Create new E0763 error code for unterminated byte constant

src/librustc_error_codes/error_codes.rs

@@ -442,6 +442,7 @@ E0758: include_str!("./error_codes/E0758.md"),
 E0760: include_str!("./error_codes/E0760.md"),
 E0761: include_str!("./error_codes/E0761.md"),
 E0762: include_str!("./error_codes/E0762.md"),
+E0763: include_str!("./error_codes/E0763.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

src/librustc_error_codes/error_codes/E0763.md

@@ -0,0 +1,13 @@
+A byte constant wasn't correctly ended.
+
+Erroneous code example:
+
+```compile_fail,E0763
+let c = b'a; // error!
+```
+
+To fix this error, add the missing quote:
+
+```
+let c = b'a'; // ok!
+```

src/librustc_parse/lexer/mod.rs

@@ -339,8 +339,15 @@ impl<'a> StringReader<'a> {
             }
             rustc_lexer::LiteralKind::Byte { terminated } => {
                 if !terminated {
-                    self.fatal_span_(start + BytePos(1), suffix_start, "unterminated byte constant")
-                        .raise()
+                    self.sess
+                        .span_diagnostic
+                        .struct_span_fatal_with_code(
+                            self.mk_sp(start + BytePos(1), suffix_start),
+                            "unterminated byte constant",
+                            error_code!(E0763),
+                        )
+                        .emit();
+                    FatalError.raise();
                 }
                 (token::Byte, Mode::Byte, 2, 1) // b' '
             }