1 // Copyright 2014 The Rust Project Developers. See the COPYRIGHT
2 // file at the top-level directory of this distribution and at
3 // http://rust-lang.org/COPYRIGHT.
5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
8 // option. This file may not be copied, modified, or distributed
9 // except according to those terms.
11 #![allow(non_snake_case)]
13 // Error messages for EXXXX errors.
14 // Each message should start and end with a new line, and be wrapped to 80 characters.
15 // In vim you can `:set tw=80` and use `gq` to wrap paragraphs. Use `:set tw=0` to disable.
16 register_long_diagnostics! {
18 Trait objects like `Box<Trait>` can only be constructed when certain
19 requirements are satisfied by the trait in question.
21 Trait objects are a form of dynamic dispatch and use a dynamically sized type
22 for the inner type. So, for a given trait `Trait`, when `Trait` is treated as a
23 type, as in `Box<Trait>`, the inner type is 'unsized'. In such cases the boxed
24 pointer is a 'fat pointer' that contains an extra pointer to a table of methods
25 (among other things) for dynamic dispatch. This design mandates some
26 restrictions on the types of traits that are allowed to be used in trait
27 objects, which are collectively termed as 'object safety' rules.
29 Attempting to create a trait object for a non object-safe trait will trigger
32 There are various rules:
34 ### The trait cannot require `Self: Sized`
36 When `Trait` is treated as a type, the type does not implement the special
37 `Sized` trait, because the type does not have a known size at compile time and
38 can only be accessed behind a pointer. Thus, if we have a trait like the
42 trait Foo where Self: Sized {
47 We cannot create an object of type `Box<Foo>` or `&Foo` since in this case
48 `Self` would not be `Sized`.
50 Generally, `Self : Sized` is used to indicate that the trait should not be used
51 as a trait object. If the trait comes from your own crate, consider removing
54 ### Method references the `Self` type in its arguments or return type
56 This happens when a trait has a method like the following:
60 fn foo(&self) -> Self;
63 impl Trait for String {
64 fn foo(&self) -> Self {
70 fn foo(&self) -> Self {
76 (Note that `&self` and `&mut self` are okay, it's additional `Self` types which
79 In such a case, the compiler cannot predict the return type of `foo()` in a
80 situation like the following:
84 fn foo(&self) -> Self;
87 fn call_foo(x: Box<Trait>) {
88 let y = x.foo(); // What type is y?
93 If only some methods aren't object-safe, you can add a `where Self: Sized` bound
94 on them to mark them as explicitly unavailable to trait objects. The
95 functionality will still be available to all other implementers, including
96 `Box<Trait>` which is itself sized (assuming you `impl Trait for Box<Trait>`).
100 fn foo(&self) -> Self where Self: Sized;
105 Now, `foo()` can no longer be called on a trait object, but you will now be
106 allowed to make a trait object, and that will be able to call any object-safe
107 methods. With such a bound, one can still call `foo()` on types implementing
108 that trait that aren't behind trait objects.
110 ### Method has generic type parameters
112 As mentioned before, trait objects contain pointers to method tables. So, if we
120 impl Trait for String {
134 At compile time each implementation of `Trait` will produce a table containing
135 the various methods (and other items) related to the implementation.
137 This works fine, but when the method gains generic parameters, we can have a
140 Usually, generic parameters get _monomorphized_. For example, if I have
148 The machine code for `foo::<u8>()`, `foo::<bool>()`, `foo::<String>()`, or any
149 other type substitution is different. Hence the compiler generates the
150 implementation on-demand. If you call `foo()` with a `bool` parameter, the
151 compiler will only generate code for `foo::<bool>()`. When we have additional
152 type parameters, the number of monomorphized implementations the compiler
153 generates does not grow drastically, since the compiler will only generate an
154 implementation if the function is called with unparametrized substitutions
155 (i.e., substitutions where none of the substituted types are themselves
158 However, with trait objects we have to make a table containing _every_ object
159 that implements the trait. Now, if it has type parameters, we need to add
160 implementations for every type that implements the trait, and there could
161 theoretically be an infinite number of types.
167 fn foo<T>(&self, on: T);
171 impl Trait for String {
172 fn foo<T>(&self, on: T) {
178 fn foo<T>(&self, on: T) {
183 // 8 more implementations
186 Now, if we have the following code:
188 ```compile_fail,E0038
189 # trait Trait { fn foo<T>(&self, on: T); }
190 # impl Trait for String { fn foo<T>(&self, on: T) {} }
191 # impl Trait for u8 { fn foo<T>(&self, on: T) {} }
192 # impl Trait for bool { fn foo<T>(&self, on: T) {} }
194 fn call_foo(thing: Box<Trait>) {
195 thing.foo(true); // this could be any one of the 8 types above
201 We don't just need to create a table of all implementations of all methods of
202 `Trait`, we need to create such a table, for each different type fed to
203 `foo()`. In this case this turns out to be (10 types implementing `Trait`)*(3
204 types being fed to `foo()`) = 30 implementations!
206 With real world traits these numbers can grow drastically.
208 To fix this, it is suggested to use a `where Self: Sized` bound similar to the
209 fix for the sub-error above if you do not intend to call the method with type
214 fn foo<T>(&self, on: T) where Self: Sized;
219 If this is not an option, consider replacing the type parameter with another
220 trait object (e.g. if `T: OtherTrait`, use `on: Box<OtherTrait>`). If the number
221 of types you intend to feed to this method is limited, consider manually listing
222 out the methods of different types.
224 ### Method has no receiver
226 Methods that do not take a `self` parameter can't be called since there won't be
227 a way to get a pointer to the method table for them.
235 This could be called as `<Foo as Foo>::foo()`, which would not be able to pick
238 Adding a `Self: Sized` bound to these methods will generally make this compile.
242 fn foo() -> u8 where Self: Sized;
246 ### The trait cannot contain associated constants
248 Just like static functions, associated constants aren't stored on the method
249 table. If the trait or any subtrait contain an associated constant, they cannot
250 be made into an object.
252 ```compile_fail,E0038
260 A simple workaround is to use a helper method instead:
268 ### The trait cannot use `Self` as a type parameter in the supertrait listing
270 This is similar to the second sub-error, but subtler. It happens in situations
276 trait Trait: Super<Self> {
281 impl Super<Foo> for Foo{}
283 impl Trait for Foo {}
286 Here, the supertrait might have methods as follows:
290 fn get_a(&self) -> A; // note that this is object safe!
294 If the trait `Foo` was deriving from something like `Super<String>` or
295 `Super<T>` (where `Foo` itself is `Foo<T>`), this is okay, because given a type
296 `get_a()` will definitely return an object of that type.
298 However, if it derives from `Super<Self>`, even though `Super` is object safe,
299 the method `get_a()` would return an object of unknown type when called on the
300 function. `Self` type parameters let us make object safe traits no longer safe,
301 so they are forbidden when specifying supertraits.
303 There's no easy fix for this, generally code will need to be refactored so that
304 you no longer need to derive from `Super<Self>`.
308 When defining a recursive struct or enum, any use of the type being defined
309 from inside the definition must occur behind a pointer (like `Box` or `&`).
310 This is because structs and enums must have a well-defined size, and without
311 the pointer, the size of the type would need to be unbounded.
313 Consider the following erroneous definition of a type for a list of bytes:
315 ```compile_fail,E0072
316 // error, invalid recursive struct type
319 tail: Option<ListNode>,
323 This type cannot have a well-defined size, because it needs to be arbitrarily
324 large (since we would be able to nest `ListNode`s to any depth). Specifically,
327 size of `ListNode` = 1 byte for `head`
328 + 1 byte for the discriminant of the `Option`
332 One way to fix this is by wrapping `ListNode` in a `Box`, like so:
337 tail: Option<Box<ListNode>>,
341 This works because `Box` is a pointer, so its size is well-known.
345 This error indicates that the compiler was unable to sensibly evaluate an
346 constant expression that had to be evaluated. Attempting to divide by 0
347 or causing integer overflow are two ways to induce this error. For example:
349 ```compile_fail,E0080
356 Ensure that the expressions given can be evaluated as the desired integer type.
357 See the FFI section of the Reference for more information about using a custom
360 https://doc.rust-lang.org/reference.html#ffi-attributes
364 This error indicates that a lifetime is missing from a type. If it is an error
365 inside a function signature, the problem may be with failing to adhere to the
366 lifetime elision rules (see below).
368 Here are some simple examples of where you'll run into this error:
370 ```compile_fail,E0106
371 struct Foo1 { x: &bool }
372 // ^ expected lifetime parameter
373 struct Foo2<'a> { x: &'a bool } // correct
375 struct Bar1 { x: Foo2 }
376 // ^^^^ expected lifetime parameter
377 struct Bar2<'a> { x: Foo2<'a> } // correct
379 enum Baz1 { A(u8), B(&bool), }
380 // ^ expected lifetime parameter
381 enum Baz2<'a> { A(u8), B(&'a bool), } // correct
384 // ^ expected lifetime parameter
385 type MyStr2<'a> = &'a str; // correct
388 Lifetime elision is a special, limited kind of inference for lifetimes in
389 function signatures which allows you to leave out lifetimes in certain cases.
390 For more background on lifetime elision see [the book][book-le].
392 The lifetime elision rules require that any function signature with an elided
393 output lifetime must either have
395 - exactly one input lifetime
396 - or, multiple input lifetimes, but the function must also be a method with a
397 `&self` or `&mut self` receiver
399 In the first case, the output lifetime is inferred to be the same as the unique
400 input lifetime. In the second case, the lifetime is instead inferred to be the
401 same as the lifetime on `&self` or `&mut self`.
403 Here are some examples of elision errors:
405 ```compile_fail,E0106
406 // error, no input lifetimes
409 // error, `x` and `y` have distinct lifetimes inferred
410 fn bar(x: &str, y: &str) -> &str { }
412 // error, `y`'s lifetime is inferred to be distinct from `x`'s
413 fn baz<'a>(x: &'a str, y: &str) -> &str { }
416 Lifetime elision in implementation headers was part of the lifetime elision
417 RFC. It is, however, [currently unimplemented][iss15872].
419 [book-le]: https://doc.rust-lang.org/nightly/book/first-edition/lifetimes.html#lifetime-elision
420 [iss15872]: https://github.com/rust-lang/rust/issues/15872
424 There are conflicting trait implementations for the same type.
425 Example of erroneous code:
427 ```compile_fail,E0119
429 fn get(&self) -> usize;
432 impl<T> MyTrait for T {
433 fn get(&self) -> usize { 0 }
440 impl MyTrait for Foo { // error: conflicting implementations of trait
441 // `MyTrait` for type `Foo`
442 fn get(&self) -> usize { self.value }
446 When looking for the implementation for the trait, the compiler finds
447 both the `impl<T> MyTrait for T` where T is all types and the `impl
448 MyTrait for Foo`. Since a trait cannot be implemented multiple times,
449 this is an error. So, when you write:
453 fn get(&self) -> usize;
456 impl<T> MyTrait for T {
457 fn get(&self) -> usize { 0 }
461 This makes the trait implemented on all types in the scope. So if you
462 try to implement it on another one after that, the implementations will
467 fn get(&self) -> usize;
470 impl<T> MyTrait for T {
471 fn get(&self) -> usize { 0 }
479 f.get(); // the trait is implemented so we can use it
484 // This shouldn't really ever trigger since the repeated value error comes first
486 A binary can only have one entry point, and by default that entry point is the
487 function `main()`. If there are multiple such functions, please rename one.
491 More than one function was declared with the `#[main]` attribute.
493 Erroneous code example:
495 ```compile_fail,E0137
502 fn f() {} // error: multiple functions with a #[main] attribute
505 This error indicates that the compiler found multiple functions with the
506 `#[main]` attribute. This is an error because there must be a unique entry
507 point into a Rust program. Example:
518 More than one function was declared with the `#[start]` attribute.
520 Erroneous code example:
522 ```compile_fail,E0138
526 fn foo(argc: isize, argv: *const *const u8) -> isize {}
529 fn f(argc: isize, argv: *const *const u8) -> isize {}
530 // error: multiple 'start' functions
533 This error indicates that the compiler found multiple functions with the
534 `#[start]` attribute. This is an error because there must be a unique entry
535 point into a Rust program. Example:
541 fn foo(argc: isize, argv: *const *const u8) -> isize { 0 } // ok!
546 #### Note: this error code is no longer emitted by the compiler.
548 There are various restrictions on transmuting between types in Rust; for example
549 types being transmuted must have the same size. To apply all these restrictions,
550 the compiler must know the exact types that may be transmuted. When type
551 parameters are involved, this cannot always be done.
553 So, for example, the following is not allowed:
556 use std::mem::transmute;
558 struct Foo<T>(Vec<T>);
560 fn foo<T>(x: Vec<T>) {
561 // we are transmuting between Vec<T> and Foo<F> here
562 let y: Foo<T> = unsafe { transmute(x) };
563 // do something with y
567 In this specific case there's a good chance that the transmute is harmless (but
568 this is not guaranteed by Rust). However, when alignment and enum optimizations
569 come into the picture, it's quite likely that the sizes may or may not match
570 with different type parameter substitutions. It's not possible to check this for
571 _all_ possible types, so `transmute()` simply only accepts types without any
572 unsubstituted type parameters.
574 If you need this, there's a good chance you're doing something wrong. Keep in
575 mind that Rust doesn't guarantee much about the layout of different structs
576 (even two structs with identical declarations may have different layouts). If
577 there is a solution that avoids the transmute entirely, try it instead.
579 If it's possible, hand-monomorphize the code by writing the function for each
580 possible type substitution. It's possible to use traits to do this cleanly,
584 use std::mem::transmute;
586 struct Foo<T>(Vec<T>);
588 trait MyTransmutableType: Sized {
589 fn transmute(_: Vec<Self>) -> Foo<Self>;
592 impl MyTransmutableType for u8 {
593 fn transmute(x: Vec<u8>) -> Foo<u8> {
594 unsafe { transmute(x) }
598 impl MyTransmutableType for String {
599 fn transmute(x: Vec<String>) -> Foo<String> {
600 unsafe { transmute(x) }
604 // ... more impls for the types you intend to transmute
606 fn foo<T: MyTransmutableType>(x: Vec<T>) {
607 let y: Foo<T> = <T as MyTransmutableType>::transmute(x);
608 // do something with y
612 Each impl will be checked for a size match in the transmute as usual, and since
613 there are no unbound type parameters involved, this should compile unless there
614 is a size mismatch in one of the impls.
616 It is also possible to manually transmute:
620 # let v = Some("value");
621 # type SomeType = &'static [u8];
623 ptr::read(&v as *const _ as *const SomeType) // `v` transmuted to `SomeType`
628 Note that this does not move `v` (unlike `transmute`), and may need a
629 call to `mem::forget(v)` in case you want to avoid destructors being called.
633 A lang item was redefined.
635 Erroneous code example:
637 ```compile_fail,E0152
638 #![feature(lang_items)]
640 #[lang = "panic_fmt"]
641 struct Foo; // error: duplicate lang item found: `panic_fmt`
644 Lang items are already implemented in the standard library. Unless you are
645 writing a free-standing application (e.g. a kernel), you do not need to provide
648 You can build a free-standing crate by adding `#![no_std]` to the crate
651 ```ignore (only-for-syntax-highlight)
655 See also https://doc.rust-lang.org/book/first-edition/no-stdlib.html
659 A generic type was described using parentheses rather than angle brackets.
662 ```compile_fail,E0214
664 let v: Vec(&str) = vec!["foo"];
668 This is not currently supported: `v` should be defined as `Vec<&str>`.
669 Parentheses are currently only used with generic types when defining parameters
670 for `Fn`-family traits.
674 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
675 message for when a particular trait isn't implemented on a type placed in a
676 position that needs that trait. For example, when the following code is
680 #![feature(on_unimplemented)]
682 fn foo<T: Index<u8>>(x: T){}
684 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
685 trait Index<Idx> { /* ... */ }
687 foo(true); // `bool` does not implement `Index<u8>`
690 There will be an error about `bool` not implementing `Index<u8>`, followed by a
691 note saying "the type `bool` cannot be indexed by `u8`".
693 As you can see, you can specify type parameters in curly braces for
694 substitution with the actual types (using the regular format string syntax) in
695 a given situation. Furthermore, `{Self}` will substitute to the type (in this
696 case, `bool`) that we tried to use.
698 This error appears when the curly braces contain an identifier which doesn't
699 match with any of the type parameters or the string `Self`. This might happen
700 if you misspelled a type parameter, or if you intended to use literal curly
701 braces. If it is the latter, escape the curly braces with a second curly brace
702 of the same type; e.g. a literal `{` is `{{`.
706 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
707 message for when a particular trait isn't implemented on a type placed in a
708 position that needs that trait. For example, when the following code is
712 #![feature(on_unimplemented)]
714 fn foo<T: Index<u8>>(x: T){}
716 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
717 trait Index<Idx> { /* ... */ }
719 foo(true); // `bool` does not implement `Index<u8>`
722 there will be an error about `bool` not implementing `Index<u8>`, followed by a
723 note saying "the type `bool` cannot be indexed by `u8`".
725 As you can see, you can specify type parameters in curly braces for
726 substitution with the actual types (using the regular format string syntax) in
727 a given situation. Furthermore, `{Self}` will substitute to the type (in this
728 case, `bool`) that we tried to use.
730 This error appears when the curly braces do not contain an identifier. Please
731 add one of the same name as a type parameter. If you intended to use literal
732 braces, use `{{` and `}}` to escape them.
736 The `#[rustc_on_unimplemented]` attribute lets you specify a custom error
737 message for when a particular trait isn't implemented on a type placed in a
738 position that needs that trait. For example, when the following code is
742 #![feature(on_unimplemented)]
744 fn foo<T: Index<u8>>(x: T){}
746 #[rustc_on_unimplemented = "the type `{Self}` cannot be indexed by `{Idx}`"]
747 trait Index<Idx> { /* ... */ }
749 foo(true); // `bool` does not implement `Index<u8>`
752 there will be an error about `bool` not implementing `Index<u8>`, followed by a
753 note saying "the type `bool` cannot be indexed by `u8`".
755 For this to work, some note must be specified. An empty attribute will not do
756 anything, please remove the attribute or add some helpful note for users of the
761 When using a lifetime like `'a` in a type, it must be declared before being
764 These two examples illustrate the problem:
766 ```compile_fail,E0261
767 // error, use of undeclared lifetime name `'a`
768 fn foo(x: &'a str) { }
771 // error, use of undeclared lifetime name `'a`
776 These can be fixed by declaring lifetime parameters:
779 fn foo<'a>(x: &'a str) {}
788 Declaring certain lifetime names in parameters is disallowed. For example,
789 because the `'static` lifetime is a special built-in lifetime name denoting
790 the lifetime of the entire program, this is an error:
792 ```compile_fail,E0262
793 // error, invalid lifetime parameter name `'static`
794 fn foo<'static>(x: &'static str) { }
799 A lifetime name cannot be declared more than once in the same scope. For
802 ```compile_fail,E0263
803 // error, lifetime name `'a` declared twice in the same scope
804 fn foo<'a, 'b, 'a>(x: &'a str, y: &'b str) { }
809 An unknown external lang item was used. Erroneous code example:
811 ```compile_fail,E0264
812 #![feature(lang_items)]
815 #[lang = "cake"] // error: unknown external lang item: `cake`
820 A list of available external lang items is available in
821 `src/librustc/middle/weak_lang_items.rs`. Example:
824 #![feature(lang_items)]
827 #[lang = "panic_fmt"] // ok!
834 This is because of a type mismatch between the associated type of some
835 trait (e.g. `T::Bar`, where `T` implements `trait Quux { type Bar; }`)
836 and another type `U` that is required to be equal to `T::Bar`, but is not.
839 Here is a basic example:
841 ```compile_fail,E0271
842 trait Trait { type AssociatedType; }
844 fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
848 impl Trait for i8 { type AssociatedType = &'static str; }
853 Here is that same example again, with some explanatory comments:
855 ```compile_fail,E0271
856 trait Trait { type AssociatedType; }
858 fn foo<T>(t: T) where T: Trait<AssociatedType=u32> {
859 // ~~~~~~~~ ~~~~~~~~~~~~~~~~~~
861 // This says `foo` can |
862 // only be used with |
864 // implements `Trait`. |
866 // This says not only must
867 // `T` be an impl of `Trait`
868 // but also that the impl
869 // must assign the type `u32`
870 // to the associated type.
874 impl Trait for i8 { type AssociatedType = &'static str; }
875 //~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
880 // ... but it is an implementation
881 // that assigns `&'static str` to
882 // the associated type.
885 // Here, we invoke `foo` with an `i8`, which does not satisfy
886 // the constraint `<i8 as Trait>::AssociatedType=u32`, and
887 // therefore the type-checker complains with this error code.
890 Here is a more subtle instance of the same problem, that can
891 arise with for-loops in Rust:
894 let vs: Vec<i32> = vec![1, 2, 3, 4];
903 The above fails because of an analogous type mismatch,
904 though may be harder to see. Again, here are some
905 explanatory comments for the same example:
909 let vs = vec![1, 2, 3, 4];
911 // `for`-loops use a protocol based on the `Iterator`
912 // trait. Each item yielded in a `for` loop has the
913 // type `Iterator::Item` -- that is, `Item` is the
914 // associated type of the concrete iterator impl.
918 // | We borrow `vs`, iterating over a sequence of
919 // | *references* of type `&Elem` (where `Elem` is
920 // | vector's element type). Thus, the associated
921 // | type `Item` must be a reference `&`-type ...
923 // ... and `v` has the type `Iterator::Item`, as dictated by
924 // the `for`-loop protocol ...
930 // ... but *here*, `v` is forced to have some integral type;
931 // only types like `u8`,`i8`,`u16`,`i16`, et cetera can
932 // match the pattern `1` ...
937 // ... therefore, the compiler complains, because it sees
938 // an attempt to solve the equations
939 // `some integral-type` = type-of-`v`
940 // = `Iterator::Item`
941 // = `&Elem` (i.e. `some reference type`)
943 // which cannot possibly all be true.
949 To avoid those issues, you have to make the types match correctly.
950 So we can fix the previous examples like this:
954 trait Trait { type AssociatedType; }
956 fn foo<T>(t: T) where T: Trait<AssociatedType = &'static str> {
960 impl Trait for i8 { type AssociatedType = &'static str; }
965 let vs = vec![1, 2, 3, 4];
977 This error occurs when there was a recursive trait requirement that overflowed
978 before it could be evaluated. Often this means that there is unbounded
979 recursion in resolving some type bounds.
981 For example, in the following code:
983 ```compile_fail,E0275
988 impl<T> Foo for T where Bar<T>: Foo {}
991 To determine if a `T` is `Foo`, we need to check if `Bar<T>` is `Foo`. However,
992 to do this check, we need to determine that `Bar<Bar<T>>` is `Foo`. To
993 determine this, we check if `Bar<Bar<Bar<T>>>` is `Foo`, and so on. This is
994 clearly a recursive requirement that can't be resolved directly.
996 Consider changing your trait bounds so that they're less self-referential.
1000 This error occurs when a bound in an implementation of a trait does not match
1001 the bounds specified in the original trait. For example:
1003 ```compile_fail,E0276
1009 fn foo<T>(x: T) where T: Copy {}
1013 Here, all types implementing `Foo` must have a method `foo<T>(x: T)` which can
1014 take any type `T`. However, in the `impl` for `bool`, we have added an extra
1015 bound that `T` is `Copy`, which isn't compatible with the original trait.
1017 Consider removing the bound from the method or adding the bound to the original
1018 method definition in the trait.
1022 You tried to use a type which doesn't implement some trait in a place which
1023 expected that trait. Erroneous code example:
1025 ```compile_fail,E0277
1026 // here we declare the Foo trait with a bar method
1031 // we now declare a function which takes an object implementing the Foo trait
1032 fn some_func<T: Foo>(foo: T) {
1037 // we now call the method with the i32 type, which doesn't implement
1039 some_func(5i32); // error: the trait bound `i32 : Foo` is not satisfied
1043 In order to fix this error, verify that the type you're using does implement
1051 fn some_func<T: Foo>(foo: T) {
1052 foo.bar(); // we can now use this method since i32 implements the
1056 // we implement the trait on the i32 type
1062 some_func(5i32); // ok!
1066 Or in a generic context, an erroneous code example would look like:
1068 ```compile_fail,E0277
1069 fn some_func<T>(foo: T) {
1070 println!("{:?}", foo); // error: the trait `core::fmt::Debug` is not
1071 // implemented for the type `T`
1075 // We now call the method with the i32 type,
1076 // which *does* implement the Debug trait.
1081 Note that the error here is in the definition of the generic function: Although
1082 we only call it with a parameter that does implement `Debug`, the compiler
1083 still rejects the function: It must work with all possible input types. In
1084 order to make this example compile, we need to restrict the generic type we're
1090 // Restrict the input type to types that implement Debug.
1091 fn some_func<T: fmt::Debug>(foo: T) {
1092 println!("{:?}", foo);
1096 // Calling the method is still fine, as i32 implements Debug.
1099 // This would fail to compile now:
1100 // struct WithoutDebug;
1101 // some_func(WithoutDebug);
1105 Rust only looks at the signature of the called function, as such it must
1106 already specify all requirements that will be used for every type parameter.
1110 #### Note: this error code is no longer emitted by the compiler.
1112 You tried to supply a type which doesn't implement some trait in a location
1113 which expected that trait. This error typically occurs when working with
1114 `Fn`-based types. Erroneous code example:
1117 fn foo<F: Fn(usize)>(x: F) { }
1120 // type mismatch: ... implements the trait `core::ops::Fn<(String,)>`,
1121 // but the trait `core::ops::Fn<(usize,)>` is required
1123 foo(|y: String| { });
1127 The issue in this case is that `foo` is defined as accepting a `Fn` with one
1128 argument of type `String`, but the closure we attempted to pass to it requires
1129 one arguments of type `usize`.
1133 This error indicates that type inference did not result in one unique possible
1134 type, and extra information is required. In most cases this can be provided
1135 by adding a type annotation. Sometimes you need to specify a generic type
1138 A common example is the `collect` method on `Iterator`. It has a generic type
1139 parameter with a `FromIterator` bound, which for a `char` iterator is
1140 implemented by `Vec` and `String` among others. Consider the following snippet
1141 that reverses the characters of a string:
1143 ```compile_fail,E0282
1144 let x = "hello".chars().rev().collect();
1147 In this case, the compiler cannot infer what the type of `x` should be:
1148 `Vec<char>` and `String` are both suitable candidates. To specify which type to
1149 use, you can use a type annotation on `x`:
1152 let x: Vec<char> = "hello".chars().rev().collect();
1155 It is not necessary to annotate the full type. Once the ambiguity is resolved,
1156 the compiler can infer the rest:
1159 let x: Vec<_> = "hello".chars().rev().collect();
1162 Another way to provide the compiler with enough information, is to specify the
1163 generic type parameter:
1166 let x = "hello".chars().rev().collect::<Vec<char>>();
1169 Again, you need not specify the full type if the compiler can infer it:
1172 let x = "hello".chars().rev().collect::<Vec<_>>();
1175 Apart from a method or function with a generic type parameter, this error can
1176 occur when a type parameter of a struct or trait cannot be inferred. In that
1177 case it is not always possible to use a type annotation, because all candidates
1178 have the same return type. For instance:
1180 ```compile_fail,E0282
1191 let number = Foo::bar();
1196 This will fail because the compiler does not know which instance of `Foo` to
1197 call `bar` on. Change `Foo::bar()` to `Foo::<T>::bar()` to resolve the error.
1201 This error occurs when the compiler doesn't have enough information
1202 to unambiguously choose an implementation.
1206 ```compile_fail,E0283
1213 impl Generator for Impl {
1214 fn create() -> u32 { 1 }
1219 impl Generator for AnotherImpl {
1220 fn create() -> u32 { 2 }
1224 let cont: u32 = Generator::create();
1225 // error, impossible to choose one of Generator trait implementation
1226 // Impl or AnotherImpl? Maybe anything else?
1230 To resolve this error use the concrete type:
1239 impl Generator for AnotherImpl {
1240 fn create() -> u32 { 2 }
1244 let gen1 = AnotherImpl::create();
1246 // if there are multiple methods with same name (different traits)
1247 let gen2 = <AnotherImpl as Generator>::create();
1253 This error indicates that the given recursion limit could not be parsed. Ensure
1254 that the value provided is a positive integer between quotes.
1256 Erroneous code example:
1258 ```compile_fail,E0296
1264 And a working example:
1267 #![recursion_limit="1000"]
1274 This error occurs when the compiler was unable to infer the concrete type of a
1275 variable. It can occur for several cases, the most common of which is a
1276 mismatch in the expected type that the compiler inferred for a variable's
1277 initializing expression, and the actual type explicitly assigned to the
1282 ```compile_fail,E0308
1283 let x: i32 = "I am not a number!";
1284 // ~~~ ~~~~~~~~~~~~~~~~~~~~
1286 // | initializing expression;
1287 // | compiler infers type `&str`
1289 // type `i32` assigned to variable `x`
1294 Types in type definitions have lifetimes associated with them that represent
1295 how long the data stored within them is guaranteed to be live. This lifetime
1296 must be as long as the data needs to be alive, and missing the constraint that
1297 denotes this will cause this error.
1299 ```compile_fail,E0309
1300 // This won't compile because T is not constrained, meaning the data
1301 // stored in it is not guaranteed to last as long as the reference
1307 This will compile, because it has the constraint on the type parameter:
1310 struct Foo<'a, T: 'a> {
1315 To see why this is important, consider the case where `T` is itself a reference
1316 (e.g., `T = &str`). If we don't include the restriction that `T: 'a`, the
1317 following code would be perfectly legal:
1319 ```compile_fail,E0309
1325 let v = "42".to_string();
1326 let f = Foo{foo: &v};
1328 println!("{}", f.foo); // but we've already dropped v!
1334 Types in type definitions have lifetimes associated with them that represent
1335 how long the data stored within them is guaranteed to be live. This lifetime
1336 must be as long as the data needs to be alive, and missing the constraint that
1337 denotes this will cause this error.
1339 ```compile_fail,E0310
1340 // This won't compile because T is not constrained to the static lifetime
1341 // the reference needs
1347 This will compile, because it has the constraint on the type parameter:
1350 struct Foo<T: 'static> {
1357 This error occurs when an `if` expression without an `else` block is used in a
1358 context where a type other than `()` is expected, for example a `let`
1361 ```compile_fail,E0317
1364 let a = if x == 5 { 1 };
1368 An `if` expression without an `else` block has the type `()`, so this is a type
1369 error. To resolve it, add an `else` block having the same type as the `if`
1374 This error indicates that some types or traits depend on each other
1375 and therefore cannot be constructed.
1377 The following example contains a circular dependency between two traits:
1379 ```compile_fail,E0391
1380 trait FirstTrait : SecondTrait {
1384 trait SecondTrait : FirstTrait {
1391 #### Note: this error code is no longer emitted by the compiler.
1393 In Rust 1.3, the default object lifetime bounds are expected to change, as
1394 described in [RFC 1156]. You are getting a warning because the compiler
1395 thinks it is possible that this change will cause a compilation error in your
1396 code. It is possible, though unlikely, that this is a false alarm.
1398 The heart of the change is that where `&'a Box<SomeTrait>` used to default to
1399 `&'a Box<SomeTrait+'a>`, it now defaults to `&'a Box<SomeTrait+'static>` (here,
1400 `SomeTrait` is the name of some trait type). Note that the only types which are
1401 affected are references to boxes, like `&Box<SomeTrait>` or
1402 `&[Box<SomeTrait>]`. More common types like `&SomeTrait` or `Box<SomeTrait>`
1405 To silence this warning, edit your code to use an explicit bound. Most of the
1406 time, this means that you will want to change the signature of a function that
1407 you are calling. For example, if the error is reported on a call like `foo(x)`,
1408 and `foo` is defined as follows:
1411 # trait SomeTrait {}
1412 fn foo(arg: &Box<SomeTrait>) { /* ... */ }
1415 You might change it to:
1418 # trait SomeTrait {}
1419 fn foo<'a>(arg: &'a Box<SomeTrait+'a>) { /* ... */ }
1422 This explicitly states that you expect the trait object `SomeTrait` to contain
1423 references (with a maximum lifetime of `'a`).
1425 [RFC 1156]: https://github.com/rust-lang/rfcs/blob/master/text/1156-adjust-default-object-bounds.md
1429 An invalid lint attribute has been given. Erroneous code example:
1431 ```compile_fail,E0452
1432 #![allow(foo = "")] // error: malformed lint attribute
1435 Lint attributes only accept a list of identifiers (where each identifier is a
1436 lint name). Ensure the attribute is of this form:
1439 #![allow(foo)] // ok!
1441 #![allow(foo, foo2)] // ok!
1446 A lint check attribute was overruled by a `forbid` directive set as an
1447 attribute on an enclosing scope, or on the command line with the `-F` option.
1449 Example of erroneous code:
1451 ```compile_fail,E0453
1452 #![forbid(non_snake_case)]
1454 #[allow(non_snake_case)]
1456 let MyNumber = 2; // error: allow(non_snake_case) overruled by outer
1457 // forbid(non_snake_case)
1461 The `forbid` lint setting, like `deny`, turns the corresponding compiler
1462 warning into a hard error. Unlike `deny`, `forbid` prevents itself from being
1463 overridden by inner attributes.
1465 If you're sure you want to override the lint check, you can change `forbid` to
1466 `deny` (or use `-D` instead of `-F` if the `forbid` setting was given as a
1467 command-line option) to allow the inner lint check attribute:
1470 #![deny(non_snake_case)]
1472 #[allow(non_snake_case)]
1474 let MyNumber = 2; // ok!
1478 Otherwise, edit the code to pass the lint check, and remove the overruled
1482 #![forbid(non_snake_case)]
1491 A lifetime bound was not satisfied.
1493 Erroneous code example:
1495 ```compile_fail,E0478
1496 // Check that the explicit lifetime bound (`'SnowWhite`, in this example) must
1497 // outlive all the superbounds from the trait (`'kiss`, in this example).
1499 trait Wedding<'t>: 't { }
1501 struct Prince<'kiss, 'SnowWhite> {
1502 child: Box<Wedding<'kiss> + 'SnowWhite>,
1503 // error: lifetime bound not satisfied
1507 In this example, the `'SnowWhite` lifetime is supposed to outlive the `'kiss`
1508 lifetime but the declaration of the `Prince` struct doesn't enforce it. To fix
1509 this issue, you need to specify it:
1512 trait Wedding<'t>: 't { }
1514 struct Prince<'kiss, 'SnowWhite: 'kiss> { // You say here that 'kiss must live
1515 // longer than 'SnowWhite.
1516 child: Box<Wedding<'kiss> + 'SnowWhite>, // And now it's all good!
1522 A reference has a longer lifetime than the data it references.
1524 Erroneous code example:
1526 ```compile_fail,E0491
1527 // struct containing a reference requires a lifetime parameter,
1528 // because the data the reference points to must outlive the struct (see E0106)
1533 // However, a nested struct like this, the signature itself does not tell
1534 // whether 'a outlives 'b or the other way around.
1535 // So it could be possible that 'b of reference outlives 'a of the data.
1536 struct Nested<'a, 'b> {
1537 ref_struct: &'b Struct<'a>, // compile error E0491
1541 To fix this issue, you can specify a bound to the lifetime like below:
1548 // 'a: 'b means 'a outlives 'b
1549 struct Nested<'a: 'b, 'b> {
1550 ref_struct: &'b Struct<'a>,
1556 A lifetime name is shadowing another lifetime name. Erroneous code example:
1558 ```compile_fail,E0496
1564 fn f<'a>(x: &'a i32) { // error: lifetime name `'a` shadows a lifetime
1565 // name that is already in scope
1570 Please change the name of one of the lifetimes to remove this error. Example:
1578 fn f<'b>(x: &'b i32) { // ok!
1588 A stability attribute was used outside of the standard library. Erroneous code
1592 #[stable] // error: stability attributes may not be used outside of the
1597 It is not possible to use stability attributes outside of the standard library.
1598 Also, for now, it is not possible to write deprecation messages either.
1602 Transmute with two differently sized types was attempted. Erroneous code
1605 ```compile_fail,E0512
1606 fn takes_u8(_: u8) {}
1609 unsafe { takes_u8(::std::mem::transmute(0u16)); }
1610 // error: transmute called with types of different sizes
1614 Please use types with same size or use the expected type directly. Example:
1617 fn takes_u8(_: u8) {}
1620 unsafe { takes_u8(::std::mem::transmute(0i8)); } // ok!
1622 unsafe { takes_u8(0u8); } // ok!
1628 This error indicates that a `#[repr(..)]` attribute was placed on an
1631 Examples of erroneous code:
1633 ```compile_fail,E0517
1641 struct Foo {bar: bool, baz: bool}
1649 * The `#[repr(C)]` attribute can only be placed on structs and enums.
1650 * The `#[repr(packed)]` and `#[repr(simd)]` attributes only work on structs.
1651 * The `#[repr(u8)]`, `#[repr(i16)]`, etc attributes only work on enums.
1653 These attributes do not work on typedefs, since typedefs are just aliases.
1655 Representations like `#[repr(u8)]`, `#[repr(i64)]` are for selecting the
1656 discriminant size for enums with no data fields on any of the variants, e.g.
1657 `enum Color {Red, Blue, Green}`, effectively setting the size of the enum to
1658 the size of the provided type. Such an enum can be cast to a value of the same
1659 type as well. In short, `#[repr(u8)]` makes the enum behave like an integer
1660 with a constrained set of allowed values.
1662 Only field-less enums can be cast to numerical primitives, so this attribute
1663 will not apply to structs.
1665 `#[repr(packed)]` reduces padding to make the struct size smaller. The
1666 representation of enums isn't strictly defined in Rust, and this attribute
1667 won't work on enums.
1669 `#[repr(simd)]` will give a struct consisting of a homogeneous series of machine
1670 types (i.e. `u8`, `i32`, etc) a representation that permits vectorization via
1671 SIMD. This doesn't make much sense for enums since they don't consist of a
1672 single list of data.
1676 This error indicates that an `#[inline(..)]` attribute was incorrectly placed
1677 on something other than a function or method.
1679 Examples of erroneous code:
1681 ```compile_fail,E0518
1691 `#[inline]` hints the compiler whether or not to attempt to inline a method or
1692 function. By default, the compiler does a pretty good job of figuring this out
1693 itself, but if you feel the need for annotations, `#[inline(always)]` and
1694 `#[inline(never)]` can override or force the compiler's decision.
1696 If you wish to apply this attribute to all methods in an impl, manually annotate
1697 each method; it is not possible to annotate the entire impl with an `#[inline]`
1702 The lang attribute is intended for marking special items that are built-in to
1703 Rust itself. This includes special traits (like `Copy` and `Sized`) that affect
1704 how the compiler behaves, as well as special functions that may be automatically
1705 invoked (such as the handler for out-of-bounds accesses when indexing a slice).
1706 Erroneous code example:
1708 ```compile_fail,E0522
1709 #![feature(lang_items)]
1712 fn cookie() -> ! { // error: definition of an unknown language item: `cookie`
1719 A closure was used but didn't implement the expected trait.
1721 Erroneous code example:
1723 ```compile_fail,E0525
1727 fn bar<T: Fn(u32)>(_: T) {}
1731 let closure = |_| foo(x); // error: expected a closure that implements
1732 // the `Fn` trait, but this closure only
1733 // implements `FnOnce`
1738 In the example above, `closure` is an `FnOnce` closure whereas the `bar`
1739 function expected an `Fn` closure. In this case, it's simple to fix the issue,
1740 you just have to implement `Copy` and `Clone` traits on `struct X` and it'll
1744 #[derive(Clone, Copy)] // We implement `Clone` and `Copy` traits.
1748 fn bar<T: Fn(u32)>(_: T) {}
1752 let closure = |_| foo(x);
1753 bar(closure); // ok!
1757 To understand better how closures work in Rust, read:
1758 https://doc.rust-lang.org/book/first-edition/closures.html
1762 The `main` function was incorrectly declared.
1764 Erroneous code example:
1766 ```compile_fail,E0580
1767 fn main() -> i32 { // error: main function has wrong type
1772 The `main` function prototype should never take arguments or return type.
1781 If you want to get command-line arguments, use `std::env::args`. To exit with a
1782 specified exit code, use `std::process::exit`.
1786 Abstract return types (written `impl Trait` for some trait `Trait`) are only
1787 allowed as function return types.
1789 Erroneous code example:
1791 ```compile_fail,E0562
1792 #![feature(conservative_impl_trait)]
1795 let count_to_ten: impl Iterator<Item=usize> = 0..10;
1796 // error: `impl Trait` not allowed outside of function and inherent method
1798 for i in count_to_ten {
1804 Make sure `impl Trait` only appears in return-type position.
1807 #![feature(conservative_impl_trait)]
1809 fn count_to_n(n: usize) -> impl Iterator<Item=usize> {
1814 for i in count_to_n(10) { // ok!
1820 See [RFC 1522] for more details.
1822 [RFC 1522]: https://github.com/rust-lang/rfcs/blob/master/text/1522-conservative-impl-trait.md
1826 Per [RFC 401][rfc401], if you have a function declaration `foo`:
1829 // For the purposes of this explanation, all of these
1830 // different kinds of `fn` declarations are equivalent:
1832 fn foo(x: S) { /* ... */ }
1833 # #[cfg(for_demonstration_only)]
1834 extern "C" { fn foo(x: S); }
1835 # #[cfg(for_demonstration_only)]
1836 impl S { fn foo(self) { /* ... */ } }
1839 the type of `foo` is **not** `fn(S)`, as one might expect.
1840 Rather, it is a unique, zero-sized marker type written here as `typeof(foo)`.
1841 However, `typeof(foo)` can be _coerced_ to a function pointer `fn(S)`,
1842 so you rarely notice this:
1847 let x: fn(S) = foo; // OK, coerces
1850 The reason that this matter is that the type `fn(S)` is not specific to
1851 any particular function: it's a function _pointer_. So calling `x()` results
1852 in a virtual call, whereas `foo()` is statically dispatched, because the type
1853 of `foo` tells us precisely what function is being called.
1855 As noted above, coercions mean that most code doesn't have to be
1856 concerned with this distinction. However, you can tell the difference
1857 when using **transmute** to convert a fn item into a fn pointer.
1859 This is sometimes done as part of an FFI:
1861 ```compile_fail,E0591
1862 extern "C" fn foo(userdata: Box<i32>) {
1866 # fn callback(_: extern "C" fn(*mut i32)) {}
1867 # use std::mem::transmute;
1869 let f: extern "C" fn(*mut i32) = transmute(foo);
1874 Here, transmute is being used to convert the types of the fn arguments.
1875 This pattern is incorrect because, because the type of `foo` is a function
1876 **item** (`typeof(foo)`), which is zero-sized, and the target type (`fn()`)
1877 is a function pointer, which is not zero-sized.
1878 This pattern should be rewritten. There are a few possible ways to do this:
1880 - change the original fn declaration to match the expected signature,
1881 and do the cast in the fn body (the preferred option)
1882 - cast the fn item fo a fn pointer before calling transmute, as shown here:
1885 # extern "C" fn foo(_: Box<i32>) {}
1886 # use std::mem::transmute;
1888 let f: extern "C" fn(*mut i32) = transmute(foo as extern "C" fn(_));
1889 let f: extern "C" fn(*mut i32) = transmute(foo as usize); // works too
1893 The same applies to transmutes to `*mut fn()`, which were observedin practice.
1894 Note though that use of this type is generally incorrect.
1895 The intention is typically to describe a function pointer, but just `fn()`
1896 alone suffices for that. `*mut fn()` is a pointer to a fn pointer.
1897 (Since these values are typically just passed to C code, however, this rarely
1898 makes a difference in practice.)
1900 [rfc401]: https://github.com/rust-lang/rfcs/blob/master/text/0401-coercions.md
1904 You tried to supply an `Fn`-based type with an incorrect number of arguments
1905 than what was expected.
1907 Erroneous code example:
1909 ```compile_fail,E0593
1910 fn foo<F: Fn()>(x: F) { }
1913 // [E0593] closure takes 1 argument but 0 arguments are required
1920 No `main` function was found in a binary crate. To fix this error, add a
1921 `main` function. For example:
1925 // Your program will start here.
1926 println!("Hello world!");
1930 If you don't know the basics of Rust, you can go look to the Rust Book to get
1931 started: https://doc.rust-lang.org/book/
1935 An unknown lint was used on the command line.
1940 rustc -D bogus omse_file.rs
1943 Maybe you just misspelled the lint name or the lint doesn't exist anymore.
1944 Either way, try to update/remove it in order to fix the error.
1948 This error code indicates a mismatch between the lifetimes appearing in the
1949 function signature (i.e., the parameter types and the return type) and the
1950 data-flow found in the function body.
1952 Erroneous code example:
1954 ```compile_fail,E0621
1955 fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 { // error: explicit lifetime
1956 // required in the type of
1958 if x > y { x } else { y }
1962 In the code above, the function is returning data borrowed from either `x` or
1963 `y`, but the `'a` annotation indicates that it is returning data only from `x`.
1964 To fix the error, the signature and the body must be made to match. Typically,
1965 this is done by updating the function signature. So, in this case, we change
1966 the type of `y` to `&'a i32`, like so:
1969 fn foo<'a>(x: &'a i32, y: &'a i32) -> &'a i32 {
1970 if x > y { x } else { y }
1974 Now the signature indicates that the function data borrowed from either `x` or
1975 `y`. Alternatively, you could change the body to not return data from `y`:
1978 fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
1985 A closure or generator was constructed that references its own type.
1989 ```compile-fail,E0644
1998 // Here, when `x` is called, the parameter `y` is equal to `x`.
2003 Rust does not permit a closure to directly reference its own type,
2004 either through an argument (as in the example above) or by capturing
2005 itself through its environment. This restriction helps keep closure
2006 inference tractable.
2008 The easiest fix is to rewrite your closure into a top-level function,
2009 or into a method. In some cases, you may also be able to have your
2010 closure call itself by capturing a `&Fn()` object or `fn()` pointer
2011 that refers to itself. That is permitting, since the closure would be
2012 invoking itself via a virtual call, and hence does not directly
2013 reference its own *type*.
2018 A `repr(transparent)` type was also annotated with other, incompatible
2019 representation hints.
2021 Erroneous code example:
2023 ```compile_fail,E0692
2024 #![feature(repr_transparent)]
2026 #[repr(transparent, C)] // error: incompatible representation hints
2030 A type annotated as `repr(transparent)` delegates all representation concerns to
2031 another type, so adding more representation hints is contradictory. Remove
2032 either the `transparent` hint or the other hints, like this:
2035 #![feature(repr_transparent)]
2037 #[repr(transparent)]
2041 Alternatively, move the other attributes to the contained type:
2044 #![feature(repr_transparent)]
2052 #[repr(transparent)]
2053 struct FooWrapper(Foo);
2056 Note that introducing another `struct` just to have a place for the other
2057 attributes may have unintended side effects on the representation:
2060 #![feature(repr_transparent)]
2062 #[repr(transparent)]
2068 #[repr(transparent)]
2069 struct Grams2(Float); // this is not equivalent to `Grams` above
2072 Here, `Grams2` is a not equivalent to `Grams` -- the former transparently wraps
2073 a (non-transparent) struct containing a single float, while `Grams` is a
2074 transparent wrapper around a float. This can make a difference for the ABI.
2078 The `impl Trait` return type captures lifetime parameters that do not
2079 appear within the `impl Trait` itself.
2081 Erroneous code example:
2083 ```compile-fail,E0909
2084 #![feature(conservative_impl_trait)]
2086 use std::cell::Cell;
2090 impl<'a, 'b> Trait<'b> for Cell<&'a u32> { }
2092 fn foo<'x, 'y>(x: Cell<&'x u32>) -> impl Trait<'y>
2099 Here, the function `foo` returns a value of type `Cell<&'x u32>`,
2100 which references the lifetime `'x`. However, the return type is
2101 declared as `impl Trait<'y>` -- this indicates that `foo` returns
2102 "some type that implements `Trait<'y>`", but it also indicates that
2103 the return type **only captures data referencing the lifetime `'y`**.
2104 In this case, though, we are referencing data with lifetime `'x`, so
2105 this function is in error.
2107 To fix this, you must reference the lifetime `'x` from the return
2108 type. For example, changing the return type to `impl Trait<'y> + 'x`
2112 #![feature(conservative_impl_trait)]
2114 use std::cell::Cell;
2118 impl<'a,'b> Trait<'b> for Cell<&'a u32> { }
2120 fn foo<'x, 'y>(x: Cell<&'x u32>) -> impl Trait<'y> + 'x
2132 register_diagnostics! {
2133 // E0006 // merged with E0005
2134 // E0101, // replaced with E0282
2135 // E0102, // replaced with E0282
2138 // E0272, // on_unimplemented #0
2139 // E0273, // on_unimplemented #1
2140 // E0274, // on_unimplemented #2
2141 E0278, // requirement is not satisfied
2142 E0279, // requirement is not satisfied
2143 E0280, // requirement is not satisfied
2144 E0284, // cannot resolve type
2145 // E0285, // overflow evaluation builtin bounds
2146 // E0300, // unexpanded macro
2147 // E0304, // expected signed integer constant
2148 // E0305, // expected constant
2149 E0311, // thing may not live long enough
2150 E0312, // lifetime of reference outlives lifetime of borrowed content
2151 E0313, // lifetime of borrowed pointer outlives lifetime of captured variable
2152 E0314, // closure outlives stack frame
2153 E0315, // cannot invoke closure outside of its lifetime
2154 E0316, // nested quantification of lifetimes
2155 E0320, // recursive overflow during dropck
2156 E0473, // dereference of reference outside its lifetime
2157 E0474, // captured variable `..` does not outlive the enclosing closure
2158 E0475, // index of slice outside its lifetime
2159 E0476, // lifetime of the source pointer does not outlive lifetime bound...
2160 E0477, // the type `..` does not fulfill the required lifetime...
2161 E0479, // the type `..` (provided as the value of a type parameter) is...
2162 E0480, // lifetime of method receiver does not outlive the method call
2163 E0481, // lifetime of function argument does not outlive the function call
2164 E0482, // lifetime of return value does not outlive the function call
2165 E0483, // lifetime of operand does not outlive the operation
2166 E0484, // reference is not valid at the time of borrow
2167 E0485, // automatically reference is not valid at the time of borrow
2168 E0486, // type of expression contains references that are not valid during...
2169 E0487, // unsafe use of destructor: destructor might be called while...
2170 E0488, // lifetime of variable does not enclose its declaration
2171 E0489, // type/lifetime parameter not in scope here
2172 E0490, // a value of type `..` is borrowed for too long
2173 E0495, // cannot infer an appropriate lifetime due to conflicting requirements
2174 E0566, // conflicting representation hints
2175 E0623, // lifetime mismatch where both parameters are anonymous regions
2176 E0628, // generators cannot have explicit arguments
2177 E0631, // type mismatch in closure arguments
2178 E0637, // "'_" is not a valid lifetime bound
2179 E0657, // `impl Trait` can only capture lifetimes bound at the fn level
2180 E0687, // in-band lifetimes cannot be used in `fn`/`Fn` syntax
2181 E0688, // in-band lifetimes cannot be mixed with explicit lifetime binders
2183 E0906, // closures cannot be static