LibJS: Add a MUST() macro, like TRY() but for the spec's `!` shortcut

1 files changed, 13 insertions, 0 deletions

diff --git a/Userland/Libraries/LibJS/Runtime/Completion.h b/Userland/Libraries/LibJS/Runtime/Completion.h
index 7b6dbb7c3c..3a9b62b4b7 100644
--- a/Userland/Libraries/LibJS/Runtime/Completion.h
+++ b/Userland/Libraries/LibJS/Runtime/Completion.h
@@ -26,6 +26,19 @@ namespace JS {
         _temporary_result.release_value();     \
     })
 
+// MUST() is to the spec's `!` what TRY() is to `?`.
+// https://tc39.es/ecma262/#sec-returnifabrupt-shorthands
+#define MUST(expression)                                           \
+    ({                                                             \
+        auto _temporary_result = (expression);                     \
+        VERIFY(!_temporary_result.is_error());                     \
+        /* The return value of "! Something()" is commonly      */ \
+        /* ignored, so we assign to a temporary variable here   */ \
+        /* to avoid having to (void) all the things.            */ \
+        auto _temporary_value = _temporary_result.release_value(); \
+        move(_temporary_value);                                    \
+    })
+
 // 6.2.3 The Completion Record Specification Type, https://tc39.es/ecma262/#sec-completion-record-specification-type
 class [[nodiscard]] Completion {
 public: