feat(postgresql): add bare_label_keyword support for column aliases without AS

[h3n4l]

Summary

• Fix parsing of statements like SELECT 1 name; where keywords are used as column aliases without AS
• Add bare_label_keyword category (455 keywords) from PostgreSQL's official grammar
• Update keyword-generator to extract and generate the new keyword category
• Add bare_col_label rule and update target_alias to use it

Problem

PostgreSQL supports using certain keywords as column aliases without the AS keyword:

SELECT 1 name;  -- 'name' is an unreserved keyword, works without AS
SELECT 1 AS year;  -- 'year' requires AS keyword

Our parser was rejecting SELECT 1 name; because target_alias only accepted identifier, not keywords.

Solution

PostgreSQL's keyword system has 5 categories (we only had 4):

Category	Count	Description
reserved_keyword	78	Cannot be used as identifiers
unreserved_keyword	330	Can always be used as identifiers
col_name_keyword	63	Can be used as column names
type_func_name_keyword	23	Can be used as type/function names
bare_label_keyword	455	Can be used as column labels WITHOUT AS

The bare_label_keyword category is orthogonal to the other categories - it's defined by the 4th field in PostgreSQL's kwlist.h (BARE_LABEL vs AS_LABEL).

Changes

1. keyword-generator/main.go: Extract and generate bare_label_keyword rule
2. PostgreSQLKeywords.g4: Now includes bare_label_keyword (auto-generated)
3. PostgreSQLParser.g4:
   • Added bare_col_label rule: identifier | bare_label_keyword
   • Updated target_alias to use bare_col_label instead of identifier
4. examples/regression/bare_col_label.sql: Test cases for bare column labels

Test plan

• SELECT 1 name; now parses correctly
• SELECT 1 year; correctly fails (requires SELECT 1 AS year;)
• All 190+ existing tests pass
• New regression test added

🤖 Generated with Claude Code