feat: Support indexing slices and arrays in deepGet

Author: rhansen

internal/template/reflect.go

@@ -2,7 +2,9 @@ package template
 
 import (
 	"log"
+	"math"
 	"reflect"
+	"strconv"
 	"strings"
 )
 
@@ -26,6 +28,21 @@ func deepGetImpl(v reflect.Value, path []string) interface{} {
 		return deepGetImpl(v.FieldByName(path[0]), path[1:])
 	case reflect.Map:
 		return deepGetImpl(v.MapIndex(reflect.ValueOf(path[0])), path[1:])
+	case reflect.Slice, reflect.Array:
+		iu64, err := strconv.ParseUint(path[0], 10, 64)
+		if err != nil {
+			log.Printf("non-negative decimal number required for array/slice index, got %#v\n", path[0])
+			return nil
+		}
+		if iu64 > math.MaxInt {
+			iu64 = math.MaxInt
+		}
+		i := int(iu64)
+		if i >= v.Len() {
+			log.Printf("index %v out of bounds", i)
+			return nil
+		}
+		return deepGetImpl(v.Index(i), path[1:])
 	default:
 		log.Printf("unable to index by %s (value %v, kind %s)\n", path[0], v, v.Kind())
 		return nil

internal/template/reflect_test.go

@@ -77,6 +77,14 @@ func TestDeepGet(t *testing.T) {
 		{"struct", s, "X", "foo"},
 		{"pointer to struct", sp, "X", "foo"},
 		{"double pointer to struct", &sp, ".X", nil},
+		{"slice index", []string{"foo", "bar"}, "1", "bar"},
+		{"slice index out of bounds", []string{}, "0", nil},
+		{"slice index negative", []string{}, "-1", nil},
+		{"slice index nonnumber", []string{}, "foo", nil},
+		{"array index", [2]string{"foo", "bar"}, "1", "bar"},
+		{"array index out of bounds", [1]string{"foo"}, "1", nil},
+		{"array index negative", [1]string{"foo"}, "-1", nil},
+		{"array index nonnumber", [1]string{"foo"}, "foo", nil},
 	} {
 		t.Run(tc.desc, func(t *testing.T) {
 			got := deepGet(tc.item, tc.path)