Apply suggestions from code review

Co-authored-by: Waffle Maybe <waffle.lapkin@gmail.com>

Author: saethlin

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -162,7 +162,7 @@ pub(super) fn get_metadata_xcoff<'a>(path: &Path, data: &'a [u8]) -> Result<&'a
             return Err(format!("Invalid metadata symbol offset: {offset}"));
         }
         // The offset specifies the location of rustc metadata in the comment section.
-        // The metadata is preceded by a 4-byte length field.
+        // The metadata is preceded by a 8-byte length field.
         let len = u64::from_le_bytes(info_data[(offset - 8)..offset].try_into().unwrap()) as usize;
         if offset + len > (info_data.len() as usize) {
             return Err(format!(

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -705,9 +705,8 @@ impl MetadataBlob {
     }
 
     fn root_pos(&self) -> NonZeroUsize {
-        let slice = &self.blob()[..];
         let offset = METADATA_HEADER.len();
-        let pos_bytes = slice[offset..][..8].try_into().unwrap();
+        let pos_bytes = self.blob()[offset..][..8].try_into().unwrap();
         let pos = u64::from_le_bytes(pos_bytes);
         NonZeroUsize::new(pos as usize).unwrap()
     }

src/tools/rust-analyzer/crates/proc-macro-api/src/version.rs

@@ -153,8 +153,7 @@ pub fn read_version(dylib_path: &AbsPath) -> io::Result<String> {
     // 1 byte for length of version string
     // so 13 or 17 bytes in total, and we should check the last of those bytes
     // to know the length
-    let mut bytes_before_version = vec![0u8; bytes_before_version];
-    uncompressed.read_exact(&mut bytes_before_version)?;
+    uncompressed.read_exact(&mut [0u8; 17][..bytes_before_version)?;
     let length = *bytes_before_version.last().unwrap();
 
     let mut version_string_utf8 = vec![0u8; length as usize];