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From: Miguel Ojeda <>
To: Daniel Xu <>
Cc: rust-for-linux <>
Subject: Re: How are rustc -Z flags enabled during build?
Date: Thu, 2 Sep 2021 07:50:44 +0200	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20210901230715.civmnrpmt3c2u72v@kashmir.localdomain>

Hi Daniel,

On Thu, Sep 2, 2021 at 1:11 AM Daniel Xu <> wrote:
> When I try to run it outside of kbuild, I get:
>     error: the option `Z` is only accepted on the nightly compiler
> How does kbuild use the -Z features on a stable rustc?

As Gary points out, it is an environment variable being set in the
top-level `Makefile` nearby the other flags. I considered adding it to
the command-line instead so that copy-pasting the lines is easier,
even if it means being a bit more verbose.

In any case, note that it is an escape hatch intended to be internal
to the compiler (which explains the error message not mentioning it)
and thus should be avoided unless a project has very special

Our goal is to drop its usage as soon as it is feasible, but it will
take a while. It is also why we only maintain support for a given
`rustc` version for the moment.


  parent reply	other threads:[~2021-09-02  5:51 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-01 23:07 How are rustc -Z flags enabled during build? Daniel Xu
2021-09-02  0:50 ` Gary Guo
2021-09-02  5:50 ` Miguel Ojeda [this message]
2021-09-02 18:41   ` Daniel Xu

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