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The implementation of that feature involves injecting nodes into the raw parsetree where explicit parentheses appear. Various places in parse_expr.c that test to see "is this child node of type Foo" need to look through such nodes, else we'll get different behavior when operator_precedence_warning is on than when it is off. Note that we only need to handle this when testing untransformed child nodes, since the AEXPR_PAREN nodes will be gone anyway after transformExprRecurse. Per report from Scott Ribe and additional code-reading. Back-patch to 9.5 where this feature was added. Report: <ED37E303-1B0A-4CD8-8E1E-B9C4C2DD9A17@elevated-dev.com>
src/backend/parser/README Parser ====== This directory does more than tokenize and parse SQL queries. It also creates Query structures for the various complex queries that are passed to the optimizer and then executor. parser.c things start here scan.l break query into tokens scansup.c handle escapes in input strings gram.y parse the tokens and produce a "raw" parse tree analyze.c top level of parse analysis for optimizable queries parse_agg.c handle aggregates, like SUM(col1), AVG(col2), ... parse_clause.c handle clauses like WHERE, ORDER BY, GROUP BY, ... parse_coerce.c handle coercing expressions to different data types parse_collate.c assign collation information in completed expressions parse_cte.c handle Common Table Expressions (WITH clauses) parse_expr.c handle expressions like col, col + 3, x = 3 or x = 4 parse_func.c handle functions, table.column and column identifiers parse_node.c create nodes for various structures parse_oper.c handle operators in expressions parse_param.c handle Params (for the cases used in the core backend) parse_relation.c support routines for tables and column handling parse_target.c handle the result list of the query parse_type.c support routines for data type handling parse_utilcmd.c parse analysis for utility commands (done at execution time) See also src/common/keywords.c, which contains the table of standard keywords and the keyword lookup function. We separated that out because various frontend code wants to use it too.