MockFileSystem Directory.EnumerateFiles returns incorrect results, based on input pattern.

[pianomanjh]

When calling Directory.EnumerateFiles on MockFileSystem, incorrect matching occurs, that differs from the real FileSystem.

Mock FileSystem

var results = Directory.EnumerateFiles(@"c:\jobfolder\result.rreq.001.afd", "*.rreq.*.*.*");
// results has no entries

Real FileSystem

var results = Directory.EnumerateFiles(@"c:\jobfolder\result.rreq.001.afd", "*.rreq.*.*.*");
// results has the entry `c:\jobfolder\result.rreq.001.afd`

[fgreinacher]

Thanks for reporting! Am I right assuming result.rreq.001.afd is a file (rather than a directory)?

[pianomanjh]

my apologies, the sample is not right. Here is something more representative.

mockFileSystem.AddFile(@"c:\test\result.rreq.001.afd", MockFileData.NullObject);
var results = mockFileSystem.Directory.EnumerateFiles(@"c:\test", "*.rreq.*.*.*");
// results has no entries, but should have `c:\test\result.rreq.001.afd`

[fgreinacher]

my apologies, the sample is not right. Here is something more representative.

mockFileSystem.AddFile(@"c:\test\result.rreq.001.afd", MockFileData.NullObject);
var results = mockFileSystem.Directory.EnumerateFiles(@"c:\test", "*.rreq.*.*.*");
// results has no entries, but should have `c:\test\result.rreq.001.afd`

This sample does also not look correct to me, the pattern has one asterisk too much:

result.rreq.001.afd
*     .rreq.*  .*  .*

The following test is passing:

// Arrange
var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
{
    { XFS.Path(@"c:\test\result.rreq.001.afd"), MockFileData.NullObject }
});

// Act
var result = fileSystem.Directory.EnumerateFiles(XFS.Path(@"c:\test"), "*.rreq.*.*");

// Assert
Assert.That(result, Is.EquivalentTo(new[]
{
    XFS.Path(@"c:\test\result.rreq.001.afd")
}));

[fgreinacher]

Now I get the problem. It seems like the real implementation ignores the .* elements at the end. This test case also succeeds 😩

// Arrange
var fileSystem = new FileSystem();
// var fileSystem = new MockFileSystem();
// fileSystem.Directory.CreateDirectory(XFS.Path(@"c:\tmp\"));

fileSystem.File.CreateText(XFS.Path(@"c:\tmp\result.rreq.001.afd")).Close();

// Act
var result = fileSystem.Directory.EnumerateFiles(XFS.Path(@"c:\tmp"), "*.rreq.*.*.*.*.*.*.*.*.*");

// Assert
Assert.That(result, Is.EquivalentTo(new[]
{
    XFS.Path(@"c:\tmp\result.rreq.001.afd")
}));

[fgreinacher]

@pianomanjh Please check whether the issue goes away once you use the "correct" pattern:

mockFileSystem.AddFile(@"c:\test\result.rreq.001.afd", MockFileData.NullObject);
mockFileSystem.Directory.EnumerateFiles(@"c:\test", "*.rreq.*.*"); // one `.*` pair less

[pianomanjh]

If I use a different pattern, the one you describe, the issue no longer reproduces, yes.
However, using a different pattern doesn't fix the bug ;) (we need that pattern in production)

[fgreinacher]

Why do you need that exact pattern? It seems wrong to me 🤔 .NET behavior seems to be much more complex than we anticipated when implementing this logic 🐙

https://github.com/dotnet/runtime/blob/cd02b0612b3c758037eac9f85faa4ec91b1fbbda/src/libraries/System.IO.FileSystem/src/System/IO/Enumeration/FileSystemName.cs has some of the logic - we might want to reuse (parts of) it.