Bug 1709352 - Allow QMResult errors to use existing stack id and to increase the frame id during error propagation; r=dom-storage-reviewers,asuth,glandium

Differential Revision: https://phabricator.services.mozilla.com/D114243

dom/quota/QMResultInlines.h

@@ -17,6 +17,39 @@
 
 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> {
+  QMResult mErrorValue;
+
+  template <typename V, typename E2>
+  friend class Result;
+
+ public:
+  explicit GenericErrorResult(const QMResult& aErrorValue)
+      : mErrorValue(aErrorValue) {
+    MOZ_ASSERT(NS_FAILED(aErrorValue.NSResult()));
+  }
+
+  explicit GenericErrorResult(QMResult&& aErrorValue)
+      : mErrorValue(std::move(aErrorValue)) {
+    MOZ_ASSERT(NS_FAILED(aErrorValue.NSResult()));
+  }
+
+  explicit GenericErrorResult(const QMResult& aErrorValue,
+                              const ErrorPropagationTag&)
+      : GenericErrorResult(aErrorValue.Propagate()) {}
+
+  explicit GenericErrorResult(QMResult&& aErrorValue,
+                              const ErrorPropagationTag&)
+      : GenericErrorResult(aErrorValue.Propagate()) {}
+
+  operator QMResult() const { return mErrorValue; }
+
+  operator nsresult() const { return mErrorValue.NSResult(); }
+};
+
 inline Result<Ok, QMResult> ToResult(const QMResult& aValue) {
   if (NS_FAILED(aValue.NSResult())) {
     return Err(aValue);

dom/quota/QuotaCommon.h

@@ -1076,6 +1076,10 @@ class MOZ_MUST_USE_TYPE GenericErrorResult<mozilla::ipc::IPCResult> {
     MOZ_ASSERT(!aErrorValue);
   }
 
+  GenericErrorResult(mozilla::ipc::IPCResult aErrorValue,
+                     const ErrorPropagationTag&)
+      : GenericErrorResult(aErrorValue) {}
+
   operator mozilla::ipc::IPCResult() const { return mErrorValue; }
 };
 

dom/quota/test/gtest/TestQMResult.cpp

@@ -79,3 +79,24 @@ TEST(DOM_Quota_QMResult, ToResult)
     ASSERT_EQ(err.NSResult(), NS_ERROR_FAILURE);
   }
 }
+
+TEST(DOM_Quota_QMResult, ErrorPropagation)
+{
+  Result<Ok, QMResult> valOrErr1 = ToResult(ToQMResult(NS_ERROR_FAILURE));
+  const auto& err1 = valOrErr1.inspectErr();
+  ASSERT_EQ(err1.StackId(), 7u);
+  ASSERT_EQ(err1.FrameId(), 1u);
+  ASSERT_EQ(err1.NSResult(), NS_ERROR_FAILURE);
+
+  Result<Ok, QMResult> valOrErr2 = valOrErr1.propagateErr();
+  const auto& err2 = valOrErr2.inspectErr();
+  ASSERT_EQ(err2.StackId(), 7u);
+  ASSERT_EQ(err2.FrameId(), 2u);
+  ASSERT_EQ(err2.NSResult(), NS_ERROR_FAILURE);
+
+  Result<Ok, QMResult> valOrErr3 = valOrErr2.propagateErr();
+  const auto& err3 = valOrErr3.inspectErr();
+  ASSERT_EQ(err3.StackId(), 7u);
+  ASSERT_EQ(err3.FrameId(), 3u);
+  ASSERT_EQ(err3.NSResult(), NS_ERROR_FAILURE);
+}

mfbt/Result.h

@@ -27,6 +27,15 @@ namespace mozilla {
  */
 struct Ok {};
 
+/**
+ * A tag used to differentiate between GenericErrorResult created by the Err
+ * function (completely new error) and GenericErrorResult created by the
+ * Result::propagateErr function (propagated error). This can be used to track
+ * error propagation and eventually produce error stacks for logging/debugging
+ * purposes.
+ */
+struct ErrorPropagationTag {};
+
 template <typename E>
 class GenericErrorResult;
 template <typename V, typename E>
@@ -563,7 +572,7 @@ class MOZ_MUST_USE_TYPE Result final {
    */
   constexpr GenericErrorResult<E> propagateErr() {
     MOZ_ASSERT(isErr());
-    return GenericErrorResult<E>{mImpl.unwrapErr()};
+    return GenericErrorResult<E>{mImpl.unwrapErr(), ErrorPropagationTag{}};
   }
 
   /**
@@ -748,6 +757,12 @@ class MOZ_MUST_USE_TYPE GenericErrorResult {
 
   explicit constexpr GenericErrorResult(E&& aErrorValue)
       : mErrorValue(std::move(aErrorValue)) {}
+
+  constexpr GenericErrorResult(const E& aErrorValue, const ErrorPropagationTag&)
+      : GenericErrorResult(aErrorValue) {}
+
+  constexpr GenericErrorResult(E&& aErrorValue, const ErrorPropagationTag&)
+      : GenericErrorResult(std::move(aErrorValue)) {}
 };
 
 template <typename E>

mfbt/ResultExtensions.h

@@ -16,6 +16,8 @@
 
 namespace mozilla {
 
+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 <>
@@ -30,6 +32,9 @@ class MOZ_MUST_USE_TYPE GenericErrorResult<nsresult> {
     MOZ_ASSERT(NS_FAILED(aErrorValue));
   }
 
+  GenericErrorResult(nsresult aErrorValue, const ErrorPropagationTag&)
+      : GenericErrorResult(aErrorValue) {}
+
   operator nsresult() const { return mErrorValue; }
 };