Sean-Kenneth-Doherty opened a new pull request, #22286:
URL: https://github.com/apache/datafusion/pull/22286
## Which issue does this PR close?
- Closes #22257.
## Rationale for this change
PostgreSQL treats an empty regular expression in `regexp_instr` as a
zero-width match. DataFusion previously special-cased empty patterns to return
`0`, so `regexp_instr('abc', '')` diverged from PostgreSQL.
## What changes are included in this PR?
- Handles empty `regexp_instr` patterns as zero-width matches at `start + N
- 1`, returning `0` when that position is past the end of the string.
- Keeps existing regex/flag validation for empty patterns.
- Lets start/N validation run before empty-string handling.
- Adds Rust unit coverage and sqllogictest coverage for empty-pattern
behavior.
## Are these changes tested?
- `cargo fmt --all`
- `cargo test -p datafusion-functions
regex::regexpinstr::tests::test_regexp_instr -- --nocapture`
- `cargo test --profile=ci --test sqllogictests -- regexp/regexp_instr.slt`
- `TMPDIR=/home/sean/Projects/datafusion-contrib/target/tmp cargo clippy
--all-targets --all-features -- -D warnings`
- `git diff --check`
## Are there any user-facing changes?
Yes. `regexp_instr` now matches PostgreSQL behavior for empty regular
expression patterns.
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