From 0bb6bc40ce8d544ca41006d3faf8bcda2152030f Mon Sep 17 00:00:00 2001
From: Aris Merchant <22333129+inquisitivecrystal@users.noreply.github.com>
Date: Mon, 21 Jun 2021 18:11:53 -0700
Subject: [PATCH] Teach rustc to accept lowercase error codes

---
 compiler/rustc_driver/src/lib.rs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/compiler/rustc_driver/src/lib.rs b/compiler/rustc_driver/src/lib.rs
index b943977e4c2bb..87bc829b48891 100644
--- a/compiler/rustc_driver/src/lib.rs
+++ b/compiler/rustc_driver/src/lib.rs
@@ -528,8 +528,12 @@ fn stderr_isatty() -> bool {
 }
 
 fn handle_explain(registry: Registry, code: &str, output: ErrorOutputType) {
-    let normalised =
-        if code.starts_with('E') { code.to_string() } else { format!("E{0:0>4}", code) };
+    let upper_cased_code = code.to_ascii_uppercase();
+    let normalised = if upper_cased_code.starts_with('E') {
+        upper_cased_code
+    } else {
+        format!("E{0:0>4}", code)
+    };
     match registry.try_find_description(&normalised) {
         Ok(Some(description)) => {
             let mut is_in_code_block = false;