Introduce IsAllFilesWildcard() and call it from MatchFileRecursionStep

Fixes dotnet#6502

Summary

This change fixes a regression in glob matching where files without extension are erroneously not matched when taking a specific globbing code path.

Customer impact

Any customer who uses a glob pattern susceptible to the bug and has files without extensions in their source tree is affected. The bug was reported by external customers.

Regression?

Yes, caused by dotnet#6151 where glob matching was optimized which internally made it take a different code path.

Changes Made

Fixes the regression by properly handling `*.*` to mean all files, not just files with a dot in the name. This convention is used in .NET APIs on all platforms and matches the pre-regression behavior.

Testing

Added unit test coverage. Also verified locally with the repro provided by the original bug reporter.

Risk

Low. The star patterns are special-cased to mean all files, other patterns are unaffected.

src/Shared/FileMatcher.cs

@@ -131,7 +131,7 @@ internal FileMatcher(IFileSystem fileSystem, GetFileSystemEntries getFileSystemE
                                     "*",
                                     directory,
                                     false));
-                        IEnumerable<string> filteredEntriesForPath = (pattern != null && pattern != "*" && pattern != "*.*")
+                        IEnumerable<string> filteredEntriesForPath = (pattern != null && !IsAllFilesWildcard(pattern))
                             ? allEntriesForPath.Where(o => IsMatch(Path.GetFileName(o), pattern))
                             : allEntriesForPath;
                         return stripProjectDirectory
@@ -886,7 +886,7 @@ struct RecursionState
                         //  The wildcard path portion of the excluded search matches the include search
                         searchToExclude.RemainingWildcardDirectory == recursionState.RemainingWildcardDirectory &&
                         //  The exclude search will match ALL filenames OR
-                        (searchToExclude.SearchData.Filespec == "*" || searchToExclude.SearchData.Filespec == "*.*" ||
+                        (IsAllFilesWildcard(searchToExclude.SearchData.Filespec) ||
                             //  The exclude search filename pattern matches the include search's pattern
                             searchToExclude.SearchData.Filespec == recursionState.SearchData.Filespec))
                     {
@@ -1091,7 +1091,11 @@ struct RecursionState
 
         private static bool MatchFileRecursionStep(RecursionState recursionState, string file)
         {
-            if (recursionState.SearchData.Filespec != null)
+            if (IsAllFilesWildcard(recursionState.SearchData.Filespec))
+            {
+                return true;
+            }
+            else if (recursionState.SearchData.Filespec != null)
             {
                 return IsMatch(Path.GetFileName(file), recursionState.SearchData.Filespec);
             }
@@ -2564,6 +2568,17 @@ private static bool DirectoryEndsWithPattern(string directoryPath, string patter
             return (index != -1 && IsMatch(directoryPath.Substring(index + 1), pattern));
         }
 
+        /// <summary>
+        /// Returns true if <paramref name="pattern"/> is <code>*</code> or <code>*.*</code>.
+        /// </summary>
+        /// <param name="pattern">The filename pattern to check.</param>
+        private static bool IsAllFilesWildcard(string pattern) => pattern?.Length switch
+        {
+            1 => pattern[0] == '*',
+            3 => pattern[0] == '*' && pattern[1] == '.' && pattern[2] == '*',
+            _ => false
+        };
+
         internal static bool IsRecursiveDirectoryMatch(string path) => path.TrimTrailingSlashes() == recursiveDirectoryMatch;
     }
 }

src/Shared/UnitTests/FileMatcher_Tests.cs

@@ -154,6 +154,7 @@ public class GetFilesComplexGlobbingMatchingInfo
                 @"src\bar.cs",
                 @"src\baz.cs",
                 @"src\foo\foo.cs",
+                @"src\foo\licence",
                 @"src\bar\bar.cs",
                 @"src\baz\baz.cs",
                 @"src\foo\inner\foo.cs",
@@ -368,7 +369,8 @@ public static IEnumerable<object[]> GetTestData()
                         ExpectedMatches = new[]
                         {
                             @"readme.txt",
-                            @"licence"
+                            @"licence",
+                            @"src\foo\licence",
                         }
                     }
                 };
@@ -422,6 +424,30 @@ public static IEnumerable<object[]> GetTestData()
                     }
                 };
 
+                // Regression test for https://github.com/Microsoft/msbuild/issues/6502
+                yield return new object[]
+                {
+                    new GetFilesComplexGlobbingMatchingInfo
+                    {
+                        Include = @"src\**",
+                        Excludes = new[]
+                        {
+                            @"**\foo\**",
+                        },
+                        ExpectedMatches = new[]
+                        {
+                            @"src\foo.cs",
+                            @"src\bar.cs",
+                            @"src\baz.cs",
+                            @"src\bar\bar.cs",
+                            @"src\baz\baz.cs",
+                            @"src\bar\inner\baz.cs",
+                            @"src\bar\inner\baz\baz.cs",
+                        },
+                        ExpectNoMatches = NativeMethodsShared.IsLinux,
+                    }
+                };
+
                 // Hits the early elimination of exclude file patterns that do not intersect with the include.
                 // The exclude is redundant and can be eliminated before starting the file system walk.
                 yield return new object[]