From 0cae953c75d14c5fe766b3e413da2989f25fd11e Mon Sep 17 00:00:00 2001
From: Gary Guo <gary@garyguo.net>
Date: Fri, 28 Aug 2026 16:35:20 +0100
Subject: [PATCH] use irrefutable pattern for `stack_pin_init`

In Rust 1.100.0, `Infallible` will become an alias of `!`. The let
binding in `stack_pin_init` will thus become unreachable and produce a
"unreachable expression" warning for subsequent match, and thus will fail
`-Dwarnings` build. For this macro, all we need to know is that the error
type is uninhabited, so replace this with a irrefutable pattern instead.

Reported-by: Mohamad Alsadhan <mo@sdhn.cc>
Closes: https://github.com/Rust-for-Linux/pin-init/pull/171
Signed-off-by: Gary Guo <gary@garyguo.net>
---
 src/lib.rs                                          | 8 +-------
 tests/ui/compile-fail/init/no_error_coercion.stderr | 4 ++--
 tests/ui/compile-fail/pin_data/missing_pin.stderr   | 2 +-
 3 files changed, 4 insertions(+), 10 deletions(-)

diff --git a/src/lib.rs b/src/lib.rs
index 7600cdbb..f1463be9 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -490,13 +490,7 @@ macro_rules! stack_pin_init {
     (let $var:ident $(: $t:ty)? = $val:expr) => {
         let val = $val;
         let mut $var = ::core::pin::pin!($crate::__internal::StackInit$(::<$t>)?::uninit());
-        let mut $var = match $crate::__internal::StackInit::init($var, val) {
-            Ok(res) => res,
-            Err(x) => {
-                let x: ::core::convert::Infallible = x;
-                match x {}
-            }
-        };
+        let Ok(mut $var) = $crate::__internal::StackInit::init($var, val);
     };
 }
 
diff --git a/tests/ui/compile-fail/init/no_error_coercion.stderr b/tests/ui/compile-fail/init/no_error_coercion.stderr
index 974c3c15..ddc13df7 100644
--- a/tests/ui/compile-fail/init/no_error_coercion.stderr
+++ b/tests/ui/compile-fail/init/no_error_coercion.stderr
@@ -7,8 +7,8 @@ error[E0277]: `?` couldn't convert the error to `std::alloc::AllocError`
 19 | |         }? AllocError)
    | |                      ^
    | |                      |
-   | |______________________the trait `From<Infallible>` is not implemented for `std::alloc::AllocError`
-   |                        this can't be annotated with `?` because it has type `Result<_, Infallible>`
+   | |______________________the trait `From<!>` is not implemented for `std::alloc::AllocError`
+   |                        this can't be annotated with `?` because it has type `Result<_, !>`
    |
    = note: the question mark operation (`?`) implicitly performs a conversion on the error value using the `From` trait
    = note: this error originates in the macro `init` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/tests/ui/compile-fail/pin_data/missing_pin.stderr b/tests/ui/compile-fail/pin_data/missing_pin.stderr
index f480b637..fa39129f 100644
--- a/tests/ui/compile-fail/pin_data/missing_pin.stderr
+++ b/tests/ui/compile-fail/pin_data/missing_pin.stderr
@@ -8,7 +8,7 @@ error[E0277]: the trait bound `impl PinInit<usize>: Init<usize, _>` is not satis
    | |__________- required by a bound introduced by this call
    |
 help: the trait `Init<usize, _>` is not implemented for `impl PinInit<usize>`
-      but trait `Init<impl PinInit<usize>, Infallible>` is implemented for it
+      but trait `Init<impl PinInit<usize>, !>` is implemented for it
   --> src/lib.rs
    |
    | unsafe impl<T> Init<T> for T {}