Bug 1542214 - Prevent registering the same CID and contract IDs durin…

…g component manager initialization. r=froydnj

Because not all static components are using the static registration yet,
we can end up in situations where a same component is registered
multiple times, which can have some unexpected consequences.

Interestingly enough, this change revealed that we did have static
registration in place for components that were kept under the old system
after bug 1478124 and bug 1524687.

There are also possibly some non-obvious things that can happen while
migrating the remaining components, like what happened to me while I
worked on @mozilla.org/widget/components;1 (see bug 1542214 comment 0).

Differential Revision: https://phabricator.services.mozilla.com/D26698

--HG--
extra : moz-landing-system : lando

xpcom/components/nsComponentManager.cpp

@@ -710,6 +710,19 @@ void nsComponentManagerImpl::RegisterCIDEntryLocked(
     return;
   }
 
+#ifdef DEBUG
+  // If we're still in the static initialization phase, check that we're not
+  // registering something that was already registered.
+  if (mStatus != NORMAL) {
+    if (StaticComponents::LookupByCID(*aEntry->cid)) {
+      MOZ_CRASH_UNSAFE_PRINTF(
+          "While registering XPCOM module %s, trying to re-register CID '%s' "
+          "already registered by a static component.",
+          aModule->Description().get(), AutoIDString(*aEntry->cid).get());
+    }
+  }
+#endif
+
   if (auto entry = mFactories.LookupForAdd(aEntry->cid)) {
     nsFactoryEntry* f = entry.Data();
     NS_WARNING("Re-registering a CID?");
@@ -740,6 +753,21 @@ void nsComponentManagerImpl::RegisterContractIDLocked(
     return;
   }
 
+#ifdef DEBUG
+  // If we're still in the static initialization phase, check that we're not
+  // registering something that was already registered.
+  if (mStatus != NORMAL) {
+    if (const StaticModule* module = StaticComponents::LookupByContractID(
+            nsAutoCString(aEntry->contractid))) {
+      MOZ_CRASH_UNSAFE_PRINTF(
+          "Could not map contract ID '%s' to CID %s because it is already "
+          "mapped to CID %s.",
+          aEntry->contractid, AutoIDString(*aEntry->cid).get(),
+          AutoIDString(module->CID()).get());
+    }
+  }
+#endif
+
   nsFactoryEntry* f = mFactories.Get(aEntry->cid);
   if (!f) {
     NS_WARNING("No CID found when attempting to map contract ID");