Add error code E744 for unterminated raw string

Author: GuillaumeGomez

src/libsyntax/error_codes.rs

@@ -518,6 +518,24 @@ undefined number of parameters to a given function (like `printf` in C). The
 equivalent in Rust would be to use macros directly.
 "##,
 
+E0744: r##"
+A raw string isn't terminated.
+
+Erroneous code example:
+
+```compile_fail,E0744
+let dolphins = r##"Dolphins!"#; // error!
+```
+
+To terminate a raw string, you have to have the same number of `#` at the end
+than at the beginning. Example:
+
+```
+let dolphins = r#"Dolphins!"#; // one `#` at the beginning, one at the end so
+                               // all good!
+```
+"##,
+
 ;
 
     E0539, // incorrect meta item

src/libsyntax/parse/lexer/mod.rs

@@ -501,8 +501,10 @@ impl<'a> StringReader<'a> {
     }
 
     fn report_unterminated_raw_string(&self, start: BytePos, n_hashes: usize) -> ! {
-        let mut err = self.struct_span_fatal(
-            start, start,
+        let mut err = struct_span_fatal!(
+            self.sess.span_diagnostic,
+            self.mk_sp(start, start),
+            E0744,
             "unterminated raw string",
         );
         err.span_label(