why '_file -/' completes files if there is no directory?

["Jun T." <takimoto-j@xxxxxxxxxxxxxxxxx>]

With the following style:
zstyle ':completion:*:warnings' format 'No match for: %d

If there is no subdirectory in the current directory,
    zsh$ cd <TAB>
gives
    No match for: `local directory'
but
    zsh$ rmdir <TAB>
completes the normal files in the current directory.
Similar behavior for 'gcc -I<TAB>' etc.
Not a serious problem, but I prefer getting a warning than being
offered a useless list of normal files.

Are there any way to stop this behavior by using zstyle?
Obviously I can't use
zstyle ':completion:*' file-patterns '*(-/)'
so I tried
zstyle ':completion:*:directories' file-patterns '*(-/)'
but it didn't' work (it seems setting file-patterns for a specific
tag has no meaning). Setting file-patterns (or tag-order?) to each
context ':completion:*:gcc:option-I-1:*' etc. may work, but I don't
want to do that even if it works.