Default to MVC 3.0 when we can't detect the Razor configuration (#1167)

* Default to MVC 3.0 when we can't detect the Razor configuration.

- Added a `Latest` configuration so we no longer need to look through every file to update the "latest" fallback configuration.
- Added understanding for MVC2.2, we default to the 2.1 configuration (there were no Razor changes between the two).

dotnet/aspnetcore#13291

* Set RazorLanguageServer default RazorVersion to 3.0

Author: ajaybhargavb

src/Razor/src/Microsoft.AspNetCore.Razor.LanguageServer/RazorDefaults.cs

@@ -15,7 +15,7 @@ public static class RazorDefaults
                 Pattern = "**/*.{cshtml,razor}"
             });
 
-        public static RazorConfiguration Configuration { get; } = FallbackRazorConfiguration.MVC_2_1;
+        public static RazorConfiguration Configuration { get; } = FallbackRazorConfiguration.Latest;
 
         public static string RootNamespace { get; } = null;
     }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/DefaultProjectSnapshotProjectEngineFactory.cs

@@ -9,7 +9,7 @@ namespace Microsoft.CodeAnalysis.Razor
 {
     internal class DefaultProjectSnapshotProjectEngineFactory : ProjectSnapshotProjectEngineFactory
     {
-        private readonly static RazorConfiguration DefaultConfiguration = FallbackRazorConfiguration.MVC_2_1;
+        private readonly static RazorConfiguration DefaultConfiguration = FallbackRazorConfiguration.Latest;
 
         private readonly IFallbackProjectEngineFactory _fallback;
         private readonly Lazy<IProjectEngineFactory, ICustomProjectEngineFactoryMetadata>[] _factories;

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/EphemeralProjectSnapshot.cs

@@ -32,7 +32,7 @@ public EphemeralProjectSnapshot(HostWorkspaceServices services, string filePath)
             _projectEngine = new Lazy<RazorProjectEngine>(CreateProjectEngine);
         }
 
-        public override RazorConfiguration Configuration => FallbackRazorConfiguration.MVC_2_1;
+        public override RazorConfiguration Configuration => FallbackRazorConfiguration.Latest;
 
         public override IEnumerable<string> DocumentFilePaths => Array.Empty<string>();
 

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/FallbackRazorConfiguration.cs

@@ -29,6 +29,12 @@ internal class FallbackRazorConfiguration : RazorConfiguration
              "MVC-2.1",
              new[] { new FallbackRazorExtension("MVC-2.1"), });
 
+        public static readonly RazorConfiguration MVC_3_0 = new FallbackRazorConfiguration(
+             RazorLanguageVersion.Version_3_0,
+             "MVC-3.0",
+             new[] { new FallbackRazorExtension("MVC-3.0"), });
+
+        public static readonly RazorConfiguration Latest = MVC_3_0;
 
         public static RazorConfiguration SelectConfiguration(Version version)
         {
@@ -44,13 +50,17 @@ public static RazorConfiguration SelectConfiguration(Version version)
             {
                 return MVC_2_0;
             }
-            else if (version.Major == 2 && version.Minor == 1)
+            else if (version.Major == 2 && version.Minor >= 1)
             {
                 return MVC_2_1;
             }
+            else if (version.Major == 3 && version.Minor == 0)
+            {
+                return MVC_3_0;
+            }
             else
             {
-                return MVC_2_1;
+                return Latest;
             }
         }