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

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

#![allow(non_snake_case)]

register_long_diagnostics! {

E0023: r##"
A pattern used to match against an enum variant must provide a sub-pattern for
each field of the enum variant. This error indicates that a pattern attempted to
extract an incorrect number of fields from a variant.

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

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

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

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

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

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

E0024: r##"
This error indicates that a pattern attempted to extract the fields of an enum
variant with no fields. Here's a tiny example of this error:

```
// This enum has two variants.
enum Number {
    // This variant has no fields.
    Zero,
    // This variant has one field.
    One(u32)
}

// Assuming x is a Number we can pattern match on its contents.
match x {
    Zero(inside) => ...,
    One(inside) => ...
}
```

The pattern match `Zero(inside)` is incorrect because the `Zero` variant
contains no fields, yet the `inside` name attempts to bind the first field of
the enum.
"##,

E0025: r##"
Each field of a struct can only be bound once in a 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 misspelt
another field name?
"##,

E0026: r##"
This error indicates that a struct pattern attempted to extract a non-existant
field from a struct. Struct fields are identified by the name used before the
colon `:` so struct patterns should resemble the declaration of the struct type
being matched.

```
// Correct matching.
struct Thing {
    x: u32,
    y: u32
}

let thing = Thing { x: 1, y: 2 };
match thing {
    Thing { x: xfield, y: yfield } => ...
}
```

If you are using shorthand field patterns but want to refer to the struct field
by a different name, you should rename it explicitly.

```
// Change this:
match thing {
    Thing { x, z } => ...
}

// To this:
match thing {
    Thing { x, y: z } => ...
}
```
"##,

E0027: r##"
This error indicates that a pattern for a struct fails to specify a sub-pattern
for every one of the struct's fields. Ensure that each field from the struct's
definition is mentioned in the pattern, or use `..` to ignore unwanted fields.

For example:

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

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

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

// This is correct (explicit).
match d {
    Dog { name: n, age: x } => ...
}

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

E0029: r##"
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.

```
// The ordering relation for strings can't 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" => ...
    _ => ...
}
```
"##,

E0030: r##"
When matching against a range, the compiler verifies that the range is
non-empty.  Range patterns include both end-points, so this is equivalent to
requiring the start of the range to be less than or equal to the end of the
range.

For example:

```
match 5u32 {
    // This range is ok, albeit pointless.
    1 ... 1 => ...
    // This range is empty, and the compiler can tell.
    1000 ... 5 => ...
}
```
"##,

E0033: r##"
This error indicates that a pointer to a trait type cannot be implicitly
dereferenced by a pattern. Every trait defines a type, but because the
size of trait implementors 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.

```
let trait_obj: &SomeTrait = ...;

// 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();
```

You can read more about trait objects in the Trait Object section of the
Reference:

http://doc.rust-lang.org/reference.html#trait-objects
"##,

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

```
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()
}
```
"##,

E0035: r##"
You tried to give a type parameter where it wasn't needed. Bad example:

```
struct Test;

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

fn main() {
    let x = Test;

    x.method::<i32>(); // Error: Test::method doesn't need type parameter!
}
```

To fix this error, just remove the type parameter:

```
struct Test;

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

fn main() {
    let x = Test;

    x.method(); // OK, we're good!
}
```
"##,

E0036: r##"
This error occurrs when you pass too many or not enough type parameters to
a method. Example:

```
struct Test;

impl Test {
    fn method<T>(&self, v: &[T]) -> usize {
        v.len()
    }
}

fn main() {
    let x = Test;
    let v = &[0i32];

    x.method::<i32, i32>(v); // error: only one type parameter is expected!
}
```

To fix it, just specify a correct number of type parameters:

```
struct Test;

impl Test {
    fn method<T>(&self, v: &[T]) -> usize {
        v.len()
    }
}

fn main() {
    let x = Test;
    let v = &[0i32];

    x.method::<i32>(v); // OK, we're good!
}
```

Please note on the last example that we could have called `method` like this:

```
x.method(v);
```
"##,

E0040: r##"
It is not allowed to manually call destructors in Rust. It is also not
necessary to do this since `drop` is called automatically whenever a value goes
out of scope.

Here's an example of this error:

```
struct Foo {
    x: i32,
}

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

fn main() {
    let mut x = Foo { x: -7 };
    x.drop(); // error: explicit use of destructor method
}
```
"##,

E0044: r##"
You can't use type parameters on foreign items. Example of erroneous code:

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

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

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

E0045: r##"
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. Examples of erroneous code:

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

To fix such code, put them in an extern "C" block:

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

E0046: r##"
When trying to make some type implement a trait `Foo`, you must, at minimum,
provide implementations for all of `Foo`'s required methods (meaning the
methods that do not have default implementations), as well as any required
trait items like associated types or constants.
"##,

E0049: r##"
This error indicates that an attempted implementation of a trait method
has the wrong number of type parameters.

For example, the trait below has a method `foo` with a type parameter `T`,
but the implementation of `foo` for the type `Bar` is missing this parameter:

```
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 }
}
```
"##,

E0050: r##"
This error indicates that an attempted implementation of a trait method
has the wrong number of function parameters.

For example, the trait below has a method `foo` with two function parameters
(`&self` and `u8`), but the implementation of `foo` for the type `Bar` omits
the `u8` parameter:

```
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 }
}
```
"##,

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

Here are a couple examples of this error:

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

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

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

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:

```
#![recursion_limit="2"]

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:

```
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:

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

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

```
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:

```
extern crate libc;
use libc::{ 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 illegal. But the following uses are allowed:

```
unsafe {
    use std::ffi::CString;

    printf(CString::new("test\n").unwrap().as_ptr());
    printf(CString::new("number = %d\n").unwrap().as_ptr(), 3);
    printf(CString::new("%d, %d\n").unwrap().as_ptr(), 10, 5);
}
```
"##,

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. Each field should
be specified exactly one time.
"##,

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. Each field should be
specified exactly once.
"##,

E0066: r##"
Box placement expressions (like C++'s "placement new") do not yet support any
place expression except the exchange heap (i.e. `std::boxed::HEAP`).
Furthermore, the syntax is changing to use `in` instead of `box`. See [RFC 470]
and [RFC 809] for more details.

[RFC 470]: https://github.com/rust-lang/rfcs/pull/470
[RFC 809]: https://github.com/rust-lang/rfcs/pull/809
"##,

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

Let's start with some bad examples:
```
use std::collections::LinkedList;

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

// ...

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

And now some good 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:

```
// 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 an lvalue expression. An
lvalue 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 here:
https://doc.rust-lang.org/reference.html#lvalues,-rvalues-and-temporaries

Now, we can go further. Here are some bad examples:
```
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 lvalue!
    some_other_func() = 4; // error : we can't 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 good 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 a structure initialization with a non-structure type.
Example of erroneous code:

```
enum Foo { FirstValue };

let u = Foo::FirstValue { value: 0i32 }; // error: Foo::FirstValue
                                         // isn't a structure!
// or even simpler, if the structure wasn't defined at all:
let u = RandomName { random_field: 0i32 }; // error: RandomName
                                           // isn't a structure!
```

To fix this, please check:
 * Did you spell it right?
 * Did you accidentaly used an enum as a struct?
 * Did you accidentaly make an enum when you intended to use a struct?

Here is the previous code with all missing information:

```
struct Inner {
    value: i32
}

enum Foo {
    FirstValue(Inner)
}

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

    let t = Inner { value: 0i32 };
}
```
"##,

E0072: r##"
When defining a recursive struct or enum, any use of the type being defined
from inside the definition must occur behind a pointer (like `Box` or `&`).
This is because structs and enums must have a well-defined size, and without
the pointer the size of the type would need to be unbounded.

Consider the following erroneous definition of a type for a list of bytes:

```
// error, illegal recursive struct type
struct ListNode {
    head: u8,
    tail: Option<ListNode>,
}
```

This type cannot have a well-defined size, because it needs to be arbitrarily
large (since we would be able to nest `ListNode`s to any depth). Specifically,

```plain
size of `ListNode` = 1 byte for `head`
                   + 1 byte for the discriminant of the `Option`
                   + size of `ListNode`
```

One way to fix this is by wrapping `ListNode` in a `Box`, like so:

```
struct ListNode {
    head: u8,
    tail: Option<Box<ListNode>>,
}
```

This works because `Box` is a pointer, so its size is well-known.
"##,

E0073: r##"
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 }`.
"##,

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.

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

// Bad.
enum Enum {
    P = 3,
    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.

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

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

E0082: r##"
The default type for enum discriminants is `isize`, but it can be adjusted by
adding the `repr` attribute to the enum declaration. This error indicates that
an integer literal given as a discriminant is not a member of the discriminant
type. For example:

```
#[repr(u8)]
enum Thing {
    A = 1024,
    B = 5
}
```

Here, 1024 lies outside the valid range for `u8`, so the discriminant for `A` is
invalid. You may want to change representation types to fix this, or else change
invalid discriminant values so that they fit within the existing type.

Note also that without a representation manually defined, the compiler will
optimize by using the smallest integer type possible.
"##,

E0083: r##"
At present, it's not possible to define a custom representation for an enum with
a single variant. As a workaround you can add a `Dummy` variant.

See: https://github.com/rust-lang/rust/issues/10292
"##,

E0084: r##"
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:

```
enum Empty {}
```
"##,

E0087: r##"
Too many type parameters were supplied for a function. For example:

```
fn foo<T>() {}

fn main() {
    foo::<f64, bool>(); // error, expected 1 parameter, found 2 parameters
}
```

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

E0088: r##"
You gave too many lifetime parameters. Erroneous code example:

```
fn f() {}

fn main() {
    f::<'static>() // error: too many lifetime parameters provided
}
```

Please check you give the right number of lifetime parameters. 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##"
Not enough type parameters were supplied for a function. For example:

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

fn main() {
    foo::<f64>(); // error, expected 2 parameters, found 1 parameter
}
```

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

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

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

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

```
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 type parameters. Example:

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

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

```
#![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_trans/trans/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:

```
#![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_trans/trans/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:

```
#![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 lifetime parameters
and verify with the function declaration in the Rust source code.
Example:

```
#![feature(intrinsics)]

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

E0101: r##"
You hit this error because the compiler the compiler lacks information
to determine a type for this expression. Erroneous code example:

```
fn main() {
    let x = |_| {}; // error: cannot determine a type for this expression
}
```

You have two possibilities to solve this situation:
 * Give an explicit definition of the expression
 * Infer the expression

Examples:

```
fn main() {
    let x = |_ : u32| {}; // ok!
    // or:
    let x = |_| {};
    x(0u32);
}
```
"##,

E0106: r##"
This error indicates that a lifetime is missing from a type. If it is an error
inside a function signature, the problem may be with failing to adhere to the
lifetime elision rules (see below).

Here are some simple examples of where you'll run into this error:

```
struct Foo { x: &bool }        // error
struct Foo<'a> { x: &'a bool } // correct

enum Bar { A(u8), B(&bool), }        // error
enum Bar<'a> { A(u8), B(&'a bool), } // correct

type MyStr = &str;        // error
type MyStr<'a> = &'a str; //correct

```

Lifetime elision is a special, limited kind of inference for lifetimes in
function signatures which allows you to leave out lifetimes in certain cases.
For more background on lifetime elision see [the book][book-le].

The lifetime elision rules require that any function signature with an elided
output lifetime must either have

 - exactly one input lifetime
 - or, multiple input lifetimes, but the function must also be a method with a
   `&self` or `&mut self` receiver

In the first case, the output lifetime is inferred to be the same as the unique
input lifetime. In the second case, the lifetime is instead inferred to be the
same as the lifetime on `&self` or `&mut self`.

Here are some examples of elision errors:

```
// error, no input lifetimes
fn foo() -> &str { ... }

// error, `x` and `y` have distinct lifetimes inferred
fn bar(x: &str, y: &str) -> &str { ... }

// error, `y`'s lifetime is inferred to be distinct from `x`'s
fn baz<'a>(x: &'a str, y: &str) -> &str { ... }
```

[book-le]: http://doc.rust-lang.org/nightly/book/lifetimes.html#lifetime-elision
"##,

E0107: r##"
This error means that an incorrect number of lifetime parameters were provided
for a type (like a struct or enum) or trait.

Some basic examples include:

```
struct Foo<'a>(&'a str);
enum Bar { A, B, C }

struct Baz<'a> {
    foo: Foo,     // error: expected 1, found 0
    bar: Bar<'a>, // error: expected 0, found 1
}
```

Here's an example that is currently an error, but may work in a future version
of Rust:

```
struct Foo<'a>(&'a str);

trait Quux { }
impl Quux for Foo { } // error: expected 1, found 0
```

Lifetime elision in implementation headers was part of the lifetime elision
RFC. It is, however, [currently unimplemented][iss15872].

[iss15872]: https://github.com/rust-lang/rust/issues/15872
"##,

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:

```
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:

```
type Bytes = Vec<u8>;

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

E0117: r##"
You got this error because because you tried to implement a foreign
trait for a foreign type (with maybe a foreign type parameter). Erroneous
code example:

```
impl Drop for u32 {}
```

The type, trait or the type parameter (or all of them) has to be defined
in your crate. Example:

```
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
}

trait Bar { // or define your trait in your crate
    fn get(&self) -> usize;
}

impl Bar for u32 { // and then you implement it on a foreign type
    fn get(&self) -> usize { 0 }
}

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

E0119: r##"
There are conflicting trait implementations for the same type.
Erroneous code example:

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

impl<T> MyTrait for T {
    fn get(&self) -> usize { 0 }
}

struct Foo {
    value: usize
}

impl MyTrait for Foo { // error: conflicting implementations for trait
                       //        `MyTrait`
    fn get(&self) -> usize { self.value }
}
```

When you write:

```
impl<T> MyTrait for T {
    fn get(&self) -> usize { 0 }
}
```

This makes the trait implemented on all types in the scope. So if you
try to implement it on another one after that, the implementations will
conflict. Example:

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

impl<T> MyTrait for T {
    fn get(&self) -> usize { 0 }
}

struct Foo;

fn main() {
    let f = Foo;

    f.get(); // the trait is implemented so we can use it
}
```
"##,

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

Examples of this error include:

```
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:

```
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!
}
```
"##,

E0128: r##"
Type parameter defaults can only use parameters that occur before them.
Erroneous code example:

```
pub struct Foo<T=U, U=()> {
    field1: T,
    filed2: U,
}
// error: type parameters with a default cannot use forward declared
// identifiers
```

Since type parameters are evaluated in-order, you may be able to fix this issue
by doing:

```
pub struct Foo<U=(), T=U> {
    field1: T,
    filed2: U,
}
```

Please also verify that this wasn't because of a name-clash and rename the type
parameter if so.
"##,

E0130: r##"
You declared a pattern as an argument in a foreign function declaration.
Erroneous code example:

```
extern {
    fn foo((a, b): (u32, u32)); // error: patterns aren't allowed in foreign
                                //        function declarations
}
```

Please replace the pattern argument with a regular one. Example:

```
struct SomeStruct {
    a: u32,
    b: u32,
}

extern {
    fn foo(s: SomeStruct); // ok!
}
// or
extern {
    fn foo(a: (u32, u32)); // ok!
}
```
"##,

E0131: r##"
It is not possible to define `main` with type parameters, or even with function
parameters. When `main` is present, it must take no arguments and return `()`.
"##,

E0132: r##"
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:

```
fn(isize, *const *const u8) -> isize
```
"##,

E0159: r##"
You tried to use a trait as a struct constructor. Erroneous code example:

```
trait TraitNotAStruct {}

TraitNotAStruct{ value: 0 }; // error: use of trait `TraitNotAStruct` as a
                             //        struct constructor
```

Please verify you used the correct type name or please implement the trait
on a struct and use this struct constructor. Example:

```
trait TraitNotAStruct {}

struct Foo {
    value: i32
}

Foo{ value: 0 }; // ok!
```
"##,

E0166: r##"
This error means that the compiler found a return expression in a function
marked as diverging. A function diverges if it has `!` in the place of the
return type in its signature. For example:

```
fn foo() -> ! { return; } // error
```

For a function that diverges, every control path in the function must never
return, for example with a `loop` that never breaks or a call to another
diverging function (such as `panic!()`).
"##,

E0178: r##"
In types, the `+` type operator has low precedence, so it is often necessary
to use parentheses.

For example:

```
trait Foo {}

struct Bar<'a> {
    w: &'a Foo + Copy,   // error, use &'a (Foo + Copy)
    x: &'a Foo + 'a,     // error, use &'a (Foo + 'a)
    y: &'a mut Foo + 'a, // error, use &'a mut (Foo + 'a)
    z: fn() -> Foo + 'a, // error, use fn() -> (Foo + 'a)
}
```

More details can be found in [RFC 438].

[RFC 438]: https://github.com/rust-lang/rfcs/pull/438
"##,

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:

```
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:

```
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:

```
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 traits with default impls. For more
information see the [opt-in builtin traits RFC](https://github.com/rust-lang/
rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
"##,

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

```
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!
    }
}
```
"##,

E0197: r##"
Inherent implementations (one that do not implement a trait but provide
methods associated with a type) are always safe because they are not
implementing an unsafe trait. Removing the `unsafe` keyword from the inherent
implementation will resolve this error.

```
struct Foo;

// this will cause this error
unsafe impl Foo { }
// converting it to this will fix it
impl Foo { }
```

"##,

E0198: r##"
A negative implementation is one that excludes a type from implementing a
particular trait. Not being able to use a trait is always a safe operation,
so negative implementations are always safe and never need to be marked as
unsafe.

```
struct Foo;

// unsafe is unnecessary
unsafe impl !Clone for Foo { }
// this will compile
impl !Clone for Foo { }
```

"##,

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.

```
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.

```
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 an associated function more than once.

For example:

```
struct Foo(u8);

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

    // error: duplicate associated function
    fn bar() {}
}

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

impl Baz for Foo {
    fn baz(&self) -> bool { true }

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

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/pull/195
[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

```
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:

```
#[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##"
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

```
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:

```
#[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 `i32` (primitive type) nor `&'static Bar`
(reference to `Bar`) is a struct or enum:

```
type Foo = i32;
impl Copy for Foo { } // error

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

E0207: r##"
You declared an unused type parameter when implementing a trait on an object.
Erroneous code example:

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

struct Foo;

impl<T> MyTrait for Foo {
    fn get(&self) -> usize {
        0
    }
}
```

Please check your object definition and remove unused type
parameter(s). Example:

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

struct Foo;

impl MyTrait for Foo {
    fn get(&self) -> usize {
        0
    }
}
```
"##,

E0211: r##"
You used an intrinsic function which doesn't correspond to its
definition. Erroneous code example:

```
#![feature(intrinsics)]

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

Please check the function definition. Example:

```
#![feature(intrinsics)]

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

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

```
trait Trait {
    type Bar;
}

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

Please verify you used the right trait or you didn't misspell the
associated type name. Example:

```
trait Trait {
    type Bar;
}

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

E0232: r##"
The attribute must have a value. Erroneous code example:

```
#[rustc_on_unimplemented] // error: this attribute must have a value
trait Bar {}
```

Please supply the missing value of the attribute. Example:

```
#[rustc_on_unimplemented = "foo"] // ok!
trait Bar {}
```
"##,

E0243: r##"
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`:

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

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

E0244: r##"
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`:

```
struct Foo { x: bool }

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

E0249: r##"
This error indicates a constant expression for the array length was found, but
it was not an integer (signed or unsigned) expression.

Some examples of code that produces this error are:

```
const A: [u32; "hello"] = []; // error
const B: [u32; true] = []; // error
const C: [u32; 0.0] = []; // error
"##,

E0250: r##"
There was an error while evaluating the expression for the length of a fixed-
size array type.

Some examples of this error are:

```
// divide by zero in the length expression
const A: [u32; 1/0] = [];

// Rust currently will not evaluate the function `foo` at compile time
fn foo() -> usize { 12 }
const B: [u32; foo()] = [];

// it is an error to try to add `u8` and `f64`
use std::{f64, u8};
const C: [u32; u8::MAX + f64::EPSILON] = [];
```
"##,

E0318: r##"
Default impls for a trait must be located in the same crate where the trait was
defined. For more information see the [opt-in builtin traits RFC](https://github
.com/rust-lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
"##,

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.
"##,

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:

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

struct Bar;

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

E0327: r##"
You cannot use associated items other than constant items as patterns. This
includes method items. Example of erroneous code:

```
enum B {}

impl B {
    fn bb() -> i32 { 0 }
}

fn main() {
    match 0 {
        B::bb => {} // error: associated items in match patterns must
                    // be constants
    }
}
```

Please check that you're not using a method as a pattern. Example:

```
enum B {
    ba,
    bb
}

fn main() {
    match B::ba {
        B::bb => {} // ok!
        _ => {}
    }
}
```
"##,

E0368: r##"
This error indicates that a binary assignment operator like `+=` or `^=` was
applied to the wrong types. For example:

```
let mut x: u16 = 5;
x ^= true; // error, `^=` cannot be applied to types `u16` and `bool`
x += ();   // error, `+=` cannot be applied to types `u16` and `()`
```

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:

```
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 types `Foo` and `Foo`
}
```

This is because the binary assignment operators currently do not work off of
traits, so it is not possible to overload them. See [RFC 953] for a proposal
to change this.

[RFC 953]: https://github.com/rust-lang/rfcs/pull/953
"##,

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:

```
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
```
"##,

E0372: r##"
Trying to implement a trait for a trait object (as in `impl Trait1 for
Trait2 { ... }`) does not work if the trait is not object-safe. Please see the
[RFC 255] for more details on object safety rules.

[RFC 255]: https://github.com/rust-lang/rfcs/pull/255
"##,

E0379: r##"
Trait methods cannot be declared `const` by design. For more information, see
[RFC 911].

[RFC 911]: https://github.com/rust-lang/rfcs/pull/911
"##,

E0380: r##"
Default impls are only allowed for traits with no methods or associated items.
For more information see the [opt-in builtin traits RFC](https://github.com/rust
-lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
"##

}

register_diagnostics! {
    E0068,
    E0074,
    E0075,
    E0076,
    E0077,
    E0085,
    E0086,
    E0090,
    E0102,
    E0103,
    E0104,
    E0118,
    E0120,
    E0122,
    E0123,
    E0127,
    E0129,
    E0141,
    E0163,
    E0164,
    E0167,
    E0168,
    E0172,
    E0173, // manual implementations of unboxed closure traits are experimental
    E0174, // explicit use of unboxed closure methods are experimental
    E0182,
    E0183,
    E0187, // can't infer the kind of the closure
    E0188, // can not cast a 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
    E0193, // cannot bound type where clause bounds may only be attached to types
           // involving type parameters
    E0194,
    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
    E0210, // type parameter is not constrained by any local type
    E0212, // cannot extract an associated type from a higher-ranked trait bound
    E0213, // associated types are not accepted in this context
    E0214, // parenthesized parameters may only be used with a trait
    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
    E0221, // ambiguous associated type in bounds
    //E0222, // Error code E0045 (variadic function must have C calling
             // convention) duplicate
    E0223, // ambiguous associated type
    E0224, // at least one non-builtin train is required for an object type
    E0225, // only the builtin traits can be used as closure or object bounds
    E0226, // only a single explicit lifetime bound is permitted
    E0227, // ambiguous lifetime bound, explicit lifetime bound required
    E0228, // explicit lifetime bound required
    E0229, // associated type bindings are not allowed here
    E0230, // there is no type parameter on trait
    E0231, // only named substitution parameters are allowed
    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, // internal error looking up a definition
    E0245, // not a trait
    E0246, // illegal recursive type
    E0247, // found module name used as a type
    E0248, // found value name used as a type
    E0319, // trait impls for defaulted traits allowed just for structs/enums
    E0320, // recursive overflow during dropck
    E0321, // extended coherence rules for defaulted traits violated
    E0323, // implemented an associated const when another trait item expected
    E0324, // implemented a method when another trait item expected
    E0325, // implemented an associated type when another trait item expected
    E0328, // cannot implement Unsize explicitly
    E0329, // associated const depends on type parameter or Self.
    E0366, // dropck forbid specialization to concrete type or region
    E0367, // dropck forbid specialization to predicate not in struct/enum
    E0369, // binary operation `<op>` cannot be applied to types
    E0374, // the trait `CoerceUnsized` may only be implemented for a coercion
           // between structures with one field being coerced, none found
    E0375, // the trait `CoerceUnsized` may only be implemented for a coercion
           // between structures with one field being coerced, but multiple
           // fields need coercions
    E0376, // the trait `CoerceUnsized` may only be implemented for a coercion
           // between structures
    E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
           // between structures with the same definition
    E0390, // only a single inherent implementation marked with
           // `#[lang = \"{}\"]` is allowed for the `{}` primitive
    E0391, // unsupported cyclic reference between types/traits detected
    E0392, // parameter `{}` is never used
    E0393, // the type parameter `{}` must be explicitly specified in an object
           // type because its default value `{}` references the type `Self`"
    E0399  // trait items need to be implemented because the associated
           // type `{}` was overridden
}