[postgresql] Ambiguity in opt_analyze.

Consider this input:

VACUUM ANALYZE brin_test;

This can be parsed in two ways:

(root (stmtblock (stmtmulti (stmt (vacuumstmt (VACUUM "VACUUM") (opt_full) (opt_freeze) (opt_verbose) (opt_analyze (analyze_keyword (ANALYZE "ANALYZE"))) (opt_vacuum_relation_list (vacuum_relation_list (vacuum_relation (qualified_name (colid (identifier (Identifier "brin_test") (opt_uescape)))) (opt_name_list)))))) (SEMI ";"))) (EOF ""))
(root (stmtblock (stmtmulti (stmt (vacuumstmt (VACUUM "VACUUM") (opt_full) (opt_freeze) (opt_verbose) (opt_analyze) (opt_vacuum_relation_list))) (stmt (analyzestmt (analyze_keyword (ANALYZE "ANALYZE")) (opt_verbose) (opt_vacuum_relation_list (vacuum_relation_list (vacuum_relation (qualified_name (colid (identifier (Identifier "brin_test") (opt_uescape)))) (opt_name_list)))))) (SEMI ";"))) (EOF ""))

The problem here is in opt_analyze in the context of a stmt.

stmtmulti
    : (stmt SEMI?)*
    ;

stmt
    : ...
    ;

opt_analyze
    : analyze_keyword
    |
    ;

The problem is that stmtmulti allows for an optional SEMI. This is a bad idea because it directly leads to this problem: Where does the VACUUM statement end?

This change was introduced with https://github.com/antlr/grammars-v4/pull/2365 (specifically https://github.com/antlr/grammars-v4/pull/2365/commits/e2d77e34395ae8b8b19a987714f6f9c28cd70e1e#diff-191019bcbd2ccd918ba1d7e6610ca830bc526d04af2ae6e6d3c5356e96274b76), deviating from the rule from in the official Bison grammar. Note in the official grammar, stmtmulti does not offer an optional semicolon! Really, you should be very, very careful in how to refactor from the official grammar gram.y!!

The fix is to change ';'? to ';'!

antlr / grammars-v4

[postgresql] Ambiguity in opt_analyze. #4302