Allow dotnet watch to refresh on changes to .razor files in referenced projects

dotnet-watch expects full paths to files to watch in all added items. For files in the current project, this
happens to work. However this does not work very well for files in referenced projects. Using the FullPath metadata
does not work during global evaluation, but we're able to do this in a target.

This change adds extensibility to the dotnet-watch tool that allows calling a target as part of "watch" evaluation.

Fixes https://github.com/dotnet/aspnetcore/issues/22219

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Sdk.Razor.CurrentVersion.props

@@ -78,6 +78,11 @@ Copyright (c) .NET Foundation. All rights reserved.
     This property affects C# projects targeting 3.0 or later.
     -->
     <RazorUpToDateReloadFileTypes>.cs;.razor;.resx;.cshtml</RazorUpToDateReloadFileTypes>
+
+    <!--
+    Target used by dotnet-watch to resolve additional items.
+    -->
+    <CustomCollectWatchItems>$(CustomCollectWatchItems);_RazorSdkCustomCollectWatchItems</CustomCollectWatchItems>
   </PropertyGroup>
 
   <ItemGroup Condition="'$(EnableDefaultItems)' == 'true' And '$(EnableDefaultContentItems)' == 'true'">

src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Sdk.Razor.CurrentVersion.targets

@@ -327,12 +327,6 @@ Copyright (c) .NET Foundation. All rights reserved.
     -->
     <UpToDateCheckBuilt Include="@(RazorIntermediateAssembly)"
       Condition="'$(RazorCompileOnBuild)'=='true' AND '@(Content->WithMetadataValue('Extension', '.cshtml'))' != ''" Set="RazorViews" />
-
-    <!-- Set up watchers for dotnet-watch -->
-    <Watch Include="@(Content->WithMetadataValue('Extension', '.razor'))" />
-
-    <Watch Include="@(Content->WithMetadataValue('Extension', '.cshtml'))"
-      Condition="'$(_Targeting30OrNewerRazorLangVersion)' == 'true' AND '$(AddCshtmlFilesToDotNetWatchList)' != 'false'" />
   </ItemGroup>
 
   <!--
@@ -870,6 +864,14 @@ Copyright (c) .NET Foundation. All rights reserved.
     </PropertyGroup>
   </Target>
 
+  <Target Name="_RazorSdkCustomCollectWatchItems">
+    <ItemGroup>
+      <Watch Include="%(Content.FullPath)" Condition="'%(Content.Extension)' == '.razor' AND '%(Content.Watch)' != 'false'" />
+      <Watch Include="%(Content.FullPath)"
+        Condition="'$(_Targeting30OrNewerRazorLangVersion)' == 'true' AND '$(AddCshtmlFilesToDotNetWatchList)' != 'false' AND '%(Content.Extension)' == '.cshtml' AND '%(Content.Watch)' != 'false'" />
+    </ItemGroup>
+  </Target>
+
   <PropertyGroup Condition="'$(RazorDesignTimeTargets)'==''">
     <RazorDesignTimeTargets>$(MSBuildExtensionsPath)\Microsoft\VisualStudio\Razor\Microsoft.NET.Sdk.Razor.DesignTime.targets</RazorDesignTimeTargets>
     <RazorDesignTimeTargets Condition="!Exists('$(RazorDesignTimeTargets)')">$(MSBuildThisFileDirectory)Microsoft.NET.Sdk.Razor.DesignTime.targets</RazorDesignTimeTargets>

src/Tools/dotnet-watch/src/assets/DotNetWatch.targets

@@ -41,6 +41,7 @@ Returns: @(Watch)
     </_CollectWatchItemsDependsOn>
     <_CollectWatchItemsDependsOn Condition=" '$(TargetFramework)' != '' ">
       _CoreCollectWatchItems;
+      $(CustomCollectWatchItems);
     </_CollectWatchItemsDependsOn>
   </PropertyGroup>
 

src/Tools/dotnet-watch/test/MsBuildFileSetFactoryTest.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Linq;
+using System.Reflection;
 using System.Text.RegularExpressions;
 using System.Threading;
 using System.Threading.Tasks;
@@ -276,6 +277,53 @@ namespace Microsoft.DotNet.Watcher.Tools.Tests
             );
         }
 
+        [Fact]
+        public async Task ProjectReferences_RazorFiles()
+        {
+            // Arrange
+            var razorSdkTargetsPath = GetType().Assembly.GetCustomAttributes<AssemblyMetadataAttribute>()
+                .First(f => f.Key == "RazorSdkPath").Value;
+
+            _tempDir
+                .SubDir("src")
+                    .SubDir("MyLibrary")
+                        .WithCSharpProject("MyLibrary", out var proj3, sdk: "Microsoft.NET.Sdk.Razor")
+                        .WithProperty("CustomCollectWatchItems", "$(CustomCollectWatchItems);_RazorSdkCustomCollectWatchItems")
+                        .WithProperty("RazorSdkCurrentVersionTargets", razorSdkTargetsPath)
+                        .WithTargetFrameworks("net5.0")
+                        .Dir()
+                        .WithFile("MyLibraryFile.razor")
+                        .WithFile("Class2.cs")
+                    .Up()
+                    .SubDir("MainApp")
+                        .WithCSharpProject("MainApp", out var target, sdk: "Microsoft.NET.Sdk.Razor")
+                        .WithProperty("CustomCollectWatchItems", "$(CustomCollectWatchItems);_RazorSdkCustomCollectWatchItems")
+                        .WithProperty("RazorSdkCurrentVersionTargets", razorSdkTargetsPath)
+                        .WithTargetFrameworks("net5.0")
+                        .WithProjectReference(proj3)
+                        .Dir()
+                        .WithFile("Class1.cs")
+                        .WithFile("Index.razor")
+                    .Up();
+
+            var fileset = await GetFileSet(target);
+
+            AssertEx.EqualFileList(
+                _tempDir.Root,
+                new[]
+                {
+                    "src/MyLibrary/MyLibraryFile.razor",
+                    "src/MyLibrary/Class2.cs",
+                    "src/MyLibrary/MyLibrary.csproj",
+                    "src/MainApp/Class1.cs",
+                    "src/MainApp/Index.razor",
+                    "src/MainApp/MainApp.csproj"
+                },
+                fileset
+            );
+        }
+
+
         private Task<IFileSet> GetFileSet(TemporaryCSharpProject target)
             => GetFileSet(new MsBuildFileSetFactory(_reporter, target.Path, waitOnError: false, trace: false));
 

src/Tools/dotnet-watch/test/TestProjects/KitchenSink/.gitignore

@@ -0,0 +1 @@
+.net

src/Tools/dotnet-watch/test/dotnet-watch.Tests.csproj

@@ -1,4 +1,4 @@
-<Project Sdk="Microsoft.NET.Sdk">
+<Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
     <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>
@@ -21,6 +21,11 @@
       <_Parameter1>DotnetPath</_Parameter1>
       <_Parameter2>$(DotNetTool)</_Parameter2>
     </AssemblyAttribute>
+
+    <AssemblyAttribute Include="System.Reflection.AssemblyMetadataAttribute">
+      <_Parameter1>RazorSdkPath</_Parameter1>
+      <_Parameter2>$(RepoRoot)src\Razor\Microsoft.NET.Sdk.Razor\src\build\netstandard2.0\Sdk.Razor.CurrentVersion.targets</_Parameter2>
+    </AssemblyAttribute>
   </ItemGroup>
 
   <Target Name="CleanTestProjects" BeforeTargets="CoreCompile">