Apply is null pattern and analyzer

.editorconfig

@@ -79,3 +79,9 @@ csharp_new_line_before_catch = true
 csharp_new_line_before_finally = true
 csharp_new_line_before_members_in_object_initializers = true
 csharp_new_line_before_members_in_anonymous_types = true
+
+# CSIsNull001: Use `is null` for null checks
+dotnet_diagnostic.CSIsNull001.severity = warning
+
+# CSIsNull002: Use `is object` for non-null checks
+dotnet_diagnostic.CSIsNull002.severity = warning

src/Directory.Build.props

@@ -24,9 +24,13 @@
     <LibGit2SharpNativeVersion>2.0.312</LibGit2SharpNativeVersion>
   </PropertyGroup>
   <ItemGroup>
-    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.8.0-5.final" PrivateAssets="all" />
+    <PackageReference Include="Microsoft.Net.Compilers.Toolset" Version="3.11.0" PrivateAssets="all" />
     <PackageReference Include="Microsoft.NETFramework.ReferenceAssemblies" Version="1.0.0" PrivateAssets="All" />
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />
+    <PackageReference Include="CSharpIsNullAnalyzer" Version="0.1.288-beta">
+      <PrivateAssets>all</PrivateAssets>
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers</IncludeAssets>
+    </PackageReference>
   </ItemGroup>
   <ItemGroup>
     <None Include="$(MSBuildThisFileDirectory)..\3rdPartyNotices.txt" Pack="true" PackagePath="" />

src/NerdBank.GitVersioning.Tests/BuildIntegrationTests.cs

@@ -219,7 +219,7 @@ public async Task GetBuildVersion_In_Git_But_Head_Lacks_VersionFile()
         var repo = new Repository(this.RepoPath); // do not assign Repo property to avoid commits being generated later
         repo.Commit("empty", this.Signer, this.Signer, new CommitOptions { AllowEmptyCommit = true });
         this.WriteVersionFile("3.4");
-        Assumes.True(repo.Index[VersionFile.JsonFileName] == null);
+        Assumes.True(repo.Index[VersionFile.JsonFileName] is null);
         var buildResult = await this.BuildAsync();
         Assert.Equal("3.4.0." + this.GetVersion().Revision, buildResult.BuildVersion);
         Assert.Equal("3.4.0+" + repo.Head.Tip.Id.Sha.Substring(0, VersionOptions.DefaultGitCommitIdShortFixedLength), buildResult.AssemblyInformationalVersion);

src/NerdBank.GitVersioning.Tests/ManagedGit/DeltaStreamReaderTests.cs

@@ -89,7 +89,7 @@ public void ReadStreamTest()
 
                 DeltaInstruction? current;
 
-                while ((current = DeltaStreamReader.Read(stream)) != null)
+                while ((current = DeltaStreamReader.Read(stream)) is not null)
                 {
                     instructions.Add(current.Value);
                 }
@@ -139,7 +139,7 @@ public void ReadStreamTest_Memory()
 
             DeltaInstruction? current;
 
-            while ((current = DeltaStreamReader.Read(ref memory)) != null)
+            while ((current = DeltaStreamReader.Read(ref memory)) is not null)
             {
                 instructions.Add(current.Value);
             }

src/NerdBank.GitVersioning.Tests/ReleaseManagerTests.cs

@@ -320,7 +320,7 @@ public void PrepareRelease_Master(
 
         // prepare release
         var releaseManager = new ReleaseManager();
-        releaseManager.PrepareRelease(this.RepoPath, releaseUnstableTag, (nextVersion == null ? null : Version.Parse(nextVersion)), parameterVersionIncrement);
+        releaseManager.PrepareRelease(this.RepoPath, releaseUnstableTag, (nextVersion is null ? null : Version.Parse(nextVersion)), parameterVersionIncrement);
 
         // check if a branch was created
         Assert.Contains(this.LibGit2Repository.Branches, branch => branch.FriendlyName == expectedBranchName);
@@ -394,7 +394,7 @@ public void PrepareRelease_MasterWithVersionDecrement(string initialVersion, str
         // running PrepareRelease should result in an error
         // because we're trying to add a prerelease tag to a version without prerelease tag
         this.AssertError(
-            () => new ReleaseManager().PrepareRelease(this.RepoPath, releaseUnstableTag, (nextVersion == null ? null : Version.Parse(nextVersion))),
+            () => new ReleaseManager().PrepareRelease(this.RepoPath, releaseUnstableTag, (nextVersion is null ? null : Version.Parse(nextVersion))),
             ReleasePreparationError.VersionDecrement);
     }
 

src/NerdBank.GitVersioning.Tests/RepoTestBase.cs

@@ -143,7 +143,7 @@ protected void AddCommits(int count = 1)
 
     protected Commit? WriteVersionTxtFile(string version = "1.2", string prerelease = "", string? relativeDirectory = null)
     {
-        if (relativeDirectory == null)
+        if (relativeDirectory is null)
         {
             relativeDirectory = string.Empty;
         }
@@ -163,7 +163,7 @@ protected void AddCommits(int count = 1)
     {
         Requires.NotNull(versionData, nameof(versionData));
 
-        if (relativeDirectory == null)
+        if (relativeDirectory is null)
         {
             relativeDirectory = string.Empty;
         }
@@ -197,7 +197,7 @@ protected void AddCommits(int count = 1)
             if (Path.GetExtension(relativeFilePath) == ".json")
             {
                 string txtFilePath = relativeFilePath.Substring(0, relativeFilePath.Length - 4) + "txt";
-                if (!File.Exists(Path.Combine(this.RepoPath, txtFilePath)) && this.LibGit2Repository.Index[txtFilePath] != null)
+                if (!File.Exists(Path.Combine(this.RepoPath, txtFilePath)) && this.LibGit2Repository.Index[txtFilePath] is not null)
                 {
                     this.LibGit2Repository.Index.Remove(txtFilePath);
                 }

src/NerdBank.GitVersioning.Tests/TestUtilities.cs

@@ -54,7 +54,7 @@ internal static void ExtractEmbeddedResource(string resourcePath, string extract
 
         using (var stream = GetEmbeddedResource(resourcePath))
         {
-            Requires.Argument(stream != null, nameof(resourcePath), "Resource not found.");
+            Requires.Argument(stream is not null, nameof(resourcePath), "Resource not found.");
             using (var extractedFile = File.OpenWrite(extractedFilePath))
             {
                 stream.CopyTo(extractedFile);

src/NerdBank.GitVersioning.Tests/VersionFileTests.cs

@@ -140,7 +140,7 @@ public void SetVersion_WritesSimplestFile(string version, string assemblyVersion
         var versionOptions = new VersionOptions
         {
             Version = SemanticVersion.Parse(version),
-            AssemblyVersion = assemblyVersion != null || precision != null ? new VersionOptions.AssemblyVersionOptions(assemblyVersion != null ? new Version(assemblyVersion) : null, precision) : null,
+            AssemblyVersion = assemblyVersion is not null || precision is not null ? new VersionOptions.AssemblyVersionOptions(assemblyVersion is not null ? new Version(assemblyVersion) : null, precision) : null,
             VersionHeightOffset = versionHeightOffset,
             Inherit = inherit,
         };

src/NerdBank.GitVersioning/AssemblyVersionOptionsConverter.cs

@@ -51,7 +51,7 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
         public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer)
         {
             var data = value as VersionOptions.AssemblyVersionOptions;
-            if (data != null)
+            if (data is not null)
             {
                 if (data.PrecisionOrDefault == VersionOptions.DefaultVersionPrecision && !this.includeDefaults)
                 {

src/NerdBank.GitVersioning/CloudBuildServices/GitLab.cs

@@ -14,13 +14,13 @@
     internal class GitLab : ICloudBuild
     {
         public string BuildingBranch =>
-            Environment.GetEnvironmentVariable("CI_COMMIT_TAG") == null ? 
+            Environment.GetEnvironmentVariable("CI_COMMIT_TAG") is null ? 
                 $"refs/heads/{Environment.GetEnvironmentVariable("CI_COMMIT_REF_NAME")}" : null;
 
         public string BuildingRef => this.BuildingBranch ?? this.BuildingTag;
 
         public string BuildingTag =>
-            Environment.GetEnvironmentVariable("CI_COMMIT_TAG") != null ?
+            Environment.GetEnvironmentVariable("CI_COMMIT_TAG") is not null ?
                 $"refs/tags/{Environment.GetEnvironmentVariable("CI_COMMIT_TAG")}" : null;
 
         public string GitCommitId => Environment.GetEnvironmentVariable("CI_COMMIT_SHA");

src/NerdBank.GitVersioning/CloudBuildServices/TeamCity.cs

@@ -19,7 +19,7 @@ internal class TeamCity : ICloudBuild
 
         public string GitCommitId => Environment.GetEnvironmentVariable("BUILD_VCS_NUMBER");
 
-        public bool IsApplicable => this.GitCommitId != null;
+        public bool IsApplicable => this.GitCommitId is not null;
 
         public bool IsPullRequest => false;
 

src/NerdBank.GitVersioning/FilterPathJsonConverter.cs

@@ -22,7 +22,7 @@ public override object ReadJson(JsonReader reader, Type objectType, object exist
                 throw new NotSupportedException();
             }
 
-            if (this.repoRelativeBaseDirectory == null)
+            if (this.repoRelativeBaseDirectory is null)
             {
                 throw new ArgumentNullException(nameof(this.repoRelativeBaseDirectory), $"Base directory must not be null to be able to deserialize filter paths. Ensure that one was passed to {nameof(VersionOptions.GetJsonSettings)}, and that the version.json file is being written to a Git repository.");
             }
@@ -37,7 +37,7 @@ public override void WriteJson(JsonWriter writer, object value, JsonSerializer s
                 throw new NotSupportedException();
             }
 
-            if (this.repoRelativeBaseDirectory == null)
+            if (this.repoRelativeBaseDirectory is null)
             {
                 throw new ArgumentNullException(nameof(this.repoRelativeBaseDirectory), $"Base directory must not be null to be able to serialize filter paths. Ensure that one was passed to {nameof(VersionOptions.GetJsonSettings)}, and that the version.json file is being written to a Git repository.");
             }

src/NerdBank.GitVersioning/LibGit2/LibGit2GitExtensions.cs

@@ -60,13 +60,13 @@ internal static int GetVersionHeight(LibGit2Context context, Version? baseVersio
             var tracker = new GitWalkTracker(context);
 
             var versionOptions = tracker.GetVersion(context.Commit);
-            if (versionOptions == null)
+            if (versionOptions is null)
             {
                 return 0;
             }
 
             var baseSemVer =
-                baseVersion != null ? SemanticVersion.Parse(baseVersion.ToString()) :
+                baseVersion is not null ? SemanticVersion.Parse(baseVersion.ToString()) :
                 versionOptions.Version ?? SemVer0;
 
             var versionHeightPosition = versionOptions.VersionHeightPosition;
@@ -174,7 +174,7 @@ public static IEnumerable<Commit> GetCommitsFromVersion(LibGit2Context context,
             var tracker = new GitWalkTracker(context);
             var possibleCommits = from commit in GetCommitsReachableFromRefs(context.Repository)
                                   let commitVersionOptions = tracker.GetVersion(commit)
-                                  where commitVersionOptions != null
+                                  where commitVersionOptions is not null
                                   where !IsCommitIdMismatch(version, commitVersionOptions, commit)
                                   where !IsVersionHeightMismatch(version, commitVersionOptions, commit, tracker)
                                   select commit;
@@ -221,7 +221,7 @@ private static bool CommitMatchesVersion(this Commit commit, SemanticVersion exp
 
             var commitVersionData = tracker.GetVersion(commit);
             var semVerFromFile = commitVersionData?.Version;
-            if (semVerFromFile == null)
+            if (semVerFromFile is null)
             {
                 return false;
             }
@@ -250,7 +250,7 @@ private static bool CommitMatchesVersion(this Commit commit, Version expectedVer
 
             var commitVersionData = tracker.GetVersion(commit);
             var semVerFromFile = commitVersionData?.Version;
-            if (semVerFromFile == null)
+            if (semVerFromFile is null)
             {
                 return false;
             }
@@ -422,7 +422,7 @@ bool ContainsRelevantChanges(IEnumerable<TreeEntryChanges> changes) =>
 
                 int height = 1;
 
-                if (includePaths != null)
+                if (includePaths is not null)
                 {
                     // If there are no include paths, or any of the include
                     // paths refer to the root of the repository, then do not
@@ -527,8 +527,8 @@ internal static Version GetIdAsVersionHelper(this Commit? commit, VersionOptions
 
             // Don't use the ?? coalescing operator here because the position property getters themselves can return null, which should NOT be overridden with our default.
             // The default value is only appropriate if versionOptions itself is null.
-            var versionHeightPosition = versionOptions != null ? versionOptions.VersionHeightPosition : SemanticVersion.Position.Build;
-            var commitIdPosition = versionOptions != null ? versionOptions.GitCommitIdPosition : SemanticVersion.Position.Revision;
+            var versionHeightPosition = versionOptions is not null ? versionOptions.VersionHeightPosition : SemanticVersion.Position.Build;
+            var commitIdPosition = versionOptions is not null ? versionOptions.GitCommitIdPosition : SemanticVersion.Position.Revision;
 
             // The compiler (due to WinPE header requirements) only allows 16-bit version components,
             // and forbids 0xffff as a value.

src/NerdBank.GitVersioning/Managed/ManagedGitContext.cs

@@ -94,7 +94,7 @@ internal override int CalculateVersionHeight(VersionOptions? committedVersion, V
             {
                 var workingCopyVersion = workingVersion?.Version?.Version;
 
-                if (workingCopyVersion == null || !workingCopyVersion.Equals(headCommitVersion))
+                if (workingCopyVersion is null || !workingCopyVersion.Equals(headCommitVersion))
                 {
                     // The working copy has changed the major.minor version.
                     // So by definition the version height is 0, since no commit represents it yet.
@@ -153,8 +153,8 @@ private Version GetIdAsVersionHelper(VersionOptions? versionOptions, int version
 
             // Don't use the ?? coalescing operator here because the position property getters themselves can return null, which should NOT be overridden with our default.
             // The default value is only appropriate if versionOptions itself is null.
-            var versionHeightPosition = versionOptions != null ? versionOptions.VersionHeightPosition : SemanticVersion.Position.Build;
-            var commitIdPosition = versionOptions != null ? versionOptions.GitCommitIdPosition : SemanticVersion.Position.Revision;
+            var versionHeightPosition = versionOptions is not null ? versionOptions.VersionHeightPosition : SemanticVersion.Position.Build;
+            var commitIdPosition = versionOptions is not null ? versionOptions.GitCommitIdPosition : SemanticVersion.Position.Revision;
 
             // The compiler (due to WinPE header requirements) only allows 16-bit version components,
             // and forbids 0xffff as a value.

src/NerdBank.GitVersioning/Managed/ManagedGitExtensions.cs

@@ -35,13 +35,13 @@ internal static int GetVersionHeight(ManagedGitContext context, Version? baseVer
             var tracker = new GitWalkTracker(context);
 
             var versionOptions = tracker.GetVersion(context.Commit.Value);
-            if (versionOptions == null)
+            if (versionOptions is null)
             {
                 return 0;
             }
 
             var baseSemVer =
-                baseVersion != null ? SemanticVersion.Parse(baseVersion.ToString()) :
+                baseVersion is not null ? SemanticVersion.Parse(baseVersion.ToString()) :
                 versionOptions.Version ?? SemVer0;
 
             var versionHeightPosition = versionOptions.VersionHeightPosition;
@@ -69,7 +69,7 @@ private static bool CommitMatchesVersion(GitCommit commit, SemanticVersion expec
 
             var commitVersionData = tracker.GetVersion(commit);
             var semVerFromFile = commitVersionData?.Version;
-            if (commitVersionData == null || semVerFromFile == null)
+            if (commitVersionData is null || semVerFromFile is null)
             {
                 return false;
             }
@@ -167,7 +167,7 @@ bool TryCalculateHeight(GitCommit commit)
 
                 int height = 1;
 
-                if (pathFilters != null)
+                if (pathFilters is not null)
                 {
                     var relevantCommit = true;
 
@@ -250,7 +250,7 @@ private static bool IsRelevantCommit(GitRepository repository, GitTree tree, Git
                         isRelevant = IsRelevantCommit(
                             repository,
                             repository.GetTree(entry.Sha),
-                            parentEntry == null ? GitTree.Empty : repository.GetTree(parentEntry.Sha),
+                            parentEntry is null ? GitTree.Empty : repository.GetTree(parentEntry.Sha),
                             $"{fullPath}/",
                             filters);
                     }
@@ -262,7 +262,7 @@ private static bool IsRelevantCommit(GitRepository repository, GitTree tree, Git
                     }
                 }
 
-                if (parentEntry != null)
+                if (parentEntry is not null)
                 {
                     parent.Children.Remove(child.Key);
                 }

src/NerdBank.GitVersioning/ManagedGit/GitCommitReader.cs

@@ -38,7 +38,7 @@ public static class GitCommitReader
         /// </returns>
         public static GitCommit Read(Stream stream, GitObjectId sha, bool readAuthor = false)
         {
-            if (stream == null)
+            if (stream is null)
             {
                 throw new ArgumentNullException(nameof(stream));
             }

src/NerdBank.GitVersioning/ManagedGit/GitObjectId.cs

@@ -174,7 +174,7 @@ public override bool Equals(object? obj)
         /// </summary>
         public override string ToString()
         {
-            if (this.sha == null)
+            if (this.sha is null)
             {
                 this.sha = this.CreateString(0, 20);
             }

src/NerdBank.GitVersioning/ManagedGit/GitPack.cs

@@ -146,7 +146,7 @@ public bool TryGetObject(GitObjectId objectId, string objectType, out Stream? va
         {
             var offset = this.GetOffset(objectId);
 
-            if (offset == null)
+            if (offset is null)
             {
                 value = null;
                 return false;
@@ -268,7 +268,7 @@ public void Dispose()
             var indexReader = this.indexReader.Value;
             var offset = indexReader.GetOffset(objectId);
 
-            if (offset != null)
+            if (offset is not null)
             {
                 this.offsets.Add(objectId, offset.Value);
             }

src/NerdBank.GitVersioning/ManagedGit/GitPackDeltafiedStream.cs

@@ -169,15 +169,15 @@ protected override void Dispose(bool disposing)
 
         private bool TryGetInstruction(out DeltaInstruction instruction)
         {
-            if (this.current != null && this.offset < this.current.Value.Size)
+            if (this.current is not null && this.offset < this.current.Value.Size)
             {
                 instruction = this.current.Value;
                 return true;
             }
 
             this.current = DeltaStreamReader.Read(this.deltaStream);
 
-            if (this.current == null)
+            if (this.current is null)
             {
                 instruction = default;
                 return false;

src/NerdBank.GitVersioning/ManagedGit/GitPackIndexMappedReader.cs

@@ -32,7 +32,7 @@ public unsafe class GitPackIndexMappedReader : GitPackIndexReader
         /// </param>
         public GitPackIndexMappedReader(FileStream stream)
         {
-            if (stream == null)
+            if (stream is null)
             {
                 throw new ArgumentNullException(nameof(stream));
             }

src/NerdBank.GitVersioning/ManagedGit/GitPackReader.cs

@@ -13,12 +13,12 @@ internal static class GitPackReader
 
         public static Stream GetObject(GitPack pack, Stream stream, long offset, string objectType, GitPackObjectType packObjectType)
         {
-            if (pack == null)
+            if (pack is null)
             {
                 throw new ArgumentNullException(nameof(pack));
             }
 
-            if (stream == null)
+            if (stream is null)
             {
                 throw new ArgumentNullException(nameof(stream));
             }