Added files option

src/CodeFormatter.cs

@@ -1,4 +1,4 @@
-// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the MIT license.  See License.txt in the project root for license information.
+// Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the MIT license.  See License.txt in the project root for license information.
 
 using System;
 using System.Collections.Generic;
@@ -160,7 +160,9 @@ void LogWorkspaceWarnings(object sender, WorkspaceDiagnosticEventArgs args)
 
                 if (filesToFormat != null)
                 {
-                    var fileInArgumentList = filesToFormat.Any(path => document.FilePath.EndsWith(path, StringComparison.OrdinalIgnoreCase));
+                    var fileInArgumentList = filesToFormat
+                        .Select(path => Path.GetRelativePath(Environment.CurrentDirectory, path))
+                        .Any(relativePath => document.FilePath.EndsWith(relativePath, StringComparison.OrdinalIgnoreCase));
 
                     if (!fileInArgumentList)
                     {

tests/CodeFormatterTests.cs

@@ -156,5 +156,22 @@ public async Task NoFilesFormattedWhenNotInList()
             Assert.Equal(0, formatResult.FilesFormatted);
             Assert.Equal(4, formatResult.FileCount);
         }
+
+        [Fact]
+        public async Task FilesFormattedDirectorySeparatorInsensitive()
+        {
+            var logger = new TestLogger();
+            var path = Path.GetFullPath("tests/projects/for_code_formatter/unformatted_project/unformatted_project.csproj", SolutionPath);
+
+            var filePath = $"other_items{Path.DirectorySeparatorChar}OtherClass.cs";
+            var files = new[] {filePath};
+            var formatResult = await CodeFormatter.FormatWorkspaceAsync(logger, path, isSolution: false, logAllWorkspaceWarnings: false, saveFormattedFiles: false, filesToFormat: files, cancellationToken: CancellationToken.None);
+
+            var filePathAlt = $"other_items{Path.AltDirectorySeparatorChar}OtherClass.cs";
+            var filesAlt = new[] {filePathAlt};
+            var formatResultAlt = await CodeFormatter.FormatWorkspaceAsync(logger, path, isSolution: false, logAllWorkspaceWarnings: false, saveFormattedFiles: false, filesToFormat: filesAlt, cancellationToken: CancellationToken.None);
+
+            Assert.True(formatResult.FilesFormatted == formatResultAlt.FilesFormatted);
+        }
     }
 }