Separate the "set for caching" and "set programmatically" for storage impl info

Slightly cleanup, and make an assertion less strict in the face of invalid
code.

Author: DougGregor

include/swift/AST/Decl.h

@@ -5295,6 +5295,9 @@ class AbstractStorageDecl : public ValueDecl {
   /// used carefully.
   void setImplInfo(StorageImplInfo implInfo);
 
+  /// Cache the implementation-info, for use by the request-evaluator.
+  void cacheImplInfo(StorageImplInfo implInfo);
+
   ReadImplKind getReadImpl() const {
     return getImplInfo().getReadImpl();
   }

lib/AST/Decl.cpp

@@ -2525,7 +2525,7 @@ AbstractStorageDecl::getAccessStrategy(AccessSemantics semantics,
                                        ResilienceExpansion expansion) const {
   switch (semantics) {
   case AccessSemantics::DirectToStorage:
-    assert(hasStorage());
+    assert(hasStorage() || getASTContext().Diags.hadAnyError());
     return AccessStrategy::getStorage();
 
   case AccessSemantics::DistributedThunk:
@@ -6407,15 +6407,23 @@ StorageImplInfo AbstractStorageDecl::getImplInfo() const {
     StorageImplInfo::getSimpleStored(StorageIsMutable));
 }
 
-void AbstractStorageDecl::setImplInfo(StorageImplInfo implInfo) {
+void AbstractStorageDecl::cacheImplInfo(StorageImplInfo implInfo) {
   LazySemanticInfo.ImplInfoComputed = 1;
   ImplInfo = implInfo;
+}
+
+void AbstractStorageDecl::setImplInfo(StorageImplInfo implInfo) {
+  cacheImplInfo(implInfo);
 
   if (isImplicit()) {
     auto &evaluator = getASTContext().evaluator;
     HasStorageRequest request{this};
     if (!evaluator.hasCachedResult(request))
       evaluator.cacheOutput(request, implInfo.hasStorage());
+    else {
+      assert(
+        evaluateOrDefault(evaluator, request, false) == implInfo.hasStorage());
+    }
   }
 }
 

lib/AST/TypeCheckRequests.cpp

@@ -687,7 +687,7 @@ StorageImplInfoRequest::getCachedResult() const {
 
 void StorageImplInfoRequest::cacheResult(StorageImplInfo value) const {
   auto *storage = std::get<0>(getStorage());
-  storage->setImplInfo(value);
+  storage->cacheImplInfo(value);
 }
 
 //----------------------------------------------------------------------------//