rustc: Remove `&str` indexing from the language.

Being able to index into the bytes of a string encourages
poor UTF-8 hygiene. To get a view of `&[u8]` from either
a `String` or `&str` slice, use the `as_bytes()` method.

Closes #12710.

[breaking-change]

2 files changed, 3 insertions, 3 deletions

diff --git a/src/libsyntax/diagnostic.rs b/src/libsyntax/diagnostic.rs
index 90569bfc132..dfaa9fb5fcb 100644
--- a/src/libsyntax/diagnostic.rs
+++ b/src/libsyntax/diagnostic.rs
@@ -415,7 +415,7 @@ fn highlight_lines(err: &mut EmitterWriter,
         }
         let orig = fm.get_line(*lines.lines.get(0) as int);
         for pos in range(0u, left-skip) {
-            let cur_char = orig.as_slice()[pos] as char;
+            let cur_char = orig.as_bytes()[pos] as char;
             // Whenever a tab occurs on the previous line, we insert one on
             // the error-point-squiggly-line as well (instead of a space).
             // That way the squiggly line will usually appear in the correct
diff --git a/src/libsyntax/parse/lexer/mod.rs b/src/libsyntax/parse/lexer/mod.rs
index ac570c88837..0f188fdf18a 100644
--- a/src/libsyntax/parse/lexer/mod.rs
+++ b/src/libsyntax/parse/lexer/mod.rs
@@ -1203,8 +1203,8 @@ impl<'a> StringReader<'a> {
 
     fn read_one_line_comment(&mut self) -> String {
         let val = self.read_to_eol();
-        assert!((val.as_slice()[0] == '/' as u8 && val.as_slice()[1] == '/' as u8)
-             || (val.as_slice()[0] == '#' as u8 && val.as_slice()[1] == '!' as u8));
+        assert!((val.as_bytes()[0] == '/' as u8 && val.as_bytes()[1] == '/' as u8)
+             || (val.as_bytes()[0] == '#' as u8 && val.as_bytes()[1] == '!' as u8));
         return val;
     }