AK+Everywhere: Disallow returning a reference from a fallible expression

This will silently make a copy. Rather than masking this behavior, let's
explicitly disallow it.

7 files changed, 45 insertions, 27 deletions

diff --git a/Userland/Libraries/LibAudio/LoaderError.h b/Userland/Libraries/LibAudio/LoaderError.h
index 2464d5cb64..e659050f38 100644
--- a/Userland/Libraries/LibAudio/LoaderError.h
+++ b/Userland/Libraries/LibAudio/LoaderError.h
@@ -66,10 +66,12 @@ struct LoaderError {
 }
 
 // Convenience TRY-like macro to convert an Error to a LoaderError
-#define LOADER_TRY(expression)                                     \
-    ({                                                             \
-        auto _temporary_result = (expression);                     \
-        if (_temporary_result.is_error())                          \
-            return LoaderError(_temporary_result.release_error()); \
-        _temporary_result.release_value();                         \
+#define LOADER_TRY(expression)                                                         \
+    ({                                                                                 \
+        auto _temporary_result = (expression);                                         \
+        if (_temporary_result.is_error())                                              \
+            return LoaderError(_temporary_result.release_error());                     \
+        static_assert(!IsLvalueReference<decltype(_temporary_result.release_value())>, \
+            "Do not return a reference from a fallible expression");                   \
+        _temporary_result.release_value();                                             \
     })
diff --git a/Userland/Libraries/LibJS/Runtime/Completion.h b/Userland/Libraries/LibJS/Runtime/Completion.h
index 0e36f3b8a0..fed974f7b6 100644
--- a/Userland/Libraries/LibJS/Runtime/Completion.h
+++ b/Userland/Libraries/LibJS/Runtime/Completion.h
@@ -25,6 +25,8 @@ namespace JS {
             VERIFY(_temporary_result.error().code() == ENOMEM);                        \
             return vm.throw_completion<JS::InternalError>(JS::ErrorType::OutOfMemory); \
         }                                                                              \
+        static_assert(!IsLvalueReference<decltype(_temporary_result.release_value())>, \
+            "Do not return a reference from a fallible expression");                   \
         _temporary_result.release_value();                                             \
     })
 
diff --git a/Userland/Libraries/LibJS/Runtime/PromiseCapability.h b/Userland/Libraries/LibJS/Runtime/PromiseCapability.h
index c2cee43deb..fac53cadb3 100644
--- a/Userland/Libraries/LibJS/Runtime/PromiseCapability.h
+++ b/Userland/Libraries/LibJS/Runtime/PromiseCapability.h
@@ -53,6 +53,9 @@ private:
             return (capability)->promise();                                                                                              \
         }                                                                                                                                \
                                                                                                                                          \
+        static_assert(!IsLvalueReference<decltype(_temporary_try_or_reject_result.release_value())>,                                     \
+            "Do not return a reference from a fallible expression");                                                                     \
+                                                                                                                                         \
         /* 2. Else if value is a Completion Record, set value to value.[[Value]]. */                                                     \
         _temporary_try_or_reject_result.release_value();                                                                                 \
     })
@@ -76,6 +79,9 @@ private:
             return Value { (capability)->promise() };                                                                             \
         }                                                                                                                         \
                                                                                                                                   \
+        static_assert(!IsLvalueReference<decltype(_temporary_try_or_reject_result.release_value())>,                              \
+            "Do not return a reference from a fallible expression");                                                              \
+                                                                                                                                  \
         /* 2. Else if value is a Completion Record, set value to value.[[Value]]. */                                              \
         _temporary_try_or_reject_result.release_value();                                                                          \
     })
diff --git a/Userland/Libraries/LibVideo/DecoderError.h b/Userland/Libraries/LibVideo/DecoderError.h
index 402b9c8c22..94a7b73993 100644
--- a/Userland/Libraries/LibVideo/DecoderError.h
+++ b/Userland/Libraries/LibVideo/DecoderError.h
@@ -77,15 +77,17 @@ private:
     DeprecatedString m_description;
 };
 
-#define DECODER_TRY(category, expression)                                  \
-    ({                                                                     \
-        auto _result = ((expression));                                     \
-        if (_result.is_error()) [[unlikely]] {                             \
-            auto _error_string = _result.release_error().string_literal(); \
-            return DecoderError::from_source_location(                     \
-                ((category)), _error_string, SourceLocation::current());   \
-        }                                                                  \
-        _result.release_value();                                           \
+#define DECODER_TRY(category, expression)                                    \
+    ({                                                                       \
+        auto _result = ((expression));                                       \
+        if (_result.is_error()) [[unlikely]] {                               \
+            auto _error_string = _result.release_error().string_literal();   \
+            return DecoderError::from_source_location(                       \
+                ((category)), _error_string, SourceLocation::current());     \
+        }                                                                    \
+        static_assert(!IsLvalueReference<decltype(_result.release_value())>, \
+            "Do not return a reference from a fallible expression");         \
+        _result.release_value();                                             \
     })
 
 #define DECODER_TRY_ALLOC(expression) DECODER_TRY(DecoderErrorCategory::Memory, expression)
diff --git a/Userland/Libraries/LibVideo/PlaybackManager.cpp b/Userland/Libraries/LibVideo/PlaybackManager.cpp
index 77d881a8fb..acb14feefb 100644
--- a/Userland/Libraries/LibVideo/PlaybackManager.cpp
+++ b/Userland/Libraries/LibVideo/PlaybackManager.cpp
@@ -273,6 +273,8 @@ bool PlaybackManager::decode_and_queue_one_sample()
             m_present_timer->start(0);                                                                                  \
             return false;                                                                                               \
         }                                                                                                               \
+        static_assert(!IsLvalueReference<decltype(_temporary_result.release_value())>,                                  \
+            "Do not return a reference from a fallible expression");                                                    \
         _temporary_result.release_value();                                                                              \
     })
 
diff --git a/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp b/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
index d0117b3c2c..b3a8c92401 100644
--- a/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
+++ b/Userland/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
@@ -42,12 +42,14 @@
 
 namespace Web::Fetch::Fetching {
 
-#define TRY_OR_IGNORE(expression)              \
-    ({                                         \
-        auto _temporary_result = (expression); \
-        if (_temporary_result.is_error())      \
-            return;                            \
-        _temporary_result.release_value();     \
+#define TRY_OR_IGNORE(expression)                                                      \
+    ({                                                                                 \
+        auto _temporary_result = (expression);                                         \
+        if (_temporary_result.is_error())                                              \
+            return;                                                                    \
+        static_assert(!IsLvalueReference<decltype(_temporary_result.release_value())>, \
+            "Do not return a reference from a fallible expression");                   \
+        _temporary_result.release_value();                                             \
     })
 
 // https://fetch.spec.whatwg.org/#concept-fetch
diff --git a/Userland/Libraries/LibWeb/WebDriver/ExecuteScript.cpp b/Userland/Libraries/LibWeb/WebDriver/ExecuteScript.cpp
index 1fa2b62263..2c414b47aa 100644
--- a/Userland/Libraries/LibWeb/WebDriver/ExecuteScript.cpp
+++ b/Userland/Libraries/LibWeb/WebDriver/ExecuteScript.cpp
@@ -31,12 +31,14 @@
 
 namespace Web::WebDriver {
 
-#define TRY_OR_JS_ERROR(expression)                          \
-    ({                                                       \
-        auto _temporary_result = (expression);               \
-        if (_temporary_result.is_error()) [[unlikely]]       \
-            return ExecuteScriptResultType::JavaScriptError; \
-        _temporary_result.release_value();                   \
+#define TRY_OR_JS_ERROR(expression)                                                    \
+    ({                                                                                 \
+        auto _temporary_result = (expression);                                         \
+        if (_temporary_result.is_error()) [[unlikely]]                                 \
+            return ExecuteScriptResultType::JavaScriptError;                           \
+        static_assert(!IsLvalueReference<decltype(_temporary_result.release_value())>, \
+            "Do not return a reference from a fallible expression");                   \
+        _temporary_result.release_value();                                             \
     })
 
 static ErrorOr<JsonValue, ExecuteScriptResultType> internal_json_clone_algorithm(JS::Realm&, JS::Value, HashTable<JS::Object*>& seen);