Don't update the reference file if no changes were detected

src/Shared/ReferenceItemExtensions.cs

@@ -14,6 +14,18 @@ public static string ToFileLine(this ReferenceItem item)
 
     public static void SaveToFile(this List<ReferenceItem> items, string outputFile)
     {
+        if (File.Exists(outputFile))
+        {
+            var currentContents = File.ReadAllLines(outputFile);
+            var newContents = items.Select(item => item.ToFileLine()).ToArray();
+            // Assuming order is the same for incremental builds, no sorting needed
+            if (currentContents.SequenceEqual(newContents))
+            {
+                // No changes, skip writing to avoid updating the timestamp, which will trigger unnecessary rebuilds
+                return;
+            }
+        }
+
         File.WriteAllLines(outputFile, items.Select(item => item.ToFileLine()));
     }
 

src/Tasks/ReferenceProtector.Tasks.IntegrationTests/ReferenceProtector.Tasks.TestBase.cs

@@ -143,7 +143,7 @@ internal async Task Build(string additionalArgs = "")
     {
         string buildArgs =
             $"build dirs.proj " +
-            $"-m:1 -t:Rebuild -restore -nologo -nodeReuse:false -noAutoResponse " +
+            $"-m:1 -restore -nologo -nodeReuse:false -noAutoResponse " +
             $"/p:Configuration=Debug " +
             $"/p:ReferenceProtectorTaskAssembly={Path.Combine(Directory.GetCurrentDirectory(), "ReferenceProtector.Tasks.dll")} " +
             $"/v:m" +

src/Tasks/ReferenceProtector.Tasks.IntegrationTests/ReferenceProtector.Tasks.Tests.cs

@@ -126,4 +126,28 @@ public async Task CollectAllReferences_PackageReferences_AreIncluded()
 
         Assert.Equal(expectedReferences, references);
     }
+
+    /// <summary>
+    /// Verifies that the CollectAllReferences task does not update the reference file timestamp if no changes were made.
+    /// </summary>
+    [Fact]
+    public async Task CollectAllReferences_IncrememtalBuild_ReferenceTimestampIsNotUpdated()
+    {
+        CreateProject("A");
+        CreateProject("B");
+        await AddProjectReference("A", "B");
+        await Build();
+
+        var generatedFiles1 = GetGeneratedReferencesFiles();
+        var timeStamps1 = generatedFiles1.Select(File.GetLastWriteTimeUtc).ToList();
+
+        // Rebuild without any changes
+        await Build();
+
+        var generatedFiles2 = GetGeneratedReferencesFiles();
+        var timeStamps2 = generatedFiles2.Select(File.GetLastWriteTimeUtc).ToList();
+
+        Assert.Equal(generatedFiles1, generatedFiles2);
+        Assert.Equal(timeStamps1, timeStamps2);
+    }
 }

src/Tasks/ReferenceProtector.Tasks/CollectAllReferences.cs

@@ -82,7 +82,9 @@ public override bool Execute()
 
         if (OutputFile is not null)
         {
-            references.SaveToFile(OutputFile);
+            // Is sorted to ensure consistent ordering for easier testing and to avoid unnecessary diffs
+            // May not needed, if msbuild guarantees a consistent order
+            references.OrderBy(x => (x.Source, x.Target, x.LinkType)).ToList().SaveToFile(OutputFile);
             return true;
         }