Add COLLATE clause support for expressions

- Add Collation field to FunctionCall and ColumnReferenceExpression AST types
- Parse COLLATE clause after expressions in SELECT elements
- Add COLLATE to excluded alias keywords to prevent misinterpretation
- Update marshalling for both FunctionCall and ColumnReferenceExpression
  to include Collation field in JSON output

Enables 4 tests: SelectWithCollation, Baselines110/120/130_SelectWithCollation

Author: claude

ast/column_reference_expression.go

@@ -4,6 +4,7 @@ package ast
 type ColumnReferenceExpression struct {
 	ColumnType          string               `json:"ColumnType,omitempty"`
 	MultiPartIdentifier *MultiPartIdentifier `json:"MultiPartIdentifier,omitempty"`
+	Collation           *Identifier          `json:"Collation,omitempty"`
 }
 
 func (*ColumnReferenceExpression) node()             {}

ast/function_call.go

@@ -50,6 +50,7 @@ type FunctionCall struct {
 	OverClause         *OverClause        `json:"OverClause,omitempty"`
 	IgnoreRespectNulls []*Identifier      `json:"IgnoreRespectNulls,omitempty"`
 	WithArrayWrapper   bool               `json:"WithArrayWrapper,omitempty"`
+	Collation          *Identifier        `json:"Collation,omitempty"`
 }
 
 func (*FunctionCall) node()             {}

parser/marshal.go

@@ -1316,6 +1316,9 @@ func scalarExpressionToJSON(expr ast.ScalarExpression) jsonNode {
 		if e.MultiPartIdentifier != nil {
 			node["MultiPartIdentifier"] = multiPartIdentifierToJSON(e.MultiPartIdentifier)
 		}
+		if e.Collation != nil {
+			node["Collation"] = identifierToJSON(e.Collation)
+		}
 		return node
 	case *ast.IntegerLiteral:
 		node := jsonNode{
@@ -1401,6 +1404,9 @@ func scalarExpressionToJSON(expr ast.ScalarExpression) jsonNode {
 			node["IgnoreRespectNulls"] = idents
 		}
 		node["WithArrayWrapper"] = e.WithArrayWrapper
+		if e.Collation != nil {
+			node["Collation"] = identifierToJSON(e.Collation)
+		}
 		return node
 	case *ast.UserDefinedTypePropertyAccess:
 		node := jsonNode{
@@ -5510,6 +5516,9 @@ func columnReferenceExpressionToJSON(c *ast.ColumnReferenceExpression) jsonNode
 	if c.MultiPartIdentifier != nil {
 		node["MultiPartIdentifier"] = multiPartIdentifierToJSON(c.MultiPartIdentifier)
 	}
+	if c.Collation != nil {
+		node["Collation"] = identifierToJSON(c.Collation)
+	}
 	return node
 }
 

parser/parse_select.go

@@ -479,6 +479,19 @@ func (p *Parser) parseSelectElement() (ast.SelectElement, error) {
 		}
 	}
 
+	// Check for COLLATE clause before creating SelectScalarExpression
+	if p.curTok.Type == TokenIdent && strings.ToUpper(p.curTok.Literal) == "COLLATE" {
+		p.nextToken() // consume COLLATE
+		collation := p.parseIdentifier()
+		// Attach collation to the expression
+		switch e := expr.(type) {
+		case *ast.FunctionCall:
+			e.Collation = collation
+		case *ast.ColumnReferenceExpression:
+			e.Collation = collation
+		}
+	}
+
 	sse := &ast.SelectScalarExpression{Expression: expr}
 
 	// Check for column alias: [alias], AS alias, or just alias
@@ -509,7 +522,7 @@ func (p *Parser) parseSelectElement() (ast.SelectElement, error) {
 	} else if p.curTok.Type == TokenIdent {
 		// Check if this is an alias (not a keyword that starts a new clause)
 		upper := strings.ToUpper(p.curTok.Literal)
-		if upper != "FROM" && upper != "WHERE" && upper != "GROUP" && upper != "HAVING" && upper != "ORDER" && upper != "OPTION" && upper != "INTO" && upper != "UNION" && upper != "EXCEPT" && upper != "INTERSECT" && upper != "GO" {
+		if upper != "FROM" && upper != "WHERE" && upper != "GROUP" && upper != "HAVING" && upper != "ORDER" && upper != "OPTION" && upper != "INTO" && upper != "UNION" && upper != "EXCEPT" && upper != "INTERSECT" && upper != "GO" && upper != "COLLATE" {
 			alias := p.parseIdentifier()
 			sse.ColumnName = &ast.IdentifierOrValueExpression{
 				Value:      alias.Value,

parser/testdata/Baselines110_SelectWithCollation/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/Baselines120_SelectWithCollation/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/Baselines130_SelectWithCollation/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}

parser/testdata/SelectWithCollation/metadata.json

@@ -1 +1 @@
-{"todo": true}
+{}