Deep merge of dictionaries

merge.lib.yaml

#@ load("@ytt:yaml", "yaml")
#@ load("@ytt:overlay", "overlay")
#@ load("@ytt:struct", "struct")

#@ def _doc(map):
--- #@ map
#@ end
---

#@ def _missing_ok(map):
#@overlay/match by=overlay.all
#@overlay/match-child-defaults missing_ok=True
--- #@ map
#@ end
---

#! merges all of "dict_b" into "dict_a" via overlaying
#@ def _deep(dict_a, dict_b):
#@   a_yaml = _doc(dict_a)
#@   b_yaml = _missing_ok(dict_b)
#@   merged_yaml = overlay.apply(a_yaml, b_yaml)[0]
#@   merged_dict = yaml.decode(yaml.encode(merged_yaml))
#@   return merged_dict
#@ end

#@ merge = struct.make(deep=_deep)

template.yaml

#@ load("merge.lib.yaml", "merge")

#@ a = {
#@   "spec": {
#@     "template": {
#@       "spec": {
#@         "name": "maximus"
#@       }
#@     }
#@   }
#@ }
#@ b = {
#@   "spec": {
#@     "replicas": 5,
#@     "template": {
#@       "spec": {
#@         "metadata": {
#@           "annotations": {
#@             "app.kubernetes.io/managed-by": "carvel"
#@           }
#@         }
#@       }
#@     },
#@   }
#@ }

---
desc: "a and b; no merge"
a: #@ a
b: #@ b
---
desc: "b merged into a (via dict.update())"
#@ b_in_a = dict(a)
#@ b_in_a.update(b)
b_in_a: #@ b_in_a
---
desc: "a merged into b (via dict.update())"
#@ a_in_b = dict(b)
#@ a_in_b.update(a)
a_in_b: #@ a_in_b
---
desc: "b merged into a (via merge.deep())"
b_in_a: #@ merge.deep(a, b)
---
desc: "a merged into b (via merge.deep())"
a_in_b: #@ merge.deep(b, a)