[suxiaogang223]

Purpose

Linked issue: close #1385

Native consumers can currently select root column names through C but cannot pass the structured read types already supported by Rust core. Add a C ReadBuilder entry point for Paimon DataField JSON so callers such as Doris can request nested ROW, ARRAY-element, and MAP-value projections with their field identities intact.

Brief change log

• Add paimon_read_builder_with_read_type_json, copying a JSON array of DataFields into the builder and forwarding it to scan planning and reading.
• Follow core precedence: the last successful name projection or explicit read type wins. NULL resets the selection, [] selects zero columns, and decoding errors preserve the previous selection.
• Reuse core read-type and format semantics; document ownership and the distinction from name-based case sensitivity.
• Exercise actual Parquet write/read and Arrow C interchange for reordered nested projections, null containers/children, empty containers, zero-column row counts, copied inputs, reset/precedence, invalid JSON/UTF-8, and null builder errors.

Tests

• cargo +1.95.0 test --locked -p paimon-c --lib: 99 passed.
• Targeted Clippy passed with -D warnings -A clippy::nonminimal_bool. Strict Clippy encounters the same six pre-existing nonminimal_bool errors reproduced on unmodified main; no source lint suppressions were added.
• cargo +1.95.0 fmt --all -- --check and git diff --check.
• Generated the C header with cbindgen 0.29.4 and checked it with cc -std=c11 -fsyntax-only; the new function is present.

Local Cargo builds used debug info disabled and incremental compilation disabled. The new end-to-end fixture covers Parquet; other formats reuse the existing core read-type path and were not newly benchmarked.

API and Format

Additive C function; existing exported structs and signatures remain unchanged. The input is the existing Paimon DataField JSON representation, not a new storage format. Explicit read types configure the read without mutating the stored table schema.

Documentation

Add a structured-projection example and configuration/ownership rules to the C integration guide.

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