Add support for /t:Publish /p:NoBuild=true

src/Tasks/Microsoft.NET.Build.Tasks/targets/Microsoft.NET.Publish.targets

@@ -36,9 +36,26 @@ Copyright (c) .NET Foundation. All rights reserved.
     The main publish entry point.
     ============================================================
     -->
+
+  <PropertyGroup Condition="'$(NoBuild)' != 'true'">
+    <_BeforePublishTargets>Build</_BeforePublishTargets>
+  </PropertyGroup>
+
+  <PropertyGroup Condition="'$(NoBuild)' == 'true'">
+    <!-- We still need to resolve references even if we are not building during publish. -->
+    <!-- BuildOnlySettings are required for RAR to find satellites and dependencies -->
+    <_BeforePublishTargets>
+      BuildOnlySettings;
+      _PreventProjectReferencesFromBuilding;
+      ResolveReferences;
+      PrepareResourceNames;
+      ComputeIntermediateSatelliteAssemblies;
+    </_BeforePublishTargets>
+  </PropertyGroup>
+
   <Target Name="Publish"
           Condition="$(IsPublishable) == 'true'"
-          DependsOnTargets="Build;
+          DependsOnTargets="$(_BeforePublishTargets);
                             PrepareForPublish;
                             ComputeAndCopyFilesToPublishDirectory;
                             GeneratePublishDependencyFile;
@@ -49,6 +66,13 @@ Copyright (c) .NET Foundation. All rights reserved.
          the published assets were copied. -->
     <Message Importance="High" Text="$(MSBuildProjectName) -&gt; $([System.IO.Path]::GetFullPath('$(PublishDir)'))" />
   </Target>
+
+  <!-- Don't let project reference resolution build project references in NoBuild case. -->
+  <Target Name="_PreventProjectReferencesFromBuilding">
+    <PropertyGroup>
+      <BuildProjectReferences>false</BuildProjectReferences>
+    </PropertyGroup>
+  </Target>
 
   <!--
     ============================================================

src/Tests/Microsoft.NET.Build.Tests/GivenThatWeWantBuildsToBeIncremental.cs

@@ -80,15 +80,5 @@ public void ResolvePackageAssets_runs_incrementally()
             var cacheWriteTime4 = File.GetLastWriteTimeUtc(assetsCachePath);
             cacheWriteTime4.Should().NotBe(cacheWriteTime3);
         }
-
-        private static void WaitForUtcNowToAdvance()
-        {
-            var start = DateTime.UtcNow;
-
-            while (DateTime.UtcNow <= start)
-            {
-                Thread.Sleep(millisecondsTimeout: 1);
-            }
-        }
     }
 }

src/Tests/Microsoft.NET.Publish.Tests/GivenThatWeWantToPublishAProjectWithAllFeatures.cs

@@ -5,6 +5,8 @@
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Xml.Linq;
 using FluentAssertions;
 using FluentAssertions.Json;
 using Microsoft.Extensions.DependencyModel;
@@ -13,7 +15,6 @@
 using Microsoft.NET.TestFramework.Commands;
 using Newtonsoft.Json.Linq;
 using Xunit;
-using System.Xml.Linq;
 using Xunit.Abstractions;
 
 namespace Microsoft.NET.Publish.Tests
@@ -28,26 +29,7 @@ public GivenThatWeWantToPublishAProjectWithAllFeatures(ITestOutputHelper log) :
         [MemberData(nameof(PublishData))]
         public void It_publishes_the_project_correctly(string targetFramework, string [] expectedPublishFiles)
         {
-            TestAsset testAsset = _testAssetsManager
-                .CopyTestAsset("KitchenSink", "KitchenSinkPublish_", targetFramework)
-                .WithSource()
-                .WithProjectChanges((path, project) =>
-                {
-                    if (Path.GetFileName(path).Equals("TestApp.csproj", StringComparison.OrdinalIgnoreCase))
-                    {
-                        var ns = project.Root.Name.Namespace;
-
-                        var targetFrameworkElement = project.Root.Elements(ns + "PropertyGroup").Elements(ns + "TargetFramework").Single();
-                        targetFrameworkElement.SetValue(targetFramework);
-                    }
-                });
-
-            testAsset.Restore(Log, "TestApp");
-            testAsset.Restore(Log, "TestLibrary");
-
-            var appProjectDirectory = Path.Combine(testAsset.TestRoot, "TestApp");
-
-            PublishCommand publishCommand = new PublishCommand(Log, appProjectDirectory);
+            PublishCommand publishCommand = GetPublishCommand(targetFramework);
             publishCommand
                 .Execute()
                 .Should()
@@ -107,6 +89,87 @@ public void It_publishes_the_project_correctly(string targetFramework, string []
                 .BeEquivalentTo(baselineConfigJsonObject);
         }
 
+        [Fact]
+        public void It_fails_when_nobuild_is_set_and_build_was_not_performed_previously()
+        {
+            var publishCommand = GetPublishCommand("netcoreapp1.0").Execute("/p:NoBuild=true");
+            publishCommand.Should().Fail().And.HaveStdOutContaining("MSB3030"); // "Could not copy ___ because it was not found."
+        }
+
+        [Theory]
+        [MemberData(nameof(PublishData))]
+        public void It_does_not_build_when_nobuild_is_set(string targetFramework, string[] expectedPublishFiles)
+        {
+            var publishCommand = GetPublishCommand(targetFramework);
+
+            // do a separate build invocation before publish
+            var buildCommand = new BuildCommand(Log, publishCommand.ProjectRootPath);
+            buildCommand.Execute().Should().Pass();
+
+            // modify all project files, which would force recompilation if we were to build during publish
+            WaitForUtcNowToAdvance();
+            foreach (string projectFile in EnumerateFiles(buildCommand, "*.csproj"))
+            {
+                File.AppendAllText(projectFile, " ");
+            }
+
+            // capture modification time of all binaries before publish
+            var modificationTimes = GetLastWriteTimesUtc(buildCommand, "*.exe", "*.dll", "*.resources", "*.pdb");
+
+            // publish (with NoBuild set)
+            WaitForUtcNowToAdvance();
+            publishCommand.Execute("/p:NoBuild=true").Should().Pass();
+            publishCommand.GetOutputDirectory(targetFramework).Should().OnlyHaveFiles(expectedPublishFiles);
+
+            // check that publish did not modify any of the build output
+            foreach (var (file, modificationTime) in modificationTimes)
+            {
+                File.GetLastWriteTimeUtc(file)
+                    .Should().Be(
+                        modificationTime, 
+                        because: $"Publish with NoBuild=true should not overwrite {file}");
+            }
+        }
+
+        private static List<(string, DateTime)> GetLastWriteTimesUtc(MSBuildCommand command, params string[] searchPatterns)
+        {
+            return EnumerateFiles(command, searchPatterns)
+                .Select(file => (file, File.GetLastWriteTimeUtc(file)))
+                .ToList();
+        }
+
+        private static IEnumerable<string> EnumerateFiles(MSBuildCommand command, params string[] searchPatterns)
+        {
+            return searchPatterns.SelectMany(
+                pattern => Directory.EnumerateFiles(
+                    Path.Combine(command.ProjectRootPath, ".."), // up one level from TestApp to also get TestLibrary P2P files
+                    pattern,
+                    SearchOption.AllDirectories));
+        }
+
+        private PublishCommand GetPublishCommand(string targetFramework, [CallerMemberName] string callingMethod = null)
+        {
+            TestAsset testAsset = _testAssetsManager
+                .CopyTestAsset("KitchenSink", callingMethod, identifier: targetFramework)
+                .WithSource()
+                .WithProjectChanges((path, project) =>
+                {
+                    if (Path.GetFileName(path).Equals("TestApp.csproj", StringComparison.OrdinalIgnoreCase))
+                    {
+                        var ns = project.Root.Name.Namespace;
+
+                        var targetFrameworkElement = project.Root.Elements(ns + "PropertyGroup").Elements(ns + "TargetFramework").Single();
+                        targetFrameworkElement.SetValue(targetFramework);
+                    }
+                });
+
+            testAsset.Restore(Log, "TestApp");
+
+            var appProjectDirectory = Path.Combine(testAsset.TestRoot, "TestApp");
+
+            return new PublishCommand(Log, appProjectDirectory);
+        }
+
         private static void VerifyDependency(
             DependencyContext dependencyContext,
             string name,

src/Tests/Microsoft.NET.TestFramework/SdkTest.cs

@@ -4,6 +4,7 @@
 using System.Reflection;
 using System.Runtime.InteropServices;
 using System.Text;
+using System.Threading;
 using Xunit.Abstractions;
 
 namespace Microsoft.NET.TestFramework
@@ -20,5 +21,15 @@ protected SdkTest(ITestOutputHelper log)
         {
             Log = log;
         }
+
+        protected static void WaitForUtcNowToAdvance()
+        {
+            var start = DateTime.UtcNow;
+
+            while (DateTime.UtcNow <= start)
+            {
+                Thread.Sleep(millisecondsTimeout: 1);
+            }
+        }
     }
 }