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

[Miguel Ojeda <ojeda@kernel.org>]

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