[4/6] kbuild: rust_is_available: check if the script was invoked from Kbuild

  Sometimes [1] users may attempt to setup the Rust support by
checking what Kbuild does and they end up finding out about
`scripts/rust_is_available.sh`. Inevitably, they run the script
directly, but unless they setup the required variables,
the result of the script is not meaningful.

We could add some defaults to the variables, but that could be
confusing for those that may override the defaults (compared
to their kernel builds), and `$CC` would not be a simple default
in any case.

Therefore, instead, print a warning when the script detects
the user may be invoking it, by testing `$MAKEFLAGS`.

Link: https://lore.kernel.org/oe-kbuild-all/Y6r4mXz5NS0+HVXo@zn.tnic/ [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 scripts/rust_is_available.sh | 10 ++++++++++
 1 file changed, 10 insertions(+)
  

On Tue, Jan 10, 2023 at 5:46 AM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> Sometimes [1] users may attempt to setup the Rust support by
> checking what Kbuild does and they end up finding out about
> `scripts/rust_is_available.sh`. Inevitably, they run the script
> directly, but unless they setup the required variables,
> the result of the script is not meaningful.
>
> We could add some defaults to the variables, but that could be
> confusing for those that may override the defaults (compared
> to their kernel builds), and `$CC` would not be a simple default
> in any case.
>
> Therefore, instead, print a warning when the script detects
> the user may be invoking it, by testing `$MAKEFLAGS`.
>
> Link: https://lore.kernel.org/oe-kbuild-all/Y6r4mXz5NS0+HVXo@zn.tnic/ [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
>  scripts/rust_is_available.sh | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/scripts/rust_is_available.sh b/scripts/rust_is_available.sh
> index cd87729ca3bf..0c082a248f15 100755
> --- a/scripts/rust_is_available.sh
> +++ b/scripts/rust_is_available.sh
> @@ -35,6 +35,16 @@ print_docs_reference()
>  warning=0
>  trap 'if [ $? -ne 0 ] || [ $warning -ne 0 ]; then print_docs_reference; fi' EXIT
>
> +# Check whether the script was invoked from Kbuild.
> +if [ -z "${MAKEFLAGS+x}" ]; then
> +       echo >&2 "***"
> +       echo >&2 "*** This script is intended to be called from Kbuild."
> +       echo >&2 "*** Please use the 'rustavailable' target to call it instead."
> +       echo >&2 "*** Otherwise, the results may not be meaningful."
> +       echo >&2 "***"
> +       warning=1
> +fi


I do not like this.
We do not need to cater to every oddity.

Checking MAKEFLAGS is too much.

You can check RUSTC/BINDGEN/CC if you persist in this.




diff --git a/scripts/rust_is_available.sh b/scripts/rust_is_available.sh
index a6f84dd2f71c..524aee03384a 100755
--- a/scripts/rust_is_available.sh
+++ b/scripts/rust_is_available.sh
@@ -34,7 +34,7 @@ warning=0
 trap 'if [ $? -ne 0 ] || [ $warning -ne 0 ]; then
print_docs_reference; fi' EXIT

 # Check that the Rust compiler exists.
-if ! command -v "$RUSTC" >/dev/null; then
+if ! command -v "${RUSTC:?RUSTC is not set}" >/dev/null; then
        echo >&2 "***"
        echo >&2 "*** Rust compiler '$RUSTC' could not be found."
        echo >&2 "***"
@@ -42,7 +42,7 @@ if ! command -v "$RUSTC" >/dev/null; then
 fi

 # Check that the Rust bindings generator exists.
-if ! command -v "$BINDGEN" >/dev/null; then
+if ! command -v "${BINDGEN:?BINDGEN is not set}" >/dev/null; then
        echo >&2 "***"
        echo >&2 "*** Rust bindings generator '$BINDGEN' could not be found."
        echo >&2 "***"
@@ -150,7 +150,7 @@ fi
 #
 # In the future, we might be able to perform a full version check, see
 # https://github.com/rust-lang/rust-bindgen/issues/2138.
-cc_name=$($(dirname $0)/cc-version.sh "$CC" | cut -f1 -d' ')
+cc_name=$($(dirname $0)/cc-version.sh ${CC:?CC is not set} | cut -f1 -d' ')
 if [ "$cc_name" = Clang ]; then
        clang_version=$( \
                LC_ALL=C "$CC" --version 2>/dev/null \
  

On Thu, Jan 12, 2023 at 6:29 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
>
> I do not like this.
> We do not need to cater to every oddity.
>
> Checking MAKEFLAGS is too much.

I agree we should not attempt to catch every possible mistake in the
script, but there have been several people hitting precisely this case
(the latest is in the linked thread in the commit message), i.e. some
people read the `Makefile` and notice the script invocation, and go
execute it, but they are unlikely to be aware of the target in that
case.

> You can check RUSTC/BINDGEN/CC if you persist in this.

This is fine, and actually we should do it regardless of `MAKEFLAGS`.
I can add it to v2.

However, that does not cover the same thing as `MAKEFLAGS` is trying
to here. The reason is that even if they see e.g. "RUSTC is not set",
they will not know about how to call the script properly, i.e. through
the `Makefile` target.

For `RUSTC` and `BINDGEN`, it does not really matter (and we could
give a default to the variable, since the name rarely would be
different). However, for `CC`, the logic that Kbuild uses is more
complex, so it seems best to me to let Kbuild tell us what the actual
compiler is.

Cheers,
Miguel
  

On Sat, Jan 14, 2023 at 8:12 AM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Thu, Jan 12, 2023 at 6:29 AM Masahiro Yamada <masahiroy@kernel.org> wrote:
> >
> > I do not like this.
> > We do not need to cater to every oddity.
> >
> > Checking MAKEFLAGS is too much.
>
> I agree we should not attempt to catch every possible mistake in the
> script, but there have been several people hitting precisely this case
> (the latest is in the linked thread in the commit message), i.e. some
> people read the `Makefile` and notice the script invocation, and go
> execute it, but they are unlikely to be aware of the target in that
> case.
>
> > You can check RUSTC/BINDGEN/CC if you persist in this.
>
> This is fine, and actually we should do it regardless of `MAKEFLAGS`.
> I can add it to v2.
>
> However, that does not cover the same thing as `MAKEFLAGS` is trying
> to here. The reason is that even if they see e.g. "RUSTC is not set",
> they will not know about how to call the script properly, i.e. through
> the `Makefile` target.
>
> For `RUSTC` and `BINDGEN`, it does not really matter (and we could
> give a default to the variable, since the name rarely would be
> different). However, for `CC`, the logic that Kbuild uses is more
> complex, so it seems best to me to let Kbuild tell us what the actual
> compiler is.
>
> Cheers,
> Miguel


OK, you maintain this script, so it is up to you.