optimized some stuff

Author: Kivooeo

compiler/rustc_driver_impl/src/lib.rs

@@ -463,6 +463,7 @@ fn handle_explain(early_dcx: &EarlyDiagCtxt, registry: Registry, code: &str, col
     // Allow "E0123" or "0123" form.
     let upper_cased_code = code.to_ascii_uppercase();
     if let Ok(code) = upper_cased_code.strip_prefix('E').unwrap_or(&upper_cased_code).parse::<u32>()
+        && code <= ErrCode::MAX_AS_U32
         && let Ok(description) = registry.try_find_description(ErrCode::from_u32(code))
     {
         let mut is_in_code_block = false;

compiler/rustc_errors/src/codes.rs

@@ -7,6 +7,7 @@
 use std::fmt;
 
 rustc_index::newtype_index! {
+    #[max = 9999]
     #[orderable]
     #[encodable]
     #[debug_format = "ErrCode({})"]