Add window function support to keyword-as-function parsing

When keywords like ANY, ALL, etc. are used as function names (e.g.,
any(number)), they were being parsed by parseKeywordAsFunction which
didn't handle OVER clause for window functions.

Added support for:
- DISTINCT inside keyword functions
- IGNORE NULLS / RESPECT NULLS modifiers
- FILTER clause for aggregate functions
- OVER clause for window functions

This fixes parsing of queries like:
  SELECT any(number) OVER () FROM numbers(2);

Author: claude

parser/expression.go

@@ -1897,22 +1897,60 @@ func (p *Parser) parseKeywordAsFunction() ast.Expression {
 		return nil
 	}
 
-	var args []ast.Expression
+	fn := &ast.FunctionCall{
+		Position: pos,
+		Name:     name,
+	}
+
+	// Handle DISTINCT
+	if p.currentIs(token.DISTINCT) {
+		fn.Distinct = true
+		p.nextToken()
+	}
+
 	// Handle view() and similar functions that take a subquery as argument
 	if name == "view" && (p.currentIs(token.SELECT) || p.currentIs(token.WITH)) {
 		subquery := p.parseSelectWithUnion()
-		args = []ast.Expression{&ast.Subquery{Position: pos, Query: subquery}}
+		fn.Arguments = []ast.Expression{&ast.Subquery{Position: pos, Query: subquery}}
 	} else if !p.currentIs(token.RPAREN) {
-		args = p.parseExpressionList()
+		fn.Arguments = p.parseExpressionList()
 	}
 
 	p.expect(token.RPAREN)
 
-	return &ast.FunctionCall{
-		Position:  pos,
-		Name:      name,
-		Arguments: args,
+	// Handle IGNORE NULLS / RESPECT NULLS (window function modifiers)
+	for p.currentIs(token.IDENT) {
+		upper := strings.ToUpper(p.current.Value)
+		if upper == "IGNORE" || upper == "RESPECT" {
+			p.nextToken()
+			if p.currentIs(token.NULLS) {
+				p.nextToken()
+			}
+		} else {
+			break
+		}
+	}
+
+	// Handle FILTER clause for aggregate functions: func() FILTER(WHERE condition)
+	if p.currentIs(token.IDENT) && strings.ToUpper(p.current.Value) == "FILTER" {
+		p.nextToken() // skip FILTER
+		if p.currentIs(token.LPAREN) {
+			p.nextToken() // skip (
+			if p.currentIs(token.WHERE) {
+				p.nextToken() // skip WHERE
+				p.parseExpression(LOWEST)
+			}
+			p.expect(token.RPAREN)
+		}
+	}
+
+	// Handle OVER clause for window functions
+	if p.currentIs(token.OVER) {
+		p.nextToken()
+		fn.Over = p.parseWindowSpec()
 	}
+
+	return fn
 }
 
 func (p *Parser) parseKeywordAsIdentifier() ast.Expression {

parser/testdata/01591_window_functions/metadata.json

@@ -11,7 +11,6 @@
     "stmt110": true,
     "stmt111": true,
     "stmt112": true,
-    "stmt28": true,
     "stmt31": true,
     "stmt34": true,
     "stmt35": true,

parser/testdata/02900_window_function_with_sparse_column/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt7": true
-  }
-}
+{}

parser/testdata/02922_respect_nulls_extensive/metadata.json

@@ -1,13 +1,6 @@
 {
   "explain_todo": {
-    "stmt36": true,
-    "stmt38": true,
     "stmt40": true,
-    "stmt41": true,
-    "stmt42": true,
-    "stmt44": true,
-    "stmt46": true,
-    "stmt47": true,
-    "stmt6": true
+    "stmt41": true
   }
 }

parser/testdata/02941_any_RESPECT_NULL_sparse_column/metadata.json

@@ -1,5 +1 @@
-{
-  "explain_todo": {
-    "stmt4": true
-  }
-}
+{}