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These things didn't work because the planner omitted to do the necessary preprocessing of a WindowFunc's argument list. Add the few dozen lines of code needed to handle that. Although this sounds like a feature addition, it's really a bug fix because the default-argument case was likely to crash previously, due to lack of checking of the number of supplied arguments in the built-in window functions. It's not a security issue because there's no way for a non-superuser to create a window function definition with defaults that refers to a built-in C function, but nonetheless people might be annoyed that it crashes rather than producing a useful error message. So back-patch as far as the patch applies easily, which turns out to be 9.2. I'll put a band-aid in earlier versions as a separate patch. (Note that these features still don't work for aggregates, and fixing that case will be harder since we represent aggregate arg lists as target lists not bare expression lists. There's no crash risk though because CREATE AGGREGATE doesn't accept defaults, and we reject named-argument notation when parsing an aggregate call.)
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 kwlookup.c turn keywords into specific tokens keywords.c table of standard keywords (passed to kwlookup.c) 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)