chore: more work done and planning with AI.

pkg/format/keywords.go

@@ -51,5 +51,23 @@ func words(s string) map[string]bool {
 	return m
 }
 
-func isKeyword(lower string) bool  { return keywords[lower] }
-func isTypeName(lower string) bool { return typeNames[lower] }
+// builtinFunctions are built-in function names controlled by BuiltinCase.
+var builtinFunctions = words(`
+abs age array_agg array_length array_lower array_ndims array_upper
+bit_length btrim cardinality ceil ceiling char_length character_length
+chr clock_timestamp coalesce concat concat_ws count
+currval decode div encode exp extract floor
+generate_series greatest initcap jsonb_agg jsonb_object_agg
+justify_days justify_hours justify_interval
+lastval least length lower lpad ltrim
+max md5 min mod now nullif
+overlay pg_sleep position power quote_ident quote_literal
+random regexp_match regexp_matches regexp_replace replace reverse round rpad rtrim
+setval split_part sqrt string_agg strpos substr substring sum
+to_char to_date to_json to_jsonb to_number to_timestamp to_tsvector
+translate trim trunc unnest upper width_bucket
+`)
+
+func isKeyword(lower string) bool       { return keywords[lower] }
+func isTypeName(lower string) bool      { return typeNames[lower] }
+func isBuiltinFunc(lower string) bool   { return builtinFunctions[lower] }