[SourceKit/DocSupport] Don't synthesize extensions for inherited protocol conformances.

The Base class already includes them, so don't duplicate them in its
subclasses. Also stops us including members from extensions of the base class
itself.

Resolves rdar://problem/50960433

Author: Nathan Hawes

lib/IDE/IDETypeChecking.cpp

@@ -471,7 +471,11 @@ struct SynthesizedExtensionAnalyzer::Implementation {
     // We want to visit the protocols of any normal conformances we see, but
     // we have to avoid doing this to self-conformances or we can end up with
     // a cycle.  Otherwise this is cycle-proof on valid code.
+    // We also want to ignore inherited conformances. Members from these will
+    // be included in the class they were inherited from.
     auto addConformance = [&](ProtocolConformance *Conf) {
+      if (isa<InheritedProtocolConformance>(Conf))
+        return;
       auto RootConf = Conf->getRootConformance();
       if (isa<NormalProtocolConformance>(RootConf))
         Unhandled.push_back(RootConf->getProtocol());
@@ -480,10 +484,6 @@ struct SynthesizedExtensionAnalyzer::Implementation {
     for (auto *Conf : Target->getLocalConformances()) {
       addConformance(Conf);
     }
-    if (auto *CD = dyn_cast<ClassDecl>(Target)) {
-      if (auto Super = CD->getSuperclassDecl())
-        Unhandled.push_back(Super);
-    }
     while (!Unhandled.empty()) {
       NominalTypeDecl* Back = Unhandled.back();
       Unhandled.pop_back();
@@ -493,10 +493,6 @@ struct SynthesizedExtensionAnalyzer::Implementation {
       for (auto *Conf : Back->getLocalConformances()) {
         addConformance(Conf);
       }
-      if (auto *CD = dyn_cast<ClassDecl>(Back)) {
-        if (auto Super = CD->getSuperclass())
-          Unhandled.push_back(Super->getAnyNominal());
-      }
     }
 
     // Merge with actual extensions.