Create new error code E0755 for unterminated multi-line comments

Author: GuillaumeGomez

src/librustc_error_codes/error_codes.rs

@@ -437,6 +437,7 @@ E0751: include_str!("./error_codes/E0751.md"),
 E0752: include_str!("./error_codes/E0752.md"),
 E0753: include_str!("./error_codes/E0753.md"),
 E0754: include_str!("./error_codes/E0754.md"),
+E0758: include_str!("./error_codes/E0758.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

src/librustc_error_codes/error_codes/E0758.md

@@ -0,0 +1,20 @@
+A multi-line (doc-)comment is unterminated.
+
+Erroneous code example:
+
+```compile_fail,E0758
+/* I am not terminated!
+```
+
+The same goes for doc comments:
+
+```compile_fail,E0758
+/*! I am not terminated!
+```
+
+You need to end your multi-line comment with `*/` in order to fix this error:
+
+```
+/* I am terminated! */
+/*! I am also terminated! */
+```

src/librustc_parse/lexer/mod.rs

@@ -204,7 +204,15 @@ impl<'a> StringReader<'a> {
                         "unterminated block comment"
                     };
                     let last_bpos = self.pos;
-                    self.fatal_span_(start, last_bpos, msg).raise();
+                    self.sess
+                        .span_diagnostic
+                        .struct_span_fatal_with_code(
+                            self.mk_sp(start, last_bpos),
+                            msg,
+                            error_code!(E0758),
+                        )
+                        .emit();
+                    FatalError.raise();
                 }
 
                 if is_doc_comment {