Snap cfgs

[rust.git] / src / librustc_typeck / error_codes.rs

// ignore-tidy-filelength

syntax::register_diagnostics! {

E0023: r##"
A pattern attempted to extract an incorrect number of fields from a variant.

Erroneous code example:

```
enum Fruit {
    Apple(String, String),
    Pear(u32),
}
```

A pattern used to match against an enum variant must provide a sub-pattern for
each field of the enum variant.

Here the `Apple` variant has two fields, and should be matched against like so:

```
enum Fruit {
    Apple(String, String),
    Pear(u32),
}

let x = Fruit::Apple(String::new(), String::new());

// Correct.
match x {
    Fruit::Apple(a, b) => {},
    _ => {}
}
```

Matching with the wrong number of fields has no sensible interpretation:

```compile_fail,E0023
enum Fruit {
    Apple(String, String),
    Pear(u32),
}

let x = Fruit::Apple(String::new(), String::new());

// Incorrect.
match x {
    Fruit::Apple(a) => {},
    Fruit::Apple(a, b, c) => {},
}
```

Check how many fields the enum was declared with and ensure that your pattern
uses the same number.
"##,

E0025: r##"
Each field of a struct can only be bound once in a pattern.

Erroneous code example:

```compile_fail,E0025
struct Foo {
    a: u8,
    b: u8,
}

fn main(){
    let x = Foo { a:1, b:2 };

    let Foo { a: x, a: y } = x;
    // error: field `a` bound multiple times in the pattern
}
```

Each occurrence of a field name binds the value of that field, so to fix this
error you will have to remove or alter the duplicate uses of the field name.
Perhaps you misspelled another field name? Example:

```
struct Foo {
    a: u8,
    b: u8,
}

fn main(){
    let x = Foo { a:1, b:2 };

    let Foo { a: x, b: y } = x; // ok!
}
```
"##,

E0026: r##"
A struct pattern attempted to extract a non-existent field from a struct.

Erroneous code example:

```compile_fail,E0026
struct Thing {
    x: u32,
    y: u32,
}

let thing = Thing { x: 0, y: 0 };

match thing {
    Thing { x, z } => {} // error: `Thing::z` field doesn't exist
}
```

If you are using shorthand field patterns but want to refer to the struct field
by a different name, you should rename it explicitly. Struct fields are
identified by the name used before the colon `:` so struct patterns should
resemble the declaration of the struct type being matched.

```
struct Thing {
    x: u32,
    y: u32,
}

let thing = Thing { x: 0, y: 0 };

match thing {
    Thing { x, y: z } => {} // we renamed `y` to `z`
}
```
"##,

E0027: r##"
A pattern for a struct fails to specify a sub-pattern for every one of the
struct's fields.

Erroneous code example:

```compile_fail,E0027
struct Dog {
    name: String,
    age: u32,
}

let d = Dog { name: "Rusty".to_string(), age: 8 };

// This is incorrect.
match d {
    Dog { age: x } => {}
}
```

To fix this error, ensure that each field from the struct's definition is
mentioned in the pattern, or use `..` to ignore unwanted fields. Example:

```
struct Dog {
    name: String,
    age: u32,
}

let d = Dog { name: "Rusty".to_string(), age: 8 };

match d {
    Dog { name: ref n, age: x } => {}
}

// This is also correct (ignore unused fields).
match d {
    Dog { age: x, .. } => {}
}
```
"##,

E0029: r##"
Something other than numbers and characters has been used for a range.

Erroneous code example:

```compile_fail,E0029
let string = "salutations !";

// The ordering relation for strings cannot be evaluated at compile time,
// so this doesn't work:
match string {
    "hello" ..= "world" => {}
    _ => {}
}

// This is a more general version, using a guard:
match string {
    s if s >= "hello" && s <= "world" => {}
    _ => {}
}
```

In a match expression, only numbers and characters can be matched against a
range. This is because the compiler checks that the range is non-empty at
compile-time, and is unable to evaluate arbitrary comparison functions. If you
want to capture values of an orderable type between two end-points, you can use
a guard.
"##,

E0033: r##"
A trait type has been dereferenced.

Erroneous code example:

```compile_fail,E0033
# trait SomeTrait { fn method_one(&self){} fn method_two(&self){} }
# impl<T> SomeTrait for T {}
let trait_obj: &SomeTrait = &"some_value";

// This tries to implicitly dereference to create an unsized local variable.
let &invalid = trait_obj;

// You can call methods without binding to the value being pointed at.
trait_obj.method_one();
trait_obj.method_two();
```

A pointer to a trait type cannot be implicitly dereferenced by a pattern. Every
trait defines a type, but because the size of trait implementers isn't fixed,
this type has no compile-time size. Therefore, all accesses to trait types must
be through pointers. If you encounter this error you should try to avoid
dereferencing the pointer.

You can read more about trait objects in the [Trait Objects] section of the
Reference.

[Trait Objects]: https://doc.rust-lang.org/reference/types.html#trait-objects
"##,

E0034: r##"
The compiler doesn't know what method to call because more than one method
has the same prototype.

Erroneous code example:

```compile_fail,E0034
struct Test;

trait Trait1 {
    fn foo();
}

trait Trait2 {
    fn foo();
}

impl Trait1 for Test { fn foo() {} }
impl Trait2 for Test { fn foo() {} }

fn main() {
    Test::foo() // error, which foo() to call?
}
```

To avoid this error, you have to keep only one of them and remove the others.
So let's take our example and fix it:

```
struct Test;

trait Trait1 {
    fn foo();
}

impl Trait1 for Test { fn foo() {} }

fn main() {
    Test::foo() // and now that's good!
}
```

However, a better solution would be using fully explicit naming of type and
trait:

```
struct Test;

trait Trait1 {
    fn foo();
}

trait Trait2 {
    fn foo();
}

impl Trait1 for Test { fn foo() {} }
impl Trait2 for Test { fn foo() {} }

fn main() {
    <Test as Trait1>::foo()
}
```

One last example:

```
trait F {
    fn m(&self);
}

trait G {
    fn m(&self);
}

struct X;

impl F for X { fn m(&self) { println!("I am F"); } }
impl G for X { fn m(&self) { println!("I am G"); } }

fn main() {
    let f = X;

    F::m(&f); // it displays "I am F"
    G::m(&f); // it displays "I am G"
}
```
"##,

E0040: r##"
It is not allowed to manually call destructors in Rust.

Erroneous code example:

```compile_fail,E0040
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
}
```

It is unnecessary to do this since `drop` is called automatically whenever a
value goes out of scope. However, if you really need to drop a value by hand,
you can use the `std::mem::drop` function:

```
struct Foo {
    x: i32,
}

impl Drop for Foo {
    fn drop(&mut self) {
        println!("kaboom");
    }
}

fn main() {
    let mut x = Foo { x: -7 };
    drop(x); // ok!
}
```
"##,

E0044: r##"
You cannot use type or const parameters on foreign items.

Erroneous code example:

```compile_fail,E0044
extern { fn some_func<T>(x: T); }
```

To fix this, replace the generic parameter with the specializations that you
need:

```
extern { fn some_func_i32(x: i32); }
extern { fn some_func_i64(x: i64); }
```
"##,

E0045: r##"
Variadic parameters have been used on a non-C ABI function.

Erroneous code example:

```compile_fail,E0045
#![feature(unboxed_closures)]

extern "rust-call" {
    fn foo(x: u8, ...); // error!
}
```

Rust only supports variadic parameters for interoperability with C code in its
FFI. As such, variadic parameters can only be used with functions which are
using the C ABI. To fix such code, put them in an extern "C" block:

```
extern "C" {
    fn foo (x: u8, ...);
}
```
"##,

E0046: r##"
Items are missing in a trait implementation.

Erroneous code example:

```compile_fail,E0046
trait Foo {
    fn foo();
}

struct Bar;

impl Foo for Bar {}
// error: not all trait items implemented, missing: `foo`
```

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
methods that do not have default implementations), as well as any required
trait items like associated types or constants. Example:

```
trait Foo {
    fn foo();
}

struct Bar;

impl Foo for Bar {
    fn foo() {} // ok!
}
```
"##,

E0049: r##"
An attempted implementation of a trait method has the wrong number of type or
const parameters.

Erroneous code example:

```compile_fail,E0049
trait Foo {
    fn foo<T: Default>(x: T) -> Self;
}

struct Bar;

// error: method `foo` has 0 type parameters but its trait declaration has 1
// type parameter
impl Foo for Bar {
    fn foo(x: bool) -> Self { Bar }
}
```

For example, the `Foo` trait has a method `foo` with a type parameter `T`,
but the implementation of `foo` for the type `Bar` is missing this parameter.
To fix this error, they must have the same type parameters:

```
trait Foo {
    fn foo<T: Default>(x: T) -> Self;
}

struct Bar;

impl Foo for Bar {
    fn foo<T: Default>(x: T) -> Self { // ok!
        Bar
    }
}
```
"##,

E0050: r##"
An attempted implementation of a trait method has the wrong number of function
parameters.

Erroneous code example:

```compile_fail,E0050
trait Foo {
    fn foo(&self, x: u8) -> bool;
}

struct Bar;

// error: method `foo` has 1 parameter but the declaration in trait `Foo::foo`
// has 2
impl Foo for Bar {
    fn foo(&self) -> bool { true }
}
```

For example, the `Foo` trait has a method `foo` with two function parameters
(`&self` and `u8`), but the implementation of `foo` for the type `Bar` omits
the `u8` parameter. To fix this error, they must have the same parameters:

```
trait Foo {
    fn foo(&self, x: u8) -> bool;
}

struct Bar;

impl Foo for Bar {
    fn foo(&self, x: u8) -> bool { // ok!
        true
    }
}
```
"##,

E0053: r##"
The parameters of any trait method must match between a trait implementation
and the trait definition.

Erroneous code example:

```compile_fail,E0053
trait Foo {
    fn foo(x: u16);
    fn bar(&self);
}

struct Bar;

impl Foo for Bar {
    // error, expected u16, found i16
    fn foo(x: i16) { }

    // error, types differ in mutability
    fn bar(&mut self) { }
}
```
"##,

E0054: r##"
It is not allowed to cast to a bool.

Erroneous code example:

```compile_fail,E0054
let x = 5;

// Not allowed, won't compile
let x_is_nonzero = x as bool;
```

If you are trying to cast a numeric type to a bool, you can compare it with
zero instead:

```
let x = 5;

// Ok
let x_is_nonzero = x != 0;
```
"##,

E0055: r##"
During a method call, a value is automatically dereferenced as many times as
needed to make the value's type match the method's receiver. The catch is that
the compiler will only attempt to dereference a number of times up to the
recursion limit (which can be set via the `recursion_limit` attribute).

For a somewhat artificial example:

```compile_fail,E0055
#![recursion_limit="5"]

struct Foo;

impl Foo {
    fn foo(&self) {}
}

fn main() {
    let foo = Foo;
    let ref_foo = &&&&&Foo;

    // error, reached the recursion limit while auto-dereferencing `&&&&&Foo`
    ref_foo.foo();
}
```

One fix may be to increase the recursion limit. Note that it is possible to
create an infinite recursion of dereferencing, in which case the only fix is to
somehow break the recursion.
"##,

E0057: r##"
When invoking closures or other implementations of the function traits `Fn`,
`FnMut` or `FnOnce` using call notation, the number of parameters passed to the
function must match its definition.

An example using a closure:

```compile_fail,E0057
let f = |x| x * 3;
let a = f();        // invalid, too few parameters
let b = f(4);       // this works!
let c = f(2, 3);    // invalid, too many parameters
```

A generic function must be treated similarly:

```
fn foo<F: Fn()>(f: F) {
    f(); // this is valid, but f(3) would not work
}
```
"##,

E0059: r##"
The built-in function traits are generic over a tuple of the function arguments.
If one uses angle-bracket notation (`Fn<(T,), Output=U>`) instead of parentheses
(`Fn(T) -> U`) to denote the function trait, the type parameter should be a
tuple. Otherwise function call notation cannot be used and the trait will not be
implemented by closures.

The most likely source of this error is using angle-bracket notation without
wrapping the function argument type into a tuple, for example:

```compile_fail,E0059
#![feature(unboxed_closures)]

fn foo<F: Fn<i32>>(f: F) -> F::Output { f(3) }
```

It can be fixed by adjusting the trait bound like this:

```
#![feature(unboxed_closures)]

fn foo<F: Fn<(i32,)>>(f: F) -> F::Output { f(3) }
```

Note that `(T,)` always denotes the type of a 1-tuple containing an element of
type `T`. The comma is necessary for syntactic disambiguation.
"##,

E0060: r##"
External C functions are allowed to be variadic. However, a variadic function
takes a minimum number of arguments. For example, consider C's variadic `printf`
function:

```
use std::os::raw::{c_char, c_int};

extern "C" {
    fn printf(_: *const c_char, ...) -> c_int;
}
```

Using this declaration, it must be called with at least one argument, so
simply calling `printf()` is invalid. But the following uses are allowed:

```
# #![feature(static_nobundle)]
# use std::os::raw::{c_char, c_int};
# #[cfg_attr(all(windows, target_env = "msvc"),
#            link(name = "legacy_stdio_definitions", kind = "static-nobundle"))]
# extern "C" { fn printf(_: *const c_char, ...) -> c_int; }
# fn main() {
unsafe {
    use std::ffi::CString;

    let fmt = CString::new("test\n").unwrap();
    printf(fmt.as_ptr());

    let fmt = CString::new("number = %d\n").unwrap();
    printf(fmt.as_ptr(), 3);

    let fmt = CString::new("%d, %d\n").unwrap();
    printf(fmt.as_ptr(), 10, 5);
}
# }
```
"##,
// ^ Note: On MSVC 2015, the `printf` function is "inlined" in the C code, and
// the C runtime does not contain the `printf` definition. This leads to linker
// error from the doc test (issue #42830).
// This can be fixed by linking to the static library
// `legacy_stdio_definitions.lib` (see https://stackoverflow.com/a/36504365/).
// If this compatibility library is removed in the future, consider changing
// `printf` in this example to another well-known variadic function.

E0061: r##"
The number of arguments passed to a function must match the number of arguments
specified in the function signature.

For example, a function like:

```
fn f(a: u16, b: &str) {}
```

Must always be called with exactly two arguments, e.g., `f(2, "test")`.

Note that Rust does not have a notion of optional function arguments or
variadic functions (except for its C-FFI).
"##,

E0062: r##"
This error indicates that during an attempt to build a struct or struct-like
enum variant, one of the fields was specified more than once. Erroneous code
example:

```compile_fail,E0062
struct Foo {
    x: i32,
}

fn main() {
    let x = Foo {
                x: 0,
                x: 0, // error: field `x` specified more than once
            };
}
```

Each field should be specified exactly one time. Example:

```
struct Foo {
    x: i32,
}

fn main() {
    let x = Foo { x: 0 }; // ok!
}
```
"##,

E0063: r##"
This error indicates that during an attempt to build a struct or struct-like
enum variant, one of the fields was not provided. Erroneous code example:

```compile_fail,E0063
struct Foo {
    x: i32,
    y: i32,
}

fn main() {
    let x = Foo { x: 0 }; // error: missing field: `y`
}
```

Each field should be specified exactly once. Example:

```
struct Foo {
    x: i32,
    y: i32,
}

fn main() {
    let x = Foo { x: 0, y: 0 }; // ok!
}
```
"##,

E0067: r##"
The left-hand side of a compound assignment expression must be a place
expression. A place expression represents a memory location and includes
item paths (ie, namespaced variables), dereferences, indexing expressions,
and field references.

Let's start with some erroneous code examples:

```compile_fail,E0067
use std::collections::LinkedList;

// Bad: assignment to non-place expression
LinkedList::new() += 1;

// ...

fn some_func(i: &mut i32) {
    i += 12; // Error : '+=' operation cannot be applied on a reference !
}
```

And now some working examples:

```
let mut i : i32 = 0;

i += 12; // Good !

// ...

fn some_func(i: &mut i32) {
    *i += 12; // Good !
}
```
"##,

E0069: r##"
The compiler found a function whose body contains a `return;` statement but
whose return type is not `()`. An example of this is:

```compile_fail,E0069
// error
fn foo() -> u8 {
    return;
}
```

Since `return;` is just like `return ();`, there is a mismatch between the
function's return type and the value being returned.
"##,

E0070: r##"
The left-hand side of an assignment operator must be a place expression. A
place expression represents a memory location and can be a variable (with
optional namespacing), a dereference, an indexing expression or a field
reference.

More details can be found in the [Expressions] section of the Reference.

[Expressions]: https://doc.rust-lang.org/reference/expressions.html#places-rvalues-and-temporaries

Now, we can go further. Here are some erroneous code examples:

```compile_fail,E0070
struct SomeStruct {
    x: i32,
    y: i32
}

const SOME_CONST : i32 = 12;

fn some_other_func() {}

fn some_function() {
    SOME_CONST = 14; // error : a constant value cannot be changed!
    1 = 3; // error : 1 isn't a valid place!
    some_other_func() = 4; // error : we cannot assign value to a function!
    SomeStruct.x = 12; // error : SomeStruct a structure name but it is used
                       // like a variable!
}
```

And now let's give working examples:

```
struct SomeStruct {
    x: i32,
    y: i32
}
let mut s = SomeStruct {x: 0, y: 0};

s.x = 3; // that's good !

// ...

fn some_func(x: &mut i32) {
    *x = 12; // that's good !
}
```
"##,

E0071: r##"
You tried to use structure-literal syntax to create an item that is
not a structure or enum variant.

Example of erroneous code:

```compile_fail,E0071
type U32 = u32;
let t = U32 { value: 4 }; // error: expected struct, variant or union type,
                          // found builtin type `u32`
```

To fix this, ensure that the name was correctly spelled, and that
the correct form of initializer was used.

For example, the code above can be fixed to:

```
enum Foo {
    FirstValue(i32)
}

fn main() {
    let u = Foo::FirstValue(0i32);

    let t = 4;
}
```
"##,

E0073: r##"
#### Note: this error code is no longer emitted by the compiler.

You cannot define a struct (or enum) `Foo` that requires an instance of `Foo`
in order to make a new `Foo` value. This is because there would be no way a
first instance of `Foo` could be made to initialize another instance!

Here's an example of a struct that has this problem:

```
struct Foo { x: Box<Foo> } // error
```

One fix is to use `Option`, like so:

```
struct Foo { x: Option<Box<Foo>> }
```

Now it's possible to create at least one instance of `Foo`: `Foo { x: None }`.
"##,

E0074: r##"
#### Note: this error code is no longer emitted by the compiler.

When using the `#[simd]` attribute on a tuple struct, the components of the
tuple struct must all be of a concrete, nongeneric type so the compiler can
reason about how to use SIMD with them. This error will occur if the types
are generic.

This will cause an error:

```
#![feature(repr_simd)]

#[repr(simd)]
struct Bad<T>(T, T, T);
```

This will not:

```
#![feature(repr_simd)]

#[repr(simd)]
struct Good(u32, u32, u32);
```
"##,

E0075: r##"
The `#[simd]` attribute can only be applied to non empty tuple structs, because
it doesn't make sense to try to use SIMD operations when there are no values to
operate on.

This will cause an error:

```compile_fail,E0075
#![feature(repr_simd)]

#[repr(simd)]
struct Bad;
```

This will not:

```
#![feature(repr_simd)]

#[repr(simd)]
struct Good(u32);
```
"##,

E0076: r##"
When using the `#[simd]` attribute to automatically use SIMD operations in tuple
struct, the types in the struct must all be of the same type, or the compiler
will trigger this error.

This will cause an error:

```compile_fail,E0076
#![feature(repr_simd)]

#[repr(simd)]
struct Bad(u16, u32, u32);
```

This will not:

```
#![feature(repr_simd)]

#[repr(simd)]
struct Good(u32, u32, u32);
```
"##,

E0077: r##"
When using the `#[simd]` attribute on a tuple struct, the elements in the tuple
must be machine types so SIMD operations can be applied to them.

This will cause an error:

```compile_fail,E0077
#![feature(repr_simd)]

#[repr(simd)]
struct Bad(String);
```

This will not:

```
#![feature(repr_simd)]

#[repr(simd)]
struct Good(u32, u32, u32);
```
"##,

E0081: r##"
Enum discriminants are used to differentiate enum variants stored in memory.
This error indicates that the same value was used for two or more variants,
making them impossible to tell apart.

```compile_fail,E0081
// Bad.
enum Enum {
    P = 3,
    X = 3,
    Y = 5,
}
```

```
// Good.
enum Enum {
    P,
    X = 3,
    Y = 5,
}
```

Note that variants without a manually specified discriminant are numbered from
top to bottom starting from 0, so clashes can occur with seemingly unrelated
variants.

```compile_fail,E0081
enum Bad {
    X,
    Y = 0
}
```

Here `X` will have already been specified the discriminant 0 by the time `Y` is
encountered, so a conflict occurs.
"##,

E0084: r##"
An unsupported representation was attempted on a zero-variant enum.

Erroneous code example:

```compile_fail,E0084
#[repr(i32)]
enum NightsWatch {} // error: unsupported representation for zero-variant enum
```

It is impossible to define an integer type to be used to represent zero-variant
enum values because there are no zero-variant enum values. There is no way to
construct an instance of the following type using only safe code. So you have
two solutions. Either you add variants in your enum:

```
#[repr(i32)]
enum NightsWatch {
    JonSnow,
    Commander,
}
```

or you remove the integer represention of your enum:

```
enum NightsWatch {}
```
"##,

// FIXME(const_generics:docs): example of inferring const parameter.
E0087: r##"
#### Note: this error code is no longer emitted by the compiler.

Too many type arguments were supplied for a function. For example:

```compile_fail,E0107
fn foo<T>() {}

fn main() {
    foo::<f64, bool>(); // error: wrong number of type arguments:
                        //        expected 1, found 2
}
```

The number of supplied arguments must exactly match the number of defined type
parameters.
"##,

E0088: r##"
#### Note: this error code is no longer emitted by the compiler.

You gave too many lifetime arguments. Erroneous code example:

```compile_fail,E0107
fn f() {}

fn main() {
    f::<'static>() // error: wrong number of lifetime arguments:
                   //        expected 0, found 1
}
```

Please check you give the right number of lifetime arguments. Example:

```
fn f() {}

fn main() {
    f() // ok!
}
```

It's also important to note that the Rust compiler can generally
determine the lifetime by itself. Example:

```
struct Foo {
    value: String
}

impl Foo {
    // it can be written like this
    fn get_value<'a>(&'a self) -> &'a str { &self.value }
    // but the compiler works fine with this too:
    fn without_lifetime(&self) -> &str { &self.value }
}

fn main() {
    let f = Foo { value: "hello".to_owned() };

    println!("{}", f.get_value());
    println!("{}", f.without_lifetime());
}
```
"##,

E0089: r##"
#### Note: this error code is no longer emitted by the compiler.

Too few type arguments were supplied for a function. For example:

```compile_fail,E0107
fn foo<T, U>() {}

fn main() {
    foo::<f64>(); // error: wrong number of type arguments: expected 2, found 1
}
```

Note that if a function takes multiple type arguments but you want the compiler
to infer some of them, you can use type placeholders:

```compile_fail,E0107
fn foo<T, U>(x: T) {}

fn main() {
    let x: bool = true;
    foo::<f64>(x);    // error: wrong number of type arguments:
                      //        expected 2, found 1
    foo::<_, f64>(x); // same as `foo::<bool, f64>(x)`
}
```
"##,

E0090: r##"
#### Note: this error code is no longer emitted by the compiler.

You gave too few lifetime arguments. Example:

```compile_fail,E0107
fn foo<'a: 'b, 'b: 'a>() {}

fn main() {
    foo::<'static>(); // error: wrong number of lifetime arguments:
                      //        expected 2, found 1
}
```

Please check you give the right number of lifetime arguments. Example:

```
fn foo<'a: 'b, 'b: 'a>() {}

fn main() {
    foo::<'static, 'static>();
}
```
"##,

E0091: r##"
You gave an unnecessary type or const parameter in a type alias. Erroneous
code example:

```compile_fail,E0091
type Foo<T> = u32; // error: type parameter `T` is unused
// or:
type Foo<A,B> = Box<A>; // error: type parameter `B` is unused
```

Please check you didn't write too many parameters. Example:

```
type Foo = u32; // ok!
type Foo2<A> = Box<A>; // ok!
```
"##,

E0092: r##"
You tried to declare an undefined atomic operation function.
Erroneous code example:

```compile_fail,E0092
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn atomic_foo(); // error: unrecognized atomic operation
                     //        function
}
```

Please check you didn't make a mistake in the function's name. All intrinsic
functions are defined in librustc_codegen_llvm/intrinsic.rs and in
libcore/intrinsics.rs in the Rust source code. Example:

```
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn atomic_fence(); // ok!
}
```
"##,

E0093: r##"
You declared an unknown intrinsic function. Erroneous code example:

```compile_fail,E0093
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn foo(); // error: unrecognized intrinsic function: `foo`
}

fn main() {
    unsafe {
        foo();
    }
}
```

Please check you didn't make a mistake in the function's name. All intrinsic
functions are defined in librustc_codegen_llvm/intrinsic.rs and in
libcore/intrinsics.rs in the Rust source code. Example:

```
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn atomic_fence(); // ok!
}

fn main() {
    unsafe {
        atomic_fence();
    }
}
```
"##,

E0094: r##"
You gave an invalid number of type parameters to an intrinsic function.
Erroneous code example:

```compile_fail,E0094
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn size_of<T, U>() -> usize; // error: intrinsic has wrong number
                                 //        of type parameters
}
```

Please check that you provided the right number of type parameters
and verify with the function declaration in the Rust source code.
Example:

```
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn size_of<T>() -> usize; // ok!
}
```
"##,

E0107: r##"
This error means that an incorrect number of generic arguments were provided:

```compile_fail,E0107
struct Foo<T> { x: T }

struct Bar { x: Foo }             // error: wrong number of type arguments:
                                  //        expected 1, found 0
struct Baz<S, T> { x: Foo<S, T> } // error: wrong number of type arguments:
                                  //        expected 1, found 2

fn foo<T, U>(x: T, y: U) {}

fn main() {
    let x: bool = true;
    foo::<bool>(x);                 // error: wrong number of type arguments:
                                    //        expected 2, found 1
    foo::<bool, i32, i32>(x, 2, 4); // error: wrong number of type arguments:
                                    //        expected 2, found 3
}

fn f() {}

fn main() {
    f::<'static>(); // error: wrong number of lifetime arguments:
                    //        expected 0, found 1
}
```

"##,

E0109: r##"
You tried to provide a generic argument to a type which doesn't need it.
Erroneous code example:

```compile_fail,E0109
type X = u32<i32>; // error: type arguments are not allowed for this type
type Y = bool<'static>; // error: lifetime parameters are not allowed on
                        //        this type
```

Check that you used the correct argument and that the definition is correct.

Example:

```
type X = u32; // ok!
type Y = bool; // ok!
```

Note that generic arguments for enum variant constructors go after the variant,
not after the enum. For example, you would write `Option::None::<u32>`,
rather than `Option::<u32>::None`.
"##,

E0110: r##"
#### Note: this error code is no longer emitted by the compiler.

You tried to provide a lifetime to a type which doesn't need it.
See `E0109` for more details.
"##,

E0116: r##"
You can only define an inherent implementation for a type in the same crate
where the type was defined. For example, an `impl` block as below is not allowed
since `Vec` is defined in the standard library:

```compile_fail,E0116
impl Vec<u8> { } // error
```

To fix this problem, you can do either of these things:

 - define a trait that has the desired associated functions/types/constants and
   implement the trait for the type in question
 - define a new type wrapping the type and define an implementation on the new
   type

Note that using the `type` keyword does not work here because `type` only
introduces a type alias:

```compile_fail,E0116
type Bytes = Vec<u8>;

impl Bytes { } // error, same as above
```
"##,

E0117: r##"
This error indicates a violation of one of Rust's orphan rules for trait
implementations. The rule prohibits any implementation of a foreign trait (a
trait defined in another crate) where

 - the type that is implementing the trait is foreign
 - all of the parameters being passed to the trait (if there are any) are also
   foreign.

Here's one example of this error:

```compile_fail,E0117
impl Drop for u32 {}
```

To avoid this kind of error, ensure that at least one local type is referenced
by the `impl`:

```
pub struct Foo; // you define your type in your crate

impl Drop for Foo { // and you can implement the trait on it!
    // code of trait implementation here
#   fn drop(&mut self) { }
}

impl From<Foo> for i32 { // or you use a type from your crate as
                         // a type parameter
    fn from(i: Foo) -> i32 {
        0
    }
}
```

Alternatively, define a trait locally and implement that instead:

```
trait Bar {
    fn get(&self) -> usize;
}

impl Bar for u32 {
    fn get(&self) -> usize { 0 }
}
```

For information on the design of the orphan rules, see [RFC 1023].

[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md
"##,

E0118: r##"
You're trying to write an inherent implementation for something which isn't a
struct nor an enum. Erroneous code example:

```compile_fail,E0118
impl (u8, u8) { // error: no base type found for inherent implementation
    fn get_state(&self) -> String {
        // ...
    }
}
```

To fix this error, please implement a trait on the type or wrap it in a struct.
Example:

```
// we create a trait here
trait LiveLongAndProsper {
    fn get_state(&self) -> String;
}

// and now you can implement it on (u8, u8)
impl LiveLongAndProsper for (u8, u8) {
    fn get_state(&self) -> String {
        "He's dead, Jim!".to_owned()
    }
}
```

Alternatively, you can create a newtype. A newtype is a wrapping tuple-struct.
For example, `NewType` is a newtype over `Foo` in `struct NewType(Foo)`.
Example:

```
struct TypeWrapper((u8, u8));

impl TypeWrapper {
    fn get_state(&self) -> String {
        "Fascinating!".to_owned()
    }
}
```
"##,

E0120: r##"
An attempt was made to implement Drop on a trait, which is not allowed: only
structs and enums can implement Drop. An example causing this error:

```compile_fail,E0120
trait MyTrait {}

impl Drop for MyTrait {
    fn drop(&mut self) {}
}
```

A workaround for this problem is to wrap the trait up in a struct, and implement
Drop on that. An example is shown below:

```
trait MyTrait {}
struct MyWrapper<T: MyTrait> { foo: T }

impl <T: MyTrait> Drop for MyWrapper<T> {
    fn drop(&mut self) {}
}

```

Alternatively, wrapping trait objects requires something like the following:

```
trait MyTrait {}

//or Box<MyTrait>, if you wanted an owned trait object
struct MyWrapper<'a> { foo: &'a MyTrait }

impl <'a> Drop for MyWrapper<'a> {
    fn drop(&mut self) {}
}
```
"##,

E0121: r##"
In order to be consistent with Rust's lack of global type inference,
type and const placeholders are disallowed by design in item signatures.

Examples of this error include:

```compile_fail,E0121
fn foo() -> _ { 5 } // error, explicitly write out the return type instead

static BAR: _ = "test"; // error, explicitly write out the type instead
```
"##,

E0124: r##"
You declared two fields of a struct with the same name. Erroneous code
example:

```compile_fail,E0124
struct Foo {
    field1: i32,
    field1: i32, // error: field is already declared
}
```

Please verify that the field names have been correctly spelled. Example:

```
struct Foo {
    field1: i32,
    field2: i32, // ok!
}
```
"##,

E0131: r##"
It is not possible to define `main` with generic parameters.
When `main` is present, it must take no arguments and return `()`.
Erroneous code example:

```compile_fail,E0131
fn main<T>() { // error: main function is not allowed to have generic parameters
}
```
"##,

E0132: r##"
A function with the `start` attribute was declared with type parameters.

Erroneous code example:

```compile_fail,E0132
#![feature(start)]

#[start]
fn f<T>() {}
```

It is not possible to declare type parameters on a function that has the `start`
attribute. Such a function must have the following type signature (for more
information, view [the unstable book][1]):

[1]: https://doc.rust-lang.org/unstable-book/language-features/lang-items.html#writing-an-executable-without-stdlib

```
# let _:
fn(isize, *const *const u8) -> isize;
```

Example:

```
#![feature(start)]

#[start]
fn my_start(argc: isize, argv: *const *const u8) -> isize {
    0
}
```
"##,

E0164: r##"
This error means that an attempt was made to match a struct type enum
variant as a non-struct type:

```compile_fail,E0164
enum Foo { B { i: u32 } }

fn bar(foo: Foo) -> u32 {
    match foo {
        Foo::B(i) => i, // error E0164
    }
}
```

Try using `{}` instead:

```
enum Foo { B { i: u32 } }

fn bar(foo: Foo) -> u32 {
    match foo {
        Foo::B{i} => i,
    }
}
```
"##,

E0184: r##"
Explicitly implementing both Drop and Copy for a type is currently disallowed.
This feature can make some sense in theory, but the current implementation is
incorrect and can lead to memory unsafety (see [issue #20126][iss20126]), so
it has been disabled for now.

[iss20126]: https://github.com/rust-lang/rust/issues/20126
"##,

E0185: r##"
An associated function for a trait was defined to be static, but an
implementation of the trait declared the same function to be a method (i.e., to
take a `self` parameter).

Here's an example of this error:

```compile_fail,E0185
trait Foo {
    fn foo();
}

struct Bar;

impl Foo for Bar {
    // error, method `foo` has a `&self` declaration in the impl, but not in
    // the trait
    fn foo(&self) {}
}
```
"##,

E0186: r##"
An associated function for a trait was defined to be a method (i.e., to take a
`self` parameter), but an implementation of the trait declared the same function
to be static.

Here's an example of this error:

```compile_fail,E0186
trait Foo {
    fn foo(&self);
}

struct Bar;

impl Foo for Bar {
    // error, method `foo` has a `&self` declaration in the trait, but not in
    // the impl
    fn foo() {}
}
```
"##,

E0191: r##"
Trait objects need to have all associated types specified. Erroneous code
example:

```compile_fail,E0191
trait Trait {
    type Bar;
}

type Foo = Trait; // error: the value of the associated type `Bar` (from
                  //        the trait `Trait`) must be specified
```

Please verify you specified all associated types of the trait and that you
used the right trait. Example:

```
trait Trait {
    type Bar;
}

type Foo = Trait<Bar=i32>; // ok!
```
"##,

E0192: r##"
Negative impls are only allowed for auto traits. For more
information see the [opt-in builtin traits RFC][RFC 19].

[RFC 19]: https://github.com/rust-lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md
"##,

E0193: r##"
#### Note: this error code is no longer emitted by the compiler.

`where` clauses must use generic type parameters: it does not make sense to use
them otherwise. An example causing this error:

```
trait Foo {
    fn bar(&self);
}

#[derive(Copy,Clone)]
struct Wrapper<T> {
    Wrapped: T
}

impl Foo for Wrapper<u32> where Wrapper<u32>: Clone {
    fn bar(&self) { }
}
```

This use of a `where` clause is strange - a more common usage would look
something like the following:

```
trait Foo {
    fn bar(&self);
}

#[derive(Copy,Clone)]
struct Wrapper<T> {
    Wrapped: T
}
impl <T> Foo for Wrapper<T> where Wrapper<T>: Clone {
    fn bar(&self) { }
}
```

Here, we're saying that the implementation exists on Wrapper only when the
wrapped type `T` implements `Clone`. The `where` clause is important because
some types will not implement `Clone`, and thus will not get this method.

In our erroneous example, however, we're referencing a single concrete type.
Since we know for certain that `Wrapper<u32>` implements `Clone`, there's no
reason to also specify it in a `where` clause.
"##,

E0195: r##"
Your method's lifetime parameters do not match the trait declaration.
Erroneous code example:

```compile_fail,E0195
trait Trait {
    fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
}

struct Foo;

impl Trait for Foo {
    fn bar<'a,'b>(x: &'a str, y: &'b str) {
    // error: lifetime parameters or bounds on method `bar`
    // do not match the trait declaration
    }
}
```

The lifetime constraint `'b` for bar() implementation does not match the
trait declaration. Ensure lifetime declarations match exactly in both trait
declaration and implementation. Example:

```
trait Trait {
    fn t<'a,'b:'a>(x: &'a str, y: &'b str);
}

struct Foo;

impl Trait for Foo {
    fn t<'a,'b:'a>(x: &'a str, y: &'b str) { // ok!
    }
}
```
"##,

E0199: r##"
Safe traits should not have unsafe implementations, therefore marking an
implementation for a safe trait unsafe will cause a compiler error. Removing
the unsafe marker on the trait noted in the error will resolve this problem.

```compile_fail,E0199
struct Foo;

trait Bar { }

// this won't compile because Bar is safe
unsafe impl Bar for Foo { }
// this will compile
impl Bar for Foo { }
```
"##,

E0200: r##"
Unsafe traits must have unsafe implementations. This error occurs when an
implementation for an unsafe trait isn't marked as unsafe. This may be resolved
by marking the unsafe implementation as unsafe.

```compile_fail,E0200
struct Foo;

unsafe trait Bar { }

// this won't compile because Bar is unsafe and impl isn't unsafe
impl Bar for Foo { }
// this will compile
unsafe impl Bar for Foo { }
```
"##,

E0201: r##"
It is an error to define two associated items (like methods, associated types,
associated functions, etc.) with the same identifier.

For example:

```compile_fail,E0201
struct Foo(u8);

impl Foo {
    fn bar(&self) -> bool { self.0 > 5 }
    fn bar() {} // error: duplicate associated function
}

trait Baz {
    type Quux;
    fn baz(&self) -> bool;
}

impl Baz for Foo {
    type Quux = u32;

    fn baz(&self) -> bool { true }

    // error: duplicate method
    fn baz(&self) -> bool { self.0 > 5 }

    // error: duplicate associated type
    type Quux = u32;
}
```

Note, however, that items with the same name are allowed for inherent `impl`
blocks that don't overlap:

```
struct Foo<T>(T);

impl Foo<u8> {
    fn bar(&self) -> bool { self.0 > 5 }
}

impl Foo<bool> {
    fn bar(&self) -> bool { self.0 }
}
```
"##,

E0202: r##"
Inherent associated types were part of [RFC 195] but are not yet implemented.
See [the tracking issue][iss8995] for the status of this implementation.

[RFC 195]: https://github.com/rust-lang/rfcs/blob/master/text/0195-associated-items.md
[iss8995]: https://github.com/rust-lang/rust/issues/8995
"##,

E0204: r##"
An attempt to implement the `Copy` trait for a struct failed because one of the
fields does not implement `Copy`. To fix this, you must implement `Copy` for the
mentioned field. Note that this may not be possible, as in the example of

```compile_fail,E0204
struct Foo {
    foo : Vec<u32>,
}

impl Copy for Foo { }
```

This fails because `Vec<T>` does not implement `Copy` for any `T`.

Here's another example that will fail:

```compile_fail,E0204
#[derive(Copy)]
struct Foo<'a> {
    ty: &'a mut bool,
}
```

This fails because `&mut T` is not `Copy`, even when `T` is `Copy` (this
differs from the behavior for `&T`, which is always `Copy`).
"##,

E0205: r##"
#### Note: this error code is no longer emitted by the compiler.

An attempt to implement the `Copy` trait for an enum failed because one of the
variants does not implement `Copy`. To fix this, you must implement `Copy` for
the mentioned variant. Note that this may not be possible, as in the example of

```compile_fail,E0204
enum Foo {
    Bar(Vec<u32>),
    Baz,
}

impl Copy for Foo { }
```

This fails because `Vec<T>` does not implement `Copy` for any `T`.

Here's another example that will fail:

```compile_fail,E0204
#[derive(Copy)]
enum Foo<'a> {
    Bar(&'a mut bool),
    Baz,
}
```

This fails because `&mut T` is not `Copy`, even when `T` is `Copy` (this
differs from the behavior for `&T`, which is always `Copy`).
"##,

E0206: r##"
You can only implement `Copy` for a struct or enum. Both of the following
examples will fail, because neither `[u8; 256]` nor `&'static mut Bar`
(mutable reference to `Bar`) is a struct or enum:

```compile_fail,E0206
type Foo = [u8; 256];
impl Copy for Foo { } // error

#[derive(Copy, Clone)]
struct Bar;
impl Copy for &'static mut Bar { } // error
```
"##,

E0207: r##"
Any type parameter or lifetime parameter of an `impl` must meet at least one of
the following criteria:

 - it appears in the _implementing type_ of the impl, e.g. `impl<T> Foo<T>`
 - for a trait impl, it appears in the _implemented trait_, e.g.
   `impl<T> SomeTrait<T> for Foo`
 - it is bound as an associated type, e.g. `impl<T, U> SomeTrait for T
   where T: AnotherTrait<AssocType=U>`

### Error example 1

Suppose we have a struct `Foo` and we would like to define some methods for it.
The following definition leads to a compiler error:

```compile_fail,E0207
struct Foo;

impl<T: Default> Foo {
// error: the type parameter `T` is not constrained by the impl trait, self
// type, or predicates [E0207]
    fn get(&self) -> T {
        <T as Default>::default()
    }
}
```

The problem is that the parameter `T` does not appear in the implementing type
(`Foo`) of the impl. In this case, we can fix the error by moving the type
parameter from the `impl` to the method `get`:


```
struct Foo;

// Move the type parameter from the impl to the method
impl Foo {
    fn get<T: Default>(&self) -> T {
        <T as Default>::default()
    }
}
```

### Error example 2

As another example, suppose we have a `Maker` trait and want to establish a
type `FooMaker` that makes `Foo`s:

```compile_fail,E0207
trait Maker {
    type Item;
    fn make(&mut self) -> Self::Item;
}

struct Foo<T> {
    foo: T
}

struct FooMaker;

impl<T: Default> Maker for FooMaker {
// error: the type parameter `T` is not constrained by the impl trait, self
// type, or predicates [E0207]
    type Item = Foo<T>;

    fn make(&mut self) -> Foo<T> {
        Foo { foo: <T as Default>::default() }
    }
}
```

This fails to compile because `T` does not appear in the trait or in the
implementing type.

One way to work around this is to introduce a phantom type parameter into
`FooMaker`, like so:

```
use std::marker::PhantomData;

trait Maker {
    type Item;
    fn make(&mut self) -> Self::Item;
}

struct Foo<T> {
    foo: T
}

// Add a type parameter to `FooMaker`
struct FooMaker<T> {
    phantom: PhantomData<T>,
}

impl<T: Default> Maker for FooMaker<T> {
    type Item = Foo<T>;

    fn make(&mut self) -> Foo<T> {
        Foo {
            foo: <T as Default>::default(),
        }
    }
}
```

Another way is to do away with the associated type in `Maker` and use an input
type parameter instead:

```
// Use a type parameter instead of an associated type here
trait Maker<Item> {
    fn make(&mut self) -> Item;
}

struct Foo<T> {
    foo: T
}

struct FooMaker;

impl<T: Default> Maker<Foo<T>> for FooMaker {
    fn make(&mut self) -> Foo<T> {
        Foo { foo: <T as Default>::default() }
    }
}
```

### Additional information

For more information, please see [RFC 447].

[RFC 447]: https://github.com/rust-lang/rfcs/blob/master/text/0447-no-unused-impl-parameters.md
"##,

E0210: r##"
This error indicates a violation of one of Rust's orphan rules for trait
implementations. The rule concerns the use of type parameters in an
implementation of a foreign trait (a trait defined in another crate), and
states that type parameters must be "covered" by a local type. To understand
what this means, it is perhaps easiest to consider a few examples.

If `ForeignTrait` is a trait defined in some external crate `foo`, then the
following trait `impl` is an error:

```compile_fail,E0210
# #[cfg(for_demonstration_only)]
extern crate foo;
# #[cfg(for_demonstration_only)]
use foo::ForeignTrait;
# use std::panic::UnwindSafe as ForeignTrait;

impl<T> ForeignTrait for T { } // error
# fn main() {}
```

To work around this, it can be covered with a local type, `MyType`:

```
# use std::panic::UnwindSafe as ForeignTrait;
struct MyType<T>(T);
impl<T> ForeignTrait for MyType<T> { } // Ok
```

Please note that a type alias is not sufficient.

For another example of an error, suppose there's another trait defined in `foo`
named `ForeignTrait2` that takes two type parameters. Then this `impl` results
in the same rule violation:

```ignore (cannot-doctest-multicrate-project)
struct MyType2;
impl<T> ForeignTrait2<T, MyType<T>> for MyType2 { } // error
```

The reason for this is that there are two appearances of type parameter `T` in
the `impl` header, both as parameters for `ForeignTrait2`. The first appearance
is uncovered, and so runs afoul of the orphan rule.

Consider one more example:

```ignore (cannot-doctest-multicrate-project)
impl<T> ForeignTrait2<MyType<T>, T> for MyType2 { } // Ok
```

This only differs from the previous `impl` in that the parameters `T` and
`MyType<T>` for `ForeignTrait2` have been swapped. This example does *not*
violate the orphan rule; it is permitted.

To see why that last example was allowed, you need to understand the general
rule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:

```ignore (only-for-syntax-highlight)
impl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }
```

where `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`
are types. One of the types `T0, ..., Tn` must be a local type (this is another
orphan rule, see the explanation for E0117). Let `i` be the smallest integer
such that `Ti` is a local type. Then no type parameter can appear in any of the
`Tj` for `j < i`.

For information on the design of the orphan rules, see [RFC 1023].

[RFC 1023]: https://github.com/rust-lang/rfcs/blob/master/text/1023-rebalancing-coherence.md
"##,

E0211: r##"
#### Note: this error code is no longer emitted by the compiler.

You used a function or type which doesn't fit the requirements for where it was
used. Erroneous code examples:

```compile_fail
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn size_of<T>(); // error: intrinsic has wrong type
}

// or:

fn main() -> i32 { 0 }
// error: main function expects type: `fn() {main}`: expected (), found i32

// or:

let x = 1u8;
match x {
    0u8..=3i8 => (),
    // error: mismatched types in range: expected u8, found i8
    _ => ()
}

// or:

use std::rc::Rc;
struct Foo;

impl Foo {
    fn x(self: Rc<Foo>) {}
    // error: mismatched self type: expected `Foo`: expected struct
    //        `Foo`, found struct `alloc::rc::Rc`
}
```

For the first code example, please check the function definition. Example:

```
#![feature(intrinsics)]

extern "rust-intrinsic" {
    fn size_of<T>() -> usize; // ok!
}
```

The second case example is a bit particular: the main function must always
have this definition:

```compile_fail
fn main();
```

They never take parameters and never return types.

For the third example, when you match, all patterns must have the same type
as the type you're matching on. Example:

```
let x = 1u8;

match x {
    0u8..=3u8 => (), // ok!
    _ => ()
}
```

And finally, for the last example, only `Box<Self>`, `&Self`, `Self`,
or `&mut Self` work as explicit self parameters. Example:

```
struct Foo;

impl Foo {
    fn x(self: Box<Foo>) {} // ok!
}
```
"##,

E0220: r##"
You used an associated type which isn't defined in the trait.
Erroneous code example:

```compile_fail,E0220
trait T1 {
    type Bar;
}

type Foo = T1<F=i32>; // error: associated type `F` not found for `T1`

// or:

trait T2 {
    type Bar;

    // error: Baz is used but not declared
    fn return_bool(&self, _: &Self::Bar, _: &Self::Baz) -> bool;
}
```

Make sure that you have defined the associated type in the trait body.
Also, verify that you used the right trait or you didn't misspell the
associated type name. Example:

```
trait T1 {
    type Bar;
}

type Foo = T1<Bar=i32>; // ok!

// or:

trait T2 {
    type Bar;
    type Baz; // we declare `Baz` in our trait.

    // and now we can use it here:
    fn return_bool(&self, _: &Self::Bar, _: &Self::Baz) -> bool;
}
```
"##,

E0221: r##"
An attempt was made to retrieve an associated type, but the type was ambiguous.
For example:

```compile_fail,E0221
trait T1 {}
trait T2 {}

trait Foo {
    type A: T1;
}

trait Bar : Foo {
    type A: T2;
    fn do_something() {
        let _: Self::A;
    }
}
```

In this example, `Foo` defines an associated type `A`. `Bar` inherits that type
from `Foo`, and defines another associated type of the same name. As a result,
when we attempt to use `Self::A`, it's ambiguous whether we mean the `A` defined
by `Foo` or the one defined by `Bar`.

There are two options to work around this issue. The first is simply to rename
one of the types. Alternatively, one can specify the intended type using the
following syntax:

```
trait T1 {}
trait T2 {}

trait Foo {
    type A: T1;
}

trait Bar : Foo {
    type A: T2;
    fn do_something() {
        let _: <Self as Bar>::A;
    }
}
```
"##,

E0223: r##"
An attempt was made to retrieve an associated type, but the type was ambiguous.
For example:

```compile_fail,E0223
trait MyTrait {type X; }

fn main() {
    let foo: MyTrait::X;
}
```

The problem here is that we're attempting to take the type of X from MyTrait.
Unfortunately, the type of X is not defined, because it's only made concrete in
implementations of the trait. A working version of this code might look like:

```
trait MyTrait {type X; }
struct MyStruct;

impl MyTrait for MyStruct {
    type X = u32;
}

fn main() {
    let foo: <MyStruct as MyTrait>::X;
}
```

This syntax specifies that we want the X type from MyTrait, as made concrete in
MyStruct. The reason that we cannot simply use `MyStruct::X` is that MyStruct
might implement two different traits with identically-named associated types.
This syntax allows disambiguation between the two.
"##,

E0225: r##"
You attempted to use multiple types as bounds for a closure or trait object.
Rust does not currently support this. A simple example that causes this error:

```compile_fail,E0225
fn main() {
    let _: Box<dyn std::io::Read + std::io::Write>;
}
```

Auto traits such as Send and Sync are an exception to this rule:
It's possible to have bounds of one non-builtin trait, plus any number of
auto traits. For example, the following compiles correctly:

```
fn main() {
    let _: Box<dyn std::io::Read + Send + Sync>;
}
```
"##,

E0229: r##"
An associated type binding was done outside of the type parameter declaration
and `where` clause. Erroneous code example:

```compile_fail,E0229
pub trait Foo {
    type A;
    fn boo(&self) -> <Self as Foo>::A;
}

struct Bar;

impl Foo for isize {
    type A = usize;
    fn boo(&self) -> usize { 42 }
}

fn baz<I>(x: &<I as Foo<A=Bar>>::A) {}
// error: associated type bindings are not allowed here
```

To solve this error, please move the type bindings in the type parameter
declaration:

```
# struct Bar;
# trait Foo { type A; }
fn baz<I: Foo<A=Bar>>(x: &<I as Foo>::A) {} // ok!
```

Or in the `where` clause:

```
# struct Bar;
# trait Foo { type A; }
fn baz<I>(x: &<I as Foo>::A) where I: Foo<A=Bar> {}
```
"##,

E0243: r##"
#### Note: this error code is no longer emitted by the compiler.

This error indicates that not enough type parameters were found in a type or
trait.

For example, the `Foo` struct below is defined to be generic in `T`, but the
type parameter is missing in the definition of `Bar`:

```compile_fail,E0107
struct Foo<T> { x: T }

struct Bar { x: Foo }
```
"##,

E0244: r##"
#### Note: this error code is no longer emitted by the compiler.

This error indicates that too many type parameters were found in a type or
trait.

For example, the `Foo` struct below has no type parameters, but is supplied
with two in the definition of `Bar`:

```compile_fail,E0107
struct Foo { x: bool }

struct Bar<S, T> { x: Foo<S, T> }
```
"##,

E0307: r##"
This error indicates that the `self` parameter in a method has an invalid
"reciever type".

Methods take a special first parameter, of which there are three variants:
`self`, `&self`, and `&mut self`. These are syntactic sugar for
`self: Self`, `self: &Self`, and `self: &mut Self` respectively.

```
# struct Foo;
trait Trait {
    fn foo(&self);
//         ^^^^^ `self` here is a reference to the receiver object
}

impl Trait for Foo {
    fn foo(&self) {}
//         ^^^^^ the receiver type is `&Foo`
}
```

The type `Self` acts as an alias to the type of the current trait
implementer, or "receiver type". Besides the already mentioned `Self`,
`&Self` and `&mut Self` valid receiver types, the following are also valid:
`self: Box<Self>`, `self: Rc<Self>`, `self: Arc<Self>`, and `self: Pin<P>`
(where P is one of the previous types except `Self`). Note that `Self` can
also be the underlying implementing type, like `Foo` in the following
example:

```
# struct Foo;
# trait Trait {
#     fn foo(&self);
# }
impl Trait for Foo {
    fn foo(self: &Foo) {}
}
```

E0307 will be emitted by the compiler when using an invalid reciver type,
like in the following example:

```compile_fail,E0307
# struct Foo;
# struct Bar;
# trait Trait {
#     fn foo(&self);
# }
impl Trait for Foo {
    fn foo(self: &Bar) {}
}
```

The nightly feature [Arbintrary self types][AST] extends the accepted
set of receiver types to also include any type that can dereference to
`Self`:

```
#![feature(arbitrary_self_types)]

struct Foo;
struct Bar;

// Because you can dereference `Bar` into `Foo`...
impl std::ops::Deref for Bar {
    type Target = Foo;

    fn deref(&self) -> &Foo {
        &Foo
    }
}

impl Foo {
    fn foo(self: Bar) {}
//         ^^^^^^^^^ ...it can be used as the receiver type
}
```

[AST]: https://doc.rust-lang.org/unstable-book/language-features/arbitrary-self-types.html
"##,

E0321: r##"
A cross-crate opt-out trait was implemented on something which wasn't a struct
or enum type. Erroneous code example:

```compile_fail,E0321
#![feature(optin_builtin_traits)]

struct Foo;

impl !Sync for Foo {}

unsafe impl Send for &'static Foo {}
// error: cross-crate traits with a default impl, like `core::marker::Send`,
//        can only be implemented for a struct/enum type, not
//        `&'static Foo`
```

Only structs and enums are permitted to impl Send, Sync, and other opt-out
trait, and the struct or enum must be local to the current crate. So, for
example, `unsafe impl Send for Rc<Foo>` is not allowed.
"##,

E0322: r##"
The `Sized` trait is a special trait built-in to the compiler for types with a
constant size known at compile-time. This trait is automatically implemented
for types as needed by the compiler, and it is currently disallowed to
explicitly implement it for a type.
"##,

E0323: r##"
An associated const was implemented when another trait item was expected.
Erroneous code example:

```compile_fail,E0323
trait Foo {
    type N;
}

struct Bar;

impl Foo for Bar {
    const N : u32 = 0;
    // error: item `N` is an associated const, which doesn't match its
    //        trait `<Bar as Foo>`
}
```

Please verify that the associated const wasn't misspelled and the correct trait
was implemented. Example:

```
struct Bar;

trait Foo {
    type N;
}

impl Foo for Bar {
    type N = u32; // ok!
}
```

Or:

```
struct Bar;

trait Foo {
    const N : u32;
}

impl Foo for Bar {
    const N : u32 = 0; // ok!
}
```
"##,

E0324: r##"
A method was implemented when another trait item was expected. Erroneous
code example:

```compile_fail,E0324
struct Bar;

trait Foo {
    const N : u32;

    fn M();
}

impl Foo for Bar {
    fn N() {}
    // error: item `N` is an associated method, which doesn't match its
    //        trait `<Bar as Foo>`
}
```

To fix this error, please verify that the method name wasn't misspelled and
verify that you are indeed implementing the correct trait items. Example:

```
struct Bar;

trait Foo {
    const N : u32;

    fn M();
}

impl Foo for Bar {
    const N : u32 = 0;

    fn M() {} // ok!
}
```
"##,

E0325: r##"
An associated type was implemented when another trait item was expected.
Erroneous code example:

```compile_fail,E0325
struct Bar;

trait Foo {
    const N : u32;
}

impl Foo for Bar {
    type N = u32;
    // error: item `N` is an associated type, which doesn't match its
    //        trait `<Bar as Foo>`
}
```

Please verify that the associated type name wasn't misspelled and your
implementation corresponds to the trait definition. Example:

```
struct Bar;

trait Foo {
    type N;
}

impl Foo for Bar {
    type N = u32; // ok!
}
```

Or:

```
struct Bar;

trait Foo {
    const N : u32;
}

impl Foo for Bar {
    const N : u32 = 0; // ok!
}
```
"##,

E0326: r##"
The types of any associated constants in a trait implementation must match the
types in the trait definition. This error indicates that there was a mismatch.

Here's an example of this error:

```compile_fail,E0326
trait Foo {
    const BAR: bool;
}

struct Bar;

impl Foo for Bar {
    const BAR: u32 = 5; // error, expected bool, found u32
}
```
"##,

E0328: r##"
The Unsize trait should not be implemented directly. All implementations of
Unsize are provided automatically by the compiler.

Erroneous code example:

```compile_fail,E0328
#![feature(unsize)]

use std::marker::Unsize;

pub struct MyType;

impl<T> Unsize<T> for MyType {}
```

If you are defining your own smart pointer type and would like to enable
conversion from a sized to an unsized type with the
[DST coercion system][RFC 982], use [`CoerceUnsized`] instead.

```
#![feature(coerce_unsized)]

use std::ops::CoerceUnsized;

pub struct MyType<T: ?Sized> {
    field_with_unsized_type: T,
}

impl<T, U> CoerceUnsized<MyType<U>> for MyType<T>
    where T: CoerceUnsized<U> {}
```

[RFC 982]: https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md
[`CoerceUnsized`]: https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html
"##,

E0329: r##"
#### Note: this error code is no longer emitted by the compiler.

An attempt was made to access an associated constant through either a generic
type parameter or `Self`. This is not supported yet. An example causing this
error is shown below:

```
trait Foo {
    const BAR: f64;
}

struct MyStruct;

impl Foo for MyStruct {
    const BAR: f64 = 0f64;
}

fn get_bar_bad<F: Foo>(t: F) -> f64 {
    F::BAR
}
```

Currently, the value of `BAR` for a particular type can only be accessed
through a concrete type, as shown below:

```
trait Foo {
    const BAR: f64;
}

struct MyStruct;

impl Foo for MyStruct {
    const BAR: f64 = 0f64;
}

fn get_bar_good() -> f64 {
    <MyStruct as Foo>::BAR
}
```
"##,

E0366: r##"
An attempt was made to implement `Drop` on a concrete specialization of a
generic type. An example is shown below:

```compile_fail,E0366
struct Foo<T> {
    t: T
}

impl Drop for Foo<u32> {
    fn drop(&mut self) {}
}
```

This code is not legal: it is not possible to specialize `Drop` to a subset of
implementations of a generic type. One workaround for this is to wrap the
generic type, as shown below:

```
struct Foo<T> {
    t: T
}

struct Bar {
    t: Foo<u32>
}

impl Drop for Bar {
    fn drop(&mut self) {}
}
```
"##,

E0367: r##"
An attempt was made to implement `Drop` on a specialization of a generic type.
An example is shown below:

```compile_fail,E0367
trait Foo{}

struct MyStruct<T> {
    t: T
}

impl<T: Foo> Drop for MyStruct<T> {
    fn drop(&mut self) {}
}
```

This code is not legal: it is not possible to specialize `Drop` to a subset of
implementations of a generic type. In order for this code to work, `MyStruct`
must also require that `T` implements `Foo`. Alternatively, another option is
to wrap the generic type in another that specializes appropriately:

```
trait Foo{}

struct MyStruct<T> {
    t: T
}

struct MyStructWrapper<T: Foo> {
    t: MyStruct<T>
}

impl <T: Foo> Drop for MyStructWrapper<T> {
    fn drop(&mut self) {}
}
```
"##,

E0368: r##"
This error indicates that a binary assignment operator like `+=` or `^=` was
applied to a type that doesn't support it. For example:

```compile_fail,E0368
let mut x = 12f32; // error: binary operation `<<` cannot be applied to
                   //        type `f32`

x <<= 2;
```

To fix this error, please check that this type implements this binary
operation. Example:

```
let mut x = 12u32; // the `u32` type does implement the `ShlAssign` trait

x <<= 2; // ok!
```

It is also possible to overload most operators for your own type by
implementing the `[OP]Assign` traits from `std::ops`.

Another problem you might be facing is this: suppose you've overloaded the `+`
operator for some type `Foo` by implementing the `std::ops::Add` trait for
`Foo`, but you find that using `+=` does not work, as in this example:

```compile_fail,E0368
use std::ops::Add;

struct Foo(u32);

impl Add for Foo {
    type Output = Foo;

    fn add(self, rhs: Foo) -> Foo {
        Foo(self.0 + rhs.0)
    }
}

fn main() {
    let mut x: Foo = Foo(5);
    x += Foo(7); // error, `+= cannot be applied to the type `Foo`
}
```

This is because `AddAssign` is not automatically implemented, so you need to
manually implement it for your type.
"##,

E0369: r##"
A binary operation was attempted on a type which doesn't support it.
Erroneous code example:

```compile_fail,E0369
let x = 12f32; // error: binary operation `<<` cannot be applied to
               //        type `f32`

x << 2;
```

To fix this error, please check that this type implements this binary
operation. Example:

```
let x = 12u32; // the `u32` type does implement it:
               // https://doc.rust-lang.org/stable/std/ops/trait.Shl.html

x << 2; // ok!
```

It is also possible to overload most operators for your own type by
implementing traits from `std::ops`.

String concatenation appends the string on the right to the string on the
left and may require reallocation. This requires ownership of the string
on the left. If something should be added to a string literal, move the
literal to the heap by allocating it with `to_owned()` like in
`"Your text".to_owned()`.

"##,

E0370: r##"
The maximum value of an enum was reached, so it cannot be automatically
set in the next enum value. Erroneous code example:

```compile_fail,E0370
#[repr(i64)]
enum Foo {
    X = 0x7fffffffffffffff,
    Y, // error: enum discriminant overflowed on value after
       //        9223372036854775807: i64; set explicitly via
       //        Y = -9223372036854775808 if that is desired outcome
}
```

To fix this, please set manually the next enum value or put the enum variant
with the maximum value at the end of the enum. Examples:

```
#[repr(i64)]
enum Foo {
    X = 0x7fffffffffffffff,
    Y = 0, // ok!
}
```

Or:

```
#[repr(i64)]
enum Foo {
    Y = 0, // ok!
    X = 0x7fffffffffffffff,
}
```
"##,

E0371: r##"
When `Trait2` is a subtrait of `Trait1` (for example, when `Trait2` has a
definition like `trait Trait2: Trait1 { ... }`), it is not allowed to implement
`Trait1` for `Trait2`. This is because `Trait2` already implements `Trait1` by
definition, so it is not useful to do this.

Example:

```compile_fail,E0371
trait Foo { fn foo(&self) { } }
trait Bar: Foo { }
trait Baz: Bar { }

impl Bar for Baz { } // error, `Baz` implements `Bar` by definition
impl Foo for Baz { } // error, `Baz` implements `Bar` which implements `Foo`
impl Baz for Baz { } // error, `Baz` (trivially) implements `Baz`
impl Baz for Bar { } // Note: This is OK
```
"##,

E0374: r##"
A struct without a field containing an unsized type cannot implement
`CoerceUnsized`. An [unsized type][1] is any type that the compiler
doesn't know the length or alignment of at compile time. Any struct
containing an unsized type is also unsized.

[1]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait

Example of erroneous code:

```compile_fail,E0374
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

struct Foo<T: ?Sized> {
    a: i32,
}

// error: Struct `Foo` has no unsized fields that need `CoerceUnsized`.
impl<T, U> CoerceUnsized<Foo<U>> for Foo<T>
    where T: CoerceUnsized<U> {}
```

`CoerceUnsized` is used to coerce one struct containing an unsized type
into another struct containing a different unsized type. If the struct
doesn't have any fields of unsized types then you don't need explicit
coercion to get the types you want. To fix this you can either
not try to implement `CoerceUnsized` or you can add a field that is
unsized to the struct.

Example:

```
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

// We don't need to impl `CoerceUnsized` here.
struct Foo {
    a: i32,
}

// We add the unsized type field to the struct.
struct Bar<T: ?Sized> {
    a: i32,
    b: T,
}

// The struct has an unsized field so we can implement
// `CoerceUnsized` for it.
impl<T, U> CoerceUnsized<Bar<U>> for Bar<T>
    where T: CoerceUnsized<U> {}
```

Note that `CoerceUnsized` is mainly used by smart pointers like `Box`, `Rc`
and `Arc` to be able to mark that they can coerce unsized types that they
are pointing at.
"##,

E0375: r##"
A struct with more than one field containing an unsized type cannot implement
`CoerceUnsized`. This only occurs when you are trying to coerce one of the
types in your struct to another type in the struct. In this case we try to
impl `CoerceUnsized` from `T` to `U` which are both types that the struct
takes. An [unsized type][1] is any type that the compiler doesn't know the
length or alignment of at compile time. Any struct containing an unsized type
is also unsized.

Example of erroneous code:

```compile_fail,E0375
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

struct Foo<T: ?Sized, U: ?Sized> {
    a: i32,
    b: T,
    c: U,
}

// error: Struct `Foo` has more than one unsized field.
impl<T, U> CoerceUnsized<Foo<U, T>> for Foo<T, U> {}
```

`CoerceUnsized` only allows for coercion from a structure with a single
unsized type field to another struct with a single unsized type field.
In fact Rust only allows for a struct to have one unsized type in a struct
and that unsized type must be the last field in the struct. So having two
unsized types in a single struct is not allowed by the compiler. To fix this
use only one field containing an unsized type in the struct and then use
multiple structs to manage each unsized type field you need.

Example:

```
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

struct Foo<T: ?Sized> {
    a: i32,
    b: T,
}

impl <T, U> CoerceUnsized<Foo<U>> for Foo<T>
    where T: CoerceUnsized<U> {}

fn coerce_foo<T: CoerceUnsized<U>, U>(t: T) -> Foo<U> {
    Foo { a: 12i32, b: t } // we use coercion to get the `Foo<U>` type we need
}
```

[1]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait
"##,

E0376: r##"
The type you are trying to impl `CoerceUnsized` for is not a struct.
`CoerceUnsized` can only be implemented for a struct. Unsized types are
already able to be coerced without an implementation of `CoerceUnsized`
whereas a struct containing an unsized type needs to know the unsized type
field it's containing is able to be coerced. An [unsized type][1]
is any type that the compiler doesn't know the length or alignment of at
compile time. Any struct containing an unsized type is also unsized.

[1]: https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait

Example of erroneous code:

```compile_fail,E0376
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

struct Foo<T: ?Sized> {
    a: T,
}

// error: The type `U` is not a struct
impl<T, U> CoerceUnsized<U> for Foo<T> {}
```

The `CoerceUnsized` trait takes a struct type. Make sure the type you are
providing to `CoerceUnsized` is a struct with only the last field containing an
unsized type.

Example:

```
#![feature(coerce_unsized)]
use std::ops::CoerceUnsized;

struct Foo<T> {
    a: T,
}

// The `Foo<U>` is a struct so `CoerceUnsized` can be implemented
impl<T, U> CoerceUnsized<Foo<U>> for Foo<T> where T: CoerceUnsized<U> {}
```

Note that in Rust, structs can only contain an unsized type if the field
containing the unsized type is the last and only unsized type field in the
struct.
"##,

E0378: r##"
The `DispatchFromDyn` trait currently can only be implemented for
builtin pointer types and structs that are newtype wrappers around them
— that is, the struct must have only one field (except for`PhantomData`),
and that field must itself implement `DispatchFromDyn`.

Examples:

```
#![feature(dispatch_from_dyn, unsize)]
use std::{
    marker::Unsize,
    ops::DispatchFromDyn,
};

struct Ptr<T: ?Sized>(*const T);

impl<T: ?Sized, U: ?Sized> DispatchFromDyn<Ptr<U>> for Ptr<T>
where
    T: Unsize<U>,
{}
```

```
#![feature(dispatch_from_dyn)]
use std::{
    ops::DispatchFromDyn,
    marker::PhantomData,
};

struct Wrapper<T> {
    ptr: T,
    _phantom: PhantomData<()>,
}

impl<T, U> DispatchFromDyn<Wrapper<U>> for Wrapper<T>
where
    T: DispatchFromDyn<U>,
{}
```

Example of illegal `DispatchFromDyn` implementation
(illegal because of extra field)

```compile-fail,E0378
#![feature(dispatch_from_dyn)]
use std::ops::DispatchFromDyn;

struct WrapperExtraField<T> {
    ptr: T,
    extra_stuff: i32,
}

impl<T, U> DispatchFromDyn<WrapperExtraField<U>> for WrapperExtraField<T>
where
    T: DispatchFromDyn<U>,
{}
```
"##,

E0390: r##"
You tried to implement methods for a primitive type. Erroneous code example:

```compile_fail,E0390
struct Foo {
    x: i32
}

impl *mut Foo {}
// error: only a single inherent implementation marked with
//        `#[lang = "mut_ptr"]` is allowed for the `*mut T` primitive
```

This isn't allowed, but using a trait to implement a method is a good solution.
Example:

```
struct Foo {
    x: i32
}

trait Bar {
    fn bar();
}

impl Bar for *mut Foo {
    fn bar() {} // ok!
}
```
"##,

E0392: r##"
This error indicates that a type or lifetime parameter has been declared
but not actually used. Here is an example that demonstrates the error:

```compile_fail,E0392
enum Foo<T> {
    Bar,
}
```

If the type parameter was included by mistake, this error can be fixed
by simply removing the type parameter, as shown below:

```
enum Foo {
    Bar,
}
```

Alternatively, if the type parameter was intentionally inserted, it must be
used. A simple fix is shown below:

```
enum Foo<T> {
    Bar(T),
}
```

This error may also commonly be found when working with unsafe code. For
example, when using raw pointers one may wish to specify the lifetime for
which the pointed-at data is valid. An initial attempt (below) causes this
error:

```compile_fail,E0392
struct Foo<'a, T> {
    x: *const T,
}
```

We want to express the constraint that Foo should not outlive `'a`, because
the data pointed to by `T` is only valid for that lifetime. The problem is
that there are no actual uses of `'a`. It's possible to work around this
by adding a PhantomData type to the struct, using it to tell the compiler
to act as if the struct contained a borrowed reference `&'a T`:

```
use std::marker::PhantomData;

struct Foo<'a, T: 'a> {
    x: *const T,
    phantom: PhantomData<&'a T>
}
```

[PhantomData] can also be used to express information about unused type
parameters.

[PhantomData]: https://doc.rust-lang.org/std/marker/struct.PhantomData.html
"##,

E0393: r##"
A type parameter which references `Self` in its default value was not specified.
Example of erroneous code:

```compile_fail,E0393
trait A<T=Self> {}

fn together_we_will_rule_the_galaxy(son: &A) {}
// error: the type parameter `T` must be explicitly specified in an
//        object type because its default value `Self` references the
//        type `Self`
```

A trait object is defined over a single, fully-defined trait. With a regular
default parameter, this parameter can just be substituted in. However, if the
default parameter is `Self`, the trait changes for each concrete type; i.e.
`i32` will be expected to implement `A<i32>`, `bool` will be expected to
implement `A<bool>`, etc... These types will not share an implementation of a
fully-defined trait; instead they share implementations of a trait with
different parameters substituted in for each implementation. This is
irreconcilable with what we need to make a trait object work, and is thus
disallowed. Making the trait concrete by explicitly specifying the value of the
defaulted parameter will fix this issue. Fixed example:

```
trait A<T=Self> {}

fn together_we_will_rule_the_galaxy(son: &A<i32>) {} // Ok!
```
"##,

E0399: r##"
You implemented a trait, overriding one or more of its associated types but did
not reimplement its default methods.

Example of erroneous code:

```compile_fail,E0399
#![feature(associated_type_defaults)]

pub trait Foo {
    type Assoc = u8;
    fn bar(&self) {}
}

impl Foo for i32 {
    // error - the following trait items need to be reimplemented as
    //         `Assoc` was overridden: `bar`
    type Assoc = i32;
}
```

To fix this, add an implementation for each default method from the trait:

```
#![feature(associated_type_defaults)]

pub trait Foo {
    type Assoc = u8;
    fn bar(&self) {}
}

impl Foo for i32 {
    type Assoc = i32;
    fn bar(&self) {} // ok!
}
```
"##,

E0436: r##"
The functional record update syntax is only allowed for structs. (Struct-like
enum variants don't qualify, for example.)

Erroneous code example:

```compile_fail,E0436
enum PublicationFrequency {
    Weekly,
    SemiMonthly { days: (u8, u8), annual_special: bool },
}

fn one_up_competitor(competitor_frequency: PublicationFrequency)
                     -> PublicationFrequency {
    match competitor_frequency {
        PublicationFrequency::Weekly => PublicationFrequency::SemiMonthly {
            days: (1, 15), annual_special: false
        },
        c @ PublicationFrequency::SemiMonthly{ .. } =>
            PublicationFrequency::SemiMonthly {
                annual_special: true, ..c // error: functional record update
                                          //        syntax requires a struct
        }
    }
}
```

Rewrite the expression without functional record update syntax:

```
enum PublicationFrequency {
    Weekly,
    SemiMonthly { days: (u8, u8), annual_special: bool },
}

fn one_up_competitor(competitor_frequency: PublicationFrequency)
                     -> PublicationFrequency {
    match competitor_frequency {
        PublicationFrequency::Weekly => PublicationFrequency::SemiMonthly {
            days: (1, 15), annual_special: false
        },
        PublicationFrequency::SemiMonthly{ days, .. } =>
            PublicationFrequency::SemiMonthly {
                days, annual_special: true // ok!
        }
    }
}
```
"##,

E0439: r##"
The length of the platform-intrinsic function `simd_shuffle`
wasn't specified. Erroneous code example:

```compile_fail,E0439
#![feature(platform_intrinsics)]

extern "platform-intrinsic" {
    fn simd_shuffle<A,B>(a: A, b: A, c: [u32; 8]) -> B;
    // error: invalid `simd_shuffle`, needs length: `simd_shuffle`
}
```

The `simd_shuffle` function needs the length of the array passed as
last parameter in its name. Example:

```
#![feature(platform_intrinsics)]

extern "platform-intrinsic" {
    fn simd_shuffle8<A,B>(a: A, b: A, c: [u32; 8]) -> B;
}
```
"##,

E0516: r##"
The `typeof` keyword is currently reserved but unimplemented.
Erroneous code example:

```compile_fail,E0516
fn main() {
    let x: typeof(92) = 92;
}
```

Try using type inference instead. Example:

```
fn main() {
    let x = 92;
}
```
"##,

E0520: r##"
A non-default implementation was already made on this type so it cannot be
specialized further. Erroneous code example:

```compile_fail,E0520
#![feature(specialization)]

trait SpaceLlama {
    fn fly(&self);
}

// applies to all T
impl<T> SpaceLlama for T {
    default fn fly(&self) {}
}

// non-default impl
// applies to all `Clone` T and overrides the previous impl
impl<T: Clone> SpaceLlama for T {
    fn fly(&self) {}
}

// since `i32` is clone, this conflicts with the previous implementation
impl SpaceLlama for i32 {
    default fn fly(&self) {}
    // error: item `fly` is provided by an `impl` that specializes
    //        another, but the item in the parent `impl` is not marked
    //        `default` and so it cannot be specialized.
}
```

Specialization only allows you to override `default` functions in
implementations.

To fix this error, you need to mark all the parent implementations as default.
Example:

```
#![feature(specialization)]

trait SpaceLlama {
    fn fly(&self);
}

// applies to all T
impl<T> SpaceLlama for T {
    default fn fly(&self) {} // This is a parent implementation.
}

// applies to all `Clone` T; overrides the previous impl
impl<T: Clone> SpaceLlama for T {
    default fn fly(&self) {} // This is a parent implementation but was
                             // previously not a default one, causing the error
}

// applies to i32, overrides the previous two impls
impl SpaceLlama for i32 {
    fn fly(&self) {} // And now that's ok!
}
```
"##,

E0527: r##"
The number of elements in an array or slice pattern differed from the number of
elements in the array being matched.

Example of erroneous code:

```compile_fail,E0527
let r = &[1, 2, 3, 4];
match r {
    &[a, b] => { // error: pattern requires 2 elements but array
                 //        has 4
        println!("a={}, b={}", a, b);
    }
}
```

Ensure that the pattern is consistent with the size of the matched
array. Additional elements can be matched with `..`:

```
#![feature(slice_patterns)]

let r = &[1, 2, 3, 4];
match r {
    &[a, b, ..] => { // ok!
        println!("a={}, b={}", a, b);
    }
}
```
"##,

E0528: r##"
An array or slice pattern required more elements than were present in the
matched array.

Example of erroneous code:

```compile_fail,E0528
#![feature(slice_patterns)]

let r = &[1, 2];
match r {
    &[a, b, c, rest @ ..] => { // error: pattern requires at least 3
                               //        elements but array has 2
        println!("a={}, b={}, c={} rest={:?}", a, b, c, rest);
    }
}
```

Ensure that the matched array has at least as many elements as the pattern
requires. You can match an arbitrary number of remaining elements with `..`:

```
#![feature(slice_patterns)]

let r = &[1, 2, 3, 4, 5];
match r {
    &[a, b, c, rest @ ..] => { // ok!
        // prints `a=1, b=2, c=3 rest=[4, 5]`
        println!("a={}, b={}, c={} rest={:?}", a, b, c, rest);
    }
}
```
"##,

E0529: r##"
An array or slice pattern was matched against some other type.

Example of erroneous code:

```compile_fail,E0529
let r: f32 = 1.0;
match r {
    [a, b] => { // error: expected an array or slice, found `f32`
        println!("a={}, b={}", a, b);
    }
}
```

Ensure that the pattern and the expression being matched on are of consistent
types:

```
let r = [1.0, 2.0];
match r {
    [a, b] => { // ok!
        println!("a={}, b={}", a, b);
    }
}
```
"##,

E0533: r##"
An item which isn't a unit struct, a variant, nor a constant has been used as a
match pattern.

Erroneous code example:

```compile_fail,E0533
struct Tortoise;

impl Tortoise {
    fn turtle(&self) -> u32 { 0 }
}

match 0u32 {
    Tortoise::turtle => {} // Error!
    _ => {}
}
if let Tortoise::turtle = 0u32 {} // Same error!
```

If you want to match against a value returned by a method, you need to bind the
value first:

```
struct Tortoise;

impl Tortoise {
    fn turtle(&self) -> u32 { 0 }
}

match 0u32 {
    x if x == Tortoise.turtle() => {} // Bound into `x` then we compare it!
    _ => {}
}
```
"##,

E0534: r##"
The `inline` attribute was malformed.

Erroneous code example:

```ignore (compile_fail not working here; see Issue #43707)
#[inline()] // error: expected one argument
pub fn something() {}

fn main() {}
```

The parenthesized `inline` attribute requires the parameter to be specified:

```
#[inline(always)]
fn something() {}
```

or:

```
#[inline(never)]
fn something() {}
```

Alternatively, a paren-less version of the attribute may be used to hint the
compiler about inlining opportunity:

```
#[inline]
fn something() {}
```

For more information about the inline attribute, read:
https://doc.rust-lang.org/reference.html#inline-attributes
"##,

E0535: r##"
An unknown argument was given to the `inline` attribute.

Erroneous code example:

```ignore (compile_fail not working here; see Issue #43707)
#[inline(unknown)] // error: invalid argument
pub fn something() {}

fn main() {}
```

The `inline` attribute only supports two arguments:

 * always
 * never

All other arguments given to the `inline` attribute will return this error.
Example:

```
#[inline(never)] // ok!
pub fn something() {}

fn main() {}
```

For more information about the inline attribute, https:
read://doc.rust-lang.org/reference.html#inline-attributes
"##,

E0559: r##"
An unknown field was specified into an enum's structure variant.

Erroneous code example:

```compile_fail,E0559
enum Field {
    Fool { x: u32 },
}

let s = Field::Fool { joke: 0 };
// error: struct variant `Field::Fool` has no field named `joke`
```

Verify you didn't misspell the field's name or that the field exists. Example:

```
enum Field {
    Fool { joke: u32 },
}

let s = Field::Fool { joke: 0 }; // ok!
```
"##,

E0560: r##"
An unknown field was specified into a structure.

Erroneous code example:

```compile_fail,E0560
struct Simba {
    mother: u32,
}

let s = Simba { mother: 1, father: 0 };
// error: structure `Simba` has no field named `father`
```

Verify you didn't misspell the field's name or that the field exists. Example:

```
struct Simba {
    mother: u32,
    father: u32,
}

let s = Simba { mother: 1, father: 0 }; // ok!
```
"##,

E0569: r##"
If an impl has a generic parameter with the `#[may_dangle]` attribute, then
that impl must be declared as an `unsafe impl.

Erroneous code example:

```compile_fail,E0569
#![feature(dropck_eyepatch)]

struct Foo<X>(X);
impl<#[may_dangle] X> Drop for Foo<X> {
    fn drop(&mut self) { }
}
```

In this example, we are asserting that the destructor for `Foo` will not
access any data of type `X`, and require this assertion to be true for
overall safety in our program. The compiler does not currently attempt to
verify this assertion; therefore we must tag this `impl` as unsafe.
"##,

E0570: r##"
The requested ABI is unsupported by the current target.

The rust compiler maintains for each target a blacklist of ABIs unsupported on
that target. If an ABI is present in such a list this usually means that the
target / ABI combination is currently unsupported by llvm.

If necessary, you can circumvent this check using custom target specifications.
"##,

E0572: r##"
A return statement was found outside of a function body.

Erroneous code example:

```compile_fail,E0572
const FOO: u32 = return 0; // error: return statement outside of function body

fn main() {}
```

To fix this issue, just remove the return keyword or move the expression into a
function. Example:

```
const FOO: u32 = 0;

fn some_fn() -> u32 {
    return FOO;
}

fn main() {
    some_fn();
}
```
"##,

E0581: r##"
In a `fn` type, a lifetime appears only in the return type,
and not in the arguments types.

Erroneous code example:

```compile_fail,E0581
fn main() {
    // Here, `'a` appears only in the return type:
    let x: for<'a> fn() -> &'a i32;
}
```

To fix this issue, either use the lifetime in the arguments, or use
`'static`. Example:

```
fn main() {
    // Here, `'a` appears only in the return type:
    let x: for<'a> fn(&'a i32) -> &'a i32;
    let y: fn() -> &'static i32;
}
```

Note: The examples above used to be (erroneously) accepted by the
compiler, but this was since corrected. See [issue #33685] for more
details.

[issue #33685]: https://github.com/rust-lang/rust/issues/33685
"##,

E0582: r##"
A lifetime appears only in an associated-type binding,
and not in the input types to the trait.

Erroneous code example:

```compile_fail,E0582
fn bar<F>(t: F)
    // No type can satisfy this requirement, since `'a` does not
    // appear in any of the input types (here, `i32`):
    where F: for<'a> Fn(i32) -> Option<&'a i32>
{
}

fn main() { }
```

To fix this issue, either use the lifetime in the inputs, or use
`'static`. Example:

```
fn bar<F, G>(t: F, u: G)
    where F: for<'a> Fn(&'a i32) -> Option<&'a i32>,
          G: Fn(i32) -> Option<&'static i32>,
{
}

fn main() { }
```

Note: The examples above used to be (erroneously) accepted by the
compiler, but this was since corrected. See [issue #33685] for more
details.

[issue #33685]: https://github.com/rust-lang/rust/issues/33685
"##,

E0587: r##"
A type has both `packed` and `align` representation hints.

Erroneous code example:

```compile_fail,E0587
#[repr(packed, align(8))] // error!
struct Umbrella(i32);
```

You cannot use `packed` and `align` hints on a same type. If you want to pack a
type to a given size, you should provide a size to packed:

```
#[repr(packed)] // ok!
struct Umbrella(i32);
```
"##,

E0588: r##"
A type with `packed` representation hint has a field with `align`
representation hint.

Erroneous code example:

```compile_fail,E0588
#[repr(align(16))]
struct Aligned(i32);

#[repr(packed)] // error!
struct Packed(Aligned);
```

Just like you cannot have both `align` and `packed` representation hints on a
same type, a `packed` type cannot contain another type with the `align`
representation hint. However, you can do the opposite:

```
#[repr(packed)]
struct Packed(i32);

#[repr(align(16))] // ok!
struct Aligned(Packed);
```
"##,

E0592: r##"
This error occurs when you defined methods or associated functions with same
name.

Erroneous code example:

```compile_fail,E0592
struct Foo;

impl Foo {
    fn bar() {} // previous definition here
}

impl Foo {
    fn bar() {} // duplicate definition here
}
```

A similar error is E0201. The difference is whether there is one declaration
block or not. To avoid this error, you must give each `fn` a unique name.

```
struct Foo;

impl Foo {
    fn bar() {}
}

impl Foo {
    fn baz() {} // define with different name
}
```
"##,

E0599: r##"
This error occurs when a method is used on a type which doesn't implement it:

Erroneous code example:

```compile_fail,E0599
struct Mouth;

let x = Mouth;
x.chocolate(); // error: no method named `chocolate` found for type `Mouth`
               //        in the current scope
```
"##,

E0600: r##"
An unary operator was used on a type which doesn't implement it.

Example of erroneous code:

```compile_fail,E0600
enum Question {
    Yes,
    No,
}

!Question::Yes; // error: cannot apply unary operator `!` to type `Question`
```

In this case, `Question` would need to implement the `std::ops::Not` trait in
order to be able to use `!` on it. Let's implement it:

```
use std::ops::Not;

enum Question {
    Yes,
    No,
}

// We implement the `Not` trait on the enum.
impl Not for Question {
    type Output = bool;

    fn not(self) -> bool {
        match self {
            Question::Yes => false, // If the `Answer` is `Yes`, then it
                                    // returns false.
            Question::No => true, // And here we do the opposite.
        }
    }
}

assert_eq!(!Question::Yes, false);
assert_eq!(!Question::No, true);
```
"##,

E0608: r##"
An attempt to index into a type which doesn't implement the `std::ops::Index`
trait was performed.

Erroneous code example:

```compile_fail,E0608
0u8[2]; // error: cannot index into a value of type `u8`
```

To be able to index into a type it needs to implement the `std::ops::Index`
trait. Example:

```
let v: Vec<u8> = vec![0, 1, 2, 3];

// The `Vec` type implements the `Index` trait so you can do:
println!("{}", v[2]);
```
"##,

E0604: r##"
A cast to `char` was attempted on a type other than `u8`.

Erroneous code example:

```compile_fail,E0604
0u32 as char; // error: only `u8` can be cast as `char`, not `u32`
```

As the error message indicates, only `u8` can be cast into `char`. Example:

```
let c = 86u8 as char; // ok!
assert_eq!(c, 'V');
```

For more information about casts, take a look at the Type cast section in
[The Reference Book][1].

[1]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions
"##,

E0605: r##"
An invalid cast was attempted.

Erroneous code examples:

```compile_fail,E0605
let x = 0u8;
x as Vec<u8>; // error: non-primitive cast: `u8` as `std::vec::Vec<u8>`

// Another example

let v = core::ptr::null::<u8>(); // So here, `v` is a `*const u8`.
v as &u8; // error: non-primitive cast: `*const u8` as `&u8`
```

Only primitive types can be cast into each other. Examples:

```
let x = 0u8;
x as u32; // ok!

let v = core::ptr::null::<u8>();
v as *const i8; // ok!
```

For more information about casts, take a look at the Type cast section in
[The Reference Book][1].

[1]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions
"##,

E0606: r##"
An incompatible cast was attempted.

Erroneous code example:

```compile_fail,E0606
let x = &0u8; // Here, `x` is a `&u8`.
let y: u32 = x as u32; // error: casting `&u8` as `u32` is invalid
```

When casting, keep in mind that only primitive types can be cast into each
other. Example:

```
let x = &0u8;
let y: u32 = *x as u32; // We dereference it first and then cast it.
```

For more information about casts, take a look at the Type cast section in
[The Reference Book][1].

[1]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions
"##,

E0607: r##"
A cast between a thin and a fat pointer was attempted.

Erroneous code example:

```compile_fail,E0607
let v = core::ptr::null::<u8>();
v as *const [u8];
```

First: what are thin and fat pointers?

Thin pointers are "simple" pointers: they are purely a reference to a memory
address.

Fat pointers are pointers referencing Dynamically Sized Types (also called DST).
DST don't have a statically known size, therefore they can only exist behind
some kind of pointers that contain additional information. Slices and trait
objects are DSTs. In the case of slices, the additional information the fat
pointer holds is their size.

To fix this error, don't try to cast directly between thin and fat pointers.

For more information about casts, take a look at the Type cast section in
[The Reference Book][1].

[1]: https://doc.rust-lang.org/reference/expressions/operator-expr.html#type-cast-expressions
"##,

E0609: r##"
Attempted to access a non-existent field in a struct.

Erroneous code example:

```compile_fail,E0609
struct StructWithFields {
    x: u32,
}

let s = StructWithFields { x: 0 };
println!("{}", s.foo); // error: no field `foo` on type `StructWithFields`
```

To fix this error, check that you didn't misspell the field's name or that the
field actually exists. Example:

```
struct StructWithFields {
    x: u32,
}

let s = StructWithFields { x: 0 };
println!("{}", s.x); // ok!
```
"##,

E0610: r##"
Attempted to access a field on a primitive type.

Erroneous code example:

```compile_fail,E0610
let x: u32 = 0;
println!("{}", x.foo); // error: `{integer}` is a primitive type, therefore
                       //        doesn't have fields
```

Primitive types are the most basic types available in Rust and don't have
fields. To access data via named fields, struct types are used. Example:

```
// We declare struct called `Foo` containing two fields:
struct Foo {
    x: u32,
    y: i64,
}

// We create an instance of this struct:
let variable = Foo { x: 0, y: -12 };
// And we can now access its fields:
println!("x: {}, y: {}", variable.x, variable.y);
```

For more information about primitives and structs, take a look at The Book:
https://doc.rust-lang.org/book/ch03-02-data-types.html
https://doc.rust-lang.org/book/ch05-00-structs.html
"##,

E0614: r##"
Attempted to dereference a variable which cannot be dereferenced.

Erroneous code example:

```compile_fail,E0614
let y = 0u32;
*y; // error: type `u32` cannot be dereferenced
```

Only types implementing `std::ops::Deref` can be dereferenced (such as `&T`).
Example:

```
let y = 0u32;
let x = &y;
// So here, `x` is a `&u32`, so we can dereference it:
*x; // ok!
```
"##,

E0615: r##"
Attempted to access a method like a field.

Erroneous code example:

```compile_fail,E0615
struct Foo {
    x: u32,
}

impl Foo {
    fn method(&self) {}
}

let f = Foo { x: 0 };
f.method; // error: attempted to take value of method `method` on type `Foo`
```

If you want to use a method, add `()` after it:

```
# struct Foo { x: u32 }
# impl Foo { fn method(&self) {} }
# let f = Foo { x: 0 };
f.method();
```

However, if you wanted to access a field of a struct check that the field name
is spelled correctly. Example:

```
# struct Foo { x: u32 }
# impl Foo { fn method(&self) {} }
# let f = Foo { x: 0 };
println!("{}", f.x);
```
"##,

E0616: r##"
Attempted to access a private field on a struct.

Erroneous code example:

```compile_fail,E0616
mod some_module {
    pub struct Foo {
        x: u32, // So `x` is private in here.
    }

    impl Foo {
        pub fn new() -> Foo { Foo { x: 0 } }
    }
}

let f = some_module::Foo::new();
println!("{}", f.x); // error: field `x` of struct `some_module::Foo` is private
```

If you want to access this field, you have two options:

1) Set the field public:

```
mod some_module {
    pub struct Foo {
        pub x: u32, // `x` is now public.
    }

    impl Foo {
        pub fn new() -> Foo { Foo { x: 0 } }
    }
}

let f = some_module::Foo::new();
println!("{}", f.x); // ok!
```

2) Add a getter function:

```
mod some_module {
    pub struct Foo {
        x: u32, // So `x` is still private in here.
    }

    impl Foo {
        pub fn new() -> Foo { Foo { x: 0 } }

        // We create the getter function here:
        pub fn get_x(&self) -> &u32 { &self.x }
    }
}

let f = some_module::Foo::new();
println!("{}", f.get_x()); // ok!
```
"##,

E0617: r##"
Attempted to pass an invalid type of variable into a variadic function.

Erroneous code example:

```compile_fail,E0617
extern {
    fn printf(c: *const i8, ...);
}

unsafe {
    printf(::std::ptr::null(), 0f32);
    // error: cannot pass an `f32` to variadic function, cast to `c_double`
}
```

Certain Rust types must be cast before passing them to a variadic function,
because of arcane ABI rules dictated by the C standard. To fix the error,
cast the value to the type specified by the error message (which you may need
to import from `std::os::raw`).
"##,

E0618: r##"
Attempted to call something which isn't a function nor a method.

Erroneous code examples:

```compile_fail,E0618
enum X {
    Entry,
}

X::Entry(); // error: expected function, tuple struct or tuple variant,
            // found `X::Entry`

// Or even simpler:
let x = 0i32;
x(); // error: expected function, tuple struct or tuple variant, found `i32`
```

Only functions and methods can be called using `()`. Example:

```
// We declare a function:
fn i_am_a_function() {}

// And we call it:
i_am_a_function();
```
"##,

E0619: r##"
#### Note: this error code is no longer emitted by the compiler.
The type-checker needed to know the type of an expression, but that type had not
yet been inferred.

Erroneous code example:

```compile_fail
let mut x = vec![];
match x.pop() {
    Some(v) => {
        // Here, the type of `v` is not (yet) known, so we
        // cannot resolve this method call:
        v.to_uppercase(); // error: the type of this value must be known in
                          //        this context
    }
    None => {}
}
```

Type inference typically proceeds from the top of the function to the bottom,
figuring out types as it goes. In some cases -- notably method calls and
overloadable operators like `*` -- the type checker may not have enough
information *yet* to make progress. This can be true even if the rest of the
function provides enough context (because the type-checker hasn't looked that
far ahead yet). In this case, type annotations can be used to help it along.

To fix this error, just specify the type of the variable. Example:

```
let mut x: Vec<String> = vec![]; // We precise the type of the vec elements.
match x.pop() {
    Some(v) => {
        v.to_uppercase(); // Since rustc now knows the type of the vec elements,
                          // we can use `v`'s methods.
    }
    None => {}
}
```
"##,

E0620: r##"
A cast to an unsized type was attempted.

Erroneous code example:

```compile_fail,E0620
let x = &[1_usize, 2] as [usize]; // error: cast to unsized type: `&[usize; 2]`
                                  //        as `[usize]`
```

In Rust, some types don't have a known size at compile-time. For example, in a
slice type like `[u32]`, the number of elements is not known at compile-time and
hence the overall size cannot be computed. As a result, such types can only be
manipulated through a reference (e.g., `&T` or `&mut T`) or other pointer-type
(e.g., `Box` or `Rc`). Try casting to a reference instead:

```
let x = &[1_usize, 2] as &[usize]; // ok!
```
"##,

E0622: r##"
An intrinsic was declared without being a function.

Erroneous code example:

```compile_fail,E0622
#![feature(intrinsics)]
extern "rust-intrinsic" {
    pub static breakpoint : unsafe extern "rust-intrinsic" fn();
    // error: intrinsic must be a function
}

fn main() { unsafe { breakpoint(); } }
```

An intrinsic is a function available for use in a given programming language
whose implementation is handled specially by the compiler. In order to fix this
error, just declare a function.
"##,

E0624: r##"
A private item was used outside of its scope.

Erroneous code example:

```compile_fail,E0624
mod inner {
    pub struct Foo;

    impl Foo {
        fn method(&self) {}
    }
}

let foo = inner::Foo;
foo.method(); // error: method `method` is private
```

Two possibilities are available to solve this issue:

1. Only use the item in the scope it has been defined:

```
mod inner {
    pub struct Foo;

    impl Foo {
        fn method(&self) {}
    }

    pub fn call_method(foo: &Foo) { // We create a public function.
        foo.method(); // Which calls the item.
    }
}

let foo = inner::Foo;
inner::call_method(&foo); // And since the function is public, we can call the
                          // method through it.
```

2. Make the item public:

```
mod inner {
    pub struct Foo;

    impl Foo {
        pub fn method(&self) {} // It's now public.
    }
}

let foo = inner::Foo;
foo.method(); // Ok!
```
"##,

E0638: r##"
This error indicates that the struct, enum or enum variant must be matched
non-exhaustively as it has been marked as `non_exhaustive`.

When applied within a crate, downstream users of the crate will need to use the
`_` pattern when matching enums and use the `..` pattern when matching structs.
Downstream crates cannot match against non-exhaustive enum variants.

For example, in the below example, since the enum is marked as
`non_exhaustive`, it is required that downstream crates match non-exhaustively
on it.

```rust,ignore (pseudo-Rust)
use std::error::Error as StdError;

#[non_exhaustive] pub enum Error {
   Message(String),
   Other,
}

impl StdError for Error {
   fn description(&self) -> &str {
        // This will not error, despite being marked as non_exhaustive, as this
        // enum is defined within the current crate, it can be matched
        // exhaustively.
        match *self {
           Message(ref s) => s,
           Other => "other or unknown error",
        }
   }
}
```

An example of matching non-exhaustively on the above enum is provided below:

```rust,ignore (pseudo-Rust)
use mycrate::Error;

// This will not error as the non_exhaustive Error enum has been matched with a
// wildcard.
match error {
   Message(ref s) => ...,
   Other => ...,
   _ => ...,
}
```

Similarly, for structs, match with `..` to avoid this error.
"##,

E0639: r##"
This error indicates that the struct, enum or enum variant cannot be
instantiated from outside of the defining crate as it has been marked
as `non_exhaustive` and as such more fields/variants may be added in
future that could cause adverse side effects for this code.

It is recommended that you look for a `new` function or equivalent in the
crate's documentation.
"##,

E0643: r##"
This error indicates that there is a mismatch between generic parameters and
impl Trait parameters in a trait declaration versus its impl.

```compile_fail,E0643
trait Foo {
    fn foo(&self, _: &impl Iterator);
}
impl Foo for () {
    fn foo<U: Iterator>(&self, _: &U) { } // error method `foo` has incompatible
                                          // signature for trait
}
```
"##,

E0646: r##"
It is not possible to define `main` with a where clause.
Erroneous code example:

```compile_fail,E0646
fn main() where i32: Copy { // error: main function is not allowed to have
                            // a where clause
}
```
"##,

E0647: r##"
It is not possible to define `start` with a where clause.
Erroneous code example:

```compile_fail,E0647
#![feature(start)]

#[start]
fn start(_: isize, _: *const *const u8) -> isize where (): Copy {
    //^ error: start function is not allowed to have a where clause
    0
}
```
"##,

E0648: r##"
`export_name` attributes may not contain null characters (`\0`).

```compile_fail,E0648
#[export_name="\0foo"] // error: `export_name` may not contain null characters
pub fn bar() {}
```
"##,

E0689: r##"
This error indicates that the numeric value for the method being passed exists
but the type of the numeric value or binding could not be identified.

The error happens on numeric literals:

```compile_fail,E0689
2.0.neg();
```

and on numeric bindings without an identified concrete type:

```compile_fail,E0689
let x = 2.0;
x.neg();  // same error as above
```

Because of this, you must give the numeric literal or binding a type:

```
use std::ops::Neg;

let _ = 2.0_f32.neg();
let x: f32 = 2.0;
let _ = x.neg();
let _ = (2.0 as f32).neg();
```
"##,

E0690: r##"
A struct with the representation hint `repr(transparent)` had zero or more than
one fields that were not guaranteed to be zero-sized.

Erroneous code example:

```compile_fail,E0690
#[repr(transparent)]
struct LengthWithUnit<U> { // error: transparent struct needs exactly one
    value: f32,            //        non-zero-sized field, but has 2
    unit: U,
}
```

Because transparent structs are represented exactly like one of their fields at
run time, said field must be uniquely determined. If there is no field, or if
there are multiple fields, it is not clear how the struct should be represented.
Note that fields of zero-typed types (e.g., `PhantomData`) can also exist
alongside the field that contains the actual data, they do not count for this
error. When generic types are involved (as in the above example), an error is
reported because the type parameter could be non-zero-sized.

To combine `repr(transparent)` with type parameters, `PhantomData` may be
useful:

```
use std::marker::PhantomData;

#[repr(transparent)]
struct LengthWithUnit<U> {
    value: f32,
    unit: PhantomData<U>,
}
```
"##,

E0691: r##"
A struct, enum, or union with the `repr(transparent)` representation hint
contains a zero-sized field that requires non-trivial alignment.

Erroneous code example:

```compile_fail,E0691
#![feature(repr_align)]

#[repr(align(32))]
struct ForceAlign32;

#[repr(transparent)]
struct Wrapper(f32, ForceAlign32); // error: zero-sized field in transparent
                                   //        struct has alignment larger than 1
```

A transparent struct, enum, or union is supposed to be represented exactly like
the piece of data it contains. Zero-sized fields with different alignment
requirements potentially conflict with this property. In the example above,
`Wrapper` would have to be aligned to 32 bytes even though `f32` has a smaller
alignment requirement.

Consider removing the over-aligned zero-sized field:

```
#[repr(transparent)]
struct Wrapper(f32);
```

Alternatively, `PhantomData<T>` has alignment 1 for all `T`, so you can use it
if you need to keep the field for some reason:

```
#![feature(repr_align)]

use std::marker::PhantomData;

#[repr(align(32))]
struct ForceAlign32;

#[repr(transparent)]
struct Wrapper(f32, PhantomData<ForceAlign32>);
```

Note that empty arrays `[T; 0]` have the same alignment requirement as the
element type `T`. Also note that the error is conservatively reported even when
the alignment of the zero-sized type is less than or equal to the data field's
alignment.
"##,

E0699: r##"
A method was called on a raw pointer whose inner type wasn't completely known.

For example, you may have done something like:

```compile_fail
# #![deny(warnings)]
let foo = &1;
let bar = foo as *const _;
if bar.is_null() {
    // ...
}
```

Here, the type of `bar` isn't known; it could be a pointer to anything. Instead,
specify a type for the pointer (preferably something that makes sense for the
thing you're pointing to):

```
let foo = &1;
let bar = foo as *const i32;
if bar.is_null() {
    // ...
}
```

Even though `is_null()` exists as a method on any raw pointer, Rust shows this
error because  Rust allows for `self` to have arbitrary types (behind the
arbitrary_self_types feature flag).

This means that someone can specify such a function:

```ignore (cannot-doctest-feature-doesnt-exist-yet)
impl Foo {
    fn is_null(self: *const Self) -> bool {
        // do something else
    }
}
```

and now when you call `.is_null()` on a raw pointer to `Foo`, there's ambiguity.

Given that we don't know what type the pointer is, and there's potential
ambiguity for some types, we disallow calling methods on raw pointers when
the type is unknown.
"##,

E0714: r##"
A `#[marker]` trait contained an associated item.

The items of marker traits cannot be overridden, so there's no need to have them
when they cannot be changed per-type anyway.  If you wanted them for ergonomic
reasons, consider making an extension trait instead.
"##,

E0715: r##"
An `impl` for a `#[marker]` trait tried to override an associated item.

Because marker traits are allowed to have multiple implementations for the same
type, it's not allowed to override anything in those implementations, as it
would be ambiguous which override should actually be used.
"##,


E0720: r##"
An `impl Trait` type expands to a recursive type.

An `impl Trait` type must be expandable to a concrete type that contains no
`impl Trait` types. For example the following example tries to create an
`impl Trait` type `T` that is equal to `[T, T]`:

```compile_fail,E0720
fn make_recursive_type() -> impl Sized {
    [make_recursive_type(), make_recursive_type()]
}
```
"##,

E0730: r##"
An array without a fixed length was pattern-matched.

Example of erroneous code:

```compile_fail,E0730
#![feature(const_generics)]

fn is_123<const N: usize>(x: [u32; N]) -> bool {
    match x {
        [1, 2, 3] => true, // error: cannot pattern-match on an
                           //        array without a fixed length
        _ => false
    }
}
```

Ensure that the pattern is consistent with the size of the matched
array. Additional elements can be matched with `..`:

```
#![feature(slice_patterns)]

let r = &[1, 2, 3, 4];
match r {
    &[a, b, ..] => { // ok!
        println!("a={}, b={}", a, b);
    }
}
```
"##,

E0731: r##"
An enum with the representation hint `repr(transparent)` had zero or more than
one variants.

Erroneous code example:

```compile_fail,E0731
#[repr(transparent)]
enum Status { // error: transparent enum needs exactly one variant, but has 2
    Errno(u32),
    Ok,
}
```

Because transparent enums are represented exactly like one of their variants at
run time, said variant must be uniquely determined. If there is no variant, or
if there are multiple variants, it is not clear how the enum should be
represented.
"##,

E0732: r##"
An `enum` with a discriminant must specify a `#[repr(inttype)]`.

A `#[repr(inttype)]` must be provided on an `enum` if it has a non-unit
variant with a discriminant, or where there are both unit variants with
discriminants and non-unit variants. This restriction ensures that there
is a well-defined way to extract a variant's discriminant from a value;
for instance:

```
#![feature(arbitrary_enum_discriminant)]

#[repr(u8)]
enum Enum {
    Unit = 3,
    Tuple(u16) = 2,
    Struct {
        a: u8,
        b: u16,
    } = 1,
}

fn discriminant(v : &Enum) -> u8 {
    unsafe { *(v as *const Enum as *const u8) }
}

assert_eq!(3, discriminant(&Enum::Unit));
assert_eq!(2, discriminant(&Enum::Tuple(5)));
assert_eq!(1, discriminant(&Enum::Struct{a: 7, b: 11}));
```
"##,

E0740: r##"
A `union` cannot have fields with destructors.
"##,

E0733: r##"
Recursion in an `async fn` requires boxing. For example, this will not compile:

```edition2018,compile_fail,E0733
async fn foo(n: usize) {
    if n > 0 {
        foo(n - 1).await;
    }
}
```

To achieve async recursion, the `async fn` needs to be desugared
such that the `Future` is explicit in the return type:

```edition2018,compile_fail,E0720
use std::future::Future;
fn foo_desugared(n: usize) -> impl Future<Output = ()> {
    async move {
        if n > 0 {
            foo_desugared(n - 1).await;
        }
    }
}
```

Finally, the future is wrapped in a pinned box:

```edition2018
use std::future::Future;
use std::pin::Pin;
fn foo_recursive(n: usize) -> Pin<Box<dyn Future<Output = ()>>> {
    Box::pin(async move {
        if n > 0 {
            foo_recursive(n - 1).await;
        }
    })
}
```

The `Box<...>` ensures that the result is of known size,
and the pin is required to keep it in the same place in memory.
"##,

E0737: r##"
`#[track_caller]` requires functions to have the `"Rust"` ABI for implicitly
receiving caller location. See [RFC 2091] for details on this and other
restrictions.

Erroneous code example:

```compile_fail,E0737
#![feature(track_caller)]

#[track_caller]
extern "C" fn foo() {}
```

[RFC 2091]: https://github.com/rust-lang/rfcs/blob/master/text/2091-inline-semantic.md
"##,

E0741: r##"
Only `structural_match` types (that is, types that derive `PartialEq` and `Eq`)
may be used as the types of const generic parameters.

```compile_fail,E0741
#![feature(const_generics)]

struct A;

struct B<const X: A>; // error!
```

To fix this example, we derive `PartialEq` and `Eq`.

```
#![feature(const_generics)]

#[derive(PartialEq, Eq)]
struct A;

struct B<const X: A>; // ok!
```
"##,

;
//  E0035, merged into E0087/E0089
//  E0036, merged into E0087/E0089
//  E0068,
//  E0085,
//  E0086,
//  E0103,
//  E0104,
//  E0122, // bounds in type aliases are ignored, turned into proper lint
//  E0123,
//  E0127,
//  E0129,
//  E0141,
//  E0159, // use of trait `{}` as struct constructor
//  E0163, // merged into E0071
//  E0167,
//  E0168,
//  E0172, // non-trait found in a type sum, moved to resolve
//  E0173, // manual implementations of unboxed closure traits are experimental
//  E0174,
//  E0182, // merged into E0229
    E0183,
//  E0187, // cannot infer the kind of the closure
//  E0188, // can not cast an immutable reference to a mutable pointer
//  E0189, // deprecated: can only cast a boxed pointer to a boxed object
//  E0190, // deprecated: can only cast a &-pointer to an &-object
//  E0194, // merged into E0403
//  E0196, // cannot determine a type for this closure
    E0203, // type parameter has more than one relaxed default bound,
           // and only one is supported
    E0208,
//  E0209, // builtin traits can only be implemented on structs or enums
    E0212, // cannot extract an associated type from a higher-ranked trait bound
//  E0213, // associated types are not accepted in this context
//  E0215, // angle-bracket notation is not stable with `Fn`
//  E0216, // parenthetical notation is only stable with `Fn`
//  E0217, // ambiguous associated type, defined in multiple supertraits
//  E0218, // no associated type defined
//  E0219, // associated type defined in higher-ranked supertrait
//  E0222, // Error code E0045 (variadic function must have C or cdecl calling
           // convention) duplicate
    E0224, // at least one non-builtin train is required for an object type
    E0227, // ambiguous lifetime bound, explicit lifetime bound required
    E0228, // explicit lifetime bound required
//  E0233,
//  E0234,
//  E0235, // structure constructor specifies a structure of type but
//  E0236, // no lang item for range syntax
//  E0237, // no lang item for range syntax
//  E0238, // parenthesized parameters may only be used with a trait
//  E0239, // `next` method of `Iterator` trait has unexpected type
//  E0240,
//  E0241,
//  E0242,
//  E0245, // not a trait
//  E0246, // invalid recursive type
//  E0247,
//  E0248, // value used as a type, now reported earlier during resolution
           // as E0412
//  E0249,
//  E0319, // trait impls for defaulted traits allowed just for structs/enums
//  E0372, // coherence not object safe
    E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
           // between structures with the same definition
//  E0558, // replaced with a generic attribute input check
//  E0563, // cannot determine a type for this `impl Trait` removed in 6383de15
//  E0564, // only named lifetimes are allowed in `impl Trait`,
           // but `{}` was found in the type `{}`
//  E0611, // merged into E0616
//  E0612, // merged into E0609
//  E0613, // Removed (merged with E0609)
    E0627, // yield statement outside of generator literal
    E0632, // cannot provide explicit generic arguments when `impl Trait` is
           // used in argument position
    E0634, // type has conflicting packed representaton hints
    E0640, // infer outlives requirements
    E0641, // cannot cast to/from a pointer with an unknown kind
//  E0645, // trait aliases not finished
    E0719, // duplicate values for associated type binding
    E0722, // Malformed `#[optimize]` attribute
    E0724, // `#[ffi_returns_twice]` is only allowed in foreign functions
}