---

yaml
---
r: 221821
b: refs/heads/auto
c: 37a84bc
h: refs/heads/master
i:
  221819: 8720a08
v: v3

Author: Manishearth

[refs]

@@ -8,7 +8,7 @@ refs/tags/release-0.3: b5f0d0f648d9a6153664837026ba1be43d3e2503
 refs/tags/release-0.3.1: 495bae036dfe5ec6ceafd3312b4dca48741e845b
 refs/tags/release-0.4: e828ea2080499553b97dfe33b3f4d472b4562ad7
 refs/tags/release-0.5: 7e3bcfbf21278251ee936ad53e92e9b719702d73
-refs/heads/auto: 5d31deeae43e8f3803604f837649bbaeb625e726
+refs/heads/auto: 37a84bc82169bfdd0c67c519e710ba4488b82d55
 refs/tags/release-0.6: b4ebcfa1812664df5e142f0134a5faea3918544c
 refs/tags/0.1: b19db808c2793fe2976759b85a355c3ad8c8b336
 refs/tags/0.2: 1754d02027f2924bed83b0160ee340c7f41d5ea1

branches/auto/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,