extensionUriReference ignored when formatting extensions to text

[wackywendell]

Summary

When converting a Substrait plan from JSON to text format, the extensionUriReference field on extension functions (and likely types) is ignored. The formatter always displays URI anchor 0 regardless of the actual reference value, then emits an error about the missing anchor.

Reproduction

Save this as repro.json:

{
  "extensionUris": [
    { "extensionUriAnchor": 1, "uri": "/functions_comparison.yaml" }
  ],
  "extensions": [
    {
      "extensionFunction": {
        "extensionUriReference": 1,
        "functionAnchor": 1,
        "name": "is_not_null:any"
      }
    }
  ],
  "relations": [
    {
      "root": {
        "input": {
          "filter": {
            "common": { "direct": {} },
            "input": {
              "read": {
                "common": { "direct": {} },
                "baseSchema": {
                  "names": ["x"],
                  "struct": {
                    "types": [{ "i64": { "nullability": "NULLABILITY_NULLABLE" } }],
                    "nullability": "NULLABILITY_REQUIRED"
                  }
                },
                "namedTable": { "names": ["my_table"] }
              }
            },
            "condition": {
              "scalarFunction": {
                "functionReference": 1,
                "outputType": { "bool": { "nullability": "NULLABILITY_REQUIRED" } },
                "arguments": [{ "value": { "selection": { "directReference": { "structField": { "field": 0 } }, "rootReference": {} } } }]
              }
            }
          }
        },
        "names": ["x"]
      }
    }
  ],
  "version": { "majorNumber": 0, "minorNumber": 48, "patchNumber": 0 }
}

Then run:

substrait-explain convert -i repro.json -t text

Expected output

=== Extensions
Functions:
  #  1 @  1: is_not_null:any

=== Plan
Root[x]
  Filter[is_not_null($0) => $0]
    Read[my_table => x:i64?]

Actual output

=== Extensions
Functions:
  #  1 @  0: is_not_null:any

=== Plan
Root[x]
  Filter[is_not_null($0) => $0]
    Read[my_table => x:i64?]
Formatting issues:
  Error adding simple extension: Missing URN anchor 0 for extension Function anchor 1 name is_not_null:any

The function is displayed as # 1 @ 0 when it should be # 1 @ 1.

Notes

• JSON→JSON round-trip preserves extensionUriReference: 1 correctly, so protobuf deserialization is fine. The bug is in the text formatting path.
• This also likely affects extensionType and extensionTypeVariation declarations, which have the same extensionUriReference field.