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

[Alice Ryhl]

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.

Alice