New example for E0536

Author: JonathanBrouwer

compiler/rustc_error_codes/src/error_codes/E0536.md

@@ -3,22 +3,20 @@ The `not` cfg-predicate was malformed.
 Erroneous code example:
 
 ```compile_fail,E0536
-#[cfg(not())] // error: expected 1 cfg-pattern
-pub fn something() {}
-
-pub fn main() {}
+pub fn main() {
+    if cfg!(not()) { }
+}
 ```
 
 The `not` predicate expects one cfg-pattern. Example:
 
 ```
-#[cfg(not(target_os = "linux"))] // ok!
-pub fn something() {}
-
-pub fn main() {}
+pub fn main() {
+    if cfg!(not(target_os = "linux")) { } // ok!
+}
 ```
 
-For more information about the `cfg` attribute, read the section on
+For more information about the `cfg` macro, read the section on
 [Conditional Compilation][conditional-compilation] in the Reference.
 
 [conditional-compilation]: https://doc.rust-lang.org/reference/conditional-compilation.html

tests/ui/span/E0536.rs

@@ -1,4 +1,3 @@
-#[cfg(not())] //~ ERROR E0536
-pub fn something() {}
-
-pub fn main() {}
+pub fn main() {
+    if cfg!(not()) { } //~ ERROR E0536
+}

tests/ui/span/E0536.stderr

@@ -1,8 +1,8 @@
 error[E0536]: expected 1 cfg-pattern
-  --> $DIR/E0536.rs:1:7
+  --> $DIR/E0536.rs:2:13
    |
-LL | #[cfg(not())]
-   |       ^^^^^
+LL |     if cfg!(not()) { }
+   |             ^^^^^
 
 error: aborting due to 1 previous error