[AST] NFC: Rename underlying type accessors of OpaqueTypeDecl

Adds a `Unique` component to the accessor names to draw the
distinction between unique and conditionally available substitutions.

Author: xedin

include/swift/AST/Decl.h

@@ -2840,7 +2840,7 @@ class OpaqueTypeDecl final :
   /// expressed as a SubstitutionMap for the opaque interface generic signature.
   /// This maps types in the interface generic signature to the outer generic
   /// signature of the original declaration.
-  Optional<SubstitutionMap> UnderlyingTypeSubstitutions;
+  Optional<SubstitutionMap> UniqueUnderlyingType;
 
   /// A set of substitutions which are used based on the availability
   /// checks performed at runtime. This set of only populated if there
@@ -2922,16 +2922,16 @@ class OpaqueTypeDecl final :
   }
 
   /// The substitutions that map the generic parameters of the opaque type to
-  /// their underlying types, when that information is known.
-  Optional<SubstitutionMap> getUnderlyingTypeSubstitutions() const {
-    return UnderlyingTypeSubstitutions;
+  /// the unique underlying types, when that information is known.
+  Optional<SubstitutionMap> getUniqueUnderlyingTypeSubstitutions() const {
+    return UniqueUnderlyingType;
   }
 
-  void setUnderlyingTypeSubstitutions(SubstitutionMap subs) {
-    assert(!UnderlyingTypeSubstitutions.hasValue() && "resetting underlying type?!");
-    UnderlyingTypeSubstitutions = subs;
+  void setUniqueUnderlyingTypeSubstitutions(SubstitutionMap subs) {
+    assert(!UniqueUnderlyingType.hasValue() && "resetting underlying type?!");
+    UniqueUnderlyingType = subs;
   }
-t
+
   void setConditionallyAvailableSubstitutions(
       ArrayRef<ConditionallyAvailableSubstitutions *> substitutions) {
     assert(!ConditionallyAvailableTypes &&

lib/AST/ASTDumper.cpp

@@ -572,7 +572,7 @@ namespace {
         << OTD->getDeclaredInterfaceType().getString();
       OS << " in "
          << OTD->getOpaqueInterfaceGenericSignature()->getAsString();
-      if (auto underlyingSubs = OTD->getUnderlyingTypeSubstitutions()) {
+      if (auto underlyingSubs = OTD->getUniqueUnderlyingTypeSubstitutions()) {
         OS << " underlying:\n";
         SmallPtrSet<const ProtocolConformance *, 4> Dumped;
         dumpSubstitutionMapRec(*underlyingSubs, OS,

lib/AST/Type.cpp

@@ -3638,7 +3638,7 @@ operator()(SubstitutableType *maybeOpaqueType) const {
     return maybeOpaqueType;
   }
 
-  auto subs = opaqueRoot->getDecl()->getUnderlyingTypeSubstitutions();
+  auto subs = opaqueRoot->getDecl()->getUniqueUnderlyingTypeSubstitutions();
   // If the body of the opaque decl providing decl has not been type checked we
   // don't have a underlying subsitution.
   if (!subs.hasValue())
@@ -3749,7 +3749,7 @@ operator()(CanType maybeOpaqueType, Type replacementType,
     return abstractRef;
   }
 
-  auto subs = opaqueRoot->getDecl()->getUnderlyingTypeSubstitutions();
+  auto subs = opaqueRoot->getDecl()->getUniqueUnderlyingTypeSubstitutions();
   // If the body of the opaque decl providing decl has not been type checked we
   // don't have a underlying subsitution.
   if (!subs.hasValue())

lib/IRGen/GenMeta.cpp

@@ -2040,7 +2040,7 @@ namespace {
     void addUnderlyingTypeAndConformances() {
       auto sig = O->getOpaqueInterfaceGenericSignature();
       auto contextSig = O->getGenericSignature().getCanonicalSignature();
-      auto subs = *O->getUnderlyingTypeSubstitutions();
+      auto subs = *O->getUniqueUnderlyingTypeSubstitutions();
 
       // Add the underlying types for each generic parameter.
       for (auto genericParam : O->getOpaqueGenericParams()) {

lib/Sema/CSApply.cpp

@@ -8442,7 +8442,7 @@ static Optional<SolutionApplicationTarget> applySolutionToInitialization(
         return expr;
       });
 
-      opaque->setUnderlyingTypeSubstitutions(substitutions);
+      opaque->setUniqueUnderlyingTypeSubstitutions(substitutions);
     }
   }
 

lib/Sema/MiscDiagnostics.cpp

@@ -2713,7 +2713,7 @@ class OpaqueUnderlyingTypeChecker : public ASTWalker {
 
     // If we have one successful candidate, then save it as the underlying
     // substitutions of the opaque decl.
-    OpaqueDecl->setUnderlyingTypeSubstitutions(
+    OpaqueDecl->setUniqueUnderlyingTypeSubstitutions(
         underlyingSubs.mapReplacementTypesOutOfContext());
   }
 

lib/Serialization/Deserialization.cpp

@@ -3571,7 +3571,7 @@ class DeclDeserializer {
       auto subMapOrError = MF.getSubstitutionMapChecked(underlyingTypeSubsID);
       if (!subMapOrError)
         return subMapOrError.takeError();
-      opaqueDecl->setUnderlyingTypeSubstitutions(subMapOrError.get());
+      opaqueDecl->setUniqueUnderlyingTypeSubstitutions(subMapOrError.get());
     }
     return opaqueDecl;
   }

lib/Serialization/Serialization.cpp

@@ -3898,7 +3898,7 @@ class Serializer::DeclSerializer : public DeclVisitor<DeclSerializer> {
     auto genericSigID = S.addGenericSignatureRef(opaqueDecl->getGenericSignature());
 
     SubstitutionMapID underlyingSubsID = 0;
-    if (auto underlying = opaqueDecl->getUnderlyingTypeSubstitutions())
+    if (auto underlying = opaqueDecl->getUniqueUnderlyingTypeSubstitutions())
       underlyingSubsID = S.addSubstitutionMapRef(*underlying);
     uint8_t rawAccessLevel =
       getRawStableAccessLevel(opaqueDecl->getFormalAccess());