Avoid creating source link .json file when no source control mapping is available

src/Microsoft.Build.Tasks.Git/RepositoryTask.cs

@@ -60,6 +60,14 @@ bool logAssemblyLoadingErrors()
             return !Log.HasLoggedErrors;
         }
 
+        private void ReportMissingRepositoryWarning(string initialPath)
+        {
+            if (!NoWarnOnMissingRepository)
+            {
+                Log.LogWarning(Resources.UnableToLocateRepository, initialPath);
+            }
+        }
+
         private protected abstract void Execute(GitRepository repository);
 
         protected abstract string? GetRepositoryId();
@@ -103,11 +111,7 @@ private void ExecuteImpl()
 
             if (!GitRepository.TryFindRepository(initialPath, out var location))
             {
-                if (!NoWarnOnMissingRepository)
-                {
-                    Log.LogWarning(Resources.UnableToLocateRepository, initialPath);
-                }
-
+                ReportMissingRepositoryWarning(initialPath);
                 return null;
             }
 
@@ -129,11 +133,7 @@ private void ExecuteImpl()
 
             if (repository?.WorkingDirectory == null)
             {
-                if (!NoWarnOnMissingRepository)
-                {
-                    Log.LogWarning(Resources.UnableToLocateRepository, initialPath);
-                }
-
+                ReportMissingRepositoryWarning(initialPath);
                 repository = null;
             }
 

src/Microsoft.Build.Tasks.Git/build/Microsoft.Build.Tasks.Git.targets

@@ -51,7 +51,8 @@
       RepositoryId="$(_GitRepositoryId)"
       ConfigurationScope="$(GitRepositoryConfigurationScope)"
       ProjectDirectory="$(MSBuildProjectDirectory)"
-      Files="@(Compile)">
+      Files="@(Compile)"
+      Condition="'$(_GitRepositoryId)' != ''">
 
       <Output TaskParameter="UntrackedFiles" ItemName="EmbeddedFiles" />
     </Microsoft.Build.Tasks.Git.GetUntrackedFiles>

src/SourceLink.Common.UnitTests/GenerateSourceLinkFileTests.cs

@@ -3,6 +3,7 @@
 // See the License.txt file in the project root for more information.
 using System;
 using System.IO;
+using System.Text;
 using Xunit;
 using TestUtilities;
 using static TestUtilities.KeyValuePairUtils;
@@ -14,23 +15,56 @@ public class GenerateSourceLinkFileTests
         private static string AdjustSeparatorsInJson(string json)
             => Path.DirectorySeparatorChar == '/' ? json.Replace(@"\\", "/") : json;
 
-        [Fact]
-        public void Empty()
+        [Theory]
+        [CombinatorialData]
+        public void Empty(bool noWarning)
         {
+            var sourceLinkFilePath = Path.Combine(TempRoot.Root, Guid.NewGuid().ToString());
+
             var engine = new MockEngine();
 
             var task = new GenerateSourceLinkFile()
             {
                 BuildEngine = engine,
+                OutputFile = sourceLinkFilePath,
                 SourceRoots = new MockItem[0],
+                NoWarnOnMissingSourceControlInformation = noWarning,
             };
 
-            var content = task.GenerateSourceLinkContent();
+            Assert.True(task.Execute());
 
             AssertEx.AssertEqualToleratingWhitespaceDifferences(
-                "WARNING : " + string.Format(Resources.SourceControlInformationIsNotAvailableGeneratedSourceLinkEmpty), engine.Log);
+                noWarning ? "" : "WARNING : " + string.Format(Resources.SourceControlInformationIsNotAvailableGeneratedSourceLinkEmpty),
+                engine.Log);
 
-            AssertEx.AreEqual(@"{""documents"":{}}", content);
+            Assert.Null(task.SourceLink);
+            Assert.Null(task.FileWrite);
+        }
+
+        [Fact]
+        public void Empty_DeleteExistingFile()
+        {
+            using var tempRoot = new TempRoot();
+
+            var sourceLinkFile = tempRoot.CreateFile();
+            sourceLinkFile.WriteAllText("XYZ");
+
+            var engine = new MockEngine();
+
+            var task = new GenerateSourceLinkFile()
+            {
+                BuildEngine = engine,
+                OutputFile = sourceLinkFile.Path,
+                SourceRoots = new MockItem[0],
+                NoWarnOnMissingSourceControlInformation = true,
+            };
+
+            Assert.True(task.Execute());
+
+            AssertEx.AssertEqualToleratingWhitespaceDifferences("", engine.Log);
+
+            Assert.Null(task.SourceLink);
+            Assert.Equal(sourceLinkFile.Path, task.FileWrite);
         }
 
         [Fact]
@@ -145,7 +179,9 @@ public void DoesNotRewriteContentIfFileContentIsSame()
         {
             using var temp = new TempRoot();
             var tempFile = temp.CreateFile();
-
+
+            tempFile.WriteAllText("XYZ");
+
             var engine = new MockEngine();
             var task = new GenerateSourceLinkFile()
             {
@@ -161,6 +197,10 @@ public void DoesNotRewriteContentIfFileContentIsSame()
 
             var beforeWriteTime = File.GetLastWriteTime(tempFile.Path);
 
+            Assert.Equal(@"{""documents"":{""/_\""_/*"":""https://raw.githubusercontent.com/repo/*""}}", File.ReadAllText(tempFile.Path, Encoding.UTF8));
+            Assert.Equal(tempFile.Path, task.SourceLink);
+            Assert.Equal(tempFile.Path, task.FileWrite);
+
             result = task.Execute();
 
             var afterWriteTime = File.GetLastWriteTime(tempFile.Path);

src/SourceLink.Common/GenerateSourceLinkFile.cs

@@ -21,15 +21,23 @@ public sealed class GenerateSourceLinkFile : Task
         [Required, NotNull]
         public string? OutputFile { get; set; }
 
+        /// <summary>
+        /// Set to <see cref="OutputFile"/> if the output file was written to, null otherwise.
+        /// </summary>
+        [Output]
+        public string? FileWrite { get; set; }
+
+        /// <summary>
+        /// Set to <see cref="OutputFile"/> if the output Source Link file should be passed to the compiler.
+        /// </summary>
+        [Output]
+        public string? SourceLink { get; set; }
+
         public bool NoWarnOnMissingSourceControlInformation { get; set; }
 
         public override bool Execute()
         {
-            var content = GenerateSourceLinkContent();
-            if (content != null)
-            {
-                WriteSourceLinkFile(content);
-            }
+            WriteSourceLinkFile(GenerateSourceLinkContent());
 
             return !Log.HasLoggedErrors;
         }
@@ -43,7 +51,7 @@ static string jsonEscape(string str)
             result.Append("{\"documents\":{");
 
             bool success = true;
-            bool first = true;
+            bool isEmpty = true;
             foreach (var root in SourceRoots)
             {
                 string mappedPath = root.GetMetadata(Names.SourceRoot.MappedPath);
@@ -79,9 +87,9 @@ static string jsonEscape(string str)
                     continue;
                 }
 
-                if (first)
+                if (isEmpty)
                 {
-                    first = false;
+                    isEmpty = false;
                 }
                 else
                 {
@@ -100,38 +108,51 @@ static string jsonEscape(string str)
 
             result.Append("}}");
 
-            if (!success)
-            {
-                return null;
-            }
+            return success && !isEmpty ? result.ToString() : null;
+        }
 
-            if (first && !NoWarnOnMissingSourceControlInformation)
+        private void WriteSourceLinkFile(string? content)
+        {
+            if (content == null && !NoWarnOnMissingSourceControlInformation)
             {
                 Log.LogWarning(Resources.SourceControlInformationIsNotAvailableGeneratedSourceLinkEmpty);
             }
 
-            return result.ToString();
-        }
-
-        private void WriteSourceLinkFile(string content)
-        {
             try
             {
                 if (File.Exists(OutputFile))
                 {
+                    if (content == null)
+                    {
+                        File.Delete(OutputFile);
+                        FileWrite = OutputFile;
+                        return;
+                    }
+
                     var originalContent = File.ReadAllText(OutputFile);
                     if (originalContent == content)
                     {
-                        // Don't rewrite the file if the contents are the same
+                        // Don't rewrite the file if the contents is the same, just pass it to the compiler.
+                        SourceLink = OutputFile;
                         return;
                     }
                 }
+                else if (content == null)
+                {
+                    // File doesn't exist and the output is empty:
+                    // Do not write the file and don't pass it to the compiler.
+                    return;
+                }
 
                 File.WriteAllText(OutputFile, content);
+                FileWrite = SourceLink = OutputFile;
             }
             catch (Exception e)
             {
                 Log.LogError(Resources.ErrorWritingToSourceLinkFile, OutputFile, e.Message);
+
+                // Part of the file might have been written.
+                FileWrite = OutputFile;
             }
         }
     }

src/SourceLink.Common/build/Microsoft.SourceLink.Common.targets

@@ -7,7 +7,7 @@
 
   <Target Name="_SetSourceLinkFilePath">
     <PropertyGroup>
-      <SourceLink>$(IntermediateOutputPath)$(MSBuildProjectName).sourcelink.json</SourceLink>
+      <_SourceLinkFilePath>$(IntermediateOutputPath)$(MSBuildProjectName).sourcelink.json</_SourceLinkFilePath>
     </PropertyGroup>
   </Target>
 
@@ -48,20 +48,23 @@
   <Target Name="_GenerateSourceLinkFile"
           DependsOnTargets="_SetSourceLinkFilePath;$(_GenerateSourceLinkFileDependsOnTargets);_InitializeSourceRootMappedPathsOpt;$(SourceLinkUrlInitializerTargets)"
           Condition="'$(EnableSourceLink)' == 'true' and '$(DebugType)' != 'none'"
-          Outputs="$(SourceLink)">
+          Outputs="$(_SourceLinkFilePath)">
 
     <!--- Suppress warning if targets are imported from an SDK without a package reference. -->
     <Microsoft.SourceLink.Common.GenerateSourceLinkFile
       SourceRoots="@(SourceRoot)"
       NoWarnOnMissingSourceControlInformation="$(PkgMicrosoft_SourceLink_Common.Equals(''))"
-      OutputFile="$(SourceLink)" />
+      OutputFile="$(_SourceLinkFilePath)">
 
-    <ItemGroup>
-      <FileWrites Include="$(SourceLink)" />
-    </ItemGroup>
+      <!-- Set SourceLink property passed to compilers -->
+      <Output TaskParameter="SourceLink" PropertyName="SourceLink" />
+
+      <!-- Log file write if the content of the file has been updated -->
+      <Output TaskParameter="FileWrite" ItemName="FileWrites" />
+    </Microsoft.SourceLink.Common.GenerateSourceLinkFile>
 
     <!-- C++ Link task currently doesn't recognize SourceLink property -->
-    <ItemGroup Condition="'$(Language)' == 'C++'">
+    <ItemGroup Condition="'$(Language)' == 'C++' and '$(SourceLink)' != ''">
       <Link Update="@(Link)">
         <AdditionalOptions>%(Link.AdditionalOptions) /sourcelink:"$(SourceLink)"</AdditionalOptions>
       </Link>

src/SourceLink.Git.IntegrationTests/CloudHostedProvidersTests.cs

@@ -26,6 +26,8 @@ public CloudHostedProvidersTests()
         [ConditionalFact(typeof(DotNetSdkAvailable))]
         public void NoRepository_Warnings()
         {
+            var sourceLinkFilePath = Path.Combine(ProjectObjDir.Path, Configuration, TargetFramework, "test.sourcelink.json");
+
             VerifyValues(
                 customProps: "",
                 customTargets: "",
@@ -36,21 +38,27 @@ public void NoRepository_Warnings()
                 expressions: new[]
                 {
                     "@(SourceRoot)",
+                    "$(SourceLink)",
                 },
                 expectedResults: new[]
                 {
-                    NuGetPackageFolders
+                    NuGetPackageFolders,
+                    "",
                 },
                 expectedWarnings: new[]
                 {
                     string.Format(Build.Tasks.Git.Resources.UnableToLocateRepository, ProjectDir.Path),
                     string.Format(Common.Resources.SourceControlInformationIsNotAvailableGeneratedSourceLinkEmpty),
                 });
+
+            Assert.False(File.Exists(sourceLinkFilePath));
         }
 
         [ConditionalFact(typeof(DotNetSdkAvailable))]
         public void NoRepository_NoWarnings()
         {
+            var sourceLinkFilePath = Path.Combine(ProjectObjDir.Path, Configuration, TargetFramework, "test.sourcelink.json");
+
             VerifyValues(
                 customProps: """
                 <PropertyGroup>
@@ -66,11 +74,15 @@ public void NoRepository_NoWarnings()
                 expressions: new[]
                 {
                     "@(SourceRoot)",
+                    "$(SourceLink)",
                 },
                 expectedResults: new[]
                 {
-                    NuGetPackageFolders
+                    NuGetPackageFolders,
+                    "",
                 });
+
+            Assert.False(File.Exists(sourceLinkFilePath));
         }
 
         [ConditionalFact(typeof(DotNetSdkAvailable))]