feat: add .first() & .last() methods to list in cel

funcs/coll_cel.go

@@ -0,0 +1,61 @@
+package funcs
+
+import (
+	"reflect"
+
+	"github.com/google/cel-go/cel"
+	"github.com/google/cel-go/common/types"
+	"github.com/google/cel-go/common/types/ref"
+)
+
+var collListFirst = cel.Function("first",
+	cel.MemberOverload("slice_first_any",
+		[]*cel.Type{
+			cel.ListType(cel.DynType),
+		},
+		cel.DynType,
+		cel.FunctionBinding(func(args ...ref.Val) ref.Val {
+			list, err := args[0].ConvertToNative(reflect.TypeOf([]any{}))
+			if err != nil {
+				return types.WrapErr(err)
+			}
+
+			l, ok := list.([]any)
+			if !ok {
+				return types.WrapErr(err)
+			}
+
+			if len(l) == 0 {
+				return types.DefaultTypeAdapter.NativeToValue("")
+			}
+
+			return types.DefaultTypeAdapter.NativeToValue(l[0])
+		}),
+	),
+)
+
+var collListLast = cel.Function("last",
+	cel.MemberOverload("slice_last_any",
+		[]*cel.Type{
+			cel.ListType(cel.DynType),
+		},
+		cel.DynType,
+		cel.FunctionBinding(func(args ...ref.Val) ref.Val {
+			list, err := args[0].ConvertToNative(reflect.TypeOf([]any{}))
+			if err != nil {
+				return types.WrapErr(err)
+			}
+
+			l, ok := list.([]any)
+			if !ok {
+				return types.WrapErr(err)
+			}
+
+			if len(l) == 0 {
+				return types.DefaultTypeAdapter.NativeToValue("")
+			}
+
+			return types.DefaultTypeAdapter.NativeToValue(l[len(l)-1])
+		}),
+	),
+)

tests/cel_test.go

@@ -80,6 +80,24 @@ func unstructure(o any) interface{} {
 	return out
 }
 
+func TestCelCollection(t *testing.T) {
+	runTests(t, []Test{
+		{nil, "[1,2,3].first()", "1"},
+		{nil, "['a', 'b', 'c'].first()", "a"},
+		{nil, "[].first()", ""},
+		{map[string]any{"my_list": []int{5, 6, 7}}, "my_list.first()", "5"},
+		{map[string]any{"my_list": []Person{{Name: "John"}, {Name: "Bob"}}}, "my_list.first().name", "John"},
+	})
+
+	runTests(t, []Test{
+		{nil, "[1,2,3].last()", "3"},
+		{nil, "['a', 'b', 'c'].last()", "c"},
+		{nil, "[].last()", ""},
+		{map[string]any{"my_list": []int{5, 6, 7}}, "my_list.last()", "7"},
+		{map[string]any{"my_list": []Person{{Name: "John"}, {Name: "Bob"}}}, "my_list.last().name", "Bob"},
+	})
+}
+
 func TestCelAws(t *testing.T) {
 	runTests(t, []Test{
 		{nil, "aws.arnToMap('arn:aws:sns:eu-west-1:123:MMS-Topic').account", "123"},