MS.CA.CSharp uses framework nullable

src/Compilers/CSharp/Portable/Compilation/CSharpCompilation.cs

@@ -1020,7 +1020,7 @@ internal override IEnumerable<ReferenceDirective> ReferenceDirectives
         {
             RoslynDebug.Assert(directive.SyntaxTree.FilePath is object);
 
-            MetadataReference reference;
+            MetadataReference? reference;
             return ReferenceDirectiveMap.TryGetValue((directive.SyntaxTree.FilePath, directive.File.ValueText), out reference) ? reference : null;
         }
 
@@ -1268,13 +1268,13 @@ internal new NamespaceSymbol GlobalNamespace
             return null;
         }
 
-        private ConcurrentDictionary<string?, NamespaceSymbol>? _externAliasTargets;
+        private ConcurrentDictionary<string, NamespaceSymbol>? _externAliasTargets;
 
-        internal bool GetExternAliasTarget(string? aliasName, out NamespaceSymbol? @namespace)
+        internal bool GetExternAliasTarget(string aliasName, out NamespaceSymbol? @namespace)
         {
             if (_externAliasTargets == null)
             {
-                Interlocked.CompareExchange(ref _externAliasTargets, new ConcurrentDictionary<string?, NamespaceSymbol>(), null);
+                Interlocked.CompareExchange(ref _externAliasTargets, new ConcurrentDictionary<string, NamespaceSymbol>(), null);
             }
             else if (_externAliasTargets.TryGetValue(aliasName, out @namespace))
             {
@@ -1443,7 +1443,7 @@ private static CSDiagnosticInfo CreateReflectionTypeNotFoundError(Type type)
             // The type or namespace name '{0}' could not be found in the global namespace (are you missing an assembly reference?)
             return new CSDiagnosticInfo(
                 ErrorCode.ERR_GlobalSingleTypeNameNotFound,
-                new object[] { type.AssemblyQualifiedName },
+                new object[] { type.AssemblyQualifiedName ?? "" },
                 ImmutableArray<Symbol>.Empty,
                 ImmutableArray<Location>.Empty
             );
@@ -2045,7 +2045,7 @@ internal BinderFactory GetBinderFactory(SyntaxTree syntaxTree)
                 binderFactories = Interlocked.CompareExchange(ref _binderFactories, binderFactories, null) ?? binderFactories;
             }
 
-            BinderFactory previousFactory;
+            BinderFactory? previousFactory;
             var previousWeakReference = binderFactories[treeNum];
             if (previousWeakReference != null && previousWeakReference.TryGetTarget(out previousFactory))
             {
@@ -2062,7 +2062,7 @@ private BinderFactory AddNewFactory(SyntaxTree syntaxTree, [NotNull] ref WeakRef
 
             while (true)
             {
-                BinderFactory previousFactory;
+                BinderFactory? previousFactory;
                 WeakReference<BinderFactory>? previousWeakReference = slot;
                 if (previousWeakReference != null && previousWeakReference.TryGetTarget(out previousFactory))
                 {
@@ -3620,7 +3620,7 @@ public IEnumerable<Symbol> GetSymbolsWithName()
             }
 
             private NamespaceOrTypeSymbol? GetCachedSymbol(MergedNamespaceOrTypeDeclaration declaration)
-                => _cache.TryGetValue(declaration, out NamespaceOrTypeSymbol symbol)
+                => _cache.TryGetValue(declaration, out NamespaceOrTypeSymbol? symbol)
                         ? symbol
                         : null;
 

src/Compilers/CSharp/Portable/Microsoft.CodeAnalysis.CSharp.csproj

@@ -15,10 +15,6 @@
     <PackageDescription>
       .NET Compiler Platform ("Roslyn") support for C#, Microsoft.CodeAnalysis.CSharp.dll.
     </PackageDescription>
-
-    <!-- Disable the nullable warnings when compiling for netcoreapp3.1 during our transition period -->
-    <DisableNullableWarnings Condition="'$(TargetFramework)' == 'netcoreapp3.1'">true</DisableNullableWarnings>
-    <DisableNullableWarnings Condition="'$(TargetFramework)' == 'netstandard2.0'">false</DisableNullableWarnings>
   </PropertyGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\Core\Portable\Microsoft.CodeAnalysis.csproj" />

src/Compilers/CSharp/Portable/Symbols/ReferenceManager.cs

@@ -828,7 +828,7 @@ private static void UpdateSymbolCacheNoLock(List<int> newSymbols, ImmutableArray
                 AssemblyIdentity assemblyIdentity,
                 ref Dictionary<AssemblyIdentity, MissingAssemblySymbol>? missingAssemblies)
             {
-                MissingAssemblySymbol missingAssembly;
+                MissingAssemblySymbol? missingAssembly;
 
                 if (missingAssemblies == null)
                 {