refactor: expose NewCustomExpression for dialects to use

internal/jet/expression.go

@@ -278,7 +278,7 @@ type customExpression struct {
 	parts []Serializer
 }
 
-func newCustomExpression(parts ...Serializer) Expression {
+func NewCustomExpression(parts ...Serializer) Expression {
 	ret := customExpression{
 		parts: parts,
 	}

internal/jet/func_expression.go

@@ -548,7 +548,7 @@ func TO_TIMESTAMP(timestampzStr, format StringExpression) TimestampzExpression {
 
 // EXTRACT extracts time component from time expression
 func EXTRACT(field string, from Expression) Expression {
-	return newCustomExpression(Token("EXTRACT("), Token(field), Token("FROM"), from, Token(")"))
+	return NewCustomExpression(Token("EXTRACT("), Token(field), Token("FROM"), from, Token(")"))
 }
 
 // CURRENT_DATE returns current date

internal/jet/group_by_clause.go

@@ -35,7 +35,7 @@ func GROUPING(expressions ...Expression) IntegerExpression {
 // WITH_ROLLUP operator is used with the GROUP BY clause to generate all prefixes of a group of columns including the empty list.
 // It creates extra rows in the result set that represent the subtotal values for each combination of columns.
 func WITH_ROLLUP(expressions ...Expression) GroupByClause {
-	return newCustomExpression(
+	return NewCustomExpression(
 		parametersSerializer(expressions), Token("WITH ROLLUP"),
 	)
 }