AST: Build scopes for if #available queries on custom availability domains.

Resolves rdar://138441298 and rdar://138441307.

Author: tshortli

include/swift/AST/AvailabilityContext.h

@@ -104,10 +104,6 @@ class AvailabilityContext {
   void constrainWithPlatformRange(const AvailabilityRange &range,
                                   const ASTContext &ctx);
 
-  /// Expand the platform version range to contain `range`.
-  void unionWithPlatformRange(const AvailabilityRange &range,
-                              const ASTContext &ctx);
-
   /// Constrain the available range for `domain` by `range`.
   void constrainWithAvailabilityRange(const AvailabilityRange &range,
                                       AvailabilityDomain domain,

include/swift/AST/AvailabilityContextStorage.h

@@ -44,7 +44,6 @@ class AvailabilityContext::DomainInfo final {
   bool isUnavailable() const { return range.isKnownUnreachable(); }
 
   bool constrainRange(const AvailabilityRange &range);
-  bool unionRange(const AvailabilityRange &range);
 
   void Profile(llvm::FoldingSetNodeID &ID) const {
     ID.AddPointer(domain.getOpaqueValue());

lib/AST/AvailabilityContext.cpp

@@ -46,15 +46,6 @@ static bool constrainRange(AvailabilityRange &existing,
   return true;
 }
 
-static bool unionRange(AvailabilityRange &existing,
-                       const AvailabilityRange &other) {
-  if (!existing.isContainedIn(other))
-    return false;
-
-  existing = other;
-  return true;
-}
-
 /// Returns true if `domainInfos` will be constrained by merging the domain
 /// availability represented by `otherDomainInfo`. Additionally, this function
 /// has a couple of side-effects:
@@ -145,11 +136,6 @@ bool AvailabilityContext::DomainInfo::constrainRange(
   return ::constrainRange(range, otherRange);
 }
 
-bool AvailabilityContext::DomainInfo::unionRange(
-    const AvailabilityRange &otherRange) {
-  return ::unionRange(range, otherRange);
-}
-
 AvailabilityContext
 AvailabilityContext::forPlatformRange(const AvailabilityRange &range,
                                       const ASTContext &ctx) {
@@ -298,18 +284,6 @@ void AvailabilityContext::constrainWithPlatformRange(
                          storage->getDomainInfos(), ctx);
 }
 
-void AvailabilityContext::unionWithPlatformRange(const AvailabilityRange &range,
-                                                 const ASTContext &ctx) {
-  auto platformRange = storage->platformRange;
-  if (!unionRange(platformRange, range))
-    return;
-
-  // FIXME: [availability] Should this remove any unavailable platform domains?
-
-  storage = Storage::get(platformRange, storage->isDeprecated,
-                         storage->getDomainInfos(), ctx);
-}
-
 void AvailabilityContext::constrainWithAvailabilityRange(
     const AvailabilityRange &range, AvailabilityDomain domain,
     const ASTContext &ctx) {