Rollup merge of #25873 - nham:update_E0015, r=Aatch

The E0397 explanation, as I've written it, isn't really an explanation, but I'm not sure what to put here. I will happily take suggestions.

Partially addresses https://github.com/rust-lang/rust/issues/25851

src/librustc/diagnostics.rs

@@ -196,9 +196,13 @@ struct X { x: (), }
 "##,
 
 E0015: r##"
-The only function calls allowed in static or constant expressions are enum
-variant constructors or struct constructors (for unit or tuple structs). This
-is because Rust currently does not support compile-time function execution.
+The only functions that can be called in static or constant expressions are
+`const` functions. Rust currently does not support more general compile-time
+function execution.
+
+See [RFC 911] for more details on the design of `const fn`s.
+
+[RFC 911]: https://github.com/rust-lang/rfcs/blob/master/text/0911-const-fn.md
 "##,
 
 E0018: r##"
@@ -842,6 +846,53 @@ struct Foo<T: 'static> {
     foo: &'static T
 }
 ```
+"##,
+
+E0378: r##"
+Method calls that aren't calls to inherent `const` methods are disallowed
+in statics, constants, and constant functions.
+
+For example:
+
+```
+const BAZ: i32 = Foo(25).bar(); // error, `bar` isn't `const`
+
+struct Foo(i32);
+
+impl Foo {
+    const fn foo(&self) -> i32 {
+        self.bar() // error, `bar` isn't `const`
+    }
+
+    fn bar(&self) -> i32 { self.0 }
+}
+```
+
+For more information about `const fn`'s, see [RFC 911].
+
+[RFC 911]: https://github.com/rust-lang/rfcs/blob/master/text/0911-const-fn.md
+"##,
+
+E0394: r##"
+From [RFC 246]:
+
+ > It is illegal for a static to reference another static by value. It is
+ > required that all references be borrowed.
+
+[RFC 246]: https://github.com/rust-lang/rfcs/pull/246
+"##,
+
+E0397: r##"
+It is not allowed for a mutable static to allocate or have destructors. For
+example:
+
+```
+// error: mutable statics are not allowed to have boxes
+static mut FOO: Option<Box<usize>> = None;
+
+// error: mutable statics are not allowed to have destructors
+static mut BAR: Option<Vec<i32>> = None;
+```
 "##
 
 }
@@ -891,9 +942,6 @@ struct Foo<T: 'static> {
     E0315, // cannot invoke closure outside of its lifetime
     E0316, // nested quantification of lifetimes
     E0370, // discriminant overflow
-    E0378, // method calls limited to constant inherent methods
-    E0394, // cannot refer to other statics by value, use the address-of
-           // operator or a constant instead
     E0395, // pointer comparison in const-expr
     E0396  // pointer dereference in const-expr
 }

src/librustc/middle/check_const.rs

@@ -273,13 +273,13 @@ fn check_static_mut_type(&self, e: &ast::Expr) {
         let suffix = if tcontents.has_dtor() {
             "destructors"
         } else if tcontents.owns_owned() {
-            "owned pointers"
+            "boxes"
         } else {
             return
         };
 
-        self.tcx.sess.span_err(e.span, &format!("mutable statics are not allowed \
-                                                 to have {}", suffix));
+        span_err!(self.tcx.sess, e.span, E0397,
+                 "mutable statics are not allowed to have {}", suffix);
     }
 
     fn check_static_type(&self, e: &ast::Expr) {

src/librustc_typeck/diagnostics.rs

@@ -170,6 +170,31 @@ struct Dog {
 http://doc.rust-lang.org/reference.html#trait-objects
 "##,
 
+E0040: r##"
+It is not allowed to manually call destructors in Rust. It is also not
+necessary to do this since `drop` is called automatically whenever a value goes
+out of scope.
+
+Here's an example of this error:
+
+```
+struct Foo {
+    x: i32,
+}
+
+impl Drop for Foo {
+    fn drop(&mut self) {
+        println!("kaboom");
+    }
+}
+
+fn main() {
+    let mut x = Foo { x: -7 };
+    x.drop(); // error: explicit use of destructor method
+}
+```
+"##,
+
 E0046: r##"
 When trying to make some type implement a trait `Foo`, you must, at minimum,
 provide implementations for all of `Foo`'s required methods (meaning the
@@ -241,7 +266,7 @@ impl Foo for Bar {
     fn foo(x: i16) { }
 
     // error, values differ in mutability
-    fn foo(&mut self) { }
+    fn bar(&mut self) { }
 }
 ```
 "##,
@@ -542,6 +567,21 @@ enum Empty {}
 ```
 "##,
 
+E0087: r##"
+Too many type parameters were supplied for a function. For example:
+
+```
+fn foo<T>() {}
+
+fn main() {
+    foo::<f64, bool>(); // error, expected 1 parameter, found 2 parameters
+}
+```
+
+The number of supplied parameters much exactly match the number of defined type
+parameters.
+"##,
+
 E0089: r##"
 Not enough type parameters were supplied for a function. For example:
 
@@ -1098,6 +1138,13 @@ impl Baz for Bar { } // Note: This is OK
 [RFC 255]: https://github.com/rust-lang/rfcs/pull/255
 "##,
 
+E0379: r##"
+Trait methods cannot be declared `const` by design. For more information, see
+[RFC 911].
+
+[RFC 911]: https://github.com/rust-lang/rfcs/pull/911
+"##,
+
 E0380: r##"
 Default impls are only allowed for traits with no methods or associated items.
 For more information see the [opt-in builtin traits RFC](https://github.com/rust
@@ -1113,7 +1160,6 @@ impl Baz for Bar { } // Note: This is OK
     E0034, // multiple applicable methods in scope
     E0035, // does not take type parameters
     E0036, // incorrect number of type parameters given for this method
-    E0040, // explicit use of destructor method
     E0044, // foreign items may not have type parameters
     E0045, // variadic function must have C calling convention
     E0057, // method has an incompatible type for trait
@@ -1128,7 +1174,6 @@ impl Baz for Bar { } // Note: This is OK
     E0077,
     E0085,
     E0086,
-    E0087,
     E0088,
     E0090,
     E0091,
@@ -1235,7 +1280,6 @@ impl Baz for Bar { } // Note: This is OK
            // between structures
     E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
            // between structures with the same definition
-    E0379,  // trait fns cannot be const
     E0390, // only a single inherent implementation marked with
            // `#[lang = \"{}\"]` is allowed for the `{}` primitive
     E0391, // unsupported cyclic reference between types/traits detected

src/test/compile-fail/static-mut-not-constant.rs

@@ -12,6 +12,6 @@
 
 static mut a: Box<isize> = box 3;
 //~^ ERROR allocations are not allowed in statics
-//~^^ ERROR mutable statics are not allowed to have owned pointers
+//~^^ ERROR mutable statics are not allowed to have boxes
 
 fn main() {}