[CALCITE-7448] Add support for : as a field/item access operator

[tmater]

Changes Proposed

This PR adds opt-in support for : as a field/item access operator behind a new SqlConformance#isColonFieldAccessAllowed() hook. No built-in conformance enables it yet, so the default parser behavior is unchanged.

It also refactors postfix parsing so colon field access composes with existing dot and bracket access. That covers cases such as v:field, v:['field name'], arr[1]:field, obj['x']:nested['y'], and colon access followed by bracket or dot postfixes.

To avoid ambiguity when colon field access is enabled, JSON_OBJECT and JSON_OBJECTAGG must use VALUE syntax instead of : or comma-separated key/value shorthand.

The Babel parser coverage is updated as well so PostgreSQL-style infix casts still require parentheses before bracket access. For example, (v::variant)[1] parses as item access on the cast result, while v::variant[1] remains invalid.

Reproduction

select v:field, v:['field name'], arr[1]:field, obj['x']:nested from t;

select json_object(key v:field value arr[1]:field);

select (v::variant)[1] from t;

Testing

Added parser coverage in SqlParserTest and BabelParserTest for valid and invalid colon field access, JSON constructor disambiguation, and :: cast interactions.

Jira Link

CALCITE-7448

[caicancai]

I might wait until the CI issue is resolved before reviewing this PR.

[sonarqubecloud]

Quality Gate passed

Issues
2 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[caicancai]

I don't understand Calcite JavaCC code very well, I might need to learn it. If no one reviews it this week, I'll start working on it next week.

[tmater]

I don't understand Calcite JavaCC code very well, I might need to learn it. If no one reviews it this week, I'll start working on it next week.

Thank you for taking a look, @caicancai. I agree this is still a fairly complex PR, and I wouldn’t claim to fully understand all of its implications yet.

That’s also why I tried to include a wide range of test variations and keep the changes gated behind a conformance config.

I’ve organized it into five commits (prior to the CI failures) to make the review easier. If it would help further, I’m happy to split it into 4–5 smaller PRs.

[mihaibudiu]

Is the behavior with :: needing parenthesis a new feature, or was this already present previously?