Consume first TFM for TagHelperDescriptor resolution.

- This makes RazorTooling consistent with the .cshtml editor.
- Added `project.json` tests to validate new behavior of throwing an appropriate error/selecting the first TFM.

#49

Author: N. Taylor Mullen

src/dotnet-razor-tooling/Internal/ResolveProtocolCommand.cs

@@ -34,9 +34,6 @@ internal static void Register(CommandLineApplication app)
             });
         }
 
-        /// <summary>
-        /// Internal for testing.
-        /// </summary>
         public static int ResolveProtocol(int clientProtocol, int pluginProtocol)
         {
             // Protocols start at 1 and increase.

src/dotnet-razor-tooling/Internal/ResolveTagHelpersCommand.cs

@@ -3,7 +3,9 @@
 
 using System;
 using System.Collections.Generic;
+using System.Globalization;
 using System.Linq;
+using dotnet_razor_tooling;
 using Microsoft.AspNetCore.Razor;
 using Microsoft.AspNetCore.Razor.Compilation.TagHelpers;
 using Microsoft.DotNet.Cli.Utils;
@@ -30,26 +32,16 @@ internal static void Register(CommandLineApplication app)
                     "[project]",
                     "Path to the project.json for the project resolving TagHelperDescriptors.",
                     multipleValues: false);
-                var framework = config.Argument(
-                    "[framework]",
-                    "The framework to resolve TagHelperDescriptors for.",
-                    multipleValues: false);
                 var assemblyNames = config.Argument(
                     "[assemblyName]",
                     "Assembly name to resolve TagHelperDescriptors in.",
                     multipleValues: true);
 
                 config.OnExecute(() =>
                 {
-                    var projectValue = project.Value;
-                    var frameworkValue = framework.Value;
-                    var projectContexts = ProjectContext.CreateContextForEachFramework(projectValue);
-                    var startupProjectContext = projectContexts
-                        .First(frameworkContext => string.Equals(
-                            frameworkContext.TargetFramework.Framework,
-                            frameworkValue,
-                            StringComparison.OrdinalIgnoreCase));
-                    var assemblyLoadContext = startupProjectContext.CreateLoadContext();
+                    var projectFilePath = project.Value;
+                    var projectContext = ResolveProjectContext(projectFilePath);
+                    var assemblyLoadContext = projectContext.CreateLoadContext();
                     var protocol = protocolOption.HasValue() ?
                         int.Parse(protocolOption.Value()) :
                         AssemblyTagHelperDescriptorResolver.DefaultProtocolVersion;
@@ -82,6 +74,20 @@ internal static void Register(CommandLineApplication app)
             });
         }
 
+        public static ProjectContext ResolveProjectContext(string projectFilePath)
+        {
+            var projectContexts = ProjectContext.CreateContextForEachFramework(projectFilePath);
+            var projectContext = projectContexts.FirstOrDefault();
+
+            if (projectContext == null)
+            {
+                throw new InvalidOperationException(
+                    string.Format(CultureInfo.CurrentCulture, Resources.InvalidProjectFile, projectFilePath));
+            }
+
+            return projectContext;
+        }
+
         private class ResolvedTagHelperDescriptorsResult
         {
             public IEnumerable<TagHelperDescriptor> Descriptors { get; set; }

src/dotnet-razor-tooling/Resources.Designer.cs

@@ -117,6 +117,9 @@
   <resheader name="writer">
     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
+  <data name="InvalidProjectFile" xml:space="preserve">
+    <value>Could not resolve any target frameworks for file '{0}'.</value>
+  </data>
   <data name="InvalidProtocolValue" xml:space="preserve">
     <value>'{0}'s cannot be resolved with protocol '{1}'. Protocol not supported.</value>
   </data>

src/dotnet-razor-tooling/Resources.resx

@@ -0,0 +1,39 @@
+// 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 System;
+using System.Globalization;
+using dotnet_razor_tooling;
+using Microsoft.AspNetCore.Tooling.Razor.Internal;
+using Xunit;
+
+namespace Microsoft.AspNetCore.Tooling.Razor
+{
+    public class ResolveTagHelpersCommandTest
+    {
+        [Fact]
+        public void ResolveProjectContext_ThrowsWhenNoTargetFrameworks()
+        {
+            // Arrange
+            var projectFilePath = "TestFiles/notfmproject.json";
+            var expectedErrorMessage = string.Format(CultureInfo.CurrentCulture, Resources.InvalidProjectFile, projectFilePath);
+
+            // Act & Assert
+            var ex = Assert.Throws<InvalidOperationException>(() => ResolveTagHelpersCommand.ResolveProjectContext(projectFilePath));
+            Assert.Equal(expectedErrorMessage, ex.Message);
+        }
+
+        [Fact]
+        public void ResolveProjectContext_ResolvesProjectContextsCorrectly()
+        {
+            // Arrange
+            var projectFilePath = "TestFiles/dnxcoreproject.json";
+
+            // Act
+            var projectContext = ResolveTagHelpersCommand.ResolveProjectContext(projectFilePath);
+
+            // Assert
+            Assert.Equal("DNXCore", projectContext.TargetFramework.Framework);
+        }
+    }
+}

test/dotnet-razor-tooling.Test/ResolveTagHelpersCommandTest.cs

@@ -0,0 +1,6 @@
+{
+  "frameworks": {
+    "dnxcore50": { },
+    "net451": { }
+  }
+}

test/dotnet-razor-tooling.Test/TestFiles/dnxcoreproject.json

@@ -0,0 +1,4 @@
+{
+  "frameworks": {
+  }
+}