Support dynamic pillar_root environment

Allow users to specify a __env__ pillar_root directory that applies
equally to all environments that are not explicitly specified.

fixes #20581
Signed-off-by: Benjamin Drung <benjamin.drung@profitbricks.com>

doc/topics/pillar/index.rst

@@ -168,6 +168,28 @@ And the actual pillar file at '/srv/pillar/common_pillar.sls':
     context.
 
 
+Dynamic Pillar Environments
+===========================
+
+If environment ``__env__`` is specified in :conf_master:`pillar_roots`, all
+environments that are not explicitly specified in :conf_master:`pillar_roots`
+will map to the directories from ``__env__``. This allows one to use dynamic
+git branch based environments for state/pillar files with the same file-based
+pillar applying to all environments. For example:
+
+.. code-block:: yaml
+
+    pillar_roots:
+      __env__:
+        - /srv/pillar
+
+    ext_pillar:
+      - git:
+        - __env__ https://example.com/git-pillar.git
+
+.. versionadded:: 2017.7.5,2018.3.1
+
+
 Pillar Namespace Flattening
 ===========================
 

salt/pillar/__init__.py

@@ -374,6 +374,15 @@ class Pillar(object):
                 opts['ext_pillar'].append(self.ext)
             else:
                 opts['ext_pillar'] = [self.ext]
+        if '__env__' in opts['file_roots']:
+            env = opts.get('pillarenv') or opts.get('saltenv') or 'base'
+            if env not in opts['file_roots']:
+                log.debug("pillar environment '%s' maps to __env__ pillar_roots directory", env)
+                opts['file_roots'][env] = opts['file_roots'].pop('__env__')
+            else:
+                log.debug("pillar_roots __env__ ignored (environment '%s' found in pillar_roots)",
+                          env)
+                opts['file_roots'].pop('__env__')
         return opts
 
     def _get_envs(self):

tests/unit/test_pillar.py

@@ -49,6 +49,33 @@ class PillarTestCase(TestCase):
             self.assertEqual(pillar.opts['environment'], 'dev')
             self.assertEqual(pillar.opts['pillarenv'], 'dev')
 
+    def test_dynamic_pillarenv(self):
+        opts = {
+            'renderer': 'json',
+            'renderer_blacklist': [],
+            'renderer_whitelist': [],
+            'state_top': '',
+            'pillar_roots': {'__env__': '/srv/pillar/__env__', 'base': '/srv/pillar/base'},
+            'file_roots': {'base': '/srv/salt/base', 'dev': '/svr/salt/dev'},
+            'extension_modules': '',
+        }
+        pillar = salt.pillar.Pillar(opts, {}, 'mocked-minion', 'base', pillarenv='dev')
+        self.assertEqual(pillar.opts['file_roots'],
+                         {'base': '/srv/pillar/base', 'dev': '/srv/pillar/__env__'})
+
+    def test_ignored_dynamic_pillarenv(self):
+        opts = {
+            'renderer': 'json',
+            'renderer_blacklist': [],
+            'renderer_whitelist': [],
+            'state_top': '',
+            'pillar_roots': {'__env__': '/srv/pillar/__env__', 'base': '/srv/pillar/base'},
+            'file_roots': {'base': '/srv/salt/base', 'dev': '/svr/salt/dev'},
+            'extension_modules': '',
+        }
+        pillar = salt.pillar.Pillar(opts, {}, 'mocked-minion', 'base', pillarenv='base')
+        self.assertEqual(pillar.opts['file_roots'], {'base': '/srv/pillar/base'})
+
     def test_malformed_pillar_sls(self):
         with patch('salt.pillar.compile_template') as compile_template:
             opts = {