Issue raised by @neelance. He said:

filter.New is a bit strange, I'd expect the bool to be the other way around: true => include
usually all filter functions that I know use true as "keep"

He provided these examples:

• https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Global_Objects/Array/filter
• http://ruby-doc.org/core-2.2.0/Array.html#method-i-select

I think that's a reasonable suggestion for an improvement. But I don't use filter package much, so if there are strong other opinions, we can punt on this.

Hi Everybody!

I noticed that the vfsutil.ReadDir used by vfstemplate.ParseGlob is incompatible with https://github.com/rakyll/statik binary file embedding tool.

The problem

// ReadDir reads the contents of the directory associated with file and
// returns a slice of FileInfo values in directory order.
func ReadDir(fs http.FileSystem, name string) ([]os.FileInfo, error) {
	f, err := fs.Open(name)
	if err != nil {
		return nil, err
	}
	defer f.Close()
	return f.Readdir(0)
}

Notice the f.Readdir(0). Some other libraries are ignoring the 0 count like rakyll/statik.

Although the file interface allows 0 for specifying the count but it would be better to specify -1 here to be more compatible with other tools.

Relevant documentation can be found here: https://golang.org/pkg/os/#File.Readdir

Summary

f.Readdir(0) should f.Readdir(-1).

The problem occured in the project called statik. Check out their implementation: https://github.com/rakyll/statik/blob/3bac566d30cdbeddef402a80f3d6305860e59f12/fs/fs.go#L190

I will make a pullrequest for them too.

As far as I can tell, the only type used (in non-test code) is the vfs.ReadSeekCloser, an interface which can easily be duplicated to avoid this unnecessary dependency, and reduce the dependency tree when importing the package.

See my PR to webdavfs, the same reasoning :)

Thanks in advance!

An issue that @VojtechVitek made me aware of is that FilesWithExtensions does not work well with filter.Keep.

When we created it (/cc @slimsag @neelance), we had filter.Skip usage in mind, e.g., to skip .html and .go files (but not folders), one could do:

filter.Skip(filter.FilesWithExtensions(".html", ".go"))

And it'd do what you'd expect.

However, that fails when you try to use filter.FilesWithExtensions with filter.Keep, e.g., to keep only ".xyz" files:

filter.Keep(filter.FilesWithExtensions(".xyz"))

That fails because none of the directories are kept, so / is not included.

Need to think about how to best resolve this. Some options are to do nothing at all, to document this, to remove FilesWithExtensions (or turn it into a documentation example), to change FilesWithExtensions or to change Keep/Skip.