Create new E0768 error code for "no valid digits found for number" error

src/librustc_error_codes/error_codes.rs

@@ -449,6 +449,7 @@
 E0765: include_str!("./error_codes/E0765.md"),
 E0766: include_str!("./error_codes/E0766.md"),
 E0767: include_str!("./error_codes/E0767.md"),
+E0768: include_str!("./error_codes/E0768.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

src/librustc_error_codes/error_codes/E0768.md

+A number in a non-decimal base has no digits.
+
+Erroneous code example:
+
+```compile_fail,E0768
+let s: i32 = 0b; // error!
+```
+
+To fix this error, add the missing digits:
+
+```
+let s: i32 = 0b1; // ok!
+```

src/librustc_parse/lexer/mod.rs

@@ -391,7 +391,14 @@ fn cook_lexer_literal(
             }
             rustc_lexer::LiteralKind::Int { base, empty_int } => {
                 return if empty_int {
-                    self.err_span_(start, suffix_start, "no valid digits found for number");
+                    self.sess
+                        .span_diagnostic
+                        .struct_span_err_with_code(
+                            self.mk_sp(start, suffix_start),
+                            "no valid digits found for number",
+                            error_code!(E0768),
+                        )
+                        .emit();
                     (token::Integer, sym::integer(0))
                 } else {
                     self.validate_int_literal(base, start, suffix_start);