[Sema] WitnessMatching: Anchor ProtocolRequirement on the requrement declaration

Locators used to support only expressions which is no longer the case.

Author: xedin

include/swift/Sema/ConstraintLocator.h

@@ -820,18 +820,6 @@ class LocatorPathElt::Witness final : public StoredPointerElement<ValueDecl> {
   }
 };
 
-class LocatorPathElt::ProtocolRequirement final : public StoredPointerElement<ValueDecl> {
-public:
-  ProtocolRequirement(ValueDecl *decl)
-      : StoredPointerElement(PathElementKind::ProtocolRequirement, decl) {}
-
-  ValueDecl *getDecl() const { return getStoredPointer(); }
-
-  static bool classof(const LocatorPathElt *elt) {
-    return elt->getKind() == PathElementKind::ProtocolRequirement;
-  }
-};
-
 class LocatorPathElt::GenericParameter final : public StoredPointerElement<GenericTypeParamType> {
 public:
   GenericParameter(GenericTypeParamType *type)

include/swift/Sema/ConstraintLocatorPathElts.def

@@ -161,7 +161,7 @@ SIMPLE_LOCATOR_PATH_ELT(ParentType)
 
 /// The requirement that we're matching during protocol conformance
 /// checking.
-CUSTOM_LOCATOR_PATH_ELT(ProtocolRequirement)
+SIMPLE_LOCATOR_PATH_ELT(ProtocolRequirement)
 
 /// Type parameter requirements.
 ABSTRACT_LOCATOR_PATH_ELT(AnyRequirement)

lib/Sema/ConstraintLocator.cpp

@@ -304,9 +304,7 @@ void LocatorPathElt::dump(raw_ostream &out) const {
     break;
   }
   case ConstraintLocator::ProtocolRequirement: {
-    auto reqElt = elt.castTo<LocatorPathElt::ProtocolRequirement>();
-    out << "protocol requirement ";
-    reqElt.getDecl()->dumpRef(out);
+    out << "protocol requirement";
     break;
   }
   case ConstraintLocator::Witness: {

lib/Sema/TypeCheckProtocol.cpp

@@ -1115,8 +1115,8 @@ swift::matchWitness(WitnessChecker::RequirementEnvironmentCache &reqEnvCache,
       selfTy = syntheticEnv->mapTypeIntoContext(selfTy);
 
     // Open up the type of the requirement.
-    reqLocator = cs->getConstraintLocator(
-        static_cast<Expr *>(nullptr), LocatorPathElt::ProtocolRequirement(req));
+    reqLocator =
+        cs->getConstraintLocator(req, ConstraintLocator::ProtocolRequirement);
     OpenedTypeMap reqReplacements;
     reqType = cs->getTypeOfMemberReference(selfTy, req, dc,
                                            /*isDynamicResult=*/false,