AST: Add verification for AvailabilityContext.

Author: tshortli

include/swift/AST/AvailabilityContext.h

@@ -112,6 +112,9 @@ class AvailabilityContext {
 
   void print(llvm::raw_ostream &os) const;
   SWIFT_DEBUG_DUMP;
+
+  /// Returns true if all internal invariants are satisfied.
+  bool verify(ASTContext &ctx) const;
 };
 
 } // end namespace swift

include/swift/AST/AvailabilityContextStorage.h

@@ -61,6 +61,9 @@ class AvailabilityContext::Info {
   bool isContainedIn(const Info &other) const;
 
   void Profile(llvm::FoldingSetNodeID &ID) const;
+
+  /// Returns true if all internal invariants are satisfied.
+  bool verify(ASTContext &ctx) const;
 };
 
 /// As an implementation detail, the values that make up an `Availability`

lib/AST/AvailabilityContext.cpp

@@ -155,6 +155,16 @@ void AvailabilityContext::Info::Profile(llvm::FoldingSetNodeID &ID) const {
   ID.AddBoolean(IsDeprecated);
 }
 
+bool AvailabilityContext::Info::verify(ASTContext &ctx) const {
+  // Unavailable domains must be sorted to ensure folding set node lookups yield
+  // consistent results.
+  if (!llvm::is_sorted(UnavailableDomains,
+                       StableAvailabilityDomainComparator()))
+    return false;
+
+  return true;
+}
+
 AvailabilityContext
 AvailabilityContext::forPlatformRange(const AvailabilityRange &range,
                                       ASTContext &ctx) {
@@ -278,3 +288,7 @@ void AvailabilityContext::print(llvm::raw_ostream &os) const {
 }
 
 void AvailabilityContext::dump() const { print(llvm::errs()); }
+
+bool AvailabilityContext::verify(ASTContext &ctx) const {
+  return storage->info.verify(ctx);
+}

lib/AST/AvailabilityScope.cpp

@@ -581,7 +581,11 @@ void AvailabilityScope::verify(const AvailabilityScope *parent,
                         {{"child", this}, {"parent", parent}});
   }
 
-  if (!getAvailabilityContext().isContainedIn(parent->getAvailabilityContext()))
+  auto context = getAvailabilityContext();
+  if (!context.verify(ctx))
+    verificationError(ctx, "context is invalid", {{"node", this}});
+
+  if (!context.isContainedIn(parent->getAvailabilityContext()))
     verificationError(ctx, "child availability range not contained",
                       {{"child", this}, {"parent", parent}});
 }