testcase.yaml

#hiera.yaml
---
version: 5
defaults:
    datadir: data
    data_hash: yaml_data

hierarchy:
    - name: test 1
      path: test1.yaml
    - name: test 2
      path: test2.yaml

#test1.yaml
---
classes: 
  - test1bar
  - test1foo
  - test1quuz
  - --test2bar
#test2.yaml
classes:
  - 'test2bar'
  - 'test2foo'
  - 'test2quuz'
  - '--test1bar'





$ puppet lookup --hiera_config $PWD/hiera.yaml classes --merge deep --knock-out-prefix "--" --merge-hash-arrays --explain
Searching for "classes"
  Global Data Provider (hiera configuration version 5)
    Using configuration "/home/oranenj/testcase/hiera.yaml"
    Merge strategy deep
      Options: {
        "sort_merge_arrays" => false,
        "merge_hash_arrays" => true,
        "knockout_prefix" => "--"
      }
      Hierarchy entry "test 1"
        Path "/home/oranenj/testcase/data/test1.yaml"
          Original path: "test1.yaml"
          Found key: "classes" value: [
            "test1bar",
            "test1foo",
            "test1quuz"
                                       <!------------------- No --test2bar?
          ]
      Hierarchy entry "test 2"
        Path "/home/oranenj/testcase/data/test2.yaml"
          Original path: "test2.yaml"
          Found key: "classes" value: [
            "test2bar",
            "test2foo",
            "test2quuz",
            "--test1bar"
          ]
      Merged result: [
        "test2foo",
        "test2quuz",
                                       <!---------------------- No test2bar ???
        "--test1bar",                  <!---------------------- but why is this here?
        "test1bar",
        "test1foo",
        "test1quuz"
      ]