Enabling nullability in NuGet.Packaging - Phase 2, declare some interfaces (#7178)

Author: nkolev92

src/NuGet.Core/NuGet.Packaging/ContentModel/ContentItemGroup.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System.Collections.Generic;
 using System.Diagnostics;
 

src/NuGet.Core/NuGet.Packaging/Core/Fingerprints.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 
@@ -18,7 +16,7 @@ public Fingerprints(IDictionary<string, string> fingerPrints)
         }
 
         // Get fingerprint from hash algorithm oid.
-        public string this[string key]
+        public string? this[string key]
         {
             get
             {

src/NuGet.Core/NuGet.Packaging/Core/FrameworkNameValidatorUtility.cs

@@ -1,5 +1,3 @@
-#nullable disable
-
 using System;
 using System.IO;
 using NuGet.Frameworks;
@@ -16,7 +14,7 @@ internal static bool IsValidFrameworkName(NuGetFramework framework)
 
         internal static bool IsValidFrameworkName(string path)
         {
-            NuGetFramework fx;
+            NuGetFramework? fx;
             try
             {
                 string effectivePath;

src/NuGet.Core/NuGet.Packaging/Core/IAsyncPackageCoreReader.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -37,7 +35,7 @@ public interface IAsyncPackageCoreReader : IDisposable
         /// The task result (<see cref="Task{TResult}.Result" />) returns a <see cref="NuGetVersion" />.</returns>
         /// <exception cref="OperationCanceledException">Thrown if <paramref name="cancellationToken" />
         /// is cancelled.</exception>
-        Task<NuGetVersion> GetMinClientVersionAsync(CancellationToken cancellationToken);
+        Task<NuGetVersion?> GetMinClientVersionAsync(CancellationToken cancellationToken);
 
         /// <summary>
         /// Asynchronously gets zero or more package types from the .nuspec.

src/NuGet.Core/NuGet.Packaging/Core/IPackageCoreReader.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.IO;
@@ -28,7 +26,7 @@ public interface IPackageCoreReader : IDisposable
         /// Gets the minimum client version needed to consume the package.
         /// </summary>
         /// <returns>A NuGet version.</returns>
-        NuGetVersion GetMinClientVersion();
+        NuGetVersion? GetMinClientVersion();
 
         /// <summary>
         /// Gets zero or more package types from the .nuspec.

src/NuGet.Core/NuGet.Packaging/Core/IRepositoryCertificateInfo.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System;
 
 namespace NuGet.Packaging.Core

src/NuGet.Core/NuGet.Packaging/Core/NuspecUtility.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System;
 using System.Collections.Generic;
 using System.Globalization;
@@ -83,7 +81,7 @@ public static IReadOnlyList<PackageType> GetPackageTypes(XElement metadataNode,
 
                 // Get the optional package type version.
                 var versionAttribute = node.Attribute(XName.Get(Version));
-                Version version;
+                Version? version;
 
                 if (versionAttribute != null)
                 {
@@ -122,7 +120,12 @@ public static bool IsServiceable(XElement metadataNode)
                 return false;
             }
 
-            var value = element.Value ?? element.Value.Trim();
+            if (element.Value == null)
+            {
+                return false;
+            }
+
+            var value = element.Value.Trim();
             return System.Xml.XmlConvert.ToBoolean(value);
         }
 
@@ -143,9 +146,9 @@ internal static IEnumerable<FrameworkReferenceGroup> GetFrameworkReferenceGroups
             if (useMetadataNamespace)
             {
                 var frameworkReferencesNode = metadataNode
-                    .Elements(XName.Get(FrameworkReferences, ns));
+                    .Elements(XName.Get(FrameworkReferences, ns!));
                 frameworkReferenceGroups = frameworkReferencesNode
-                    .Elements(XName.Get(Group, ns));
+                    .Elements(XName.Get(Group, ns!));
             }
             else
             {
@@ -159,10 +162,10 @@ internal static IEnumerable<FrameworkReferenceGroup> GetFrameworkReferenceGroups
                 var groupFramework = GetAttributeValue(frameworkRefGroup, TargetFramework);
 
                 var frameworkReferences = useMetadataNamespace ?
-                    frameworkRefGroup.Elements(XName.Get(FrameworkReference, ns)) :
+                    frameworkRefGroup.Elements(XName.Get(FrameworkReference, ns!)) :
                     frameworkRefGroup.Elements().Where(x => x.Name.LocalName == FrameworkReference);
 
-                var framework = NuGetFramework.Parse(groupFramework, frameworkProvider);
+                var framework = NuGetFramework.Parse(groupFramework!, frameworkProvider);
                 var frameworkRefs = GetFrameworkReferences(frameworkReferences);
 
                 yield return new FrameworkReferenceGroup(framework, frameworkRefs.Select(e => new FrameworkReference(e)));
@@ -171,10 +174,10 @@ internal static IEnumerable<FrameworkReferenceGroup> GetFrameworkReferenceGroups
 
         private static IEnumerable<string> GetFrameworkReferences(IEnumerable<XElement> nodes)
         {
-            return new HashSet<string>(nodes.Select(e => GetAttributeValue(e, Name)), ComparisonUtility.FrameworkReferenceNameComparer);
+            return new HashSet<string>(nodes.Select(e => GetAttributeValue(e, Name)!), ComparisonUtility.FrameworkReferenceNameComparer);
         }
 
-        private static string GetAttributeValue(XElement element, string attributeName)
+        private static string? GetAttributeValue(XElement element, string attributeName)
         {
             var attribute = element.Attribute(XName.Get(attributeName));
             return attribute == null ? null : attribute.Value;

src/NuGet.Core/NuGet.Packaging/Definitions/IAsyncPackageContentReader.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;

src/NuGet.Core/NuGet.Packaging/Definitions/INuspecReader.cs

@@ -1,8 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
+using System;
 using System.Collections.Generic;
 using NuGet.Packaging.Core;
 
@@ -11,6 +10,7 @@ namespace NuGet.Packaging
     /// <summary>
     /// A development package nuspec reader
     /// </summary>
+    [Obsolete("This interface is unused and does not contain any implementations. It will be removed in a future release.")]
     public interface INuspecReader : INuspecCoreReader
     {
         IEnumerable<PackageDependencyGroup> GetDependencyGroups();

src/NuGet.Core/NuGet.Packaging/Definitions/IPackageContentReader.cs

@@ -1,8 +1,6 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
-#nullable disable
-
 using System.Collections.Generic;
 
 namespace NuGet.Packaging