[PATCH 1/2] rust: allow `clippy::collapsible_match` globally

[PATCH 1/2] rust: allow `clippy::collapsible_match` globally

[Miguel Ojeda]

The `clippy::collapsible_match` lint [1] can make code harder to read
in certain cases [2], e.g.

      CLIPPY P rust/libmacros.so - due to command line change
    warning: this `if` can be collapsed into the outer `match`
      --> rust/pin-init/internal/src/helpers.rs:91:17
       |
    91 | /                 if nesting == 1 {
    92 | |                     impl_generics.push(tt.clone());
    93 | |                     impl_generics.push(tt);
    94 | |                     skip_until_comma = false;
    95 | |                 }
       | |_________________^
       |
       = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
       = note: `-W clippy::collapsible-match` implied by `-W clippy::all`
       = help: to override `-W clippy::all` add `#[allow(clippy::collapsible_match)]`
    help: collapse nested if block
       |
    90 ~             TokenTree::Punct(p) if skip_until_comma && p.as_char() == ','
    91 ~                 && nesting == 1 => {
    92 |                     impl_generics.push(tt.clone());
    93 |                     impl_generics.push(tt);
    94 |                     skip_until_comma = false;
    95 ~                 }
       |

The lint does not have much upside -- when the suggestion may be a good
one, it would still read fine when nested anyway. And it is the kind of
lint that may easily bias people to just apply the suggestion instead
of allowing it.

Thus just let developers decide on their own.

Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Link: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match [1]
Link: https://lore.kernel.org/rust-for-linux/CANiq72nWYJna_hdFxjQCQZK6yJBrr1Mb86iKavivV0U0BgufeA@mail.gmail.com/ [2]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/Makefile b/Makefile
index 54e1ae602000..e2a810bc4409 100644
--- a/Makefile
+++ b/Makefile
@@ -486,6 +486,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::as_ptr_cast_mut \
 			    -Wclippy::as_underscore \
 			    -Wclippy::cast_lossless \
+			    -Aclippy::collapsible_match \
 			    -Wclippy::ignored_unit_patterns \
 			    -Aclippy::incompatible_msrv \
 			    -Wclippy::mut_mut \

base-commit: 897d54018cc9aa97fd1529ca08a53b429d05a566
-- 
2.53.0

[PATCH 2/2] rust: allow `clippy::collapsible_if` globally

[Miguel Ojeda]

Similar to `clippy::collapsible_match` (globally allowed in the previous
commit), the `clippy::collapsible_if` lint [1] can make code harder to
read in certain cases.

Thus just let developers decide on their own.

In addition, remove the existing `expect` we had.

Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
Suggested-by: Gary Guo <gary@garyguo.net>
Link: https://lore.kernel.org/rust-for-linux/DGROP5CHU1QZ.1OKJRAUZXE9WC@garyguo.net/
Link: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_if [1]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
 Makefile                                    | 1 +
 drivers/android/binder/range_alloc/array.rs | 1 -
 2 files changed, 1 insertion(+), 1 deletion(-)

diff --git a/Makefile b/Makefile
index e2a810bc4409..d0a515b661a0 100644
--- a/Makefile
+++ b/Makefile
@@ -486,6 +486,7 @@ export rust_common_flags := --edition=2021 \
 			    -Wclippy::as_ptr_cast_mut \
 			    -Wclippy::as_underscore \
 			    -Wclippy::cast_lossless \
+			    -Aclippy::collapsible_if \
 			    -Aclippy::collapsible_match \
 			    -Wclippy::ignored_unit_patterns \
 			    -Aclippy::incompatible_msrv \
diff --git a/drivers/android/binder/range_alloc/array.rs b/drivers/android/binder/range_alloc/array.rs
index ada1d1b4302e..081d19b09d4b 100644
--- a/drivers/android/binder/range_alloc/array.rs
+++ b/drivers/android/binder/range_alloc/array.rs
@@ -204,7 +204,6 @@ pub(crate) fn reservation_abort(&mut self, offset: usize) -> Result<FreedRange>
         // caller will mark them as unused, which means that they can be freed if the system comes
         // under memory pressure.
         let mut freed_range = FreedRange::interior_pages(offset, size);
-        #[expect(clippy::collapsible_if)] // reads better like this
         if offset % PAGE_SIZE != 0 {
             if i == 0 || self.ranges[i - 1].endpoint() <= (offset & PAGE_MASK) {
                 freed_range.start_page_idx -= 1;
-- 
2.53.0

Re: [PATCH 2/2] rust: allow `clippy::collapsible_if` globally

[Gary Guo]

On Sun Apr 26, 2026 at 3:42 PM BST, Miguel Ojeda wrote:
> Similar to `clippy::collapsible_match` (globally allowed in the previous
> commit), the `clippy::collapsible_if` lint [1] can make code harder to
> read in certain cases.
> 
> Thus just let developers decide on their own.
> 
> In addition, remove the existing `expect` we had.
> 
> Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Suggested-by: Gary Guo <gary@garyguo.net>
> Link: https://lore.kernel.org/rust-for-linux/DGROP5CHU1QZ.1OKJRAUZXE9WC@garyguo.net/
> Link: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_if [1]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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

> ---
>  Makefile                                    | 1 +
>  drivers/android/binder/range_alloc/array.rs | 1 -
>  2 files changed, 1 insertion(+), 1 deletion(-)

Re: [PATCH 1/2] rust: allow `clippy::collapsible_match` globally

[Gary Guo]

On Sun Apr 26, 2026 at 3:42 PM BST, Miguel Ojeda wrote:
> The `clippy::collapsible_match` lint [1] can make code harder to read
> in certain cases [2], e.g.
>
>       CLIPPY P rust/libmacros.so - due to command line change
>     warning: this `if` can be collapsed into the outer `match`
>       --> rust/pin-init/internal/src/helpers.rs:91:17
>        |
>     91 | /                 if nesting == 1 {
>     92 | |                     impl_generics.push(tt.clone());
>     93 | |                     impl_generics.push(tt);
>     94 | |                     skip_until_comma = false;
>     95 | |                 }
>        | |_________________^
>        |
>        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
>        = note: `-W clippy::collapsible-match` implied by `-W clippy::all`
>        = help: to override `-W clippy::all` add `#[allow(clippy::collapsible_match)]`
>     help: collapse nested if block
>        |
>     90 ~             TokenTree::Punct(p) if skip_until_comma && p.as_char() == ','
>     91 ~                 && nesting == 1 => {
>     92 |                     impl_generics.push(tt.clone());
>     93 |                     impl_generics.push(tt);
>     94 |                     skip_until_comma = false;
>     95 ~                 }
>        |
>
> The lint does not have much upside -- when the suggestion may be a good
> one, it would still read fine when nested anyway. And it is the kind of
> lint that may easily bias people to just apply the suggestion instead
> of allowing it.

It's also just wrong.

    pattern => {
        if x {
            ...
        }
    }

is not equal to

    pattern if x => { ... }

because the former prevents other arms later (e.g. a `_`) from being to act
while the latter doesn't.

See https://github.com/rust-lang/rust-clippy/pull/16878

>
> Thus just let developers decide on their own.
>
> Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Link: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match [1]
> Link: https://lore.kernel.org/rust-for-linux/CANiq72nWYJna_hdFxjQCQZK6yJBrr1Mb86iKavivV0U0BgufeA@mail.gmail.com/ [2]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

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

Best,
Gary

> ---
>  Makefile | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/Makefile b/Makefile
> index 54e1ae602000..e2a810bc4409 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -486,6 +486,7 @@ export rust_common_flags := --edition=2021 \
>  			    -Wclippy::as_ptr_cast_mut \
>  			    -Wclippy::as_underscore \
>  			    -Wclippy::cast_lossless \
> +			    -Aclippy::collapsible_match \
>  			    -Wclippy::ignored_unit_patterns \
>  			    -Aclippy::incompatible_msrv \
>  			    -Wclippy::mut_mut \
>
> base-commit: 897d54018cc9aa97fd1529ca08a53b429d05a566

Re: [PATCH 1/2] rust: allow `clippy::collapsible_match` globally

[Miguel Ojeda]

On Sun, Apr 26, 2026 at 4:42 PM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> The `clippy::collapsible_match` lint [1] can make code harder to read
> in certain cases [2], e.g.
>
>       CLIPPY P rust/libmacros.so - due to command line change
>     warning: this `if` can be collapsed into the outer `match`
>       --> rust/pin-init/internal/src/helpers.rs:91:17
>        |
>     91 | /                 if nesting == 1 {
>     92 | |                     impl_generics.push(tt.clone());
>     93 | |                     impl_generics.push(tt);
>     94 | |                     skip_until_comma = false;
>     95 | |                 }
>        | |_________________^
>        |
>        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match
>        = note: `-W clippy::collapsible-match` implied by `-W clippy::all`
>        = help: to override `-W clippy::all` add `#[allow(clippy::collapsible_match)]`
>     help: collapse nested if block
>        |
>     90 ~             TokenTree::Punct(p) if skip_until_comma && p.as_char() == ','
>     91 ~                 && nesting == 1 => {
>     92 |                     impl_generics.push(tt.clone());
>     93 |                     impl_generics.push(tt);
>     94 |                     skip_until_comma = false;
>     95 ~                 }
>        |
>
> The lint does not have much upside -- when the suggestion may be a good
> one, it would still read fine when nested anyway. And it is the kind of
> lint that may easily bias people to just apply the suggestion instead
> of allowing it.
>
> Thus just let developers decide on their own.
>
> Cc: stable@vger.kernel.org # Needed in 6.12.y and later (Rust is pinned in older LTSs).
> Link: https://rust-lang.github.io/rust-clippy/master/index.html#collapsible_match [1]
> Link: https://lore.kernel.org/rust-for-linux/CANiq72nWYJna_hdFxjQCQZK6yJBrr1Mb86iKavivV0U0BgufeA@mail.gmail.com/ [2]
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Applied (both patches) to `rust-fixes` -- thanks!

    [ In addition, as Gary points out [3], the suggestion is also wrong [4] and
      in the process of being fixed [5], possibly for Rust 1.97.0:

      Link: https://lore.kernel.org/rust-for-linux/DI3YV94TH9I3.1SOHW51552497@garyguo.net/
[3]
      Link: https://github.com/rust-lang/rust-clippy/issues/16875 [4]
      Link: https://github.com/rust-lang/rust-clippy/pull/16878 [5]

        - Miguel ]

Ideally, we would have an `Acked-by` on the second one from Binder
maintainers, but it is trivial.

Cheers,
Miguel