adriangb opened a new pull request, #2458:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2458
## Motivation
`supports_lambda_functions()` gates two different spellings of the same
feature:
- the arrow form, `x -> x + 1`
- the `LAMBDA` keyword form, `LAMBDA x : x + 1`
Because they share one flag, a dialect cannot have one without the other.
That
shuts out any dialect that already gives `->` a meaning. PostgreSQL is the
obvious case: `->` is JSON member access, so turning the flag on silently
reinterprets existing expressions rather than adding a capability.
Concretely, with the flag enabled, `a -> 'b'` no longer parses as a binary
operator. It parses as a lambda with parameter `a` and body `'b'`, because
`parse_prefix` treats any unreserved word followed by `->` as a lambda
parameter. Note `->>` is unaffected, so the breakage is partial and easy to
miss.
The `LAMBDA` keyword form has no such conflict: it does not claim `->`.
## Change
Adds `Dialect::supports_lambda_keyword_syntax()`, which gates only the
`LAMBDA`
keyword form, and defaults to `supports_lambda_functions()`.
No existing dialect changes behavior. Dialects that support the arrow form
keep
both spellings; dialects that support neither still get neither. A dialect
that
uses `->` for something else can now override just the new method to get
lambdas
without disturbing its operator.
No dialect shipped here opts in; this only makes the capability reachable.
## Tests
Two tests in `tests/sqlparser_custom_dialect.rs`:
- a dialect enabling only `supports_lambda_keyword_syntax` parses
`lambda x : x + 1` while `->` stays a `BinaryOperator::Arrow`
- a dialect enabling only `supports_lambda_functions` still accepts both
spellings, pinning the defaulting behavior
Full suite, `cargo fmt --check`, and `cargo clippy --all-targets
--all-features`
all pass.
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