---

yaml
---
r: 228727
b: refs/heads/try
c: 37a84bc
h: refs/heads/master
i:
  228725: ef9d4ea
  228723: 55045b7
  228719: 8416b0c
v: v3

Author: Manishearth

[refs]

@@ -1,7 +1,7 @@
 ---
 refs/heads/master: aca2057ed5fb7af3f8905b2bc01f72fa001c35c8
 refs/heads/snap-stage3: 1af31d4974e33027a68126fa5a5a3c2c6491824f
-refs/heads/try: 5d31deeae43e8f3803604f837649bbaeb625e726
+refs/heads/try: 37a84bc82169bfdd0c67c519e710ba4488b82d55
 refs/tags/release-0.1: 1f5c5126e96c79d22cb7862f75304136e204f105
 refs/tags/release-0.2: c870d2dffb391e14efb05aa27898f1f6333a9596
 refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503

branches/try/src/librustc/diagnostics.rs

@@ -375,7 +375,7 @@ fn main() {
 ```
 
 Remember: you can't use a function call inside a const's initialization
-expression! However, you can totally use it elsewhere you want:
+expression! However, you can totally use it anywhere else:
 
 ```
 fn main() {
@@ -392,6 +392,24 @@ This error indicates that an attempt was made to divide by zero (or take the
 remainder of a zero divisor) in a static or constant expression.
 "##,
 
+E0022: r##"
+Constant functions are not allowed to mutate anything. Thus, binding to an
+argument with a mutable pattern is not allowed. For example,
+
+```
+const fn foo(mut x: u8) {
+    // do stuff
+}
+```
+
+is bad because the function body may not mutate `x`.
+
+Remove any mutable bindings from the argument list to fix this error. In case
+you need to mutate the argument, try lazily initializing a global variable
+instead of using a const fn, or refactoring the code to a functional style to
+avoid mutation if possible.
+"##,
+
 E0030: r##"
 When matching against a range, the compiler verifies that the range is
 non-empty.  Range patterns include both end-points, so this is equivalent to
@@ -1277,7 +1295,6 @@ contain references (with a maximum lifetime of `'a`).
 
 register_diagnostics! {
     // E0006 // merged with E0005
-    E0022,
     E0038,
 //  E0134,
 //  E0135,