Fix for crash 28328. A decl's computeNominalType() can return null, but a bunch of places expect getDeclaredTypeInContext() to never be null so use ErrorType instead.

Author: gregomni

lib/AST/Decl.cpp

@@ -1995,8 +1995,10 @@ Type NominalTypeDecl::getDeclaredTypeInContext() const {
     return DeclaredTyInContext;
 
   auto *decl = const_cast<NominalTypeDecl *>(this);
-  decl->DeclaredTyInContext =
-      computeNominalType(decl, DeclTypeKind::DeclaredTypeInContext);
+  auto Ty = computeNominalType(decl, DeclTypeKind::DeclaredTypeInContext);
+  if (!Ty)
+    Ty = ErrorType::get(getASTContext());
+  decl->DeclaredTyInContext = Ty;
   return DeclaredTyInContext;
 }
 

validation-test/compiler_crashers/28328-swift-typebase-getdesugaredtype.swift renamed to validation-test/compiler_crashers_fixed/28328-swift-typebase-getdesugaredtype.swift

@@ -5,5 +5,5 @@
 // See http://swift.org/LICENSE.txt for license information
 // See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
 
-// RUN: not --crash %target-swift-frontend %s -parse
+// RUN: not %target-swift-frontend %s -parse
 let a{extension{enum k:String{{{}}case