Add --builtin-filter-dirs

[kelleyma49]

• fzf's builtin filesystem walker is faster then overridding via FZF_DEFAULT_COMMAND, especially on Windows
• If this switch is specified, fzf will read directories instead of files if FZF_DEFAULT_COMMAND is not specified and there's no input from tty

[junegunn]

Thanks, but I would rather not add options for file system traversal, because that is not really the responsibility of fzf.

Is it really not possible to find a performant external command on Windows?

[kelleyma49]

I'm open to ideas, but using FZF_DEFAULT_COMMAND or passing through std-in is way slower than using the default walker in fzf.

[kelleyma49]

I agree that design-wise it makes sense, but pragmatically it's just faster to walk the filesystem in native Go.

[kelleyma49]

Here's an example comparing the Window's dir built-in command (left side) vs. built-in go walker (right side):

[junegunn]

Thanks. Is the performance difference due to the performance limit of dir, or is it a fundamental limitation of the pipe mechanism in Windows? I mean, can we achieve better performance by using another program that is faster than dir?

[junegunn]

Closed in #3649.