kyaml: initial support for yaml and resource manipulation

kyaml/yaml/merge3/merge3.go

@@ -0,0 +1,88 @@
+// Copyright 2019 The Kubernetes Authors.
+// SPDX-License-Identifier: Apache-2.0
+
+// Package merge contains libraries for merging fields from one RNode to another
+// RNode
+package merge3
+
+import (
+	"sigs.k8s.io/kustomize/kyaml/yaml"
+	"sigs.k8s.io/kustomize/kyaml/yaml/walk"
+)
+
+const Help = `
+Description:
+
+  merge3 identifies changes between an original source + updated source and merges the result
+  into a destination, overriding the destination fields where they have changed between
+  original and updated.
+
+  ### Resource MergeRules
+
+  - Resources present in the original and deleted from the update are deleted.
+  - Resources missing from the original and added in the update are added.
+  - Resources present only in the dest are kept without changes.
+  - Resources present in both the update and the dest are merged *original + update + dest => dest*.
+
+  ### Field Merge Rules
+
+  Fields are recursively merged using the following rules:
+
+  - scalars
+    - if present in either dest or updated and 'null', clear the value
+    - if unchanged between original and updated, keep dest value
+    - if changed between original and updated (added, deleted, changed), take the updated value
+
+  - non-associative lists -- lists without a merge key
+    - if present in either dest or updated and 'null', clear the value
+    - if unchanged between original and updated, keep dest value
+    - if changed between original and updated (added, deleted, changed), take the updated value
+
+  - map keys and fields -- paired by the map-key / field-name
+    - if present in either dest or updated and 'null', clear the value
+    - if present only in the dest, it keeps its value
+    - if not-present in the dest, add the delta between original-updated as a field
+    - otherwise recursively merge the value between original, updated, dest
+
+  - associative list elements -- paired by the associative key
+    - if present only in the dest, it keeps its value
+    - if not-present in the dest, add the delta between original-updated as a field
+    - otherwise recursively merge the value between original, updated, dest
+
+  ### Associative Keys
+
+  Associative keys are used to identify "same" elements within 2 different lists, and merge them.
+  The following fields are recognized as associative keys:
+
+` + "[`mountPath`, `devicePath`, `ip`, `type`, `topologyKey`, `name`, `containerPort`]" + `
+
+  Any lists where all of the elements contain associative keys will be merged as associative lists.
+`
+
+func Merge(dest, original, update *yaml.RNode) (*yaml.RNode, error) {
+	// if update == nil && original != nil => declarative deletion
+
+	return walk.Walker{Visitor: Visitor{},
+		Sources: []*yaml.RNode{dest, original, update}}.Walk()
+}
+
+func MergeStrings(dest, original, update string) (string, error) {
+	srcOriginal, err := yaml.Parse(original)
+	if err != nil {
+		return "", err
+	}
+	srcUpdated, err := yaml.Parse(update)
+	if err != nil {
+		return "", err
+	}
+	d, err := yaml.Parse(dest)
+	if err != nil {
+		return "", err
+	}
+
+	result, err := Merge(d, srcOriginal, srcUpdated)
+	if err != nil {
+		return "", err
+	}
+	return result.String()
+}