Watch _ViewImports outside the pages root for changes

Fixes #6428

src/Microsoft.AspNetCore.Mvc.Core/Internal/ActionDescriptorCollectionProvider.cs

@@ -43,6 +43,11 @@ namespace Microsoft.AspNetCore.Mvc.Internal
 
         private IChangeToken GetCompositeChangeToken()
         {
+            if (_actionDescriptorChangeProviders.Length == 1)
+            {
+                return _actionDescriptorChangeProviders[0].GetChangeToken();
+            }
+
             var changeTokens = new IChangeToken[_actionDescriptorChangeProviders.Length];
             for (var i = 0; i < _actionDescriptorChangeProviders.Length; i++)
             {

src/Microsoft.AspNetCore.Mvc.RazorPages/Internal/PageActionDescriptorChangeProvider.cs

@@ -2,8 +2,11 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
+using System.Diagnostics;
+using System.Linq;
 using Microsoft.AspNetCore.Mvc.Infrastructure;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.Options;
 using Microsoft.Extensions.Primitives;
@@ -14,11 +17,18 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
     {
         private readonly IFileProvider _fileProvider;
         private readonly string _searchPattern;
+        private readonly string[] _additionalFilesToTrack;
 
         public PageActionDescriptorChangeProvider(
+            RazorTemplateEngine templateEngine,
             IRazorViewEngineFileProviderAccessor fileProviderAccessor,
             IOptions<RazorPagesOptions> razorPagesOptions)
         {
+            if (templateEngine == null)
+            {
+                throw new ArgumentNullException(nameof(templateEngine));
+            }
+
             if (fileProviderAccessor == null)
             {
                 throw new ArgumentNullException(nameof(fileProviderAccessor));
@@ -30,9 +40,35 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             }
 
             _fileProvider = fileProviderAccessor.FileProvider;
-            _searchPattern = razorPagesOptions.Value.RootDirectory.TrimEnd('/') +  "/**/*.cshtml";
+
+            var rootDirectory = razorPagesOptions.Value.RootDirectory;
+            Debug.Assert(!string.IsNullOrEmpty(rootDirectory));
+            rootDirectory = rootDirectory.TrimEnd('/');
+
+            var importFileAtPagesRoot = rootDirectory + "/" + templateEngine.Options.ImportsFileName;
+            _additionalFilesToTrack = templateEngine.GetImportItems(importFileAtPagesRoot)
+                .Select(item => item.Path)
+                .ToArray();
+
+            _searchPattern = rootDirectory + "/**/*.cshtml";
         }
 
-        public IChangeToken GetChangeToken() => _fileProvider.Watch(_searchPattern);
+        public IChangeToken GetChangeToken()
+        {
+            var wildcardChangeToken = _fileProvider.Watch(_searchPattern);
+            if (_additionalFilesToTrack.Length == 0)
+            {
+                return wildcardChangeToken;
+            }
+
+            var changeTokens = new IChangeToken[_additionalFilesToTrack.Length + 1];
+            for (var i = 0; i < _additionalFilesToTrack.Length; i++)
+            {
+                changeTokens[i] = _fileProvider.Watch(_additionalFilesToTrack[i]);
+            }
+
+            changeTokens[changeTokens.Length - 1] = wildcardChangeToken;
+            return new CompositeChangeToken(changeTokens);
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.RazorPages.Test/Internal/PageActionDescriptorChangeProviderTest.cs

@@ -1,8 +1,11 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using Microsoft.AspNetCore.Mvc.Razor;
 using Microsoft.AspNetCore.Mvc.Razor.Internal;
+using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.Extensions.FileProviders;
+using Microsoft.Extensions.Primitives;
 using Moq;
 using Xunit;
 
@@ -14,13 +17,16 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         public void GetChangeToken_WatchesAllCshtmlFilesUnderFileSystemRoot()
         {
             // Arrange
-            var options = new TestOptionsManager<RazorPagesOptions>();
             var fileProvider = new Mock<IFileProvider>();
+            var templateEngine = new RazorTemplateEngine(
+                RazorEngine.Create(),
+                new FileProviderRazorProject(fileProvider.Object));
+            var options = new TestOptionsManager<RazorPagesOptions>();
             var fileProviderAccessor = new Mock<IRazorViewEngineFileProviderAccessor>();
             fileProviderAccessor
                 .Setup(f => f.FileProvider)
                 .Returns(fileProvider.Object);
-            var changeProvider = new PageActionDescriptorChangeProvider(fileProviderAccessor.Object, options);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, fileProviderAccessor.Object, options);
 
             // Act
             var changeToken = changeProvider.GetChangeToken();
@@ -35,14 +41,17 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
         public void GetChangeToken_WatchesAllCshtmlFilesUnderSpecifiedRootDirectory(string rootDirectory)
         {
             // Arrange
+            var fileProvider = new Mock<IFileProvider>();
+            var templateEngine = new RazorTemplateEngine(
+                RazorEngine.Create(),
+                new FileProviderRazorProject(fileProvider.Object));
             var options = new TestOptionsManager<RazorPagesOptions>();
             options.Value.RootDirectory = rootDirectory;
-            var fileProvider = new Mock<IFileProvider>();
             var fileProviderAccessor = new Mock<IRazorViewEngineFileProviderAccessor>();
             fileProviderAccessor
                 .Setup(f => f.FileProvider)
                 .Returns(fileProvider.Object);
-            var changeProvider = new PageActionDescriptorChangeProvider(fileProviderAccessor.Object, options);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, fileProviderAccessor.Object, options);
 
             // Act
             var changeToken = changeProvider.GetChangeToken();
@@ -50,5 +59,30 @@ namespace Microsoft.AspNetCore.Mvc.RazorPages.Internal
             // Assert
             fileProvider.Verify(f => f.Watch("/pages-base-dir/**/*.cshtml"));
         }
+
+        [Fact]
+        public void GetChangeToken_WatchesViewImportsOutsidePagesRoot()
+        {
+            // Arrange
+            var fileProvider = new TestFileProvider();
+            var templateEngine = new RazorTemplateEngine(
+                RazorEngine.Create(),
+                new FileProviderRazorProject(fileProvider));
+            templateEngine.Options.ImportsFileName = "_ViewImports.cshtml";
+            var options = new TestOptionsManager<RazorPagesOptions>();
+            options.Value.RootDirectory = "/dir1/dir2";
+            var fileProviderAccessor = new Mock<IRazorViewEngineFileProviderAccessor>();
+            fileProviderAccessor
+                .Setup(f => f.FileProvider)
+                .Returns(fileProvider);
+            var changeProvider = new PageActionDescriptorChangeProvider(templateEngine, fileProviderAccessor.Object, options);
+
+            // Act & Assert
+            var compositeChangeToken = Assert.IsType<CompositeChangeToken>(changeProvider.GetChangeToken());
+            Assert.Collection(compositeChangeToken.ChangeTokens,
+                changeToken => Assert.Same(fileProvider.GetChangeToken("/dir1/_ViewImports.cshtml"), changeToken),
+                changeToken => Assert.Same(fileProvider.GetChangeToken("/_ViewImports.cshtml"), changeToken),
+                changeToken => Assert.Same(fileProvider.GetChangeToken("/dir1/dir2/**/*.cshtml"), changeToken));
+        }
     }
 }