Fix incremental builds

src/dotnet-ef/Project.cs

@@ -53,16 +53,35 @@ public static Project FromFile(
 
         Directory.CreateDirectory(buildExtensionsDir);
 
+        byte[] efTargets;
+        using (var input = typeof(Resources).Assembly.GetManifestResourceStream(
+                   "Microsoft.EntityFrameworkCore.Tools.Resources.EntityFrameworkCore.targets")!)
+        {
+            efTargets = new byte[input.Length];
+            input.Read(efTargets);
+        }
+
         var efTargetsPath = Path.Combine(
             buildExtensionsDir,
             Path.GetFileName(file) + ".EntityFrameworkCore.targets");
-        using (var input = typeof(Resources).Assembly.GetManifestResourceStream(
-                   "Microsoft.EntityFrameworkCore.Tools.Resources.EntityFrameworkCore.targets")!)
-        using (var output = File.OpenWrite(efTargetsPath))
+
+        bool FileMatches()
+        {
+            try
+            {
+                return !File.ReadAllBytes(efTargetsPath).SequenceEqual(efTargets);
+            }
+            catch
+            {
+                return false;
+            }
+        }
+
+        // Avoid touching the targets file, if it matches what we need, to enable incremental builds
+        if (!File.Exists(efTargetsPath) || !FileMatches())
         {
-            // NB: Copy always in case it changes
             Reporter.WriteVerbose(Resources.WritingFile(efTargetsPath));
-            input.CopyTo(output);
+            File.WriteAllBytes(efTargetsPath, efTargets);
         }
 
         IDictionary<string, string> metadata;

test/EFCore.Design.Tests/Scaffolding/Internal/ModelCodeGeneratorTestFixture.cs

@@ -12,14 +12,14 @@ public ModelCodeGeneratorTestFixture()
 
         using (var input = typeof(ModelCodeGeneratorTestBase).Assembly.GetManifestResourceStream(
                    "Microsoft.EntityFrameworkCore.Resources.CSharpDbContextGenerator.tt"))
-        using (var output = File.OpenWrite(Path.Combine(templatesDir, "DbContext.t4")))
+        using (var output = File.Create(Path.Combine(templatesDir, "DbContext.t4")))
         {
             input.CopyTo(output);
         }
 
         using (var input = typeof(ModelCodeGeneratorTestBase).Assembly.GetManifestResourceStream(
                    "Microsoft.EntityFrameworkCore.Resources.CSharpEntityTypeGenerator.tt"))
-        using (var output = File.OpenWrite(Path.Combine(templatesDir, "EntityType.t4")))
+        using (var output = File.Create(Path.Combine(templatesDir, "EntityType.t4")))
         {
             input.CopyTo(output);
         }

test/EFCore.Specification.Tests/TestUtilities/BuildSource.cs

@@ -60,7 +60,7 @@ public BuildFileResult Build()
 
         var targetPath = Path.Combine(TargetDir ?? Path.GetTempPath(), projectName + ".dll");
 
-        using (var stream = File.OpenWrite(targetPath))
+        using (var stream = File.Create(targetPath))
         {
             var result = compilation.Emit(stream);
             if (!result.Success)