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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 16 Feb 2018 11:17:52 -0800
Message-ID: <CA+55aFwQLrrBeXZXK_qUXiGVFNv3qPJS4tNKFacuk0Y0WgZjCA@mail.gmail.com>
Subject: Re: [PATCH 11/23] kconfig: add 'shell-stdout' function
To:     Masahiro Yamada <yamada.masahiro@socionext.com>
Cc:     Linux Kbuild mailing list <linux-kbuild@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Kees Cook <keescook@chromium.org>,
        Randy Dunlap <rdunlap@infradead.org>,
        Ulf Magnusson <ulfalizer@gmail.com>,
        Sam Ravnborg <sam@ravnborg.org>,
        Michal Marek <michal.lkml@markovi.net>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Fri, Feb 16, 2018 at 10:38 AM, Masahiro Yamada
<yamada.masahiro@socionext.com> wrote:
> This is the second built-in function, which retrieves the first line
> of stdout from the given shell command.

This is the only part I really don't much like in your patch series.

Most of it is just lovely and looks very nice and powerful, but the
difference between "$(shell ..." and "$(shell-stdout ..." to me is
bvery ugly.

Can we *please* make "shell-stdout" go away, and make this just be "shell"?

The rule would be very simple:

 - if the result of the shell command is a failure, the result is 'n'

 - otherwise, the result is the first line of stdout

 - if the result is empty, we replace it with 'y'.

So doing $(shell true) would be 100% equivalent to $(shell echo y),
and you could still do that

          default $(shell $CC --version | grep -q gcc)

because it would just automatically do the right thing.

Basically, the only difference is how $(shell ) works in the success
case: the result won't necessarily be 'y', it will be whatever output.
But if you want to always turn it into 'y' (say, you don't have a "-q"
flag for the grep equivalent above), you can always do so with

          default $(shell $CC --version | noqgrep gcc > /dev/null)

So it seems to me that there is never any fundamental reason why we'd
want both "shell" and "shell-stdout", since "shell-stdout" is
fundamentally more powerful than "shell", and can always be used as
such (and just renamed to "shell").

Because I really think that it's just much prettier and more intuitive
to be able to say

        default "/boot/config-$(shell uname --release)"

without that "-stdout" thing.

Hmm?

But I do want to say how much I liked this series. Just this part
seemed to result in uglier Kconfig scripts.

         Linus