[PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Miguel Ojeda]

`rustfmt` is configured via the `.rustfmt.toml` file in the source tree,
and we apply `rustfmt` to the macro expanded sources generated by the
`.rsi` target.

However, under an `O=` pointing to an external folder (i.e. not just
a subdir), `rustfmt` will not find the file when checking the parent
folders. Since the edition is configured in this file, this can lead to
errors when it encounters newer syntax, e.g.

    error: expected one of `!`, `.`, `::`, `;`, `?`, `where`, `{`, or an operator, found `"rust_minimal"`
      --> samples/rust/rust_minimal.rsi:29:49
       |
    28 | impl ::kernel::ModuleMetadata for RustMinimal {
       |                                               - while parsing this item list starting here
    29 |     const NAME: &'static ::kernel::str::CStr = c"rust_minimal";
       |                                                 ^^^^^^^^^^^^^^ expected one of 8 possible tokens
    30 | }
       | - the item list ends here
       |
       = note: you may be trying to write a c-string literal
       = note: c-string literals require Rust 2021 or later
       = help: pass `--edition 2024` to `rustc`
       = note: for more on editions, read https://doc.rust-lang.org/edition-guide

A workaround is to use `RUSTFMT=n`, which is documented in the `Makefile`
help for cases where macro expanded source may happen to break `rustfmt`
for other reasons, but this is not one of those cases.

One solution would be to pass `--edition`, but we want `rustfmt` to
use the entire configuration, even if currently we essentially use the
default configuration.

Thus explicitly give the path to the config file to `rustfmt` instead.

Reported-by: Alice Ryhl <aliceryhl@google.com>
Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
Cc: stable@vger.kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 scripts/Makefile.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 5037f4715d74..0c838c467c76 100644
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -356,7 +356,7 @@ $(obj)/%.o: $(obj)/%.rs FORCE
 quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
       cmd_rustc_rsi_rs = \
 	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
-	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@
+	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) --config-path $(srctree)/.rustfmt.toml $@
 
 $(obj)/%.rsi: $(obj)/%.rs FORCE
 	+$(call if_changed_dep,rustc_rsi_rs)

base-commit: 74e15ac34b098934895fd27655d098971d2b43d9
-- 
2.52.0

Re: [PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Nathan Chancellor]

On Thu, Jan 15, 2026 at 07:38:32PM +0100, Miguel Ojeda wrote:
> `rustfmt` is configured via the `.rustfmt.toml` file in the source tree,
> and we apply `rustfmt` to the macro expanded sources generated by the
> `.rsi` target.
> 
> However, under an `O=` pointing to an external folder (i.e. not just
> a subdir), `rustfmt` will not find the file when checking the parent
> folders. Since the edition is configured in this file, this can lead to
> errors when it encounters newer syntax, e.g.
> 
>     error: expected one of `!`, `.`, `::`, `;`, `?`, `where`, `{`, or an operator, found `"rust_minimal"`
>       --> samples/rust/rust_minimal.rsi:29:49
>        |
>     28 | impl ::kernel::ModuleMetadata for RustMinimal {
>        |                                               - while parsing this item list starting here
>     29 |     const NAME: &'static ::kernel::str::CStr = c"rust_minimal";
>        |                                                 ^^^^^^^^^^^^^^ expected one of 8 possible tokens
>     30 | }
>        | - the item list ends here
>        |
>        = note: you may be trying to write a c-string literal
>        = note: c-string literals require Rust 2021 or later
>        = help: pass `--edition 2024` to `rustc`
>        = note: for more on editions, read https://doc.rust-lang.org/edition-guide
> 
> A workaround is to use `RUSTFMT=n`, which is documented in the `Makefile`
> help for cases where macro expanded source may happen to break `rustfmt`
> for other reasons, but this is not one of those cases.
> 
> One solution would be to pass `--edition`, but we want `rustfmt` to
> use the entire configuration, even if currently we essentially use the
> default configuration.
> 
> Thus explicitly give the path to the config file to `rustfmt` instead.
> 
> Reported-by: Alice Ryhl <aliceryhl@google.com>
> Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Nathan Chancellor <nathan@kernel.org>

I assume you will take this via the Rust tree?

> ---
>  scripts/Makefile.build | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/scripts/Makefile.build b/scripts/Makefile.build
> index 5037f4715d74..0c838c467c76 100644
> --- a/scripts/Makefile.build
> +++ b/scripts/Makefile.build
> @@ -356,7 +356,7 @@ $(obj)/%.o: $(obj)/%.rs FORCE
>  quiet_cmd_rustc_rsi_rs = $(RUSTC_OR_CLIPPY_QUIET) $(quiet_modtag) $@
>        cmd_rustc_rsi_rs = \
>  	$(rust_common_cmd) -Zunpretty=expanded $< >$@; \
> -	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) $@
> +	command -v $(RUSTFMT) >/dev/null && $(RUSTFMT) --config-path $(srctree)/.rustfmt.toml $@
>  
>  $(obj)/%.rsi: $(obj)/%.rs FORCE
>  	+$(call if_changed_dep,rustc_rsi_rs)
> 
> base-commit: 74e15ac34b098934895fd27655d098971d2b43d9
> -- 
> 2.52.0
> 

Re: [PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Gary Guo]

On Thu Jan 15, 2026 at 6:38 PM GMT, Miguel Ojeda wrote:
> `rustfmt` is configured via the `.rustfmt.toml` file in the source tree,
> and we apply `rustfmt` to the macro expanded sources generated by the
> `.rsi` target.
> 
> However, under an `O=` pointing to an external folder (i.e. not just
> a subdir), `rustfmt` will not find the file when checking the parent
> folders. Since the edition is configured in this file, this can lead to
> errors when it encounters newer syntax, e.g.
> 
>     error: expected one of `!`, `.`, `::`, `;`, `?`, `where`, `{`, or an operator, found `"rust_minimal"`
>       --> samples/rust/rust_minimal.rsi:29:49
>        |
>     28 | impl ::kernel::ModuleMetadata for RustMinimal {
>        |                                               - while parsing this item list starting here
>     29 |     const NAME: &'static ::kernel::str::CStr = c"rust_minimal";
>        |                                                 ^^^^^^^^^^^^^^ expected one of 8 possible tokens
>     30 | }
>        | - the item list ends here
>        |
>        = note: you may be trying to write a c-string literal
>        = note: c-string literals require Rust 2021 or later
>        = help: pass `--edition 2024` to `rustc`
>        = note: for more on editions, read https://doc.rust-lang.org/edition-guide
> 
> A workaround is to use `RUSTFMT=n`, which is documented in the `Makefile`
> help for cases where macro expanded source may happen to break `rustfmt`
> for other reasons, but this is not one of those cases.
> 
> One solution would be to pass `--edition`, but we want `rustfmt` to
> use the entire configuration, even if currently we essentially use the
> default configuration.
> 
> Thus explicitly give the path to the config file to `rustfmt` instead.
> 
> Reported-by: Alice Ryhl <aliceryhl@google.com>
> Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Reviewed-by: Gary Guo <gary@garyguo.net>

> ---
>  scripts/Makefile.build | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Re: [PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Miguel Ojeda]

On Fri, Jan 16, 2026 at 6:00 AM Nathan Chancellor <nathan@kernel.org> wrote:
>
> Reviewed-by: Nathan Chancellor <nathan@kernel.org>
>
> I assume you will take this via the Rust tree?

Yeah, either way is fine, but I can put it in `rust-fixes` since I
will send a PR in a few days.

Thanks!

Cheers,
Miguel

Re: [PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Miguel Ojeda]

On Thu, Jan 15, 2026 at 7:38 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> `rustfmt` is configured via the `.rustfmt.toml` file in the source tree,
> and we apply `rustfmt` to the macro expanded sources generated by the
> `.rsi` target.
>
> However, under an `O=` pointing to an external folder (i.e. not just
> a subdir), `rustfmt` will not find the file when checking the parent
> folders. Since the edition is configured in this file, this can lead to
> errors when it encounters newer syntax, e.g.
>
>     error: expected one of `!`, `.`, `::`, `;`, `?`, `where`, `{`, or an operator, found `"rust_minimal"`
>       --> samples/rust/rust_minimal.rsi:29:49
>        |
>     28 | impl ::kernel::ModuleMetadata for RustMinimal {
>        |                                               - while parsing this item list starting here
>     29 |     const NAME: &'static ::kernel::str::CStr = c"rust_minimal";
>        |                                                 ^^^^^^^^^^^^^^ expected one of 8 possible tokens
>     30 | }
>        | - the item list ends here
>        |
>        = note: you may be trying to write a c-string literal
>        = note: c-string literals require Rust 2021 or later
>        = help: pass `--edition 2024` to `rustc`
>        = note: for more on editions, read https://doc.rust-lang.org/edition-guide
>
> A workaround is to use `RUSTFMT=n`, which is documented in the `Makefile`
> help for cases where macro expanded source may happen to break `rustfmt`
> for other reasons, but this is not one of those cases.
>
> One solution would be to pass `--edition`, but we want `rustfmt` to
> use the entire configuration, even if currently we essentially use the
> default configuration.
>
> Thus explicitly give the path to the config file to `rustfmt` instead.
>
> Reported-by: Alice Ryhl <aliceryhl@google.com>
> Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
> Cc: stable@vger.kernel.org
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Applied to `rust-fixes` -- thanks everyone!

Cheers,
Miguel

Re: [PATCH] rust: kbuild: give `--config-path` to `rustfmt` in `.rsi` target

[Alice Ryhl]

On Sun, Jan 18, 2026 at 8:43 PM Miguel Ojeda
<miguel.ojeda.sandonis@gmail.com> wrote:
>
> On Thu, Jan 15, 2026 at 7:38 PM Miguel Ojeda <ojeda@kernel.org> wrote:
> >
> > `rustfmt` is configured via the `.rustfmt.toml` file in the source tree,
> > and we apply `rustfmt` to the macro expanded sources generated by the
> > `.rsi` target.
> >
> > However, under an `O=` pointing to an external folder (i.e. not just
> > a subdir), `rustfmt` will not find the file when checking the parent
> > folders. Since the edition is configured in this file, this can lead to
> > errors when it encounters newer syntax, e.g.
> >
> >     error: expected one of `!`, `.`, `::`, `;`, `?`, `where`, `{`, or an operator, found `"rust_minimal"`
> >       --> samples/rust/rust_minimal.rsi:29:49
> >        |
> >     28 | impl ::kernel::ModuleMetadata for RustMinimal {
> >        |                                               - while parsing this item list starting here
> >     29 |     const NAME: &'static ::kernel::str::CStr = c"rust_minimal";
> >        |                                                 ^^^^^^^^^^^^^^ expected one of 8 possible tokens
> >     30 | }
> >        | - the item list ends here
> >        |
> >        = note: you may be trying to write a c-string literal
> >        = note: c-string literals require Rust 2021 or later
> >        = help: pass `--edition 2024` to `rustc`
> >        = note: for more on editions, read https://doc.rust-lang.org/edition-guide
> >
> > A workaround is to use `RUSTFMT=n`, which is documented in the `Makefile`
> > help for cases where macro expanded source may happen to break `rustfmt`
> > for other reasons, but this is not one of those cases.
> >
> > One solution would be to pass `--edition`, but we want `rustfmt` to
> > use the entire configuration, even if currently we essentially use the
> > default configuration.
> >
> > Thus explicitly give the path to the config file to `rustfmt` instead.
> >
> > Reported-by: Alice Ryhl <aliceryhl@google.com>
> > Fixes: 2f7ab1267dc9 ("Kbuild: add Rust support")
> > Cc: stable@vger.kernel.org
> > Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
>
> Applied to `rust-fixes` -- thanks everyone!

Thanks Miguel for looking into this.

Alice