ClangImporter: Fix diagnostics for NS* prefix stripping from generic types

We were failing to create an unavailable TypeAlias for the old name
in the case the renamed type was generic, leading to poor diagnostics.

Also, Sema resolves generic TypeAliases very early, while building
a Type from a TypeRepr -- this means the unavailable/deprecated
check runs too late to catch generic TypeAlises.

Add a hack where we preserve a reference to the original TypeAliasDecl
by way of constructing a SubstitutedType which desugars to the
replacement type, rather than resolving the replacement type
directly, so that the availability check can pick it up.

A better fix for this would be to introduce a BoundGenericAliasType
sugared type, but that's a bigger change that can come later.

Fixes <rdar://problem/26206263>.

Author: slavapestov

lib/ClangImporter/ImportDecl.cpp

@@ -1311,10 +1311,19 @@ namespace {
       auto typeDecl = dyn_cast_or_null<TypeDecl>(importedDecl);
       if (!typeDecl) return nullptr;
 
-      // FIXME: We cannot currently handle generic types.
+      // Handle generic types.
+      GenericParamList *genericParams = nullptr;
+      GenericSignature *genericSig = nullptr;
+      auto underlyingType = typeDecl->getDeclaredInterfaceType();
+
       if (auto generic = dyn_cast<GenericTypeDecl>(typeDecl)) {
-        if (generic->getGenericSignature() && !isa<ProtocolDecl>(typeDecl))
-          return nullptr;
+        if (generic->getGenericSignature() && !isa<ProtocolDecl>(typeDecl)) {
+          genericParams = generic->getGenericParams();
+          genericSig = generic->getGenericSignature();
+
+          underlyingType = ArchetypeBuilder::mapTypeIntoContext(
+              generic, underlyingType);
+        }
       }
 
       // Import the declaration context where this name will go. Note that
@@ -1326,15 +1335,15 @@ namespace {
       if (!dc) return nullptr;
 
       // Create the type alias.
-      auto underlyingType = typeDecl->getDeclaredInterfaceType();
       auto alias = Impl.createDeclWithClangNode<TypeAliasDecl>(
                      decl,
                      Impl.importSourceLoc(decl->getLocStart()),
                      swift2Name.Imported.getBaseName(),
                      Impl.importSourceLoc(decl->getLocation()),
                      TypeLoc::withoutLoc(underlyingType),
-                     /*genericparams*/nullptr, dc);
+                     genericParams, dc);
       alias->computeType();
+      alias->setGenericSignature(genericSig);
 
       // Record that this is the Swift 2 version of this declaration.
       Impl.ImportedDecls[{decl->getCanonicalDecl(), true}] = alias;

lib/Sema/ConstraintSystem.cpp

@@ -629,7 +629,11 @@ namespace {
           arguments.push_back(TypeLoc::withoutLoc(
                               replacements[gp->getCanonicalType()]));
         }
-        
+
+        // FIXME: For some reason we can end up with unbound->getDecl()
+        // pointing at a generic TypeAliasDecl here. If we find a way to
+        // handle generic TypeAliases elsewhere, this can just become a
+        // call to BoundGenericType::get().
         return cs.TC.applyUnboundGenericArguments(unbound, SourceLoc(), cs.DC,
                                                   arguments,
                                                   /*isGenericSignature*/false,

lib/Sema/TypeCheckType.cpp

@@ -503,7 +503,15 @@ Type TypeChecker::applyUnboundGenericArguments(
       subs.push_back(Substitution(t.getType(), {}));
 
     auto subst = TAD->getGenericParams()->getSubstitutionMap(subs);
-    return TAD->getUnderlyingType().subst(TAD->getParentModule(), subst, None);
+
+    // FIXME: return a SubstitutedType to preserve the fact that
+    // we resolved a generic TypeAlias, for availability diagnostics.
+    // A better fix might be to introduce a BoundGenericAliasType
+    // which desugars as appropriate.
+    return SubstitutedType::get(
+        TAD->getDeclaredType(),
+        TAD->getUnderlyingType().subst(TAD->getParentModule(), subst, None),
+        Context);
   }
 
   // Form the bound generic type.

test/ClangModules/swift2_warnings.swift

@@ -12,6 +12,8 @@ func testOldTypeNames() {
 
 
   _ = NSPostingStyle(rawValue: 1) // expected-error{{'NSPostingStyle' has been renamed to 'PostingStyle'}}{{7-21=PostingStyle}}
+
+  _ = NSSoapDispenser<AnyObject>() // expected-error{{'NSSoapDispenser' has been renamed to 'SoapDispenser'}}{{7-22=SoapDispenser}}
 }
 
 func testOldMethodNames(array: NSArray) {

test/Inputs/clang-importer-sdk/usr/include/Foundation.h

@@ -1015,5 +1015,9 @@ extern NSString *NSHTTPRequestKey;
 -(void)messageSomeObject:(nonnull id)object selector:(SEL)selector;
 @end
 
+@interface NSSoapDispenser<Fragrance> : NSObject
+
+@end
+
 #define NSTimeIntervalSince1970 978307200.0
 #define NS_DO_SOMETHING 17

test/attr/attr_availability.swift

@@ -42,6 +42,11 @@ extension MyCollection {
   func append(element: T) { } // expected-error {{'T' has been renamed to 'Element'}} {{24-25=Element}}
 }
 
+@available(*, unavailable, renamed: "MyCollection")
+typealias YourCollection<Element> = MyCollection<Element> // expected-note {{'YourCollection' has been explicitly marked unavailable here}}
+
+var x : YourCollection<Int> // expected-error {{'YourCollection' has been renamed to 'MyCollection'}}{{9-23=MyCollection}}
+
 var x : int // expected-error {{'int' is unavailable: oh no you don't}}
 var y : float // expected-error {{'float' has been renamed to 'Float'}}{{9-14=Float}}