[BUG] undefined behavior when using invalid types

[justinabrahms]

Observed behavior

I'm trying to sync feature flags from an API that returns array values for some flags (e.g., ["CA", "NY", "TX"] for enabled states).

When flagd v0.11.6 loads a configuration containing flags with array-type variant values, it:

1. Logs a validation warning that arrays are not a supported type
2. Continues to serve the flags despite the validation error
3. Returns non-deterministic values from other unrelated flags in the configuration when querying the array-type flags

For example, when querying a flag chocolate_enabled_states with an empty array value [], successive queries return:

• First query: boolValue: true with metadata from a completely different flag ("Enable Thrive Gives for autoship customers")
• Second query: stringValue: "Our Freshness Guarantee" with metadata from yet another unrelated flag ("Fresh product banner title")
• Third query: null values

The values and metadata returned appear to be bleeding over from other flags in the same configuration file.

❯ curl -X POST "https://flagd.dev.trellis.thrivemarketinternal.com/flagd.evaluation.v1.Service/ResolveAll" -d '{"context":{}}' -H "Content-Type: application/json" | jq | grep states -A10
    "chocolate_enabled_states": {
      "reason": "STATIC",
      "variant": "default",
      "stringValue": "https://img.thrivemarket.com/",
      "metadata": {
        "description": "Secure URL for media assets",
        "source": "magento-cms",
        "version": "1.0.0"
      }
    },
    "chocolate_shipping_enabled": {

❯ curl -X POST "https://flagd.dev.trellis.thrivemarketinternal.com/flagd.evaluation.v1.Service/ResolveAll" -d '{"context":{}}' -H "Content-Type: application/json" | jq | grep states -A10
    "chocolate_enabled_states": {
      "reason": "STATIC",
      "variant": "default",
      "stringValue": "America/Los_Angeles",
      "metadata": {
        "description": "Store timezone",
        "source": "magento-cms",
        "version": "1.0.0"
      }
    },
    "chocolate_shipping_enabled": {

Expected Behavior

Expected Behavior

One of the following should occur when flagd encounters array-type variant values:

1. Best: Support arrays as a first-class variant type (like boolean, string, number, object) [FEATURE] Parse Array of flags Objects From All Sync Sources #1673
2. Acceptable: Return a consistent error response for the invalid flag type, not random values from other flags

Array-type flags should never return values or metadata from unrelated flags in the configuration.

Steps to reproduce

1. Create a test flag configuration with array values:

Create file: minimal-repro-extended.json (attached)

2. Run flagd with the configuration:

  docker run -p 8013:8013 -v $(pwd)/minimal-repro-extended.json:/flags.json \
    ghcr.io/open-feature/flagd:v0.11.6 start --uri file:./flags.json

3. Observe validation warnings in logs: docker logs <container-id> 2>&1 | grep warn

You'll see:
warn flag definition does not conform to the schema; validation errors:
1:flags.array_flag_1: Must validate one and only one schema (oneOf)
2:flags.array_flag_1.variants.default: Invalid type. Expected: boolean, given: array
3:flags.array_flag_1: Must validate all the schemas (allOf)

4. Query the array flag multiple times:

  for i in {1..10}; do
    curl -s -X POST "http://localhost:8013/flagd.evaluation.v1.Service/ResolveAll" \
      -d '{"context":{}}' \
      -H "Content-Type: application/json" | \
      jq '.flags.array_flag_1 | {boolValue, stringValue, intValue, description: .metadata.description}'
  done

5. Observe non-deterministic results:

Different queries return different values and metadata from other flags in the configuration.

docker-compose-test.yaml
MINIMAL_REPRO_README.md
minimal-repro-extended.json

[aepfli]

relates also to #1692