1 files changed, 24 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0001.md b/compiler/rustc_error_codes/src/error_codes/E0001.md
new file mode 100644
index 000000000..90756780d
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0001.md
@@ -0,0 +1,24 @@
+#### Note: this error code is no longer emitted by the compiler.
+
+This error suggests that the expression arm corresponding to the noted pattern
+will never be reached as for all possible values of the expression being
+matched, one of the preceding patterns will match.
+
+This means that perhaps some of the preceding patterns are too general, this
+one is too specific or the ordering is incorrect.
+
+For example, the following `match` block has too many arms:
+
+```
+match Some(0) {
+    Some(bar) => {/* ... */}
+    x => {/* ... */} // This handles the `None` case
+    _ => {/* ... */} // All possible cases have already been handled
+}
+```
+
+`match` blocks have their patterns matched in order, so, for example, putting
+a wildcard arm above a more specific arm will make the latter arm irrelevant.
+
+Ensure the ordering of the match arm is correct and remove any superfluous
+arms.