Re: [PATCH] Kbuild: add RUSTC_BOOTSTRAP to rustc-option

[Alice Ryhl]

On 10/8/24 4:24 PM, Alice Ryhl wrote:
> On Tue, Oct 8, 2024 at 3:49 PM Alice Ryhl <aliceryhl@xxxxxxxxxx> wrote:
> > When using unstable features with the Rust compiler, you must either use
> > a nightly compiler release or set the RUSTC_BOOTSTRAP environment
> > variable. Otherwise, the compiler will emit a compiler error. This
> > environment variable is missing when rustc-option is executed, so add
> > the environment variable.
> >
> > This change is necessary to avoid two kinds of problems:
> >
> > 1. When using rustc-option to test whether a -Z flag is available, the
> >     check will always fail, even if the flag is available.
> > 2. If KBUILD_RUSTFLAGS happens to contain any -Z flags from the
> >     environment, even if unrelated to the flag being tested, then all
> >     invocations of rustc-option everywhere will fail.
> >
> > I was not actually able to trigger the second kind of problem with the
> > makefiles that exist today, but it seems like it could easily start
> > being a problem due to complicated interactions between changes. It is
> > better to fix this now so it doesn't surprise us later.
> >
> > I added the flag under try-run as this seemed like the easiest way to
> > make sure that the fix applies to all variations of rustc-option,
> > including new ones added in the future.
> >
> > Signed-off-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
>
> It should be "export". Also, this doesn't seem to be sufficient at
> all. Now I'm running into this error:
>
> make[1]: Entering directory '/home/aliceryhl/lout'
> warning: ignoring --out-dir flag due to -o flag
>
> error[E0463]: can't find crate for `std`
>    |
>    = note: the `aarch64-unknown-none` target may not be installed
>    = help: consider downloading the target with `rustup target add
> aarch64-unknown-none`
>    = help: consider building the standard library from source with
> `cargo build -Zbuild-std`
>
> error: aborting due to 1 previous error; 1 warning emitted
>
> For more information about this error, try `rustc --explain E0463`.
>
> I think this patch is going to need more work. Sorry for sending it prematurely.
v2 is here:
https://lore.kernel.org/all/20241008-rustc-option-bootstrap-v2-1-e6e155b8f9f3@xxxxxxxxxx/