1 files changed, 70 insertions, 0 deletions

diff --git a/src/WixToolset.Core.Native/AssemblyExtensions.cs b/src/WixToolset.Core.Native/AssemblyExtensions.cs
new file mode 100644
index 00000000..590a6887
--- /dev/null
+++ b/src/WixToolset.Core.Native/AssemblyExtensions.cs
@@ -0,0 +1,70 @@
+// Copyright (c) .NET Foundation and contributors. All rights reserved. Licensed under the Microsoft Reciprocal License. See LICENSE.TXT file in the project root for full license information.
+
+namespace WixToolset.Core.Native
+{
+    using System;
+    using System.IO;
+    using System.Reflection;
+    using System.Text;
+
+    internal static class AssemblyExtensions
+    {
+        internal static FindAssemblyRelativeFileResult FindFileRelativeToAssembly(this Assembly assembly, string relativePath, bool searchNativeDllDirectories)
+        {
+            // First try using the Assembly.Location. This works in almost all cases with
+            // no side-effects.
+            var path = Path.Combine(Path.GetDirectoryName(assembly.Location), relativePath);
+            var possiblePaths = new StringBuilder(path);
+
+            var found = File.Exists(path);
+            if (!found)
+            {
+                // Fallback to the Assembly.CodeBase to handle "shadow copy" scenarios (like unit tests) but
+                // only check codebase if it is different from the Assembly.Location path.
+                var codebase = Path.Combine(Path.GetDirectoryName(new Uri(assembly.CodeBase).LocalPath), relativePath);
+
+                if (!codebase.Equals(path, StringComparison.OrdinalIgnoreCase))
+                {
+                    path = codebase;
+                    possiblePaths.Append(Path.PathSeparator + path);
+
+                    found = File.Exists(path);
+                }
+
+                if (!found && searchNativeDllDirectories && AppContext.GetData("NATIVE_DLL_SEARCH_DIRECTORIES") is string searchDirectoriesString)
+                {
+                    // If instructed to search native DLL search directories, try to find our file there.
+                    possiblePaths.Append(Path.PathSeparator + searchDirectoriesString);
+
+                    var searchDirectories = searchDirectoriesString?.Split(Path.PathSeparator);
+                    foreach (var directoryPath in searchDirectories)
+                    {
+                        var possiblePath = Path.Combine(directoryPath, relativePath);
+                        if (File.Exists(possiblePath))
+                        {
+                            path = possiblePath;
+                            found = true;
+                            break;
+                        }
+                    }
+                }
+            }
+
+            return new FindAssemblyRelativeFileResult
+            {
+                Found = found,
+                Path = found ? path : null,
+                PossiblePaths = possiblePaths.ToString()
+            };
+        }
+
+        internal class FindAssemblyRelativeFileResult
+        {
+            public bool Found { get; set; }
+
+            public string Path { get; set; }
+
+            public string PossiblePaths { get; set; }
+        }
+    }
+}