Rollup merge of #111609 - LegionMammal978:internal-unsafe, r=thomcc

Mark internal functions and traits unsafe to reflect preconditions

No semantics are changed in this PR; I only mark some functions and and a trait `unsafe` which already had implicit preconditions. Although it seems somewhat redundant for `numfmt::Part::Copy` to contain a `&[u8]` instead of a `&str`, given that all of its current consumers ultimately expect valid UTF-8. Is the type also intended to work for byte-slice formatting in the future?

1 files changed, 7 insertions, 4 deletions

diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 43203c5824d..febdeb51463 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -733,8 +733,9 @@ impl<'a> Components<'a> {
         }
     }
 
-    // parse a given byte sequence into the corresponding path component
-    fn parse_single_component<'b>(&self, comp: &'b [u8]) -> Option<Component<'b>> {
+    // parse a given byte sequence following the OsStr encoding into the
+    // corresponding path component
+    unsafe fn parse_single_component<'b>(&self, comp: &'b [u8]) -> Option<Component<'b>> {
         match comp {
             b"." if self.prefix_verbatim() => Some(Component::CurDir),
             b"." => None, // . components are normalized away, except at
@@ -754,7 +755,8 @@ impl<'a> Components<'a> {
             None => (0, self.path),
             Some(i) => (1, &self.path[..i]),
         };
-        (comp.len() + extra, self.parse_single_component(comp))
+        // SAFETY: `comp` is a valid substring, since it is split on a separator.
+        (comp.len() + extra, unsafe { self.parse_single_component(comp) })
     }
 
     // parse a component from the right, saying how many bytes to consume to
@@ -766,7 +768,8 @@ impl<'a> Components<'a> {
             None => (0, &self.path[start..]),
             Some(i) => (1, &self.path[start + i + 1..]),
         };
-        (comp.len() + extra, self.parse_single_component(comp))
+        // SAFETY: `comp` is a valid substring, since it is split on a separator.
+        (comp.len() + extra, unsafe { self.parse_single_component(comp) })
     }
 
     // trim away repeated separators (i.e., empty components) on the left