syntax_pos: Store multibyte char size as u8 instead of u32.

src/libsyntax/codemap.rs

@@ -819,10 +819,10 @@ impl CodeMap {
             if mbc.pos < bpos {
                 // every character is at least one byte, so we only
                 // count the actual extra bytes.
-                total_extra_bytes += mbc.bytes - 1;
+                total_extra_bytes += mbc.bytes as u32 - 1;
                 // We should never see a byte position in the middle of a
                 // character
-                assert!(bpos.to_u32() >= mbc.pos.to_u32() + mbc.bytes);
+                assert!(bpos.to_u32() >= mbc.pos.to_u32() + mbc.bytes as u32);
             } else {
                 break;
             }

src/libsyntax_pos/analyze_filemap.rs

@@ -263,7 +263,7 @@ fn analyze_filemap_generic(src: &str,
                 assert!(char_len >=2 && char_len <= 4);
                 let mbc = MultiByteChar {
                     pos,
-                    bytes: char_len as u32,
+                    bytes: char_len as u8,
                 };
                 multi_byte_chars.push(mbc);
             }

src/libsyntax_pos/lib.rs

@@ -663,7 +663,7 @@ pub struct MultiByteChar {
     /// The absolute offset of the character in the CodeMap
     pub pos: BytePos,
     /// The number of bytes, >=2
-    pub bytes: u32,
+    pub bytes: u8,
 }
 
 /// Identifies an offset of a non-narrow character in a FileMap