1 files changed, 41 insertions, 0 deletions
diff --git a/compiler/rustc_error_codes/src/error_codes/E0408.md b/compiler/rustc_error_codes/src/error_codes/E0408.md
new file mode 100644
index 000000000..3acdbb740
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0408.md
@@ -0,0 +1,41 @@
+An "or" pattern was used where the variable bindings are not consistently bound
+across patterns.
+
+Erroneous code example:
+
+```compile_fail,E0408
+match x {
+    Some(y) | None => { /* use y */ } // error: variable `y` from pattern #1 is
+                                      //        not bound in pattern #2
+    _ => ()
+}
+```
+
+Here, `y` is bound to the contents of the `Some` and can be used within the
+block corresponding to the match arm. However, in case `x` is `None`, we have
+not specified what `y` is, and the block will use a nonexistent variable.
+
+To fix this error, either split into multiple match arms:
+
+```
+let x = Some(1);
+match x {
+    Some(y) => { /* use y */ }
+    None => { /* ... */ }
+}
+```
+
+or, bind the variable to a field of the same type in all sub-patterns of the
+or pattern:
+
+```
+let x = (0, 2);
+match x {
+    (0, y) | (y, 0) => { /* use y */}
+    _ => {}
+}
+```
+
+In this example, if `x` matches the pattern `(0, _)`, the second field is set
+to `y`. If it matches `(_, 0)`, the first field is set to `y`; so in all
+cases `y` is set to some value.