[fudianchn]

What

Re-enable PostgreSQL composite row expansion (function_call).*, e.g. SELECT (json_populate_record(NULL::users, data)).* FROM staging_users. JSQLParser currently rejects the trailing .*.

This builds on #2207, which added the feature and then had to disable it.

Why

FunctionAllColumns (the AST node, deparser, validator and all four visitors) was fully implemented in #2207 but the grammar call site was commented out afterwards. The reason was a severe performance regression: the original LOOKAHEAD(FunctionAllColumns()) at the PrimaryExpression entry was a speculative syntactic lookahead that triggered catastrophic backtracking on every primary expression (393 ms/op vs ~86 ms/op). Issue #2412 is the user-visible symptom of that disabled feature.

The maintainer explicitly invited a re-enablement "once performance can be proved" and suggested treating (((( FUNCTION )))).* as a single-Function ParenthesedExpressionList followed by .*.

How

The feature is wired into the existing ParenthesedExpressionList branch of PrimaryExpression, but via a bounded semantic follower check instead of a speculative production:

• A new helper isFunctionAllColumnsAhead(Expression) first peeks the next two tokens; only when they are . * does it unwrap nested ParenthesedExpressionList wrappers and confirm the inner expression is a Function. The common case (a parenthesised expression not followed by .*) therefore bails out in two comparisons, with no speculative production and no backtracking.
• Only then is the result wrapped into the existing FunctionAllColumns.
• TablesNamesFinder now descends into the wrapped function, so column/table references inside the expansion are not lost.

Root cause

Not a missing feature but a feature disabled for the wrong reason: the perf toll came from the speculative syntactic lookahead, not from the feature itself. Removing the speculation (post-parse follower check) keeps the feature without the toll.

Scope / limitation

Only (function_call).* is supported (the shape the existing FunctionAllColumns AST and #2207 cover). Arbitrary (non-function expression).* (e.g. (a + b).*, (tbl.col).*) remains unsupported and still fails cleanly, as before. Redundant surrounding parentheses are unwrapped to the inner function (so (((( f() )))).* round-trips as (f()).*, semantically equivalent).

Testing

CompositeRowExpansionTest covers the issue case, simple/no-arg functions, the INSERT ... SELECT use case, multiple surrounding parentheses, and negative cases (no trailing .*, a RowGetExpression, a non-function expression). The positive tests fail on master and pass with this change.

Local: spotlessApply, checkstyleMain/Test, spotbugsMain/Test, and the full test suite (4731 tests) all green, no regression.

Performance

gradle jmh, JSQLParserBenchmark.parseSQLStatements on performance.sql, version=latest, 10 forks × 10 iterations (100 samples) on a dedicated 32-core host:

build	ms/op
master (feature disabled)	3.632 ± 0.020
this change	3.639 ± 0.023

The +0.19% delta lies within the confidence intervals (the CIs overlap almost entirely) and is far from the 393 ms/op toll that motivated disabling the feature.

Verification of the original issue

SELECT (json_populate_record(NULL::users, data)).* FROM staging_users

fails on master (Encountered: ".") and parses + round-trips with this change, yielding a FunctionAllColumns select item.

Fixes #2412