perf: skip redundant lookahead simulations in expression dispatch

[fudianchn]

AI disclosure: this change was prepared with AI coding agents, reviewed and revised line by line by me.

What

Skip redundant lookahead simulations on hot expression parse paths: the deep jj_2 phase simulation guarding the main branch of Condition() / SQLCondition(), and the Oracle/PostgresNamedFunctionParameter probes in ComplexExpressionList().

Also replace five complete single-token probes with exact token predicates: PRIOR, SQLCondition's OVERLAPS, time-key expressions, ALL, and boolean values.

Why

The main branch of Condition() / SQLCondition() is the last alternative of its choice, so its lookahead can only accept or reject what the productions themselves accept or reject immediately after: entering it directly and letting them fail is equivalent, without re-walking the whole expression tree first. Under JFR profiling of parseSQLStatements this simulation collected about 17% of the execution samples, paid by every plain condition on top of the real parse.

The named-parameter probes can never match a dotted name (f(a.b => 1) fails to parse on master with or without this change), so a check of the second token decides them exactly like the 2-token scan did.

How

• Condition() / SQLCondition(): gate the main alternative with LOOKAHEAD({ !interrupted }) instead of the implicit deep simulation; the EXISTS alternatives ahead of it are unchanged.
• ComplexExpressionList(): gate the four named-parameter alternatives with isNamedParameterAssignmentAhead(), a two-kind check on getToken(2). Keep the syntactic probes that validate the name.
• Replace the five complete single-token syntactic probes with token predicates, retaining their existing interruption checks. Leave the multi-token disambiguation for Oracle (+), named-parameter names and ANY comparisons in place.

Root cause

Not applicable (performance).

Testing

• Remote Linux verification (Core i9-13900KS, JDK 17.0.20): check jmhJar --no-daemon --max-workers=4, with a per-run repository mirror init script, passed on both the PR commit and master bdf8ac31.
• PR: 10,404 tests discovered, 10,379 passed, 25 skipped, zero failures/errors. Master: 10,352 discovered, 10,327 passed, the same 25 skipped, zero failures/errors. Existing test sources and per-suite counts are unchanged; 52 cases were added. The earlier Mockito initialization and file-access failures did not reproduce.
• The previously unverified WithItemTest.testInterruptedWithItemLookaheadStopsReading and CCJSqlParserUtilTest.testParserInterruptedByTimeout both passed remotely; ParserExecutionTest passed all 7 cases. The focused run completed 129 cases with 2 existing disabled cases and zero failures/errors.
• LookaheadDispatchTest: 52 cases passed, checking AST kinds and operands, EOF consumption, round trips, quoted/non-reserved names, first/later named arguments, invalid names and malformed conditions. The two already-interrupted numeric-fragment cases document the !interrupted gate: master accepts the fragment, the PR rejects it before consumption, and removing the gate makes both tests fail.
• The benchmark corpus produces 54 non-null statements on both versions, with identical deparse SHA-256. No JavaCC choice conflicts.

Remote JMH JSQLParserBenchmark.parseSQLStatements (version=latest, unmodified performance.sql): 3 forks per window, 3 × 3 s warmup and 10 × 1 s measurement per fork, 30 samples per window; master → branch → master → branch. Errors are JMH 99.9% confidence intervals.

Pair	master (ms/op)	PR (ms/op)	latency change
1	22.426 ± 0.299	19.277 ± 0.317	-14.0%
2	22.511 ± 0.332	19.230 ± 0.343	-14.6%

The measurements cover the complete PR relative to master.

Malformed conditions can fail inside the productions instead of at choice dispatch; their failure class remains unchanged in the tested cases.

Verification of the original issue

Not applicable (no issue).

[manticore-projects]

This is a good one and to be honest: most of the Lookaheads where set arbitrarily when the Parser Generator requested for it. Nothing of that really went through a clean design ever. I would not be surprised when there are many obsolete Lookaheads left.

Does anyone have a good idea how to clean those up?