wombatu-kun opened a new pull request, #16362:
URL: https://github.com/apache/iceberg/pull/16362
## What
Resolves the long-standing `TODO: translate truncate(col) == value to
startsWith(value)` in `UnboundPredicate.bindLiteralOperation`. When the term of
an `EQ`/`NOT_EQ` predicate is a **string** `truncate[W]` transform, binding now
produces an exactly-equivalent predicate on the untransformed source column.
The equivalence depends on the literal length vs. the truncate width `W`:
| Condition | `truncate[W](col) == v` | `truncate[W](col) != v` |
|---|---|---|
| `len(v) > W` | `alwaysFalse()` | `alwaysTrue()` |
| `len(v) == W` | `col STARTS_WITH v` | `col NOT_STARTS_WITH v` |
| `len(v) < W` | `col == v` | `col != v` |
Integer/long/decimal/binary truncate and all other operators are
intentionally left unchanged — they have no exact source-column equivalence.
## Why
This rewrite is already assumed by the rest of the engine.
`InclusiveMetricsEvaluator.startsWith()` returns `ROWS_MIGHT_MATCH` for
non-identity transform terms with the explicit comment *"truncate must be
rewritten in binding"*. Until now the binder never performed that rewrite for
equality, so `truncate(col) == v` kept an opaque `BoundTransform` term and
metrics/dictionary/partition pruning could not use the column. After this
change such predicates prune correctly (e.g. `equal(truncate("str",3),"xyz")`
against bounds `["abc","abe"]` now skips the file instead of reading it).
## Implementation notes
- The `< / == / > width` decision is centralized in a single
`Truncate.lengthRewrite` helper, shared by predicate binding and by
`TruncateString.project` / `projectStrict`, so the two paths cannot diverge.
- Removing the `BoundTransform` term would otherwise defeat
`ProjectionUtil.projectTransformPredicate` (which matches partition transforms
by `toString()`) and collapse strict projection to `False`. To preserve the
previous precision, `TruncateString` now projects EXACT-length (`len(v) < W`)
`EQ`/`NOT_EQ` predicates directly onto the partition value — provably the same
result the old transform-term path produced, since `truncate[W](x) == v ⟺ x ==
v` when `len(v) < W`.
- New public API is additive only (`Transforms.StringTruncateRewrite` enum +
`Transforms.stringTruncateRewrite`); `revapi` passes with no accepted-breaks
entry.
## Testing
- `TestPredicateBinding`: all three length classes for `EQ`/`NOT_EQ`,
empty-string literal, plus negatives (non-string truncate, non-truncate
transforms, other operators unchanged).
- `TestStartsWith`: runtime-equivalence check via `Evaluator`, including the
EXACT-vs-prefix distinction.
- `TestInclusiveMetricsEvaluatorWithTransforms`: a pruning case that now
prunes where it previously could not.
- Full `:iceberg-api:test` and `:iceberg-core:test`, all
transform/projection/residual regression suites, `spotlessCheck`, and
`:iceberg-api:revapi` pass.
🤖 Generated with [Claude Code](https://claude.com/claude-code)
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