Avoid using once_cell

Author: kornelski

Cargo.toml

@@ -35,7 +35,6 @@ arrayvec = "0.7.4"
 rgb = { version = "0.8.47", default-features = false, features = ["bytemuck"] }
 rayon = { version = "1.10.0", optional = true }
 thread_local = { version = "1.1.8", optional = true }
-once_cell = "1.19.0"
 
 [dev-dependencies]
 lodepng = "3.10"

src/error.rs

@@ -49,6 +49,12 @@ impl fmt::Display for Error {
     }
 }
 
+impl From<core::convert::Infallible> for Error {
+    fn from(e: core::convert::Infallible) -> Self {
+        match e {}
+    }
+}
+
 impl From<TryReserveError> for Error {
     #[cold]
     fn from(_: TryReserveError) -> Self {

src/rayoff.rs

@@ -1,5 +1,5 @@
 use core::slice::ChunksMut;
-use once_cell::unsync::OnceCell;
+use core::cell::OnceCell;
 
 pub(crate) struct ThreadLocal<T>(OnceCell<T>);
 
@@ -15,8 +15,9 @@ impl<T> ThreadLocal<T> {
     }
 
     #[inline(always)]
-    pub fn get_or_try<E>(&self, f: impl FnOnce() -> Result<T, E>) -> Result<&T, E> {
-        self.0.get_or_try_init(f)
+    pub fn get_or_try<E>(&self, f: impl FnOnce() -> Result<T, E>) -> Result<&T, core::convert::Infallible> {
+        // https://github.com/rust-lang/rust/issues/109737
+        Ok(self.0.get_or_init(move || f().ok().unwrap()))
     }
 }
 
@@ -40,19 +41,19 @@ impl<T> FakeRayonIter for T where Self: Sized {
 }
 
 pub(crate) trait FakeRayonIntoIter<T> {
-    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T>;
+    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T>;
 }
 
 impl<'a, T> FakeRayonIntoIter<T> for &'a mut [T] {
     #[inline(always)]
-    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T> {
+    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
         self.chunks_mut(chunk_size)
     }
 }
 
 impl<'a, T> FakeRayonIntoIter<T> for Box<[T]> {
     #[inline(always)]
-    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<T> {
+    fn par_chunks_mut(&mut self, chunk_size: usize) -> ChunksMut<'_, T> {
         self.chunks_mut(chunk_size)
     }
 }

src/remap.rs

@@ -57,6 +57,7 @@ pub(crate) fn remap_to_palette<'x, 'b: 'x>(px: &mut DynamicRows, background: Opt
 
     let remapping_error = output_pixels.rows_mut().enumerate().par_bridge().map(|(row, output_pixels_row)| {
         let mut remapping_error = 0.;
+        #[allow(irrefutable_let_patterns)]
         let Ok(tls_res) = tls.get_or_try(per_thread_buffers) else { return f64::NAN };
         let (kmeans, temp_row, temp_row_f, temp_row_f_bg) = &mut *tls_res.0.borrow_mut();