[psteinroe]

Three follow-ups to identifierTooLong from #885 (recommended, so it runs on every statement).

Cost

The rule ran pgls_query::scan on every statement, because the parser has already truncated the names in the AST. Scanning costs about as much as parsing, and the rule was about 84% of the cost of all rules ported in #885.

It now skips the scan unless the statement could contain a long identifier: a run of more than 63 bytes that can be part of an unquoted identifier ([A-Za-z0-9_$] or a non-ASCII byte), or more than 63 bytes between two quotes. A name is never longer than its text (downcasing keeps the length, "" and Unicode escapes are longer than what they stand for), so the check can't miss one. Quotes in strings or comments can't hide a quoted identifier either: inside one, quotes come in pairs, so only an odd run of quotes counts as a boundary.

Measured on a debug build as on-CPU thread time (minimum of 5 runs; the machine was busy, so wall-clock is meaningless):

	before	after
scan step over the PG 15–18 regression corpus (172,586 statements)	2.36 s	0.28 s (1,850 statements, 1.1%, still get scanned)
rule over the PG 18 corpus, minus the no-rule baseline (46,158 statements)	+0.93 s	+0.19 s or less, within noise
rule on a synthetic 10k-statement migration, minus the baseline	+279 ms	~0 ms

For comparison, 6.3% of the corpus statements contain a ", so "skip unless there's a quote" would have scanned six times as many.

U&"..." identifiers

Only IDENT tokens were checked, so this was silent although Postgres prints a truncation notice:

create table U&"aaaa…(64 bytes)…" (id int);
create table U&"x!0061!0061…(80 escapes)" uescape '!' (id int);

UIDENT tokens are now decoded like str_udeescape does (4- and 6-digit escapes, surrogate pairs, doubled escape characters, and the UESCAPE character as check_uescapechar allows it). Identifiers whose escapes Postgres rejects are skipped. Each case in the spec was checked against Postgres for the NOTICE.

One diagnostic per name

A long table name used three times in a statement gave three identical diagnostics. Each distinct name is now reported once per statement, at its first occurrence. Unquoted names are compared, and shown, downcased like Postgres does (ASCII only), so Long_Name… and long_name… are the same name.

Tests

Spec files edge_cases.sql (multi-byte names, doubled quotes, strings/comments/dollar-quoted bodies, a quote in a string next to a long quoted identifier with spaces, the repeated name) and unicode_escapes.sql; unit tests for the pre-filter (including the cases that must pass it) and the U& decoding.

Not covered

libpg_query (PG 17) fails to parse a comment between U&"..." and UESCAPE, which Postgres accepts, so such a statement is reported as a syntax error and never reaches the rule.