[suxiaogang223]

Purpose

Linked issue: close #1384

Legacy Java schema JSON can omit version. Rust currently rejects it, and accepting the JSON alone would still select the wrong bucket/file-format defaults for older schemas. Interpret stored schemas using the Java 2.1.0 version boundaries in the shared deserializer, covering filesystem history and catalog-free C construction.

Brief change log

• Default an absent version to Paimon 0.7 (1), an absent legacy bucket to 1 for version <= 1, and an absent file format to ORC for version <= 2. Explicit options remain authoritative.
• Match Java's missing creation-time default and retain errors for malformed explicit versions.
• Cover version boundaries, round trips, explicit options, historical SchemaManager loading/cache, and C table construction.

Tests

• Confirmed the new legacy tests fail before the fix with a missing-version error.
• cargo +1.95.0 test --locked -p paimon --lib: 4,864 passed, 6 ignored.
• cargo +1.95.0 test --locked -p paimon-c --lib: 98 passed.
• cargo +1.95.0 fmt --all -- --check and git diff --check: passed.
• Targeted Clippy passed with -D warnings -A clippy::nonminimal_bool. The unmodified expressions in vector-read/merge modules trigger six nonminimal_bool errors under strict Rust 1.95 Clippy; no lint suppressions were added to source.

Local Cargo builds used debug info disabled and incremental compilation disabled. No new Java runtime fixture was executed; compatibility rules were checked against Java 2.1.0 SchemaSerializer.

API and Format

No public signatures or schema version numbers change. Legacy JSON receives version-dependent defaults during deserialization; current-version schemas and serialization retain their existing shape.

Documentation

The compatibility rule is documented beside the deserializer and in regression cases. No new configuration is needed.

AI assistance: Codex helped develop the implementation, tests, and this description.