Use FnOnce for slice_owned instead of Fn

Author: WaffleLapkin

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -37,7 +37,7 @@ pub struct DefaultMetadataLoader;
 
 fn load_metadata_with(
     path: &Path,
-    f: impl for<'a> Fn(&'a [u8]) -> Result<&'a [u8], String>,
+    f: impl for<'a> FnOnce(&'a [u8]) -> Result<&'a [u8], String>,
 ) -> Result<MetadataRef, String> {
     let file =
         File::open(path).map_err(|e| format!("failed to open file '{}': {}", path.display(), e))?;

compiler/rustc_data_structures/src/owned_slice.rs

@@ -59,7 +59,7 @@ pub struct OwnedSlice {
 pub fn slice_owned<O, F>(owner: O, slicer: F) -> OwnedSlice
 where
     O: Send + Sync + 'static,
-    F: Fn(&O) -> &[u8],
+    F: FnOnce(&O) -> &[u8],
 {
     try_slice_owned(owner, |x| Ok::<_, !>(slicer(x))).into_ok()
 }
@@ -70,7 +70,7 @@ where
 pub fn try_slice_owned<O, F, E>(owner: O, slicer: F) -> Result<OwnedSlice, E>
 where
     O: Send + Sync + 'static,
-    F: Fn(&O) -> Result<&[u8], E>,
+    F: FnOnce(&O) -> Result<&[u8], E>,
 {
     // We box the owner of the bytes, so it doesn't move.
     //