CLI: --output=json list-refs emits one object per retention property instead of per ref #4098

Apache Iceberg version

None

Please describe the bug 🐞

Apache Iceberg version

main (development)

Please describe the bug

JsonOutput.describe_refs() emits one JSON object for each retention property rather than one object per snapshot reference.

As a result, pyiceberg --output=json list-refs <table> can return three objects for a table containing only one snapshot reference.

Reproduction

from pyiceberg.cli.output import JsonOutput
from pyiceberg.table.refs import SnapshotRefType

JsonOutput().describe_refs([
    (
        "main",
        SnapshotRefType.BRANCH,
        {
            "min_snapshots_to_keep": "1",
            "max_snapshot_age_ms": "432000000",
            "max_ref_age_ms": "forever",
        },
    )
])

Actual output

[
  {"name": "main", "type": "branch", "min_snapshots_to_keep": "1"},
  {"name": "main", "type": "branch", "max_snapshot_age_ms": "432000000"},
  {"name": "main", "type": "branch", "max_ref_age_ms": "forever"}
]

Expected output

[
  {
    "name": "main",
    "type": "branch",
    "min_snapshots_to_keep": "1",
    "max_snapshot_age_ms": "432000000",
    "max_ref_age_ms": "forever"
  }
]

Root cause

In pyiceberg/cli/output.py, JsonOutput.describe_refs() uses a nested list comprehension:

[
    {"name": name, "type": type, detail_key: detail_val}
    for name, type, detail in refs
    for detail_key, detail_val in detail.items()
]

The inner loop creates a separate object for every entry in detail.

This is inconsistent with ConsoleOutput.describe_refs(), which renders one row per reference.

Suggested fix

Construct one dictionary per reference and merge the retention properties into it. Add a regression test ensuring that one input reference produces one complete JSON object, ideally also covering multiple references.

I reproduced the incorrect output by executing the current list-comprehension logic in isolation. I have not yet run the full CLI against a catalog.

Willingness to contribute

I'd be happy to submit a focused fix with regression tests if the proposed JSON structure is correct.

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time