Bugfix: when looking for a match in CODEOWNERS, do not emit error m…

…essage for commented out paths (#5366)

tools/code-owners-parser/Azure.Sdk.Tools.RetrieveCodeOwners.Tests/CodeownersManualAnalysisTests.cs

@@ -331,7 +331,7 @@ private static void WriteOwnersToCsv(
     }
 
     // Possible future work:
-    // instead of returning lines with issues, consider returning the  modified & fixed CODEOWNERS file. 
+    // instead of returning lines with issues, consider returning the modified & fixed CODEOWNERS file. 
     // It could work by reading all the lines, then replacing the wrong
     // lines by using dict replacement. Need to be careful about retaining spaces to not misalign,
     // e.g.
@@ -352,6 +352,7 @@ private static List<string> PathsWithIssues(
         outputLines.AddRange(PathsWithMissingPrefixSlash(entries));
         outputLines.AddRange(PathsWithMissingSuffixSlash(targetDir, entries, paths));
         outputLines.AddRange(InvalidPaths(entries));
+        // TODO: add a check here for CODEOWNERS paths that do not match any dir or file.
 
         return outputLines;
     }
@@ -414,9 +415,15 @@ private static List<string> PathsWithMissingSuffixSlash(
     private static bool MatchesNamePrefix(string[] paths, string trimmedPathExpression)
         => paths.Any(
             path =>
-                path.TrimStart('/').StartsWith(trimmedPathExpression)
-                && path.TrimStart('/').Length != trimmedPathExpression.Length
-                && !path.TrimStart('/').Substring(trimmedPathExpression.Length).StartsWith('/'));
+            {
+                string trimmedPath = path.TrimStart('/');
+                bool pathIsChildDir = trimmedPath.Contains("/")
+                                      && trimmedPath.Length > trimmedPathExpression.Length
+                                      && trimmedPath.Substring(trimmedPathExpression.Length).StartsWith('/');
+                return trimmedPath.StartsWith(trimmedPathExpression)
+                       && trimmedPath.Length != trimmedPathExpression.Length
+                       && !pathIsChildDir;
+            });
 
     private static bool MatchesDirExactly(string targetDir, string trimmedPathExpression)
     {

tools/code-owners-parser/CodeOwnersParser/MatchedCodeownersEntry.cs

@@ -59,7 +59,8 @@ public class MatchedCodeownersEntry
         /// See the class comment to understand this method purpose.
         /// </summary>
         public static bool IsCodeownersPathValid(string codeownersPathExpression)
-            => !ContainsUnsupportedCharacters(codeownersPathExpression) 
+            => !IsCommentedOutPath(codeownersPathExpression)
+               && !ContainsUnsupportedCharacters(codeownersPathExpression) 
                && !ContainsUnsupportedSequences(codeownersPathExpression);
 
         /// <summary>
@@ -128,6 +129,16 @@ private CodeownersEntry GetMatchingCodeownersEntry(
 
         private CodeownersEntry NoMatchCodeownersEntry { get; } = new CodeownersEntry();
 
+        /// <summary>
+        /// We do not output any error message in case the path is commented out,
+        /// as a) such paths are expected to be processed and discarded by this logic
+        /// and b) outputting error messages would possibly result in output
+        /// truncation, truncating the resulting json, and thus making the output of the
+        /// calling tool malformed.
+        /// </summary>
+        private static bool IsCommentedOutPath(string codeownersPathExpression)
+            => codeownersPathExpression.Trim().StartsWith("#");
+
         /// <summary>
         /// See the comment on unsupportedChars.
         /// </summary>