apache/iceberg-go

The iceberg CLI picks its Output from --output with a switch over text and json; the default arm calls log.Fatal("unimplemented output type"). That aborts with a bare message and bypasses the graceful, --output-aware error handling the rest of main uses for bad input. Replace the log.Fatal with a clear error that names the unsupported value and lists the supported output types (text, json), then exit non-zero the same way the surrounding pre-catalog validation does (the subcommand checks and the DynamoDB "not implemented" path just below it). Tests: if there is a testable seam around arg handling, assert that an unrecognized --output surfaces the supported-types error instead of aborting.

Parent: #830 After PR #934, snapshotProducer.commit() appends a validate closure to txn.validators for every producer, including fastAppendFiles and mergeAppendFiles whose validate() is a deliberate no-op. Long transactions (multi-step Append + Overwrite chains) accumulate O(N) no-op closures, all of which run at final doCommit. Cheap per call, but wasteful and noisy in profiles. Add a small interface method to producerImpl, something like needsValidation() bool. Default to true; have fastAppendFiles and mergeAppendFiles return false. Skip the validator registration in snapshotProducer.commit() when needsValidation() is false. The no-op validate methods can stay as belt-and-suspenders or be removed once the registration is gated. Lock the behavior with a small unit test that asserts a fast-append commit leaves txn.validators empty. Flagged as a smell in #928's round-1 review and deferred — landing it now makes the validator slice trustworthy as a registration surface.