Rollup merge of #31295 - steveklabnik:gh31266, r=alexcrichton

[rust.git] / src / librustc_resolve / 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)]

// Error messages for EXXXX errors.  Each message should start and end with a
// new line, and be wrapped to 80 characters.  In vim you can `:set tw=80` and
// use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
register_long_diagnostics! {

E0154: r##"
Imports (`use` statements) are not allowed after non-item statements, such as
variable declarations and expression statements.

Here is an example that demonstrates the error:

```
fn f() {
    // Variable declaration before import
    let x = 0;
    use std::io::Read;
    ...
}
```

The solution is to declare the imports at the top of the block, function, or
file.

Here is the previous example again, with the correct order:

```
fn f() {
    use std::io::Read;
    let x = 0;
    ...
}
```

See the Declaration Statements section of the reference for more information
about what constitutes an Item declaration and what does not:

https://doc.rust-lang.org/reference.html#statements
"##,

E0251: r##"
Two items of the same name cannot be imported without rebinding one of the
items under a new local name.

An example of this error:

```
use foo::baz;
use bar::*; // error, do `use foo::baz as quux` instead on the previous line

fn main() {}

mod foo {
    pub struct baz;
}

mod bar {
    pub mod baz {}
}
```
"##,

E0252: r##"
Two items of the same name cannot be imported without rebinding one of the
items under a new local name.

An example of this error:

```
use foo::baz;
use bar::baz; // error, do `use bar::baz as quux` instead

fn main() {}

mod foo {
    pub struct baz;
}

mod bar {
    pub mod baz {}
}
```
"##,

E0253: r##"
Attempt was made to import an unimportable value. This can happen when
trying to import a method from a trait. An example of this error:

```
mod foo {
    pub trait MyTrait {
        fn do_something();
    }
}
use foo::MyTrait::do_something;
```

It's invalid to directly import methods belonging to a trait or concrete type.
"##,

E0255: r##"
You can't import a value whose name is the same as another value defined in the
module.

An example of this error:

```
use bar::foo; // error, do `use bar::foo as baz` instead

fn foo() {}

mod bar {
     pub fn foo() {}
}

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

E0256: r##"
You can't import a type or module when the name of the item being imported is
the same as another type or submodule defined in the module.

An example of this error:

```
use foo::Bar; // error

type Bar = u32;

mod foo {
    pub mod Bar { }
}

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

E0259: r##"
The name chosen for an external crate conflicts with another external crate that
has been imported into the current module.

Wrong example:

```
extern crate a;
extern crate crate_a as a;
```

The solution is to choose a different name that doesn't conflict with any
external crate imported into the current module.

Correct example:

```
extern crate a;
extern crate crate_a as other_name;
```
"##,

E0260: r##"
The name for an item declaration conflicts with an external crate's name.

For instance,

```
extern crate abc;

struct abc;
```

There are two possible solutions:

Solution #1: Rename the item.

```
extern crate abc;

struct xyz;
```

Solution #2: Import the crate with a different name.

```
extern crate abc as xyz;

struct abc;
```

See the Declaration Statements section of the reference for more information
about what constitutes an Item declaration and what does not:

https://doc.rust-lang.org/reference.html#statements
"##,

E0317: r##"
User-defined types or type parameters cannot shadow the primitive types.
This error indicates you tried to define a type, struct or enum with the same
name as an existing primitive type:

```
struct u8 {
    // ...
}
```

To fix this, simply name it something else.

Such an error may also occur if you define a type parameter which shadows a
primitive type. An example would be something like:

```
impl<u8> MyTrait for Option<u8> {
    // ...
}
```

In such a case, if you meant for `u8` to be a generic type parameter (i.e. any
type can be used in its place), use something like `T` instead:

```
impl<T> MyTrait for Option<T> {
    // ...
}
```

On the other hand, if you wished to refer to the specific type `u8`, remove it
from the type parameter list:

```
impl MyTrait for Option<u8> {
    // ...
}

See the Types section of the reference for more information about the primitive
types:

https://doc.rust-lang.org/reference.html#types
"##,

E0364: r##"
Private items cannot be publicly re-exported.  This error indicates that
you attempted to `pub use` a type or value that was not itself public.

Here is an example that demonstrates the error:

```
mod foo {
    const X: u32 = 1;
}
pub use foo::X;
```

The solution to this problem is to ensure that the items that you are
re-exporting are themselves marked with `pub`:

```
mod foo {
    pub const X: u32 = 1;
}
pub use foo::X;
```

See the 'Use Declarations' section of the reference for more information
on this topic:

https://doc.rust-lang.org/reference.html#use-declarations
"##,

E0365: r##"
Private modules cannot be publicly re-exported.  This error indicates
that you attempted to `pub use` a module that was not itself public.

Here is an example that demonstrates the error:

```
mod foo {
    pub const X: u32 = 1;
}
pub use foo as foo2;

```
The solution to this problem is to ensure that the module that you are
re-exporting is itself marked with `pub`:

```
pub mod foo {
    pub const X: u32 = 1;
}
pub use foo as foo2;
```

See the 'Use Declarations' section of the reference for more information
on this topic:

https://doc.rust-lang.org/reference.html#use-declarations
"##,

E0401: r##"
Inner items do not inherit type parameters from the functions they are
embedded in. For example, this will not compile:

```
fn foo<T>(x: T) {
    fn bar(y: T) { // T is defined in the "outer" function
        // ..
    }
    bar(x);
}
```

nor will this:

```
fn foo<T>(x: T) {
    type MaybeT = Option<T>;
    // ...
}
```

or this:

```
fn foo<T>(x: T) {
    struct Foo {
        x: T,
    }
    // ...
}
```

Items inside functions are basically just like top-level items, except
that they can only be used from the function they are in.

There are a couple of solutions for this.

If the item is a function, you may use a closure:

```
fn foo<T>(x: T) {
    let bar = |y: T| { // explicit type annotation may not be necessary
        // ..
    }
    bar(x);
}
```

For a generic item, you can copy over the parameters:

```
fn foo<T>(x: T) {
    fn bar<T>(y: T) {
        // ..
    }
    bar(x);
}
```

```
fn foo<T>(x: T) {
    type MaybeT<T> = Option<T>;
}
```

Be sure to copy over any bounds as well:

```
fn foo<T: Copy>(x: T) {
    fn bar<T: Copy>(y: T) {
        // ..
    }
    bar(x);
}
```

```
fn foo<T: Copy>(x: T) {
    struct Foo<T: Copy> {
        x: T,
    }
}
```

This may require additional type hints in the function body.

In case the item is a function inside an `impl`, defining a private helper
function might be easier:

```
impl<T> Foo<T> {
    pub fn foo(&self, x: T) {
        self.bar(x);
    }
    fn bar(&self, y: T) {
        // ..
    }
}
```

For default impls in traits, the private helper solution won't work, however
closures or copying the parameters should still work.
"##,

E0403: r##"
Some type parameters have the same name. Example of erroneous code:

```
fn foo<T, T>(s: T, u: T) {} // error: the name `T` is already used for a type
                            //        parameter in this type parameter list
```

Please verify that none of the type parameterss are misspelled, and rename any
clashing parameters. Example:

```
fn foo<T, Y>(s: T, u: Y) {} // ok!
```
"##,

E0404: r##"
You tried to implement something which was not a trait on an object. Example of
erroneous code:

```
struct Foo;
struct Bar;

impl Foo for Bar {} // error: `Foo` is not a trait
```

Please verify that you didn't misspell the trait's name or otherwise use the
wrong identifier. Example:

```
trait Foo {
    // some functions
}
struct Bar;

impl Foo for Bar { // ok!
    // functions implementation
}
```
"##,

E0405: r##"
An unknown trait was implemented. Example of erroneous code:

```
struct Foo;

impl SomeTrait for Foo {} // error: use of undeclared trait name `SomeTrait`
```

Please verify that the name of the trait wasn't misspelled and ensure that it
was imported. Example:

```
// solution 1:
use some_file::SomeTrait;

// solution 2:
trait SomeTrait {
    // some functions
}

struct Foo;

impl SomeTrait for Foo { // ok!
    // implements functions
}
```
"##,

E0407: r##"
A definition of a method not in the implemented trait was given in a trait
implementation. Example of erroneous code:

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

struct Bar;

impl Foo for Bar {
    fn a() {}
    fn b() {} // error: method `b` is not a member of trait `Foo`
}
```

Please verify you didn't misspell the method name and you used the correct
trait. First example:

```
trait Foo {
    fn a();
    fn b();
}

struct Bar;

impl Foo for Bar {
    fn a() {}
    fn b() {} // ok!
}
```

Second example:

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

struct Bar;

impl Foo for Bar {
    fn a() {}
}

impl Bar {
    fn b() {}
}
```
"##,

E0411: r##"
The `Self` keyword was used outside an impl or a trait. Erroneous
code example:

```
<Self>::foo; // error: use of `Self` outside of an impl or trait
```

The `Self` keyword represents the current type, which explains why it
can only be used inside an impl or a trait. It gives access to the
associated items of a type:

```
trait Foo {
    type Bar;
}

trait Baz : Foo {
    fn bar() -> Self::Bar; // like this
}
```

However, be careful when two types has a common associated type:

```
trait Foo {
    type Bar;
}

trait Foo2 {
    type Bar;
}

trait Baz : Foo + Foo2 {
    fn bar() -> Self::Bar;
    // error: ambiguous associated type `Bar` in bounds of `Self`
}
```

This problem can be solved by specifying from which trait we want
to use the `Bar` type:

```
trait Baz : Foo + Foo2 {
    fn bar() -> <Self as Foo>::Bar; // ok!
}
```
"##,

E0412: r##"
An undeclared type name was used. Example of erroneous codes:

```
impl Something {} // error: use of undeclared type name `Something`
// or:
trait Foo {
    fn bar(N); // error: use of undeclared type name `N`
}
// or:
fn foo(x: T) {} // error: use of undeclared type name `T`
```

To fix this error, please verify you didn't misspell the type name,
you did declare it or imported it into the scope. Examples:

```
struct Something;

impl Something {} // ok!
// or:
trait Foo {
    type N;

    fn bar(Self::N); // ok!
}
//or:
fn foo<T>(x: T) {} // ok!
```
"##,

E0413: r##"
A declaration shadows an enum variant or unit-like struct in scope.
Example of erroneous code:

```
struct Foo;

let Foo = 12i32; // error: declaration of `Foo` shadows an enum variant or
                 //        unit-like struct in scope
```


To fix this error, rename the variable such that it doesn't shadow any enum
variable or structure in scope. Example:

```
struct Foo;

let foo = 12i32; // ok!
```

Or:

```
struct FooStruct;

let Foo = 12i32; // ok!
```

The goal here is to avoid a conflict of names.
"##,

E0415: r##"
More than one function parameter have the same name. Example of erroneous
code:

```
fn foo(f: i32, f: i32) {} // error: identifier `f` is bound more than
                          //        once in this parameter list
```

Please verify you didn't misspell parameters' name. Example:

```
fn foo(f: i32, g: i32) {} // ok!
```
"##,

E0416: r##"
An identifier is bound more than once in a pattern. Example of erroneous
code:

```
match (1, 2) {
    (x, x) => {} // error: identifier `x` is bound more than once in the
                 //        same pattern
}
```

Please verify you didn't misspell identifiers' name. Example:

```
match (1, 2) {
    (x, y) => {} // ok!
}
```

Or maybe did you mean to unify? Consider using a guard:

```
match (A, B, C) {
    (x, x2, see) if x == x2 => { /* A and B are equal, do one thing */ }
    (y, z, see) => { /* A and B unequal; do another thing */ }
}
```
"##,

E0417: r##"
A static variable was referenced in a pattern. Example of erroneous code:

```
static FOO : i32 = 0;

match 0 {
    FOO => {} // error: static variables cannot be referenced in a
              //        pattern, use a `const` instead
    _ => {}
}
```

The compiler needs to know the value of the pattern at compile time;
compile-time patterns can defined via const or enum items. Please verify
that the identifier is spelled correctly, and if so, use a const instead
of static to define it. Example:

```
const FOO : i32 = 0;

match 0 {
    FOO => {} // ok!
    _ => {}
}
```
"##,

E0419: r##"
An unknown enum variant, struct or const was used. Example of
erroneous code:

```
match 0 {
    Something::Foo => {} // error: unresolved enum variant, struct
                         //        or const `Foo`
}
```

Please verify you didn't misspell it and the enum variant, struct or const has
been declared and imported into scope. Example:

```
enum Something {
    Foo,
    NotFoo,
}

match Something::NotFoo {
    Something::Foo => {} // ok!
    _ => {}
}
```
"##,

E0422: r##"
You are trying to use an identifier that is either undefined or not a
struct. For instance:
```
fn main () {
    let x = Foo { x: 1, y: 2 };
}
```

In this case, `Foo` is undefined, so it inherently isn't anything, and
definitely not a struct.

```
fn main () {
    let foo = 1;
    let x = foo { x: 1, y: 2 };
}
```

In this case, `foo` is defined, but is not a struct, so Rust can't use
it as one.
"##,

E0423: r##"
A `struct` variant name was used like a function name. Example of
erroneous code:

```
struct Foo { a: bool};

let f = Foo();
// error: `Foo` is a struct variant name, but this expression uses
//        it like a function name
```

Please verify you didn't misspell the name of what you actually wanted
to use here. Example:

```
fn Foo() -> u32 { 0 }

let f = Foo(); // ok!
```
"##,

E0424: r##"
The `self` keyword was used in a static method. Example of erroneous code:

```
struct Foo;

impl Foo {
    fn bar(self) {}

    fn foo() {
        self.bar(); // error: `self` is not available in a static method.
    }
}
```

Please check if the method's argument list should have contained `self`,
`&self`, or `&mut self` (in case you didn't want to create a static
method), and add it if so. Example:

```
struct Foo;

impl Foo {
    fn bar(self) {}

    fn foo(self) {
        self.bar(); // ok!
    }
}
```
"##,

E0425: r##"
An unresolved name was used. Example of erroneous codes:

```
something_that_doesnt_exist::foo;
// error: unresolved name `something_that_doesnt_exist::foo`

// or:
trait Foo {
    fn bar() {
        Self; // error: unresolved name `Self`
    }
}

// or:
let x = unknown_variable;  // error: unresolved name `unknown_variable`
```

Please verify that the name wasn't misspelled and ensure that the
identifier being referred to is valid for the given situation. Example:

```
enum something_that_does_exist {
    foo
}

// or:
mod something_that_does_exist {
    pub static foo : i32 = 0i32;
}

something_that_does_exist::foo; // ok!

// or:
let unknown_variable = 12u32;
let x = unknown_variable; // ok!
```
"##,

E0426: r##"
An undeclared label was used. Example of erroneous code:

```
loop {
    break 'a; // error: use of undeclared label `'a`
}
```

Please verify you spelt or declare the label correctly. Example:

```
'a: loop {
    break 'a; // ok!
}
```
"##,

E0428: r##"
A type or module has been defined more than once. Example of erroneous
code:

```
struct Bar;
struct Bar; // error: duplicate definition of value `Bar`
```

Please verify you didn't misspell the type/module's name or remove/rename the
duplicated one. Example:

```
struct Bar;
struct Bar2; // ok!
```
"##,

E0430: r##"
The `self` import appears more than once in the list. Erroneous code example:

```
use something::{self, self}; // error: `self` import can only appear once in
                             //        the list
```

Please verify you didn't misspell the import name or remove the duplicated
`self` import. Example:

```
use something::self; // ok!
```
"##,

E0431: r##"
`self` import was made. Erroneous code example:

```
use {self}; // error: `self` import can only appear in an import list with a
            //        non-empty prefix
```

You cannot import the current module into itself, please remove this import
or verify you didn't misspell it.
"##,

E0432: r##"
An import was unresolved. Erroneous code example:

```
use something::Foo; // error: unresolved import `something::Foo`.
```

Please verify you didn't misspell the import name or the import does exist
in the module from where you tried to import it. Example:

```
use something::Foo; // ok!

mod something {
    pub struct Foo;
}
```

Or, if you tried to use a module from an external crate, you may have missed
the `extern crate` declaration:

```
extern crate homura; // Required to use the `homura` crate

use homura::Madoka;
```
"##,

E0433: r##"
Invalid import. Example of erroneous code:

```
use something_which_doesnt_exist;
// error: unresolved import `something_which_doesnt_exist`
```

Please verify you didn't misspell the import's name.
"##,

E0435: r##"
A non-constant value was used to initialise a constant. Example of erroneous
code:

```
let foo = 42u32;
const FOO : u32 = foo; // error: attempt to use a non-constant value in a
                       //        constant
```

To fix this error, please replace the value with a constant. Example:

```
const FOO : u32 = 42u32; // ok!

// or:
const OTHER_FOO : u32 = 42u32;
const FOO : u32 = OTHER_FOO; // ok!
```
"##,

E0437: r##"
Trait implementations can only implement associated types that are members of
the trait in question. This error indicates that you attempted to implement
an associated type whose name does not match the name of any associated type
in the trait.

Here is an example that demonstrates the error:

```
trait Foo {}

impl Foo for i32 {
    type Bar = bool;
}
```

The solution to this problem is to remove the extraneous associated type:

```
trait Foo {}

impl Foo for i32 {}
```
"##,

E0438: r##"
Trait implementations can only implement associated constants that are
members of the trait in question. This error indicates that you
attempted to implement an associated constant whose name does not
match the name of any associated constant in the trait.

Here is an example that demonstrates the error:

```
#![feature(associated_consts)]

trait Foo {}

impl Foo for i32 {
    const BAR: bool = true;
}
```

The solution to this problem is to remove the extraneous associated constant:

```
trait Foo {}

impl Foo for i32 {}
```
"##

}

register_diagnostics! {
//  E0153, unused error code
//  E0157, unused error code
    E0254, // import conflicts with imported crate in this module
    E0257,
    E0258,
    E0402, // cannot use an outer type parameter in this context
    E0406, // undeclared associated type
    E0408, // variable from pattern #1 is not bound in pattern #
    E0409, // variable is bound with different mode in pattern # than in
           // pattern #1
    E0410, // variable from pattern is not bound in pattern 1
    E0414, // only irrefutable patterns allowed here
    E0418, // is not an enum variant, struct or const
    E0420, // is not an associated const
    E0421, // unresolved associated const
    E0427, // cannot use `ref` binding mode with ...
    E0429, // `self` imports are only allowed within a { } list
    E0434, // can't capture dynamic environment in a fn item
}