Add a method to check that MVIDs match

Add a utility method to check that MVIDs match.

Given a path to an assembly and a loaded `Assembly` object,
`AssemblyUtilities.MvidsMatch` returns true if their MVIDs (Module
Version IDs) match, and false otherwise.

This commit contains the code itself and unit tests; a later commit will
wire this into the compilers/VS.

src/Compilers/Core/CodeAnalysisTest/AssemblyUtilitiesTests.cs

@@ -2,7 +2,9 @@
 
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
+using System.Reflection;
 using System.Text;
 using System.Threading.Tasks;
 using Roslyn.Test.Utilities;
@@ -71,5 +73,34 @@ public void FindAssemblySet_TransitiveDependencies()
             Assert.Contains(gammaDll.Path, results, StringComparer.OrdinalIgnoreCase);
             Assert.Contains(deltaDll.Path, results, StringComparer.OrdinalIgnoreCase);
         }
+
+        [Fact]
+        public void MvidsMatch_True()
+        {
+            var directory = Temp.CreateDirectory();
+
+            var alphaDll = directory.CreateFile("Alpha.dll").WriteAllBytes(TestResources.AssemblyLoadTests.AssemblyLoadTests.Alpha);
+
+            var assembly = Assembly.Load(File.ReadAllBytes(alphaDll.Path));
+
+            var result = AssemblyUtilities.MvidsMatch(alphaDll.Path, assembly);
+
+            Assert.True(result);
+        }
+
+        [Fact]
+        public void MvidsMatch_False()
+        {
+            var directory = Temp.CreateDirectory();
+
+            var alphaDll = directory.CreateFile("Alpha.dll").WriteAllBytes(TestResources.AssemblyLoadTests.AssemblyLoadTests.Alpha);
+            var betaDll = directory.CreateFile("Beta.dll").WriteAllBytes(TestResources.AssemblyLoadTests.AssemblyLoadTests.Beta);
+
+            var assembly = Assembly.Load(File.ReadAllBytes(betaDll.Path));
+
+            var result = AssemblyUtilities.MvidsMatch(alphaDll.Path, assembly);
+
+            Assert.False(result);
+        }
     }
 }

src/Compilers/Core/Portable/AssemblyUtilities.cs

@@ -4,6 +4,7 @@
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.IO;
+using System.Reflection;
 using System.Reflection.Metadata;
 using System.Reflection.PortableExecutable;
 
@@ -24,6 +25,11 @@ internal static class AssemblyUtilities
         /// </remarks>
         public static ImmutableArray<string> FindAssemblySet(string filePath)
         {
+            if (filePath == null)
+            {
+                throw new ArgumentNullException(nameof(filePath));
+            }
+
             Queue<string> workList = new Queue<string>();
             HashSet<string> assemblySet = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
 
@@ -60,5 +66,31 @@ public static ImmutableArray<string> FindAssemblySet(string filePath)
 
             return ImmutableArray.CreateRange(assemblySet);
         }
+
+        /// <summary>
+        /// Given a path to an assembly and a loaded <see cref="Assembly"/>, returns
+        /// true if their MVIDs match, and false otherwise.
+        /// </summary>
+        public static bool MvidsMatch(string filePath, Assembly assembly)
+        {
+            if (filePath == null)
+            {
+                throw new ArgumentNullException(nameof(filePath));
+            }
+
+            if (assembly == null)
+            {
+                throw new ArgumentNullException(nameof(assembly));
+            }
+
+            using (var reader = new PEReader(FileUtilities.OpenRead(filePath)))
+            {
+                var metadataReader = reader.GetMetadataReader();
+                var mvidHandle = metadataReader.GetModuleDefinition().Mvid;
+                var fileMvid = metadataReader.GetGuid(mvidHandle);
+
+                return fileMvid == assembly.ManifestModule.ModuleVersionId;
+            }
+        }
     }
 }