replace NormalizeTargetPath with regex manipulation

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

@@ -89,37 +89,11 @@ private static bool Matches(string targetPath, CodeOwnerEntry entry)
         {
             string codeownersPath = entry.PathExpression;
 
-            targetPath = NormalizeTargetPath(targetPath, codeownersPath);
-
-            Regex regex = ConvertToRegex(codeownersPath);
+            Regex regex = ConvertToRegex(targetPath, codeownersPath);
             return regex.IsMatch(targetPath);
         }
 
-        private static string NormalizeTargetPath(string targetPath, string codeownersPath)
-        {
-            // If the considered CODEOWNERS path ends with "/", it means we can
-            // assume targetPath also is a path to directory.
-            //
-            // This works in all 3 cases, which are:
-            //
-            // 1. The targetPath is the same as the CODEOWNERS path, except
-            // the targetPath doesn't have "/" at the end. If so,
-            // it might be a path to a file or directory,
-            // but the exact path match with CODEOWNERS path and our validation
-            // guarantees it is an existing directory, hence we can append "/".
-            //
-            // 2. The targetPath is a prefix path of CODEOWNERS path. In such case
-            // there won't be a match, and appending "/" won't change that.
-            //
-            // 3. The CODEOWNERS path is a prefix path of targetPath. In such case
-            // there will be a match, and appending "/" won't change that.
-            if (codeownersPath.EndsWith("/") && !targetPath.EndsWith("/"))
-                targetPath += "/";
-
-            return targetPath;
-        }
-
-        private static Regex ConvertToRegex(string codeownersPath)
+        private static Regex ConvertToRegex(string targetPath, string codeownersPath)
         {
             codeownersPath = ConvertPathIfInvalid(codeownersPath);
 
@@ -132,7 +106,10 @@ private static Regex ConvertToRegex(string codeownersPath)
 
             pattern = Regex.Escape(pattern);
 
-            pattern = AddStringAnchors(pattern);
+            // Denote that all paths are absolute by pre-pending "beginning of string" symbol.
+            pattern = "^" + pattern;
+
+            pattern = SetPatternSuffix(targetPath, pattern);
 
             // Note that the "/**/" case is implicitly covered by "**/".
             pattern = pattern.Replace("_DOUBLE_STAR_/", "(.*)");
@@ -141,25 +118,12 @@ private static Regex ConvertToRegex(string codeownersPath)
             // This case is necessary to cover inline **, e.g. "/a**b/".
             pattern = pattern.Replace("_DOUBLE_STAR_", "(.*)");
             pattern = pattern.Replace("_SINGLE_STAR_", "([^/]*)");
-            return new Regex(pattern);
-        }
 
-        private static string ConvertPathIfInvalid(string codeownersPath)
-        {
-            // CODEOWNERS paths that do not start with "/" are relative and considered invalid.
-            // However, here we handle such cases to accomodate for parsing CODEOWNERS file
-            // paths that somehow slipped through validation. We do so by instead treating
-            // such paths as if they were absolute to repository root, i.e. starting with "/".
-            if (!IsCodeOwnersPathValid(codeownersPath))
-                codeownersPath = "/" + codeownersPath;
-            return codeownersPath;
+            return new Regex(pattern);
         }
 
-        private static string AddStringAnchors(string pattern)
+        private static string SetPatternSuffix(string targetPath, string pattern)
         {
-            // Denote that all paths are absolute by pre-pending "beginning of string" symbol.
-            pattern = "^" + pattern;
-
             // Lack of slash at the end denotes the path is a path to a file,
             // per our validation logic.
             // Note we assume this is path to a file even if the path is invalid,
@@ -170,10 +134,44 @@ private static string AddStringAnchors(string pattern)
                 // not a substring, as we are dealing with a file.
                 pattern += "$";
             }
+            // If the CODEOWNERS pattern is matching only against directories,
+            // but the targetPath may not be a directory, we need to trim
+            // the "/" from the pattern to ensure match is present.
+            //
+            // To illustrate this, consider following cases:
+            //
+            //   targetPath: /a   ,  /a*/
+            //      pattern: /a/  ,  /abc
+            //
+            // Without trimming pattern to be "/a" and "/a*" respectively,
+            // these wouldn't match, but they should.
+            //
+            // On the other hand, trimming the suffix "/" when it is not
+            // necessary won't lead to issues. E.g.:
+            //
+            //   targetPath: /a/b
+            //      pattern: /a/
+            //
+            // Here we still have a prefix match even if we trim pattern to "/a"
+            else if (pattern.EndsWith("/") && !targetPath.EndsWith("/"))
+            {
+                pattern = pattern.TrimEnd('/');
+            }
 
             return pattern;
         }
 
+        private static string ConvertPathIfInvalid(string codeownersPath)
+        {
+            // CODEOWNERS paths that do not start with "/" are relative and considered invalid.
+            // However, here we handle such cases to accomodate for parsing CODEOWNERS file
+            // paths that somehow slipped through validation. We do so by instead treating
+            // such paths as if they were absolute to repository root, i.e. starting with "/".
+            if (!IsCodeOwnersPathValid(codeownersPath))
+                codeownersPath = "/" + codeownersPath;
+            return codeownersPath;
+        }
+
         /// <summary>
         /// The entry is valid if it obeys following conditions:
         /// - The Value was obtained with a call to