Support conflict resolution when multiple precompiled views have the same path

Fixes #7223

src/Microsoft.AspNetCore.Mvc.Core/ApplicationParts/ApplicationPartManager.cs

@@ -19,10 +19,15 @@ namespace Microsoft.AspNetCore.Mvc.ApplicationParts
             new List<IApplicationFeatureProvider>();
 
         /// <summary>
-        /// Gets the list of <see cref="ApplicationPart"/>s.
+        /// Gets the list of <see cref="ApplicationPart"/> instances.
+        /// <para>
+        /// Instances in this collection are stored in precedence order. An <see cref="ApplicationPart"/> that appears
+        /// earlier in the list has a higher precendence.
+        /// An <see cref="IApplicationFeatureProvider"/> may choose to use this an interface as a way to resolve conflicts when
+        /// multiple <see cref="ApplicationPart"/> instances resolve equivalent feature values.
+        /// </para>
         /// </summary>
-        public IList<ApplicationPart> ApplicationParts { get; } =
+        public IList<ApplicationPart> ApplicationParts { get; } = new List<ApplicationPart>();
-            new List<ApplicationPart>();
 
         /// <summary>
         /// Populates the given <paramref name="feature"/> using the list of

src/Microsoft.AspNetCore.Mvc.Core/ApplicationParts/AssemblyPart.cs

@@ -10,7 +10,7 @@ using Microsoft.Extensions.DependencyModel;
 namespace Microsoft.AspNetCore.Mvc.ApplicationParts
 {
     /// <summary>
-    /// An <see cref="ApplicationPart"/> backed by an <see cref="Assembly"/>.
+    /// An <see cref="ApplicationPart"/> backed by an <see cref="System.Reflection.Assembly"/>.
     /// </summary>
     public class AssemblyPart :
         ApplicationPart,
@@ -20,15 +20,10 @@ namespace Microsoft.AspNetCore.Mvc.ApplicationParts
         /// <summary>
         /// Initializes a new <see cref="AssemblyPart"/> instance.
         /// </summary>
-        /// <param name="assembly"></param>
+        /// <param name="assembly">The backing <see cref="System.Reflection.Assembly"/>.</param>
         public AssemblyPart(Assembly assembly)
         {
-            if (assembly == null)
+            Assembly = assembly ?? throw new ArgumentNullException(nameof(assembly));
-            {
-                throw new ArgumentNullException(nameof(assembly));
-            }
-
-            Assembly = assembly;
         }
 
         /// <summary>

src/Microsoft.AspNetCore.Mvc.Core/ApplicationParts/IApplicationFeatureProviderOfT.cs

@@ -14,10 +14,14 @@ namespace Microsoft.AspNetCore.Mvc.ApplicationParts
         /// <summary>
         /// Updates the <paramref name="feature"/> instance.
         /// </summary>
-        /// <param name="parts">The list of <see cref="ApplicationPart"/>s of the
+        /// <param name="parts">The list of <see cref="ApplicationPart"/> instances in the application.
-        /// application.
         /// </param>
         /// <param name="feature">The feature instance to populate.</param>
+        /// <remarks>
+        /// <see cref="ApplicationPart"/> instances in <paramref name="parts"/> appear in the same ordered sequence they
+        /// are stored in <see cref="ApplicationPartManager.ApplicationParts"/>. This ordering may be used by the feature
+        /// provider to make precedence decisions.
+        /// </remarks>
         void PopulateFeature(IEnumerable<ApplicationPart> parts, TFeature feature);
     }
 }

src/Microsoft.AspNetCore.Mvc.Core/DependencyInjection/MvcCoreServiceCollectionExtensions.cs

@@ -81,12 +81,17 @@ namespace Microsoft.Extensions.DependencyInjection
                 manager = new ApplicationPartManager();
 
                 var environment = GetServiceFromCollection<IHostingEnvironment>(services);
-                if (string.IsNullOrEmpty(environment?.ApplicationName))
+                var entryAssemblyName = environment?.ApplicationName;
+                if (string.IsNullOrEmpty(entryAssemblyName))
                 {
                     return manager;
                 }
 
-                var parts = DefaultAssemblyPartDiscoveryProvider.DiscoverAssemblyParts(environment.ApplicationName);
+                // Parts appear in the ApplicationParts collection in precedence order. The part that represents the
+                // current application appears first, followed by all other parts sorted by name.
+                var parts = DefaultAssemblyPartDiscoveryProvider.DiscoverAssemblyParts(entryAssemblyName)
+                    .OrderBy(part => string.Equals(entryAssemblyName, part.Name, StringComparison.Ordinal) ? 0 : 1)
+                    .ThenBy(part => part.Name, StringComparer.Ordinal);
                 foreach (var part in parts)
                 {
                     manager.ApplicationParts.Add(part);

src/Microsoft.AspNetCore.Mvc.Razor/Compilation/ViewsFeatureProvider.cs

@@ -27,15 +27,23 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
         /// <inheritdoc />
         public void PopulateFeature(IEnumerable<ApplicationPart> parts, ViewsFeature feature)
         {
+            var knownIdentifiers = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
+            var descriptors = new List<CompiledViewDescriptor>();
             foreach (var assemblyPart in parts.OfType<AssemblyPart>())
             {
                 var attributes = GetViewAttributes(assemblyPart);
                 var items = LoadItems(assemblyPart);
 
                 var merged = Merge(items, attributes);
-                foreach (var entry in merged)
+                foreach (var item in merged)
                 {
-                    feature.ViewDescriptors.Add(new CompiledViewDescriptor(entry.item, entry.attribute));
+                    var descriptor = new CompiledViewDescriptor(item.item, item.attribute);
+                    // We iterate through ApplicationPart instances appear in precendence order.
+                    // If a view path appears in multiple views, we'll use the order to break ties.
+                    if (knownIdentifiers.Add(descriptor.RelativePath))
+                    {
+                        feature.ViewDescriptors.Add(descriptor);
+                    }
                 }
             }
         }

test/Microsoft.AspNetCore.Mvc.FunctionalTests/BasicTests.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using System.Net;
 using System.Net.Http;
 using System.Net.Http.Headers;
@@ -489,5 +490,22 @@ namespace Microsoft.AspNetCore.Mvc.FunctionalTests
             Assert.Equal(422, (int)response.StatusCode);
             Assert.Equal("Can't process this!", await response.Content.ReadAsStringAsync());
         }
+
+        [Fact]
+        public async Task ApplicationAssemblyPartIsListedAsFirstAssembly()
+        {
+            // Act
+            var response = await Client.GetStringAsync("Home/GetAssemblyPartData");
+            var assemblyParts = JsonConvert.DeserializeObject<IList<string>>(response);
+            var expected = new[]
+            {
+                "BasicWebSite",
+                "Microsoft.AspNetCore.Mvc.TagHelpers",
+                "Microsoft.AspNetCore.Mvc.Razor",
+            };
+
+            // Assert
+            Assert.Equal(expected, assemblyParts);
+        }
     }
 }

test/Microsoft.AspNetCore.Mvc.Razor.Test/Compilation/ViewsFeatureProviderTest.cs

@@ -20,7 +20,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
         {
             // Arrange
             var partManager = new ApplicationPartManager();
-            partManager.ApplicationParts.Add(new AssemblyPart(typeof(ViewsFeatureProviderTest).GetTypeInfo().Assembly));
+            partManager.ApplicationParts.Add(new AssemblyPart(typeof(ViewsFeatureProviderTest).Assembly));
             partManager.FeatureProviders.Add(new ViewsFeatureProvider());
             var feature = new ViewsFeature();
 
@@ -35,8 +35,8 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
         public void PopulateFeature_ReturnsViewsFromAllAvailableApplicationParts()
         {
             // Arrange
-            var part1 = new AssemblyPart(typeof(object).GetTypeInfo().Assembly);
+            var part1 = new AssemblyPart(typeof(object).Assembly);
-            var part2 = new AssemblyPart(GetType().GetTypeInfo().Assembly);
+            var part2 = new AssemblyPart(GetType().Assembly);
 
             var items = new Dictionary<AssemblyPart, IReadOnlyList<RazorCompiledItem>>
             {
@@ -141,6 +141,39 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
                 });
         }
 
+        [Fact]
+        public void PopulateFeature_PrefersViewsFromPartsWithHigherPrecedence()
+        {
+            // Arrange
+            var part1 = new AssemblyPart(typeof(ViewsFeatureProvider).Assembly);
+            var item1 = new TestRazorCompiledItem(typeof(StringBuilder), "mvc.1.0.view", "/Areas/Admin/Views/Shared/_Layout.cshtml", new object[] { });
+
+            var part2 = new AssemblyPart(GetType().Assembly);
+            var item2 = new TestRazorCompiledItem(typeof(string), "mvc.1.0.view", "/Areas/Admin/Views/Shared/_Layout.cshtml", new object[] { });
+            var item3 = new TestRazorCompiledItem(typeof(string), "mvc.1.0.view", "/Areas/Admin/Views/Shared/_Partial.cshtml", new object[] { });
+
+            var items = new Dictionary<AssemblyPart, IReadOnlyList<RazorCompiledItem>>
+            {
+                { part1, new[] { item1 } },
+                { part2, new[] { item2, item3, } },
+            };
+
+            var featureProvider = new TestableViewsFeatureProvider(items, attributes: new Dictionary<AssemblyPart, IEnumerable<RazorViewAttribute>>());
+            var partManager = new ApplicationPartManager();
+            partManager.ApplicationParts.Add(part1);
+            partManager.ApplicationParts.Add(part2);
+            partManager.FeatureProviders.Add(featureProvider);
+            var feature = new ViewsFeature();
+
+            // Act
+            partManager.PopulateFeature(feature);
+
+            // Assert
+            Assert.Collection(feature.ViewDescriptors.OrderBy(f => f.RelativePath, StringComparer.Ordinal),
+                view => Assert.Same(item1, view.Item),
+                view => Assert.Same(item3, view.Item));
+        }
+
         [Fact]
         public void PopulateFeature_ReturnsEmptySequenceIfNoDynamicAssemblyPartHasViewAssembly()
         {
@@ -160,7 +193,6 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
             Assert.Empty(feature.ViewDescriptors);
         }
 
-
         [Fact]
         public void PopulateFeature_DoesNotFail_IfAssemblyHasEmptyLocation()
         {
@@ -212,7 +244,12 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
 
             protected override IEnumerable<RazorViewAttribute> GetViewAttributes(AssemblyPart assemblyPart)
             {
-                return _attributes[assemblyPart];
+                if (_attributes.TryGetValue(assemblyPart, out var attributes))
+                {
+                    return attributes;
+                }
+
+                return Enumerable.Empty<RazorViewAttribute>();
             }
 
             protected override IReadOnlyList<RazorCompiledItem> LoadItems(AssemblyPart assemblyPart)
@@ -225,7 +262,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Compilation
         {
             public override string Location => string.Empty;
 
-            public override string FullName => typeof(ViewsFeatureProviderTest).GetTypeInfo().Assembly.FullName;
+            public override string FullName => typeof(ViewsFeatureProviderTest).Assembly.FullName;
 
             public override IEnumerable<TypeInfo> DefinedTypes
             {

test/WebSites/BasicWebSite/Controllers/HomeController.cs

@@ -2,10 +2,12 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System.Collections.Generic;
+using System.Linq;
 using System.Threading.Tasks;
 using BasicWebSite.Models;
 using Microsoft.AspNetCore.Http;
 using Microsoft.AspNetCore.Mvc;
+using Microsoft.AspNetCore.Mvc.ApplicationParts;
 using Newtonsoft.Json.Serialization;
 
 namespace BasicWebSite.Controllers
@@ -120,5 +122,16 @@ namespace BasicWebSite.Controllers
         {
             return RedirectToAction();
         }
+
+        [HttpGet]
+        public IActionResult GetAssemblyPartData([FromServices] ApplicationPartManager applicationPartManager)
+        {
+            // Ensures that the entry assembly part is marked correctly.
+            var assemblyPartMetadata = applicationPartManager.ApplicationParts
+                .Select(part => part.Name)
+                .ToArray();
+
+            return Ok(assemblyPartMetadata);
+        }
     }
-}
+}