Add better error messages for index out of bounds errors

expr-lang · May 12, 2024 · 6cf0edb · 6cf0edb
1 parent 45c1ae7
commit 6cf0edb
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Showing 2 changed files with 14 additions and 2 deletions.
diff --git a/expr_test.go b/expr_test.go
@@ -1329,7 +1329,9 @@ func TestExpr(t *testing.T) {
 }
 
 func TestExpr_error(t *testing.T) {
-	env := mock.Env{}
+	env := mock.Env{
+		ArrayOfAny: []any{1, "2", 3, true},
+	}
 
 	tests := []struct {
 		code string
@@ -1341,6 +1343,12 @@ func TestExpr_error(t *testing.T) {
  | filter(1..9, # > 9)[0]
  | ...................^`,
 		},
+		{
+			`ArrayOfAny[-7]`,
+			`index out of range: -3 (array length is 4) (1:11)
+ | ArrayOfAny[-7]
+ | ..........^`,
+		},
 	}
 
 	for _, tt := range tests {

diff --git a/vm/runtime/runtime.go b/vm/runtime/runtime.go
@@ -35,8 +35,12 @@ func Fetch(from, i any) any {
 	switch v.Kind() {
 	case reflect.Array, reflect.Slice, reflect.String:
 		index := ToInt(i)
+		l := v.Len()
 		if index < 0 {
-			index = v.Len() + index
+			index = l + index
+		}
+		if index < 0 || index >= l {
+			panic(fmt.Sprintf("index out of range: %v (array length is %v)", index, l))
 		}
 		value := v.Index(index)
 		if value.IsValid() {