jobs.
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertHistory([
+            dict(name='test-job1', result='SUCCESS', changes='1,1'),
+            dict(name='test-job2', result='SUCCESS', changes='1,1'),
+        ], ordered=False)
+
+    def test_supplied_branch_matchers(self):
+        self.create_branch('org/project1', 'stable/pike')
+        self.create_branch('org/project2', 'stable/jewel')
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project1', 'stable/pike'))
+        self.fake_gerrit.addEvent(
+            self.fake_gerrit.getFakeBranchCreatedEvent(
+                'org/project2', 'stable/jewel'))
+        self.waitUntilSettled()
+        # We want the jobs defined on the stable/pike branch of
+        # project1 to apply to the stable/jewel branch of project2.
+
+        # First, without the pragma line, the jobs should not run
+        # because in project1 they have branch matchers for pike, so
+        # they will not match a jewel change.
+        B = self.fake_gerrit.addFakeChange('org/project2', 'stable/jewel', 'B')
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertHistory([])
+
+        # Add a pragma line to disable implied branch matchers in
+        # project1, so that the jobs and templates apply to both
+        # branches.
+        with open(os.path.join(FIXTURE_DIR,
+                               'config/pragma-multibranch/git/',
+                               'org_project1/zuul.yaml')) as f:
+            config = f.read()
+        extra_conf = textwrap.dedent(
+            """
+            - pragma:
+                implied-branches:
+                  - stable/pike
+                  - stable/jewel
+            """)
+        config = extra_conf + config
+        file_dict = {'zuul.yaml': config}
+        A = self.fake_gerrit.addFakeChange('org/project1', 'stable/pike', 'A',
+                                           files=file_dict)
+        A.addApproval('Code-Review', 2)
+        self.fake_gerrit.addEvent(A.addApproval('Approved', 1))
+        self.waitUntilSettled()
+        self.fake_gerrit.addEvent(A.getChangeMergedEvent())
+        self.waitUntilSettled()
+        # Now verify that when we propose a change to jewel, we get
+        # the pike/jewel jobs.
+        self.fake_gerrit.addEvent(B.getPatchsetCreatedEvent(1))
+        self.waitUntilSettled()
+        self.assertHistory([
+            dict(name='test-job1', result='SUCCESS', changes='1,1'),
+            dict(name='test-job2', result='SUCCESS', changes='1,1'),
+        ], ordered=False)
+
+
 class TestBaseJobs(ZuulTestCase):
     tenant_config_file = 'config/base-jobs/main.yaml'
 
diff --git a/zuul/configloader.py b/zuul/configloader.py
index 227e352..71c4ccc 100644
--- a/zuul/configloader.py
+++ b/zuul/configloader.py
@@ -358,6 +358,7 @@
 class PragmaParser(object):
     pragma = {
         'implied-branch-matchers': bool,
+        'implied-branches': to_list(str),
         '_source_context': model.SourceContext,
         '_start_mark': ZuulMark,
     }
@@ -372,11 +373,14 @@
             self.schema(conf)
 
         bm = conf.get('implied-branch-matchers')
-        if bm is None:
-            return
 
         source_context = conf['_source_context']
-        source_context.implied_branch_matchers = bm
+        if bm is not None:
+            source_context.implied_branch_matchers = bm
+
+        branches = conf.get('implied-branches')
+        if branches is not None:
+            source_context.implied_branches = as_list(branches)
 
 
 class NodeSetParser(object):
@@ -528,6 +532,8 @@
         # If the user has set a pragma directive for this, use the
         # value (if unset, the value is None).
         if job.source_context.implied_branch_matchers is True:
+            if job.source_context.implied_branches is not None:
+                return job.source_context.implied_branches
             return [job.source_context.branch]
         elif job.source_context.implied_branch_matchers is False:
             return None
@@ -543,6 +549,8 @@
         if len(branches) == 1:
             return None
 
+        if job.source_context.implied_branches is not None:
+            return job.source_context.implied_branches
         return [job.source_context.branch]
 
     @staticmethod
@@ -781,7 +789,11 @@
 
         job = {str: vs.Any(str, JobParser.job_attributes)}
         job_list = [vs.Any(str, job)]
-        pipeline_contents = {'queue': str, 'jobs': job_list}
+        pipeline_contents = {
+            'queue': str,
+            'debug': bool,
+            'jobs': job_list,
+        }
 
         for p in self.layout.pipelines.values():
             project_template[p.name] = pipeline_contents
@@ -801,6 +813,7 @@
             project_pipeline = model.ProjectPipelineConfig()
             project_template.pipelines[pipeline.name] = project_pipeline
             project_pipeline.queue_name = conf_pipeline.get('queue')
+            project_pipeline.debug = conf_pipeline.get('debug')
             self.parseJobList(
                 conf_pipeline.get('jobs', []),
                 source_context, start_mark, project_pipeline.job_list)
@@ -851,7 +864,11 @@
 
         job = {str: vs.Any(str, JobParser.job_attributes)}
         job_list = [vs.Any(str, job)]
-        pipeline_contents = {'queue': str, 'jobs': job_list}
+        pipeline_contents = {
+            'queue': str,
+            'debug': bool,
+            'jobs': job_list
+        }
 
         for p in self.layout.pipelines.values():
             project[p.name] = pipeline_contents
@@ -912,6 +929,7 @@
         for pipeline in self.layout.pipelines.values():
             project_pipeline = model.ProjectPipelineConfig()
             queue_name = None
+            debug = False
             # For every template, iterate over the job tree and replace or
             # create the jobs in the final definition as needed.
             pipeline_defined = False
@@ -924,8 +942,12 @@
                         implied_branch)
                     if template_pipeline.queue_name:
                         queue_name = template_pipeline.queue_name
+                    if template_pipeline.debug is not None:
+                        debug = template_pipeline.debug
             if queue_name:
                 project_pipeline.queue_name = queue_name
+            if debug:
+                project_pipeline.debug = True
             if pipeline_defined:
                 project_config.pipelines[pipeline.name] = project_pipeline
         return project_config
diff --git a/zuul/model.py b/zuul/model.py
index e53a357..77770b7 100644
--- a/zuul/model.py
+++ b/zuul/model.py
@@ -641,6 +641,7 @@
         self.path = path
         self.trusted = trusted
         self.implied_branch_matchers = None
+        self.implied_branches = None
 
     def __str__(self):
         return '%s/%s@%s' % (self.project, self.path, self.branch)
@@ -1336,6 +1337,7 @@
         self.unable_to_merge = False
         self.config_error = None  # None or an error message string.
         self.failing_reasons = []
+        self.debug_messages = []
         self.merge_state = self.NEW
         self.nodesets = {}  # job -> nodeset
         self.node_requests = {}  # job -> reqs
@@ -1500,6 +1502,17 @@
     def setReportedResult(self, result):
         self.current_build_set.result = result
 
+    def debug(self, msg, indent=0):
+        ppc = self.layout.getProjectPipelineConfig(self.change.project,
+                                                   self.pipeline)
+        if not ppc.debug:
+            return
+        if indent:
+            indent = '  ' * indent
+        else:
+            indent = ''
+        self.current_build_set.debug_messages.append(indent + msg)
+
     def freezeJobGraph(self):
         """Find or create actual matching jobs for this item's change and
         store the resulting job tree."""
@@ -2219,6 +2232,7 @@
     def __init__(self):
         self.job_list = JobList()
         self.queue_name = None
+        self.debug = False
         self.merge_mode = None
 
 
@@ -2544,7 +2558,8 @@
     def addProjectConfig(self, project_config):
         self.project_configs[project_config.name] = project_config
 
-    def collectJobs(self, jobname, change, path=None, jobs=None, stack=None):
+    def collectJobs(self, item, jobname, change, path=None, jobs=None,
+                    stack=None):
         if stack is None:
             stack = []
         if jobs is None:
@@ -2553,13 +2568,20 @@
             path = []
         path.append(jobname)
         matched = False
+        indent = len(path) + 1
+        item.debug("Collecting job variants for {jobname}".format(
+            jobname=jobname), indent=indent)
         for variant in self.getJobs(jobname):
             if not variant.changeMatches(change):
                 self.log.debug("Variant %s did not match %s", repr(variant),
                                change)
+                item.debug("Variant {variant} did not match".format(
+                    variant=repr(variant)), indent=indent)
                 continue
             else:
                 self.log.debug("Variant %s matched %s", repr(variant), change)
+                item.debug("Variant {variant} matched".format(
+                    variant=repr(variant)), indent=indent)
             if not variant.isBase():
                 parent = variant.parent
                 if not jobs and parent is None:
@@ -2569,30 +2591,38 @@
             if parent and parent not in path:
                 if parent in stack:
                     raise Exception("Dependency cycle in jobs: %s" % stack)
-                self.collectJobs(parent, change, path, jobs, stack + [jobname])
+                self.collectJobs(item, parent, change, path, jobs,
+                                 stack + [jobname])
             matched = True
             jobs.append(variant)
         if not matched:
+            self.log.debug("No matching parents for job %s and change %s",
+                           jobname, change)
+            item.debug("No matching parent for {jobname}".format(
+                jobname=repr(jobname)), indent=indent)
             raise NoMatchingParentError()
         return jobs
 
     def _createJobGraph(self, item, job_list, job_graph):
         change = item.change
         pipeline = item.pipeline
+        item.debug("Freezing job graph")
         for jobname in job_list.jobs:
             # This is the final job we are constructing
             frozen_job = None
             self.log.debug("Collecting jobs %s for %s", jobname, change)
+            item.debug("Freezing job {jobname}".format(
+                jobname=jobname), indent=1)
             try:
-                variants = self.collectJobs(jobname, change)
+                variants = self.collectJobs(item, jobname, change)
             except NoMatchingParentError:
-                self.log.debug("No matching parents for job %s and change %s",
-                               jobname, change)
                 variants = None
             if not variants:
                 # A change must match at least one defined job variant
                 # (that is to say that it must match more than just
                 # the job that is defined in the tree).
+                item.debug("No matching variants for {jobname}".format(
+                    jobname=jobname), indent=2)
                 continue
             for variant in variants:
                 if frozen_job is None:
@@ -2611,12 +2641,18 @@
                     matched = True
                     self.log.debug("Pipeline variant %s matched %s",
                                    repr(variant), change)
+                    item.debug("Pipeline variant {variant} matched".format(
+                        variant=repr(variant)), indent=2)
             else:
                 self.log.debug("Pipeline variant %s did not match %s",
                                repr(variant), change)
+                item.debug("Pipeline variant {variant} did not match".format(
+                    variant=repr(variant)), indent=2)
             if not matched:
                 # A change must match at least one project pipeline
                 # job variant.
+                item.debug("No matching pipeline variants for {jobname}".
+                           format(jobname=jobname), indent=2)
                 continue
             if (frozen_job.allowed_projects and
                 change.project.name not in frozen_job.allowed_projects):
diff --git a/zuul/reporter/__init__.py b/zuul/reporter/__init__.py
index 49181a7..ecf8855 100644
--- a/zuul/reporter/__init__.py
+++ b/zuul/reporter/__init__.py
@@ -64,6 +64,10 @@
         a reporter taking free-form text."""
         ret = self._getFormatter()(item, with_jobs)
 
+        if item.current_build_set.debug_messages:
+            debug = '\n  '.join(item.current_build_set.debug_messages)
+            ret += '\nDebug information:\n  ' + debug + '\n'
+
         if item.pipeline.footer_message:
             ret += '\n' + item.pipeline.footer_message