File system should be case-sensitive on Unix

[rkoeninger]

The MockFileSystem uses a case-insensitive dictionary, but only on Windows is the file system case insensitive. MockFileSystem won't exhibit correct case-sensitivity behavior on Unix.

Relevant line in current HEAD

[fgreinacher]

Good catch - thanks! We have to consider back compat here though whenever someone starts working on it.

[robkeim]

@fgreinacher how do we typically handle backwards compat for "breaking" changes like this?

This looks like an easy one that I could try to pick up, I just need some guidance on handling backwards compat.

[fgreinacher]

Hm, not sure about how it was handled up to now, but what do you think about something like this:

New types (names to be discussed):

public enum CasingBehavior 
{
   IgnoreCase,
   InheritFromOperatingSystem
}

// Immutable class, extensible for adding new options in the future
public sealed class MockFileSystemOptions
{
    // The default instance would have an empty current directory
    // and CasingBehavior.IgnoreCase
    public static MockFileSystemOptions Default { get; };

    public MockFileSystemOptions WithCurrentDirectory(string currentDirectory);
    public MockFileSystemOptions WithCasingBehavior(CasingBehavior casingBehavior);
}

New constructor setup for MockFileSystem:

public MockFileSystem()
   : this(null, MockFileSystemOptions.Default)
{
}

public MockFileSystem(IDictionary<string, MockFileData> files)
   : this(files, MockFileSystemOptions.Default)
{
}

public MockFileSystem(IDictionary<string, MockFileData> files, string currentDirectory)
   : this(files, MockFileSystemOptions.Default.WithCurrentDirectory(currentDirectory))
{
}

// New primary constructor
public MockFileSystem(IDictionary<string, MockFileData> files, MockFileSystemOptions options)
{
}

Sample usage:

var mockFileSystem = new MockFileSystem(
   files,
   MockFileSystemOptions.Default.WithCasingBehavior(CasingBehavior.InheritFromOperationSystem)
);

[rkoeninger]

MockFileSystem.CurrentPlatform(files?, currentDirectory?) would be a nice convenience. Even just in the test suite for this library.

Although, the thought did cross my mind earlier that we could have both MockWindowsFileSystem and MockUnixFileSystem as two different implementations so one could test their code against both Windows and Unix behavior on the same machine. Would be a lot of work. Couldn't depend on System.IO.Path like it does now. Not suggesting as a part of this issue.

[fgreinacher]

In a world where it’s super simple to run tests in multiple environments I think it’s not necessary to invest a lot of time trying to mirror platform behaviors in a lib like this.

Regarding the convenience method: I am a big fan of immutability so I’d rather not like to have a method that changes an objects behavior drastically after it has been constructed. If you need a different file system just construct a new one.

[rkoeninger]

MockFileSystem.CurrentPlatform was intended to be a static method, as it would pick one of two concrete classes to return.

Ignoring any out there ideas like mirroring platforms, this starts as a one-line change. The MockFileSystem constructor would just pick whether to use a case sensitive or insensitive comparator when it makes it's dictionary. There would be more changes necessary like here and I don't know where else. I guess do a search for "OrdinalIgnoreCase".

This would be more similar to current behavior where Unix/Windows behavior is not controllable and just reacts to what platform you're running on.

Case sensitivity/insensitivity tests can be added with WindowsOnly/UnixOnly.