[mle] update Mle::GetParent() to return reference (#4419)

src/core/api/thread_api.cpp

@@ -311,7 +311,7 @@ otError otThreadGetParentInfo(otInstance *aInstance, otRouterInfo *aParentInfo)
     VerifyOrExit(instance.Get<Mle::MleRouter>().GetRole() == OT_DEVICE_ROLE_CHILD, error = OT_ERROR_INVALID_STATE);
 #endif
 
-    parent = instance.Get<Mle::MleRouter>().GetParent();
+    parent = &instance.Get<Mle::MleRouter>().GetParent();
 
     aParentInfo->mExtAddress     = parent->GetExtAddress();
     aParentInfo->mRloc16         = parent->GetRloc16();
@@ -334,12 +334,10 @@ otError otThreadGetParentAverageRssi(otInstance *aInstance, int8_t *aParentRssi)
 {
     otError   error    = OT_ERROR_NONE;
     Instance &instance = *static_cast<Instance *>(aInstance);
-    Router *  parent;
 
     assert(aParentRssi != NULL);
 
-    parent       = instance.Get<Mle::MleRouter>().GetParent();
-    *aParentRssi = parent->GetLinkInfo().GetAverageRss();
+    *aParentRssi = instance.Get<Mle::MleRouter>().GetParent().GetLinkInfo().GetAverageRss();
 
     VerifyOrExit(*aParentRssi != OT_RADIO_RSSI_INVALID, error = OT_ERROR_FAILED);
 
@@ -351,12 +349,10 @@ otError otThreadGetParentLastRssi(otInstance *aInstance, int8_t *aLastRssi)
 {
     otError   error    = OT_ERROR_NONE;
     Instance &instance = *static_cast<Instance *>(aInstance);
-    Router *  parent;
 
     assert(aLastRssi != NULL);
 
-    parent     = instance.Get<Mle::MleRouter>().GetParent();
-    *aLastRssi = parent->GetLinkInfo().GetLastRss();
+    *aLastRssi = instance.Get<Mle::MleRouter>().GetParent().GetLinkInfo().GetLastRss();
 
     VerifyOrExit(*aLastRssi != OT_RADIO_RSSI_INVALID, error = OT_ERROR_FAILED);
 

src/core/mac/data_poll_sender.cpp

@@ -138,7 +138,7 @@ otError DataPollSender::GetPollDestinationAddress(Mac::Address &aDest) const
 
     VerifyOrExit((parent != NULL) && parent->IsStateValidOrRestoring(), error = OT_ERROR_ABORT);
 
-    if ((Get<Mac::Mac>().GetShortAddress() == Mac::kShortAddrInvalid) || (parent != Get<Mle::MleRouter>().GetParent()))
+    if ((Get<Mac::Mac>().GetShortAddress() == Mac::kShortAddrInvalid) || (parent != &Get<Mle::MleRouter>().GetParent()))
     {
         aDest.SetExtended(parent->GetExtAddress());
     }

src/core/thread/key_manager.cpp

@@ -119,7 +119,7 @@ otError KeyManager::SetMasterKey(const MasterKey &aKey)
     ComputeKey(mKeySequence, mKey);
 
     // reset parent frame counters
-    parent = Get<Mle::MleRouter>().GetParent();
+    parent = &Get<Mle::MleRouter>().GetParent();
     parent->SetKeySequence(0);
     parent->SetLinkFrameCounter(0);
     parent->SetMleFrameCounter(0);

src/core/thread/mle.cpp

@@ -3959,11 +3959,6 @@ bool Mle::IsMeshLocalAddress(const Ip6::Address &aAddress) const
     return aAddress.PrefixMatch(GetMeshLocal16()) >= Ip6::Address::kMeshLocalPrefixLength;
 }
 
-Router *Mle::GetParent(void)
-{
-    return &mParent;
-}
-
 Router *Mle::GetParentCandidate(void)
 {
     Router *rval;

src/core/thread/mle.hpp

@@ -747,12 +747,12 @@ public:
     }
 
     /**
-     * This method returns a pointer to the parent when operating in End Device mode.
+     * This method gets the parent when operating in End Device mode.
      *
-     * @returns A pointer to the parent.
+     * @returns A reference to the parent.
      *
      */
-    Router *GetParent(void);
+    Router &GetParent(void) { return mParent; }
 
     /**
      * This method returns a pointer to the parent candidate or parent.

src/core/utils/child_supervision.cpp

@@ -209,7 +209,7 @@ void SupervisionListener::UpdateOnReceive(const Mac::Address &aSourceAddress, bo
     // If listener is enabled and device is a child and it received a secure frame from its parent, restart the timer.
 
     VerifyOrExit(mTimer.IsRunning() && aIsSecure && (Get<Mle::MleRouter>().GetRole() == OT_DEVICE_ROLE_CHILD) &&
-                 (Get<Mle::MleRouter>().GetNeighbor(aSourceAddress) == Get<Mle::MleRouter>().GetParent()));
+                 (Get<Mle::MleRouter>().GetNeighbor(aSourceAddress) == &Get<Mle::MleRouter>().GetParent()));
 
     RestartTimer();