From 127d23a022286e9c819206da78e52b8ed5dc1498 Mon Sep 17 00:00:00 2001
From: Pranav K <prkrishn@hotmail.com>
Date: Mon, 31 Jul 2017 17:13:08 -0700
Subject: [PATCH] Parse LanguageVersion correctly

Fixes https://github.com/aspnet/Mvc/issues/6611
---
 .../Internal/CSharpCompiler.cs                     | 14 ++++++++++----
 .../Internal/CSharpCompilerTest.cs                 |  2 +-
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/src/Microsoft.AspNetCore.Mvc.Razor/Internal/CSharpCompiler.cs b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/CSharpCompiler.cs
index 107040ef4e..d95de2584b 100644
--- a/src/Microsoft.AspNetCore.Mvc.Razor/Internal/CSharpCompiler.cs
+++ b/src/Microsoft.AspNetCore.Mvc.Razor/Internal/CSharpCompiler.cs
@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.Linq;
 using System.Reflection;
 using Microsoft.AspNetCore.Hosting;
@@ -154,11 +155,16 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
 
             var parseOptions = new CSharpParseOptions(preprocessorSymbols: defines);
 
-            LanguageVersion languageVersion;
-            if (!string.IsNullOrEmpty(dependencyContextOptions.LanguageVersion) &&
-                Enum.TryParse(dependencyContextOptions.LanguageVersion, ignoreCase: true, result: out languageVersion))
+            if (!string.IsNullOrEmpty(dependencyContextOptions.LanguageVersion))
             {
-                parseOptions = parseOptions.WithLanguageVersion(languageVersion);
+                if (LanguageVersionFacts.TryParse(dependencyContextOptions.LanguageVersion, out var languageVersion))
+                {
+                    parseOptions = parseOptions.WithLanguageVersion(languageVersion);
+                }
+                else
+                {
+                    Debug.Fail($"LanguageVersion {languageVersion} specified in the deps file could not be parsed.");
+                }
             }
 
             return parseOptions;
diff --git a/test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/CSharpCompilerTest.cs b/test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/CSharpCompilerTest.cs
index b25b4127b0..c6d9b94dd2 100644
--- a/test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/CSharpCompilerTest.cs
+++ b/test/Microsoft.AspNetCore.Mvc.Razor.Test/Internal/CSharpCompilerTest.cs
@@ -151,7 +151,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor.Internal
             // Arrange
             var dependencyContextOptions = new DependencyContextCompilationOptions(
                 new[] { "MyDefine" },
-                languageVersion: "CSharp7_1",
+                languageVersion: "7.1",
                 platform: null,
                 allowUnsafe: true,
                 warningsAsErrors: null,