Add len(filter()) optimization

optimizer/filter_len.go

@@ -0,0 +1,22 @@
+package optimizer
+
+import (
+	. "github.com/antonmedv/expr/ast"
+)
+
+type filterLen struct{}
+
+func (*filterLen) Visit(node *Node) {
+	if ln, ok := (*node).(*BuiltinNode); ok &&
+		ln.Name == "len" &&
+		len(ln.Arguments) == 1 {
+		if filter, ok := ln.Arguments[0].(*BuiltinNode); ok &&
+			filter.Name == "filter" &&
+			len(filter.Arguments) == 2 {
+			Patch(node, &BuiltinNode{
+				Name:      "count",
+				Arguments: filter.Arguments,
+			})
+		}
+	}
+}

optimizer/optimizer.go

@@ -33,5 +33,6 @@ func Optimize(node *Node, config *conf.Config) error {
 	}
 	Walk(node, &inRange{})
 	Walk(node, &constRange{})
+	Walk(node, &filterLen{})
 	return nil
 }

optimizer/optimizer_test.go

@@ -138,3 +138,30 @@ func TestOptimize_const_expr(t *testing.T) {
 
 	assert.Equal(t, ast.Dump(expected), ast.Dump(tree.Node))
 }
+
+func TestOptimize_filter_len(t *testing.T) {
+	tree, err := parser.Parse(`len(filter(users, .Name == "Bob"))`)
+	require.NoError(t, err)
+
+	err = optimizer.Optimize(&tree.Node, nil)
+	require.NoError(t, err)
+
+	expected := &ast.BuiltinNode{
+		Name: "count",
+		Arguments: []ast.Node{
+			&ast.IdentifierNode{Value: "users"},
+			&ast.ClosureNode{
+				Node: &ast.BinaryNode{
+					Operator: "==",
+					Left: &ast.MemberNode{
+						Node:     &ast.PointerNode{},
+						Property: &ast.StringNode{Value: "Name"},
+					},
+					Right: &ast.StringNode{Value: "Bob"},
+				},
+			},
+		},
+	}
+
+	assert.Equal(t, ast.Dump(expected), ast.Dump(tree.Node))
+}