[Type checker] Minor cleanups for @objc inference from witnesses.

(cherry picked from commit 4820453)

Author: DougGregor

lib/Sema/TypeCheckProtocol.cpp

@@ -4853,6 +4853,7 @@ TypeChecker::findWitnessedObjCRequirements(const ValueDecl *witness,
     // We only care about Objective-C protocols.
     if (!proto->isObjC()) continue;
 
+    Optional<ProtocolConformance *> conformance;
     for (auto req : proto->lookupDirect(name, true)) {
       // Skip anything in a protocol extension.
       if (req->getDeclContext() != proto) continue;
@@ -4861,7 +4862,6 @@ TypeChecker::findWitnessedObjCRequirements(const ValueDecl *witness,
       if (isa<TypeDecl>(req)) continue;
 
       // Dig out the conformance.
-      Optional<ProtocolConformance *> conformance;
       if (!conformance.hasValue()) {
         SmallVector<ProtocolConformance *, 2> conformances;
         nominal->lookupConformance(dc->getParentModule(), proto,

test/attr/attr_objc.swift

@@ -2147,20 +2147,18 @@ extension ClassInfersFromProtocol3 {
   func method1(value: String) { }
 }
 
+// Inference for subclasses.
 class SuperclassImplementsProtocol : InferFromProtocol { }
 
-// Note: no inference for subclasses
 class SubclassInfersFromProtocol1 : SuperclassImplementsProtocol {
   // CHECK: {{^}} @objc func method1(value: Int)
   func method1(value: Int) { }
 }
 
-// Note: no inference for subclasses
 class SubclassInfersFromProtocol2 : SuperclassImplementsProtocol {
 }
 
 extension SubclassInfersFromProtocol2 {
   // CHECK: {{^}} @objc dynamic func method1(value: Int)
   func method1(value: Int) { }
 }
-