hareshkh opened a new pull request, #10670:
URL: https://github.com/apache/arrow-rs/pull/10670
# Which issue does this PR close?
- Related: #9021, #9272 (prior art, both went stale); a step toward #8987
but does not close it.
# Rationale for this change
- The JSON writer has been extensible since #7015 (`EncoderFactory`, plus a
public `make_encoder` to delegate to defaults). The reader has no equivalent.
- Small now because #9272's prefactors already merged (#9266, #9270, #9271):
`DecoderContext` sits on `main` as public-but-inert API.
On exposing the tape, the one substantive objection on #9272:
- `mod tape` stays private - only `Tape`/`TapeElement` are re-exported, so
`TapeDecoder` stays internal and downstream can never construct a `Tape`.
- `TapeElement` is `#[non_exhaustive]`, so the encoding can change. Aimed at
#9329: skipping discarded values won't break downstream matches.
- #3629 is unaffected - it changes tape *production*, which stays private.
# What changes are included in this PR?
- `TapeElement` `#[non_exhaustive]`, documenting numbers as `Number` (JSON
text) or native `i32`/`i64`/`f32`/`f64` (serde path), 64-bit spanning two
elements.
- `ArrayDecoder` public; `pos` holds one tape index per output row.
- New `DecoderFactory`, consulted before the reader's dispatch; `Ok(None)`
accepts the default.
- `DecoderContext::make_decoder` public, so a factory can delegate to the
decoder the reader would otherwise use - without it, overriding a nested type
means reimplementing its children (@scovich's point on #9021).
- `ReaderBuilder::with_decoder_factory`.
# Are these changes tested?
Yes. Unit tests and a doctest decoding `Binary` from a JSON int array - the
inverse of the existing `EncoderFactory` doctest, so the two round-trip, no new
dependency.
# Are there any user-facing changes?
New: `arrow_json::{Tape, TapeElement, ArrayDecoder, DecoderFactory}`,
`DecoderContext::{make_decoder, decoder_factory}`,
`ReaderBuilder::with_decoder_factory`.
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