Bug 1729598 - Replace MOZ_MUST_USE_TYPE with [[nodiscard]]. r=static-analysis-reviewers,andi

Differential Revision: https://phabricator.services.mozilla.com/D125504

dom/quota/QMResultInlines.h

@@ -25,7 +25,7 @@ namespace mozilla {
 // Allow QMResult errors to use existing stack id and to increase the frame id
 // during error propagation.
 template <>
-class MOZ_MUST_USE_TYPE GenericErrorResult<QMResult> {
+class [[nodiscard]] GenericErrorResult<QMResult> {
   QMResult mErrorValue;
 
   template <typename V, typename E2>

dom/quota/QuotaCommon.h

@@ -1161,7 +1161,7 @@ auto CollectWhile(const Cond& aCond, const Body& aBody)
 }
 
 template <>
-class MOZ_MUST_USE_TYPE GenericErrorResult<mozilla::ipc::IPCResult> {
+class [[nodiscard]] GenericErrorResult<mozilla::ipc::IPCResult> {
   mozilla::ipc::IPCResult mErrorValue;
 
   template <typename V, typename E2>

image/ImgDrawResult.h

@@ -55,17 +55,10 @@ namespace image {
  * NOT_SUPPORTED: The requested operation is not supported, but the image is
  *                otherwise valid.
  */
-enum class MOZ_MUST_USE_TYPE ImgDrawResult : uint8_t {
-  SUCCESS,
-  SUCCESS_NOT_COMPLETE,
-  INCOMPLETE,
-  WRONG_SIZE,
-  NOT_READY,
-  TEMPORARY_ERROR,
-  BAD_IMAGE,
-  BAD_ARGS,
-  NOT_SUPPORTED
-};
+enum class [[nodiscard]] ImgDrawResult : uint8_t{
+    SUCCESS,      SUCCESS_NOT_COMPLETE, INCOMPLETE, WRONG_SIZE,
+    NOT_READY,    TEMPORARY_ERROR,      BAD_IMAGE,  BAD_ARGS,
+    NOT_SUPPORTED};
 
 /**
  * You can combine ImgDrawResults with &. By analogy to bitwise-&, the result is

layout/style/ServoBindingTypes.h

@@ -58,7 +58,7 @@
 //
 // TODO(heycam): We should perhaps have a similar struct for Owned types with a
 // Consume() method to convert them into a UniquePtr.  The struct for Strong
-// types at least have MOZ_MUST_USE_TYPE on them.
+// types at least have [[nodiscard]] on them.
 //
 //
 // Using these types in Rust =========================

mfbt/AlreadyAddRefed.h

@@ -38,7 +38,11 @@ struct unused_t;
  * Otherwise, use std::move(RefPtr/nsCOMPtr/etc).
  */
 template <class T>
-struct MOZ_MUST_USE_TYPE MOZ_NON_AUTOABLE already_AddRefed {
+struct
+#if !defined(MOZ_CLANG_PLUGIN) && !defined(XGILL_PLUGIN)
+    [[nodiscard]]
+#endif
+    MOZ_NON_AUTOABLE already_AddRefed {
   already_AddRefed() : mRawPtr(nullptr) {}
 
   // For simplicity, allow returning nullptr from functions returning

mfbt/Result.h

@@ -439,7 +439,7 @@ constexpr auto ToResult(Result<V, E>&& aValue)
  * V* const, E> is not possible.)
  */
 template <typename V, typename E>
-class MOZ_MUST_USE_TYPE Result final {
+class [[nodiscard]] Result final {
   // See class comment on Result<const V, E> and Result<V, const E>.
   static_assert(!std::is_const_v<V>);
   static_assert(!std::is_const_v<E>);
@@ -745,7 +745,7 @@ class MOZ_MUST_USE_TYPE Result final {
  * useful in error-handling macros; see MOZ_TRY for an example.
  */
 template <typename E>
-class MOZ_MUST_USE_TYPE GenericErrorResult {
+class [[nodiscard]] GenericErrorResult {
   E mErrorValue;
 
   template <typename V, typename E2>

mfbt/ResultExtensions.h

@@ -21,7 +21,7 @@ struct ErrorPropagationTag;
 // Allow nsresult errors to automatically convert to nsresult values, so MOZ_TRY
 // can be used in XPCOM methods with Result<T, nserror> results.
 template <>
-class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult> {
+class [[nodiscard]] GenericErrorResult<nsresult> {
   nsresult mErrorValue;
 
   template <typename V, typename E2>

servo/ports/geckolib/cbindgen.toml

@@ -473,8 +473,8 @@ renaming_overrides_prefixing = true
   inline bool IsRight() const;
 """
 
-# TODO(emilio): Add hooks to cbindgen to be able to generate MOZ_MUST_USE_TYPE
-# or [[nodiscard]] on the functions.
+# TODO(emilio): Add hooks to cbindgen to be able to generate [[nodiscard]]
+# on the functions.
 "Owned" = """
   UniquePtr<GeckoType> Consume() {
     UniquePtr<GeckoType> ret(ptr);

xpcom/base/nscore.h

@@ -234,9 +234,9 @@ struct UnusedZero<nsresult> {
 }  // namespace detail
 
 template <typename T>
-class MOZ_MUST_USE_TYPE GenericErrorResult;
+class GenericErrorResult;
 template <>
-class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult>;
+class GenericErrorResult<nsresult>;
 
 struct Ok;
 template <typename V, typename E>

xpcom/docs/xpidl.rst

@@ -290,7 +290,7 @@ to OOM).
 The ``must_use`` property is useful if the result of a method call or an
 attribute get/set should always (or usually) be checked, which is frequently
 the case.  (e.g. a method that opens a file should almost certainly have its
-result checked.) This property will cause ``MOZ_MUST_USE`` to be added to the
+result checked.) This property will cause ``[[nodiscard]]`` to be added to the
 generated function declarations, which means certain compilers (e.g. clang and
 GCC) will reports errors if these results are not used.