Cleanup strategies from merged pillars

If a merge strategy (__: something) had been present in a pillar that
didn't need merging at all, it wasn't removed. This resulted in the `__`
key being present in the final pillar.

This change deeply scrubs merging strategy keys from pillar data. Due to
this scrubbing, which essentially rebuilds all nested dicts and lists on
merge, the previous deepcopy isn't needed anymore.

CHANGELOG.md

@@ -8,6 +8,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 ### Added
 - Add require option to tower.get
 - Experimental: Support custom context in template injected `render` function
+- Deep scrubbing of merge strategies (`__`) from merged pillar data
 
 ## [1.5.2] - 2021-02-10
 ### Fixed

salt_tower/pillar/tower.py

@@ -262,7 +262,7 @@ def _compile(
         ctx["pillar"] = self
         ctx["tower"] = self
 
-        def render(path, context=None, renderer='text'):
+        def render(path, context=None, renderer="text"):
             if isinstance(context, dict):
                 context = {**ctx, **context}
             else:
@@ -318,15 +318,27 @@ def get_field(self, key, args, kwargs):
 def _merge(tgt, *objects, strategy="merge-last"):
     for obj in objects:
         if isinstance(tgt, dict):
-            tgt = _merge_dict(tgt, copy.deepcopy(obj), strategy)
+            tgt = _merge_dict(tgt, obj, strategy)
         elif isinstance(tgt, list):
-            tgt = _merge_list(tgt, copy.deepcopy(obj), strategy)
+            tgt = _merge_list(tgt, obj, strategy)
         else:
             raise TypeError(f"Cannot merge {type(tgt)}")
 
     return tgt
 
 
+def _merge_clean(obj):
+    if isinstance(obj, dict):
+        return {k: _merge_clean(v) for k, v in obj.items() if k != "__"}
+
+    if isinstance(obj, list):
+        if obj and isinstance(obj[0], dict) and len(obj[0]) == 1 and "__" in obj[0]:
+            obj = obj[1:]
+        return [_merge_clean(v) for v in obj]
+
+    return obj
+
+
 def _merge_dict(tgt, obj, strategy="merge-last"):
     if not isinstance(obj, dict):
         raise TypeError(f"Cannot merge non-dict type, but is {type(obj)}")
@@ -346,7 +358,7 @@ def _merge_dict(tgt, obj, strategy="merge-last"):
             elif key in tgt and isinstance(tgt[key], list) and isinstance(val, list):
                 _merge_list(tgt[key], val, strategy)
             else:
-                tgt[key] = val
+                tgt[key] = _merge_clean(val)
 
     elif strategy == "merge-first":
         for key, val in obj.items():
@@ -355,11 +367,11 @@ def _merge_dict(tgt, obj, strategy="merge-last"):
             elif key in tgt and isinstance(tgt[key], list) and isinstance(val, list):
                 _merge_list(tgt[key], val, strategy)
             elif key not in tgt:
-                tgt[key] = val
+                tgt[key] = _merge_clean(val)
 
     elif strategy == "overwrite":
         tgt.clear()
-        tgt.update(obj)
+        tgt.update(_merge_clean(obj))
 
     else:
         raise ValueError(f"Unknown strategy: {strategy}")
@@ -380,15 +392,15 @@ def _merge_list(tgt, lst, strategy="merge-last"):
                 tgt.remove(val)
 
     elif strategy == "merge-last":
-        tgt.extend(lst)
+        tgt.extend(_merge_clean(lst))
 
     elif strategy == "merge-first":
-        for val in lst:
+        for val in _merge_clean(lst):
             tgt.insert(0, val)
 
     elif strategy == "overwrite":
         del tgt[:]
-        tgt.extend(lst)
+        tgt.extend(_merge_clean(lst))
 
     else:
         raise ValueError(f"Unknown strategy: {strategy}")

test/pillar/test_tower_tower.py

@@ -124,6 +124,24 @@ def test_merge_list_strategy_merge_overwrite(tower):
     assert tgt == ['c']
 
 
+def test_merge_list_remove_nested_doubledash(tower):
+    tgt = {'a': 0}
+    mod = {'a': [{'__': 'overwrite'}, 'a', 'b']}
+
+    tower.merge(tgt, mod)
+
+    assert tgt == {'a': ['a', 'b']}
+
+
+def test_merge_list_remove_nested_doubledash_list(tower):
+    tgt = [0]
+    mod = [[{'__': 'overwrite'}, 1]]
+
+    tower.merge(tgt, mod)
+
+    assert tgt == [0, [1]]
+
+
 def test_merge_dict_strategy_remove(tower):
     tgt = {'a': 0, 'b': 1}
     mod = {'__': 'remove', 'a': None}
@@ -160,6 +178,15 @@ def test_merge_dict_strategy_merge_overwrite(tower):
     assert tgt == {'c': 2}
 
 
+def test_merge_dict_remove_nested_doubledash(tower):
+    tgt = {'a': 0}
+    mod = {'a': {'__': 'overwrite', 'key': 1}}
+
+    tower.merge(tgt, mod)
+
+    assert tgt == {'a': {'key': 1}}
+
+
 def test_format(tower):
     tower.update({'app': {'name': 'MyApp'}})