Add SETOF support for PostgreSQL function return types

[fmguerreiro]

PostgreSQL functions can return sets via RETURNS SETOF <type>. This is currently not supported by the parser, which fails when encountering SETOF after RETURNS.

Changes

• Add SETOF keyword
• Add DataType::SetOf(Box<DataType>) variant
• Handle SETOF in parse_data_type_helper() so any DataType::SetOf round-trips through Display → parse
• Tests for SETOF with TEXT, INTEGER, RECORD, and schema-qualified custom types

Example

CREATE FUNCTION get_users() RETURNS SETOF TEXT LANGUAGE sql AS 'SELECT name FROM users';
CREATE FUNCTION get_all() RETURNS SETOF my_schema."MyType" LANGUAGE sql AS 'SELECT * FROM t';

Reference

• PostgreSQL CREATE FUNCTION docs

[iffyio]

would it make sense to represent this as a qualifier around the return type of a function instead? e.g.

enum FunctionReturnType {
    DataType(DataType),
    Setof(DataType)
}
CreateFunction { ... return_type: FunctionReturnType ... }

Thinking that would probably be better because it would be a bit confusing having a SETOF DataType that isn't a valid data type in any dialect

[fmguerreiro]

yep, makes sense! 62385ea

[iffyio]

Can we instead move the link to the postgres docs here? since the enum itself applies to all dialects, whereas only this variant is pg specific

[iffyio]

is there any changes in this diff (if not can we revert it)?

[iffyio]

Suggested change

	///
	/// Handles `RETURNS SETOF <type>` and plain `RETURNS <type>`.