Any reason of adding `.` at the end of command on Windows?

[chansey97]

I saw in rg.el there are the following lines

(when (member system-type '(darwin windows-nt))
  (list ".")))))

Anyone know why need this . thing on Windows (and Mac OS)?

First of all, it seems that at the moment we have to use the . on Windows, otherwise rg.el won't display anything. It has little to do with rg.el though, I still want to discuss.

Let's do some experiments via clean Emacs interface:

1. Try the following three commands (no .) in Windows standard console

   ...> "C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe" SomeTextInFiles
   ...> "cmd.exe" /c "C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe SomeTextInFiles"
   ...> "C:/green/emacs/libexec/emacs/28.2/x86_64-w64-mingw32/cmdproxy.exe" -c "C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe SomeTextInFiles"
   

   All work, i.e. they can display results in the console.

2. Try the same command (no .) in Emacs with start-process

   (apply 'start-process "rg" "newbuffer123"
          "C:/green/emacs/libexec/emacs/28.2/x86_64-w64-mingw32/cmdproxy.exe"
          (list "-c" "\"C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe\" SomeTextInFiles"))
   

   This doesn't work, i.e. it displayed nothing in "newbuffer123" (also for rg.exe only and cmd.exe /c).

3. The way to fix this problem is adding . at the end of command, i.e.

   (apply 'start-process "rg" "newbuffer123"
          "C:/green/emacs/libexec/emacs/28.2/x86_64-w64-mingw32/cmdproxy.exe"
          (list "-c" "\"C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe\" SomeTextInFiles ."))
   

   Then works, but why?

4. Not all of the ripgrep commands can't display, -h can do for example:

   (apply 'start-process "rg" "newbuffer123"
          "C:/green/emacs/libexec/emacs/28.2/x86_64-w64-mingw32/cmdproxy.exe"
          (list  "-c" "\"C:/env/ripgrep/ripgrep-14.1.0-x86_64-pc-windows-msvc/rg.exe\" -h"))
   

   This can display help information in "newbuffer123"

I found this patch was added by @drvink from https://github.com/dajva/rg.el/pull/10 but no explanation. Also, there are two related commits https://github.com/dajva/rg.el/commit/842452ccb9bba80582c13fb309bebdb399c1e890 and https://github.com/dajva/rg.el/commit/89343e9858787fa8d3651cd03ff7b0d03309dee8.

Nevertheless, the . solution works fine, until someone want to add rg-command-line-flags to rg.el.

For example, suppose I'd like to search only two specific directories under the current directory (multiple directories search):

(defun test-rg ()
  (interactive)
  (let ((rg-command-line-flags '("\"./folder1\" \"./folder2\"")))
    (call-interactively 'rg)))

In the current rg.el implementation, these two directories will be combined with the current directory (i.e. .), which causes these two flags meaningless, i.e. it still searches the entire current directory.

Of course, this problem can be workaround via deleting (list ".") in the code above, but that breaks the code.

So anyone know why we have to add . on Windows (and Mac)? Is this related to Emacs or ripgrep?

Thanks.