Fix up bugs in parsing special chracters in EditorConfig

src/Compilers/Core/MSBuildTask/GenerateMSBuildEditorConfig.cs

@@ -3,6 +3,7 @@
 // See the LICENSE file in the project root for more information.
 
 using System;
+using System.IO;
 using System.Linq;
 using System.Text;
 using Microsoft.Build.Framework;
@@ -38,6 +39,10 @@ namespace Microsoft.CodeAnalysis.BuildTasks
     /// </remarks>
     public sealed class GenerateMSBuildEditorConfig : Task
     {
+        /// <remarks>
+        /// Although this task does its own writing to disk, this
+        /// output parameter is here for testing purposes.
+        /// </remarks>
         [Output]
         public string ConfigFileContents { get; set; }
 
@@ -47,11 +52,15 @@ public sealed class GenerateMSBuildEditorConfig : Task
         [Required]
         public ITaskItem[] PropertyItems { get; set; }
 
+        [Required]
+        public ITaskItem File { get; set; }
+
         public GenerateMSBuildEditorConfig()
         {
             ConfigFileContents = string.Empty;
             MetadataItems = Array.Empty<ITaskItem>();
             PropertyItems = Array.Empty<ITaskItem>();
+            File = new TaskItem();
         }
 
         public override bool Execute()
@@ -98,7 +107,43 @@ public override bool Execute()
             }
 
             ConfigFileContents = builder.ToString();
-            return true;
+            return WriteMSBuildEditorConfig();
+        }
+
+        public bool WriteMSBuildEditorConfig()
+        {
+            try
+            {
+                var directoryPath = Path.GetDirectoryName(NormalizeWithForwardSlash(File.ItemSpec));
+                Directory.CreateDirectory(directoryPath);
+                try
+                {
+                    if (System.IO.File.Exists(File.ItemSpec))
+                    {
+                        string existingContents = System.IO.File.ReadAllText(File.ItemSpec);
+                        if (existingContents.Length == ConfigFileContents.Length)
+                        {
+                            if (existingContents.Equals(ConfigFileContents))
+                            {
+                                return true;
+                            }
+                        }
+                    }
+                }
+                catch (IOException ex)
+                {
+                    Log.LogErrorFromException(ex);
+                }
+
+                var encoding = new UTF8Encoding(encoderShouldEmitUTF8Identifier: false, throwOnInvalidBytes: true);
+                System.IO.File.WriteAllText(File.ItemSpec, ConfigFileContents, encoding);
+                return true;
+            }
+            catch (Exception ex)
+            {
+                Log.LogErrorFromException(ex);
+                return false;
+            }
         }
 
         /// <remarks>

src/Compilers/Core/MSBuildTask/Microsoft.Managed.Core.targets

@@ -186,14 +186,10 @@
     <!-- Transform the collected properties and items into an editor config file -->
     <GenerateMSBuildEditorConfig
       PropertyItems="@(_GeneratedEditorConfigProperty)"
-      MetadataItems="@(_GeneratedEditorConfigMetadata)">
-
-      <Output TaskParameter="ConfigFileContents"
-          PropertyName="_GeneratedEditorConfigFileContent" />
+      MetadataItems="@(_GeneratedEditorConfigMetadata)"
+      File="$(GeneratedMSBuildEditorConfigFile)">
     </GenerateMSBuildEditorConfig>
 
-    <!-- Write the output to the generated file, if it's changed -->
-    <WriteLinesToFile Lines="$(_GeneratedEditorConfigFileContent)" File="$(GeneratedMSBuildEditorConfigFile)" Overwrite="True" WriteOnlyWhenDifferent="True" />
   </Target>
 
   <!--

src/Compilers/Core/Portable/CommandLine/AnalyzerConfig.SectionNameMatching.cs

@@ -114,15 +114,35 @@ public bool IsMatch(string s)
                 numberRangePairs.ToImmutableAndFree());
         }
 
+        internal static bool TryUnescapeSectionName(string sectionName, out string? escapedSectionName)
+        {
+            escapedSectionName = default;
+            var sb = new StringBuilder();
+            SectionNameLexer lexer = new SectionNameLexer(sectionName);
+            while (!lexer.IsDone)
+            {
+                var tokenKind = lexer.Lex();
+                if (tokenKind == TokenKind.BadToken)
+                {
+                    return false;
+                }
+                else
+                {
+                    sb.Append(lexer.EatCurrentCharacter());
+                }
+            }
+            escapedSectionName = sb.ToString();
+            return true;
+        }
+
         /// <summary>
-        /// Test if a section name is an absolute path with no special chars
+        /// Test if a section name is an absolute path
         /// </summary>
         internal static bool IsAbsoluteEditorConfigPath(string sectionName)
         {
             // NOTE: editorconfig paths must use '/' as a directory separator character on all OS.
 
             // on all unix systems this is thus a simple test: does the path start with '/'
-            // and contain no special chars?
 
             // on windows, a path can be either drive rooted or not (e.g. start with 'c:' or just '')
             // in addition to being absolute or relative.
@@ -147,7 +167,7 @@ internal static bool IsAbsoluteEditorConfigPath(string sectionName)
             int logicalIndex = 0;
             while (!nameLexer.IsDone)
             {
-                if (nameLexer.Lex() != TokenKind.SimpleCharacter)
+                if (nameLexer.Lex() == TokenKind.BadToken)
                 {
                     return false;
                 }

src/Compilers/Core/Portable/CommandLine/AnalyzerConfig.cs

@@ -203,7 +203,8 @@ public static AnalyzerConfig Parse(SourceText text, string? pathToFile)
                 {
                     addNewSection();
 
-                    var sectionName = sectionMatches[0].Groups[1].Value;
+                    var escapedSectionName = TryUnescapeSectionName(sectionMatches[0].Groups[1].Value, out var sectionName);
+                    Debug.Assert(escapedSectionName == true);
                     Debug.Assert(!string.IsNullOrEmpty(sectionName));
 
                     activeSectionName = sectionName;