fix(dbless): nest duplicate entity primary key errors for children

[flrgh]

summary

This makes a change to the shape/structure of dbless errors. Before this change, an upstream with duplicate targets would yield a response like this:

{
  "code": 14,
  "fields": {
    "targets": [
      null,
      "uniqueness violation: 'targets' entity with primary key set to '48322e4a-b3b0-591b-8ed6-fd95a6d75019' already declared"
    ]
  },
  "message": "declarative config is invalid: {targets={[2]=\"uniqueness violation: 'targets' entity with primary key set to '48322e4a-b3b0-591b-8ed6-fd95a6d75019' already declared\"}}",
  "name": "invalid declarative configuration"
}

This is bad because the error-flattening code cannot associate this error with the input. The linkage between the upstream->target from the input has been lost.

After this change, the errors are nested under the parent upstream:

{
  "code": 14,
  "fields": {
    "upstreams": [
      null,
      {
        "targets": [
          null,
          "uniqueness violation: 'targets' entity with primary key set to '48322e4a-b3b0-591b-8ed6-fd95a6d75019' already declared"
        ]
      }
    ]
  },
  "message": "declarative config is invalid: {upstreams={[2]={targets={[2]=\"uniqueness violation: 'targets' entity with primary key set to '48322e4a-b3b0-591b-8ed6-fd95a6d75019' already declared\"}}}}",
  "name": "invalid declarative configuration"
}

As a result, the error can now be properly mapped to the input target ($input.upstreams[2].targets[2]), so POST /config?flatten_errors=1 returns a helpful result, including the [generated] target ID and the upstream ID:

{
  "code": 14,
  "fields": {},
  "flattened_errors": [
    {
      "entity": {
        "id": "48322e4a-b3b0-591b-8ed6-fd95a6d75019",
        "tags": [
          "target-2"
        ],
        "target": "10.244.0.12:80",
        "upstream": {
          "id": "f9792964-6797-482c-bfdf-08220a4f6839"
        },
        "weight": 1
      },
      "entity_id": "48322e4a-b3b0-591b-8ed6-fd95a6d75019",
      "entity_tags": [
        "target-2"
      ],
      "entity_type": "target",
      "errors": [
        {
          "message": "uniqueness violation: 'targets' entity with primary key set to '48322e4a-b3b0-591b-8ed6-fd95a6d75019' already declared",
          "type": "entity"
        }
      ]
    }
  ],
  "message": "declarative config is invalid: {}",
  "name": "invalid declarative configuration"
}

Checklist

• The Pull Request has tests
• A changelog file has been created under changelog/unreleased/kong

Issue reference

KAG-4144

[flrgh]

This fixes some buggy behavior negatively impacting Konnect/KIC, so although unplanned I think we should prioritize merging it for 3.7.

[team-gateway-bot]

Successfully created cherry-pick PR for master:

• https://github.com/kong/kong-ee/pull/8891