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2010YOUY01 merged 4 commits into from
Sep 22, 2026
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docs: Document the convention for internal public APIs #25495

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docs: Document the convention for internal public APIs
2010YOUY01 Sep 19, 2026
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fix doc test
2010YOUY01 Sep 19, 2026
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update submodule
2010YOUY01 Sep 21, 2026
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review: improve explanation
2010YOUY01 Sep 22, 2026
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8 changes: 5 additions & 3 deletions datafusion/physical-plan/src/joins/hash_join/partitioned_hash_eval.rs
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Expand Up @@ -293,9 +293,11 @@ impl HashTableLookupExpr {
/// * `random_state` - SeededRandomState for hashing
/// * `map` - Map to check membership (hash table or array map)
/// * `description` - Description for debugging
/// # Note
/// This is public for internal testing purposes only and is not
/// guaranteed to be stable across versions.
///
/// # Public Only for Internal Use:
/// `datafusion-proto` tests require this constructor, but it is not part of
/// the supported public API.
#[doc(hidden)]
pub fn new(
on_columns: Vec<PhysicalExprRef>,
random_state: SeededRandomState,
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29 changes: 29 additions & 0 deletions docs/source/contributor-guide/api-health.md
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Expand Up @@ -43,6 +43,35 @@ Examples of non-breaking changes include:
- Marking a function as deprecated (`#[deprecated]`)
- Adding a new function to a `trait` with a default implementation

### DataFusion-internal Public APIs

Some internal implementation details require `pub` visibility because they are
shared across DataFusion crates. These APIs are not intended as downstream
extension points. They are hidden from generated documentation and are not part
of DataFusion's supported public API, so they may be changed or removed without
notice or a deprecation period. Examples include:

1. Test helpers.

@alamb alamb Sep 21, 2026

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I think in general multiple types of APIs just makes DataFUsion more complicated and I would like to suggest we minimize the number of such APIs as much as possible

For example, for test helpers, we could potentially use a feature (test_helpers for example) to mark that they are not part of the public API rather than marking them as a doc

2. Operator APIs required by the optimizer to inspect or rewrite execution plans

@rluvaton rluvaton Sep 22, 2026 •
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Nit: Please add another example - benchmarks, which was the original reason why GroupColumn was exposed and now people use it which complicate changing its api

across crate boundaries.

For APIs intended only for internal use, add `#[doc(hidden)]` and a doc comment
section headed `# Public Only for Internal Use:`. Name the crate or component
that requires access and explain why the API is not intended for downstream use.
For example:

```txt
impl HashTableLookupExpr {
/// ...
///
/// # Public Only for Internal Use:
/// `datafusion-proto` tests require this constructor, but it is not part of
/// the supported public API.
#[doc(hidden)]
pub fn new(...) {...}
}
```

### What is the public SQL API and what is a breaking SQL change?

DataFusion is also used as a SQL engine, so changes to SQL semantics (the
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