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 register_long_diagnostics! {
16 A pattern used to match against an enum variant must provide a sub-pattern for
17 each field of the enum variant. This error indicates that a pattern attempted to
18 extract an incorrect number of fields from a variant.
22 Apple(String, String),
27 Here the `Apple` variant has two fields, and should be matched against like so:
31 Apple(String, String),
35 let x = Fruit::Apple(String::new(), String::new());
39 Fruit::Apple(a, b) => {},
44 Matching with the wrong number of fields has no sensible interpretation:
48 Apple(String, String),
52 let x = Fruit::Apple(String::new(), String::new());
56 Fruit::Apple(a) => {},
57 Fruit::Apple(a, b, c) => {},
61 Check how many fields the enum was declared with and ensure that your pattern
66 Each field of a struct can only be bound once in a pattern. Erroneous code
76 let x = Foo { a:1, b:2 };
78 let Foo { a: x, a: y } = x;
79 // error: field `a` bound multiple times in the pattern
83 Each occurrence of a field name binds the value of that field, so to fix this
84 error you will have to remove or alter the duplicate uses of the field name.
85 Perhaps you misspelled another field name? Example:
94 let x = Foo { a:1, b:2 };
96 let Foo { a: x, b: y } = x; // ok!
102 This error indicates that a struct pattern attempted to extract a non-existent
103 field from a struct. Struct fields are identified by the name used before the
104 colon `:` so struct patterns should resemble the declaration of the struct type
114 let thing = Thing { x: 1, y: 2 };
117 Thing { x: xfield, y: yfield } => {}
121 If you are using shorthand field patterns but want to refer to the struct field
122 by a different name, you should rename it explicitly.
126 ```compile_fail,E0026
132 let thing = Thing { x: 0, y: 0 };
147 let thing = Thing { x: 0, y: 0 };
150 Thing { x, y: z } => {}
156 This error indicates that a pattern for a struct fails to specify a sub-pattern
157 for every one of the struct's fields. Ensure that each field from the struct's
158 definition is mentioned in the pattern, or use `..` to ignore unwanted fields.
162 ```compile_fail,E0027
168 let d = Dog { name: "Rusty".to_string(), age: 8 };
170 // This is incorrect.
176 This is correct (explicit):
184 let d = Dog { name: "Rusty".to_string(), age: 8 };
187 Dog { name: ref n, age: x } => {}
190 // This is also correct (ignore unused fields).
192 Dog { age: x, .. } => {}
198 In a match expression, only numbers and characters can be matched against a
199 range. This is because the compiler checks that the range is non-empty at
200 compile-time, and is unable to evaluate arbitrary comparison functions. If you
201 want to capture values of an orderable type between two end-points, you can use
204 ```compile_fail,E0029
205 let string = "salutations !";
207 // The ordering relation for strings can't be evaluated at compile time,
208 // so this doesn't work:
210 "hello" ... "world" => {}
214 // This is a more general version, using a guard:
216 s if s >= "hello" && s <= "world" => {}
223 This error indicates that a pointer to a trait type cannot be implicitly
224 dereferenced by a pattern. Every trait defines a type, but because the
225 size of trait implementors isn't fixed, this type has no compile-time size.
226 Therefore, all accesses to trait types must be through pointers. If you
227 encounter this error you should try to avoid dereferencing the pointer.
230 let trait_obj: &SomeTrait = ...;
232 // This tries to implicitly dereference to create an unsized local variable.
233 let &invalid = trait_obj;
235 // You can call methods without binding to the value being pointed at.
236 trait_obj.method_one();
237 trait_obj.method_two();
240 You can read more about trait objects in the Trait Object section of the
243 https://doc.rust-lang.org/reference.html#trait-objects
247 The compiler doesn't know what method to call because more than one method
248 has the same prototype. Erroneous code example:
250 ```compile_fail,E0034
261 impl Trait1 for Test { fn foo() {} }
262 impl Trait2 for Test { fn foo() {} }
265 Test::foo() // error, which foo() to call?
269 To avoid this error, you have to keep only one of them and remove the others.
270 So let's take our example and fix it:
279 impl Trait1 for Test { fn foo() {} }
282 Test::foo() // and now that's good!
286 However, a better solution would be using fully explicit naming of type and
300 impl Trait1 for Test { fn foo() {} }
301 impl Trait2 for Test { fn foo() {} }
304 <Test as Trait1>::foo()
321 impl F for X { fn m(&self) { println!("I am F"); } }
322 impl G for X { fn m(&self) { println!("I am G"); } }
327 F::m(&f); // it displays "I am F"
328 G::m(&f); // it displays "I am G"
334 You tried to give a type parameter where it wasn't needed. Erroneous code
337 ```compile_fail,E0035
347 x.method::<i32>(); // Error: Test::method doesn't need type parameter!
351 To fix this error, just remove the type parameter:
363 x.method(); // OK, we're good!
369 This error occurrs when you pass too many or not enough type parameters to
370 a method. Erroneous code example:
372 ```compile_fail,E0036
376 fn method<T>(&self, v: &[T]) -> usize {
385 x.method::<i32, i32>(v); // error: only one type parameter is expected!
389 To fix it, just specify a correct number of type parameters:
395 fn method<T>(&self, v: &[T]) -> usize {
404 x.method::<i32>(v); // OK, we're good!
408 Please note on the last example that we could have called `method` like this:
416 It is not allowed to manually call destructors in Rust. It is also not
417 necessary to do this since `drop` is called automatically whenever a value goes
420 Here's an example of this error:
422 ```compile_fail,E0040
434 let mut x = Foo { x: -7 };
435 x.drop(); // error: explicit use of destructor method
441 You can't use type parameters on foreign items. Example of erroneous code:
443 ```compile_fail,E0044
444 extern { fn some_func<T>(x: T); }
447 To fix this, replace the type parameter with the specializations that you
451 extern { fn some_func_i32(x: i32); }
452 extern { fn some_func_i64(x: i64); }
457 Rust only supports variadic parameters for interoperability with C code in its
458 FFI. As such, variadic parameters can only be used with functions which are
459 using the C ABI. Examples of erroneous code:
462 #![feature(unboxed_closures)]
464 extern "rust-call" { fn foo(x: u8, ...); }
468 fn foo(x: u8, ...) {}
471 To fix such code, put them in an extern "C" block:
481 Items are missing in a trait implementation. Erroneous code example:
483 ```compile_fail,E0046
491 // error: not all trait items implemented, missing: `foo`
494 When trying to make some type implement a trait `Foo`, you must, at minimum,
495 provide implementations for all of `Foo`'s required methods (meaning the
496 methods that do not have default implementations), as well as any required
497 trait items like associated types or constants. Example:
513 This error indicates that an attempted implementation of a trait method
514 has the wrong number of type parameters.
516 For example, the trait below has a method `foo` with a type parameter `T`,
517 but the implementation of `foo` for the type `Bar` is missing this parameter:
519 ```compile_fail,E0049
521 fn foo<T: Default>(x: T) -> Self;
526 // error: method `foo` has 0 type parameters but its trait declaration has 1
529 fn foo(x: bool) -> Self { Bar }
535 This error indicates that an attempted implementation of a trait method
536 has the wrong number of function parameters.
538 For example, the trait below has a method `foo` with two function parameters
539 (`&self` and `u8`), but the implementation of `foo` for the type `Bar` omits
542 ```compile_fail,E0050
544 fn foo(&self, x: u8) -> bool;
549 // error: method `foo` has 1 parameter but the declaration in trait `Foo::foo`
552 fn foo(&self) -> bool { true }
558 The parameters of any trait method must match between a trait implementation
559 and the trait definition.
561 Here are a couple examples of this error:
563 ```compile_fail,E0053
572 // error, expected u16, found i16
575 // error, types differ in mutability
576 fn bar(&mut self) { }
582 It is not allowed to cast to a bool. If you are trying to cast a numeric type
583 to a bool, you can compare it with zero instead:
585 ```compile_fail,E0054
588 // Not allowed, won't compile
589 let x_is_nonzero = x as bool;
596 let x_is_nonzero = x != 0;
601 During a method call, a value is automatically dereferenced as many times as
602 needed to make the value's type match the method's receiver. The catch is that
603 the compiler will only attempt to dereference a number of times up to the
604 recursion limit (which can be set via the `recursion_limit` attribute).
606 For a somewhat artificial example:
608 ```compile_fail,E0055
609 #![recursion_limit="2"]
621 // error, reached the recursion limit while auto-dereferencing &&Foo
626 One fix may be to increase the recursion limit. Note that it is possible to
627 create an infinite recursion of dereferencing, in which case the only fix is to
628 somehow break the recursion.
632 When invoking closures or other implementations of the function traits `Fn`,
633 `FnMut` or `FnOnce` using call notation, the number of parameters passed to the
634 function must match its definition.
636 An example using a closure:
638 ```compile_fail,E0057
640 let a = f(); // invalid, too few parameters
641 let b = f(4); // this works!
642 let c = f(2, 3); // invalid, too many parameters
645 A generic function must be treated similarly:
648 fn foo<F: Fn()>(f: F) {
649 f(); // this is valid, but f(3) would not work
655 The built-in function traits are generic over a tuple of the function arguments.
656 If one uses angle-bracket notation (`Fn<(T,), Output=U>`) instead of parentheses
657 (`Fn(T) -> U`) to denote the function trait, the type parameter should be a
658 tuple. Otherwise function call notation cannot be used and the trait will not be
659 implemented by closures.
661 The most likely source of this error is using angle-bracket notation without
662 wrapping the function argument type into a tuple, for example:
664 ```compile_fail,E0059
665 #![feature(unboxed_closures)]
667 fn foo<F: Fn<i32>>(f: F) -> F::Output { f(3) }
670 It can be fixed by adjusting the trait bound like this:
673 #![feature(unboxed_closures)]
675 fn foo<F: Fn<(i32,)>>(f: F) -> F::Output { f(3) }
678 Note that `(T,)` always denotes the type of a 1-tuple containing an element of
679 type `T`. The comma is necessary for syntactic disambiguation.
683 External C functions are allowed to be variadic. However, a variadic function
684 takes a minimum number of arguments. For example, consider C's variadic `printf`
689 use libc::{ c_char, c_int };
692 fn printf(_: *const c_char, ...) -> c_int;
696 Using this declaration, it must be called with at least one argument, so
697 simply calling `printf()` is invalid. But the following uses are allowed:
701 use std::ffi::CString;
703 printf(CString::new("test\n").unwrap().as_ptr());
704 printf(CString::new("number = %d\n").unwrap().as_ptr(), 3);
705 printf(CString::new("%d, %d\n").unwrap().as_ptr(), 10, 5);
711 The number of arguments passed to a function must match the number of arguments
712 specified in the function signature.
714 For example, a function like:
717 fn f(a: u16, b: &str) {}
720 Must always be called with exactly two arguments, e.g. `f(2, "test")`.
722 Note that Rust does not have a notion of optional function arguments or
723 variadic functions (except for its C-FFI).
727 This error indicates that during an attempt to build a struct or struct-like
728 enum variant, one of the fields was specified more than once. Erroneous code
731 ```compile_fail,E0062
739 x: 0, // error: field `x` specified more than once
744 Each field should be specified exactly one time. Example:
752 let x = Foo { x: 0 }; // ok!
758 This error indicates that during an attempt to build a struct or struct-like
759 enum variant, one of the fields was not provided. Erroneous code example:
761 ```compile_fail,E0063
768 let x = Foo { x: 0 }; // error: missing field: `y`
772 Each field should be specified exactly once. Example:
781 let x = Foo { x: 0, y: 0 }; // ok!
787 Box placement expressions (like C++'s "placement new") do not yet support any
788 place expression except the exchange heap (i.e. `std::boxed::HEAP`).
789 Furthermore, the syntax is changing to use `in` instead of `box`. See [RFC 470]
790 and [RFC 809] for more details.
792 [RFC 470]: https://github.com/rust-lang/rfcs/pull/470
793 [RFC 809]: https://github.com/rust-lang/rfcs/pull/809
797 The left-hand side of a compound assignment expression must be an lvalue
798 expression. An lvalue expression represents a memory location and includes
799 item paths (ie, namespaced variables), dereferences, indexing expressions,
800 and field references.
802 Let's start with some erroneous code examples:
804 ```compile_fail,E0067
805 use std::collections::LinkedList;
807 // Bad: assignment to non-lvalue expression
808 LinkedList::new() += 1;
812 fn some_func(i: &mut i32) {
813 i += 12; // Error : '+=' operation cannot be applied on a reference !
817 And now some working examples:
826 fn some_func(i: &mut i32) {
833 The compiler found a function whose body contains a `return;` statement but
834 whose return type is not `()`. An example of this is:
836 ```compile_fail,E0069
843 Since `return;` is just like `return ();`, there is a mismatch between the
844 function's return type and the value being returned.
848 The left-hand side of an assignment operator must be an lvalue expression. An
849 lvalue expression represents a memory location and can be a variable (with
850 optional namespacing), a dereference, an indexing expression or a field
853 More details can be found here:
854 https://doc.rust-lang.org/reference.html#lvalues-rvalues-and-temporaries
856 Now, we can go further. Here are some erroneous code examples:
858 ```compile_fail,E0070
864 const SOME_CONST : i32 = 12;
866 fn some_other_func() {}
869 SOME_CONST = 14; // error : a constant value cannot be changed!
870 1 = 3; // error : 1 isn't a valid lvalue!
871 some_other_func() = 4; // error : we can't assign value to a function!
872 SomeStruct.x = 12; // error : SomeStruct a structure name but it is used
877 And now let's give working examples:
884 let mut s = SomeStruct {x: 0, y: 0};
886 s.x = 3; // that's good !
890 fn some_func(x: &mut i32) {
891 *x = 12; // that's good !
897 You tried to use structure-literal syntax to create an item that is
898 not a structure or enum variant.
900 Example of erroneous code:
902 ```compile_fail,E0071
904 let t = U32 { value: 4 }; // error: expected struct, variant or union type,
905 // found builtin type `u32`
908 To fix this, ensure that the name was correctly spelled, and that
909 the correct form of initializer was used.
911 For example, the code above can be fixed to:
919 let u = Foo::FirstValue(0i32);
927 You cannot define a struct (or enum) `Foo` that requires an instance of `Foo`
928 in order to make a new `Foo` value. This is because there would be no way a
929 first instance of `Foo` could be made to initialize another instance!
931 Here's an example of a struct that has this problem:
934 struct Foo { x: Box<Foo> } // error
937 One fix is to use `Option`, like so:
940 struct Foo { x: Option<Box<Foo>> }
943 Now it's possible to create at least one instance of `Foo`: `Foo { x: None }`.
947 When using the `#[simd]` attribute on a tuple struct, the components of the
948 tuple struct must all be of a concrete, nongeneric type so the compiler can
949 reason about how to use SIMD with them. This error will occur if the types
952 This will cause an error:
955 #![feature(repr_simd)]
958 struct Bad<T>(T, T, T);
964 #![feature(repr_simd)]
967 struct Good(u32, u32, u32);
972 The `#[simd]` attribute can only be applied to non empty tuple structs, because
973 it doesn't make sense to try to use SIMD operations when there are no values to
976 This will cause an error:
978 ```compile_fail,E0075
979 #![feature(repr_simd)]
988 #![feature(repr_simd)]
996 When using the `#[simd]` attribute to automatically use SIMD operations in tuple
997 struct, the types in the struct must all be of the same type, or the compiler
998 will trigger this error.
1000 This will cause an error:
1002 ```compile_fail,E0076
1003 #![feature(repr_simd)]
1006 struct Bad(u16, u32, u32);
1012 #![feature(repr_simd)]
1015 struct Good(u32, u32, u32);
1020 When using the `#[simd]` attribute on a tuple struct, the elements in the tuple
1021 must be machine types so SIMD operations can be applied to them.
1023 This will cause an error:
1025 ```compile_fail,E0077
1026 #![feature(repr_simd)]
1035 #![feature(repr_simd)]
1038 struct Good(u32, u32, u32);
1043 Enum variants which contain no data can be given a custom integer
1044 representation. This error indicates that the value provided is not an integer
1045 literal and is therefore invalid.
1047 For example, in the following code:
1049 ```compile_fail,E0079
1055 We try to set the representation to a string.
1057 There's no general fix for this; if you can work with an integer then just set
1066 However if you actually wanted a mapping between variants and non-integer
1067 objects, it may be preferable to use a method with a match instead:
1072 fn get_str(&self) -> &'static str {
1082 Enum discriminants are used to differentiate enum variants stored in memory.
1083 This error indicates that the same value was used for two or more variants,
1084 making them impossible to tell apart.
1086 ```compile_fail,E0081
1104 Note that variants without a manually specified discriminant are numbered from
1105 top to bottom starting from 0, so clashes can occur with seemingly unrelated
1108 ```compile_fail,E0081
1115 Here `X` will have already been specified the discriminant 0 by the time `Y` is
1116 encountered, so a conflict occurs.
1120 When you specify enum discriminants with `=`, the compiler expects `isize`
1121 values by default. Or you can add the `repr` attibute to the enum declaration
1122 for an explicit choice of the discriminant type. In either cases, the
1123 discriminant values must fall within a valid range for the expected type;
1124 otherwise this error is raised. For example:
1134 Here, 1024 lies outside the valid range for `u8`, so the discriminant for `A` is
1135 invalid. Here is another, more subtle example which depends on target word size:
1138 enum DependsOnPointerSize {
1143 Here, `1 << 32` is interpreted as an `isize` value. So it is invalid for 32 bit
1144 target (`target_pointer_width = "32"`) but valid for 64 bit target.
1146 You may want to change representation types to fix this, or else change invalid
1147 discriminant values so that they fit within the existing type.
1151 An unsupported representation was attempted on a zero-variant enum.
1153 Erroneous code example:
1155 ```compile_fail,E0084
1157 enum NightsWatch {} // error: unsupported representation for zero-variant enum
1160 It is impossible to define an integer type to be used to represent zero-variant
1161 enum values because there are no zero-variant enum values. There is no way to
1162 construct an instance of the following type using only safe code. So you have
1163 two solutions. Either you add variants in your enum:
1173 or you remove the integer represention of your enum:
1181 Too many type parameters were supplied for a function. For example:
1183 ```compile_fail,E0087
1187 foo::<f64, bool>(); // error, expected 1 parameter, found 2 parameters
1191 The number of supplied parameters must exactly match the number of defined type
1196 You gave too many lifetime parameters. Erroneous code example:
1198 ```compile_fail,E0088
1202 f::<'static>() // error: too many lifetime parameters provided
1206 Please check you give the right number of lifetime parameters. Example:
1216 It's also important to note that the Rust compiler can generally
1217 determine the lifetime by itself. Example:
1225 // it can be written like this
1226 fn get_value<'a>(&'a self) -> &'a str { &self.value }
1227 // but the compiler works fine with this too:
1228 fn without_lifetime(&self) -> &str { &self.value }
1232 let f = Foo { value: "hello".to_owned() };
1234 println!("{}", f.get_value());
1235 println!("{}", f.without_lifetime());
1241 Not enough type parameters were supplied for a function. For example:
1243 ```compile_fail,E0089
1247 foo::<f64>(); // error, expected 2 parameters, found 1 parameter
1251 Note that if a function takes multiple type parameters but you want the compiler
1252 to infer some of them, you can use type placeholders:
1254 ```compile_fail,E0089
1255 fn foo<T, U>(x: T) {}
1259 foo::<f64>(x); // error, expected 2 parameters, found 1 parameter
1260 foo::<_, f64>(x); // same as `foo::<bool, f64>(x)`
1266 You gave an unnecessary type parameter in a type alias. Erroneous code
1269 ```compile_fail,E0091
1270 type Foo<T> = u32; // error: type parameter `T` is unused
1272 type Foo<A,B> = Box<A>; // error: type parameter `B` is unused
1275 Please check you didn't write too many type parameters. Example:
1278 type Foo = u32; // ok!
1279 type Foo2<A> = Box<A>; // ok!
1284 You tried to declare an undefined atomic operation function.
1285 Erroneous code example:
1287 ```compile_fail,E0092
1288 #![feature(intrinsics)]
1290 extern "rust-intrinsic" {
1291 fn atomic_foo(); // error: unrecognized atomic operation
1296 Please check you didn't make a mistake in the function's name. All intrinsic
1297 functions are defined in librustc_trans/trans/intrinsic.rs and in
1298 libcore/intrinsics.rs in the Rust source code. Example:
1301 #![feature(intrinsics)]
1303 extern "rust-intrinsic" {
1304 fn atomic_fence(); // ok!
1310 You declared an unknown intrinsic function. Erroneous code example:
1312 ```compile_fail,E0093
1313 #![feature(intrinsics)]
1315 extern "rust-intrinsic" {
1316 fn foo(); // error: unrecognized intrinsic function: `foo`
1326 Please check you didn't make a mistake in the function's name. All intrinsic
1327 functions are defined in librustc_trans/trans/intrinsic.rs and in
1328 libcore/intrinsics.rs in the Rust source code. Example:
1331 #![feature(intrinsics)]
1333 extern "rust-intrinsic" {
1334 fn atomic_fence(); // ok!
1346 You gave an invalid number of type parameters to an intrinsic function.
1347 Erroneous code example:
1349 ```compile_fail,E0094
1350 #![feature(intrinsics)]
1352 extern "rust-intrinsic" {
1353 fn size_of<T, U>() -> usize; // error: intrinsic has wrong number
1354 // of type parameters
1358 Please check that you provided the right number of type parameters
1359 and verify with the function declaration in the Rust source code.
1363 #![feature(intrinsics)]
1365 extern "rust-intrinsic" {
1366 fn size_of<T>() -> usize; // ok!
1372 You hit this error because the compiler lacks the information to
1373 determine a type for this expression. Erroneous code example:
1375 ```compile_fail,E0101
1376 let x = |_| {}; // error: cannot determine a type for this expression
1379 You have two possibilities to solve this situation:
1381 * Give an explicit definition of the expression
1382 * Infer the expression
1387 let x = |_ : u32| {}; // ok!
1395 You hit this error because the compiler lacks the information to
1396 determine the type of this variable. Erroneous code example:
1398 ```compile_fail,E0102
1399 // could be an array of anything
1400 let x = []; // error: cannot determine a type for this local variable
1403 To solve this situation, constrain the type of the variable.
1407 #![allow(unused_variables)]
1410 let x: [u8; 0] = [];
1416 This error means that an incorrect number of lifetime parameters were provided
1417 for a type (like a struct or enum) or trait:
1419 ```compile_fail,E0107
1420 struct Foo<'a, 'b>(&'a str, &'b str);
1421 enum Bar { A, B, C }
1424 foo: Foo<'a>, // error: expected 2, found 1
1425 bar: Bar<'a>, // error: expected 0, found 1
1431 You can only define an inherent implementation for a type in the same crate
1432 where the type was defined. For example, an `impl` block as below is not allowed
1433 since `Vec` is defined in the standard library:
1435 ```compile_fail,E0116
1436 impl Vec<u8> { } // error
1439 To fix this problem, you can do either of these things:
1441 - define a trait that has the desired associated functions/types/constants and
1442 implement the trait for the type in question
1443 - define a new type wrapping the type and define an implementation on the new
1446 Note that using the `type` keyword does not work here because `type` only
1447 introduces a type alias:
1449 ```compile_fail,E0116
1450 type Bytes = Vec<u8>;
1452 impl Bytes { } // error, same as above
1457 This error indicates a violation of one of Rust's orphan rules for trait
1458 implementations. The rule prohibits any implementation of a foreign trait (a
1459 trait defined in another crate) where
1461 - the type that is implementing the trait is foreign
1462 - all of the parameters being passed to the trait (if there are any) are also
1465 Here's one example of this error:
1467 ```compile_fail,E0117
1468 impl Drop for u32 {}
1471 To avoid this kind of error, ensure that at least one local type is referenced
1475 pub struct Foo; // you define your type in your crate
1477 impl Drop for Foo { // and you can implement the trait on it!
1478 // code of trait implementation here
1481 impl From<Foo> for i32 { // or you use a type from your crate as
1483 fn from(i: Foo) -> i32 {
1489 Alternatively, define a trait locally and implement that instead:
1493 fn get(&self) -> usize;
1497 fn get(&self) -> usize { 0 }
1501 For information on the design of the orphan rules, see [RFC 1023].
1503 [RFC 1023]: https://github.com/rust-lang/rfcs/pull/1023
1507 You're trying to write an inherent implementation for something which isn't a
1508 struct nor an enum. Erroneous code example:
1510 ```compile_fail,E0118
1511 impl (u8, u8) { // error: no base type found for inherent implementation
1512 fn get_state(&self) -> String {
1518 To fix this error, please implement a trait on the type or wrap it in a struct.
1522 // we create a trait here
1523 trait LiveLongAndProsper {
1524 fn get_state(&self) -> String;
1527 // and now you can implement it on (u8, u8)
1528 impl LiveLongAndProsper for (u8, u8) {
1529 fn get_state(&self) -> String {
1530 "He's dead, Jim!".to_owned()
1535 Alternatively, you can create a newtype. A newtype is a wrapping tuple-struct.
1536 For example, `NewType` is a newtype over `Foo` in `struct NewType(Foo)`.
1540 struct TypeWrapper((u8, u8));
1543 fn get_state(&self) -> String {
1544 "Fascinating!".to_owned()
1551 There are conflicting trait implementations for the same type.
1552 Example of erroneous code:
1554 ```compile_fail,E0119
1556 fn get(&self) -> usize;
1559 impl<T> MyTrait for T {
1560 fn get(&self) -> usize { 0 }
1567 impl MyTrait for Foo { // error: conflicting implementations of trait
1568 // `MyTrait` for type `Foo`
1569 fn get(&self) -> usize { self.value }
1573 When looking for the implementation for the trait, the compiler finds
1574 both the `impl<T> MyTrait for T` where T is all types and the `impl
1575 MyTrait for Foo`. Since a trait cannot be implemented multiple times,
1576 this is an error. So, when you write:
1580 fn get(&self) -> usize;
1583 impl<T> MyTrait for T {
1584 fn get(&self) -> usize { 0 }
1588 This makes the trait implemented on all types in the scope. So if you
1589 try to implement it on another one after that, the implementations will
1594 fn get(&self) -> usize;
1597 impl<T> MyTrait for T {
1598 fn get(&self) -> usize { 0 }
1606 f.get(); // the trait is implemented so we can use it
1612 An attempt was made to implement Drop on a trait, which is not allowed: only
1613 structs and enums can implement Drop. An example causing this error:
1615 ```compile_fail,E0120
1618 impl Drop for MyTrait {
1619 fn drop(&mut self) {}
1623 A workaround for this problem is to wrap the trait up in a struct, and implement
1624 Drop on that. An example is shown below:
1628 struct MyWrapper<T: MyTrait> { foo: T }
1630 impl <T: MyTrait> Drop for MyWrapper<T> {
1631 fn drop(&mut self) {}
1636 Alternatively, wrapping trait objects requires something like the following:
1641 //or Box<MyTrait>, if you wanted an owned trait object
1642 struct MyWrapper<'a> { foo: &'a MyTrait }
1644 impl <'a> Drop for MyWrapper<'a> {
1645 fn drop(&mut self) {}
1651 In order to be consistent with Rust's lack of global type inference, type
1652 placeholders are disallowed by design in item signatures.
1654 Examples of this error include:
1656 ```compile_fail,E0121
1657 fn foo() -> _ { 5 } // error, explicitly write out the return type instead
1659 static BAR: _ = "test"; // error, explicitly write out the type instead
1664 An attempt was made to add a generic constraint to a type alias. While Rust will
1665 allow this with a warning, it will not currently enforce the constraint.
1666 Consider the example below:
1671 type MyType<R: Foo> = (R, ());
1678 We're able to declare a variable of type `MyType<u32>`, despite the fact that
1679 `u32` does not implement `Foo`. As a result, one should avoid using generic
1680 constraints in concert with type aliases.
1684 You declared two fields of a struct with the same name. Erroneous code
1687 ```compile_fail,E0124
1690 field1: i32, // error: field is already declared
1694 Please verify that the field names have been correctly spelled. Example:
1705 Type parameter defaults can only use parameters that occur before them.
1706 Erroneous code example:
1708 ```compile_fail,E0128
1709 struct Foo<T=U, U=()> {
1713 // error: type parameters with a default cannot use forward declared
1717 Since type parameters are evaluated in-order, you may be able to fix this issue
1721 struct Foo<U=(), T=U> {
1727 Please also verify that this wasn't because of a name-clash and rename the type
1732 It is not possible to define `main` with type parameters, or even with function
1733 parameters. When `main` is present, it must take no arguments and return `()`.
1734 Erroneous code example:
1736 ```compile_fail,E0131
1737 fn main<T>() { // error: main function is not allowed to have type parameters
1743 A function with the `start` attribute was declared with type parameters.
1745 Erroneous code example:
1747 ```compile_fail,E0132
1754 It is not possible to declare type parameters on a function that has the `start`
1755 attribute. Such a function must have the following type signature (for more
1756 information: http://doc.rust-lang.org/stable/book/no-stdlib.html):
1759 fn(isize, *const *const u8) -> isize;
1768 fn my_start(argc: isize, argv: *const *const u8) -> isize {
1775 This error means that an attempt was made to match a struct type enum
1776 variant as a non-struct type:
1778 ```compile_fail,E0164
1779 enum Foo { B { i: u32 } }
1781 fn bar(foo: Foo) -> u32 {
1783 Foo::B(i) => i, // error E0164
1788 Try using `{}` instead:
1791 enum Foo { B { i: u32 } }
1793 fn bar(foo: Foo) -> u32 {
1802 You bound an associated type in an expression path which is not
1805 Erroneous code example:
1807 ```compile_fail,E0182
1813 impl Foo for isize {
1815 fn bar() -> isize { 42 }
1818 // error: unexpected binding of associated item in expression path
1819 let x: isize = Foo::<A=usize>::bar();
1822 To give a concrete type when using the Universal Function Call Syntax,
1823 use "Type as Trait". Example:
1831 impl Foo for isize {
1833 fn bar() -> isize { 42 }
1836 let x: isize = <isize as Foo>::bar(); // ok!
1841 Explicitly implementing both Drop and Copy for a type is currently disallowed.
1842 This feature can make some sense in theory, but the current implementation is
1843 incorrect and can lead to memory unsafety (see [issue #20126][iss20126]), so
1844 it has been disabled for now.
1846 [iss20126]: https://github.com/rust-lang/rust/issues/20126
1850 An associated function for a trait was defined to be static, but an
1851 implementation of the trait declared the same function to be a method (i.e. to
1852 take a `self` parameter).
1854 Here's an example of this error:
1856 ```compile_fail,E0185
1864 // error, method `foo` has a `&self` declaration in the impl, but not in
1872 An associated function for a trait was defined to be a method (i.e. to take a
1873 `self` parameter), but an implementation of the trait declared the same function
1876 Here's an example of this error:
1878 ```compile_fail,E0186
1886 // error, method `foo` has a `&self` declaration in the trait, but not in
1894 Trait objects need to have all associated types specified. Erroneous code
1897 ```compile_fail,E0191
1902 type Foo = Trait; // error: the value of the associated type `Bar` (from
1903 // the trait `Trait`) must be specified
1906 Please verify you specified all associated types of the trait and that you
1907 used the right trait. Example:
1914 type Foo = Trait<Bar=i32>; // ok!
1919 Negative impls are only allowed for traits with default impls. For more
1920 information see the [opt-in builtin traits RFC](https://github.com/rust-lang/
1921 rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
1925 `where` clauses must use generic type parameters: it does not make sense to use
1926 them otherwise. An example causing this error:
1933 #[derive(Copy,Clone)]
1938 impl Foo for Wrapper<u32> where Wrapper<u32>: Clone {
1943 This use of a `where` clause is strange - a more common usage would look
1944 something like the following:
1951 #[derive(Copy,Clone)]
1955 impl <T> Foo for Wrapper<T> where Wrapper<T>: Clone {
1960 Here, we're saying that the implementation exists on Wrapper only when the
1961 wrapped type `T` implements `Clone`. The `where` clause is important because
1962 some types will not implement `Clone`, and thus will not get this method.
1964 In our erroneous example, however, we're referencing a single concrete type.
1965 Since we know for certain that `Wrapper<u32>` implements `Clone`, there's no
1966 reason to also specify it in a `where` clause.
1970 A type parameter was declared which shadows an existing one. An example of this
1973 ```compile_fail,E0194
1975 fn do_something(&self) -> T;
1976 fn do_something_else<T: Clone>(&self, bar: T);
1980 In this example, the trait `Foo` and the trait method `do_something_else` both
1981 define a type parameter `T`. This is not allowed: if the method wishes to
1982 define a type parameter, it must use a different name for it.
1986 Your method's lifetime parameters do not match the trait declaration.
1987 Erroneous code example:
1989 ```compile_fail,E0195
1991 fn bar<'a,'b:'a>(x: &'a str, y: &'b str);
1996 impl Trait for Foo {
1997 fn bar<'a,'b>(x: &'a str, y: &'b str) {
1998 // error: lifetime parameters or bounds on method `bar`
1999 // do not match the trait declaration
2004 The lifetime constraint `'b` for bar() implementation does not match the
2005 trait declaration. Ensure lifetime declarations match exactly in both trait
2006 declaration and implementation. Example:
2010 fn t<'a,'b:'a>(x: &'a str, y: &'b str);
2015 impl Trait for Foo {
2016 fn t<'a,'b:'a>(x: &'a str, y: &'b str) { // ok!
2023 Inherent implementations (one that do not implement a trait but provide
2024 methods associated with a type) are always safe because they are not
2025 implementing an unsafe trait. Removing the `unsafe` keyword from the inherent
2026 implementation will resolve this error.
2028 ```compile_fail,E0197
2031 // this will cause this error
2033 // converting it to this will fix it
2039 A negative implementation is one that excludes a type from implementing a
2040 particular trait. Not being able to use a trait is always a safe operation,
2041 so negative implementations are always safe and never need to be marked as
2045 #![feature(optin_builtin_traits)]
2049 // unsafe is unnecessary
2050 unsafe impl !Clone for Foo { }
2056 #![feature(optin_builtin_traits)]
2062 impl Enterprise for .. { }
2064 impl !Enterprise for Foo { }
2067 Please note that negative impls are only allowed for traits with default impls.
2071 Safe traits should not have unsafe implementations, therefore marking an
2072 implementation for a safe trait unsafe will cause a compiler error. Removing
2073 the unsafe marker on the trait noted in the error will resolve this problem.
2075 ```compile_fail,E0199
2080 // this won't compile because Bar is safe
2081 unsafe impl Bar for Foo { }
2082 // this will compile
2083 impl Bar for Foo { }
2088 Unsafe traits must have unsafe implementations. This error occurs when an
2089 implementation for an unsafe trait isn't marked as unsafe. This may be resolved
2090 by marking the unsafe implementation as unsafe.
2092 ```compile_fail,E0200
2095 unsafe trait Bar { }
2097 // this won't compile because Bar is unsafe and impl isn't unsafe
2098 impl Bar for Foo { }
2099 // this will compile
2100 unsafe impl Bar for Foo { }
2105 It is an error to define two associated items (like methods, associated types,
2106 associated functions, etc.) with the same identifier.
2110 ```compile_fail,E0201
2114 fn bar(&self) -> bool { self.0 > 5 }
2115 fn bar() {} // error: duplicate associated function
2120 fn baz(&self) -> bool;
2126 fn baz(&self) -> bool { true }
2128 // error: duplicate method
2129 fn baz(&self) -> bool { self.0 > 5 }
2131 // error: duplicate associated type
2136 Note, however, that items with the same name are allowed for inherent `impl`
2137 blocks that don't overlap:
2143 fn bar(&self) -> bool { self.0 > 5 }
2147 fn bar(&self) -> bool { self.0 }
2153 Inherent associated types were part of [RFC 195] but are not yet implemented.
2154 See [the tracking issue][iss8995] for the status of this implementation.
2156 [RFC 195]: https://github.com/rust-lang/rfcs/pull/195
2157 [iss8995]: https://github.com/rust-lang/rust/issues/8995
2161 An attempt to implement the `Copy` trait for a struct failed because one of the
2162 fields does not implement `Copy`. To fix this, you must implement `Copy` for the
2163 mentioned field. Note that this may not be possible, as in the example of
2165 ```compile_fail,E0204
2170 impl Copy for Foo { }
2173 This fails because `Vec<T>` does not implement `Copy` for any `T`.
2175 Here's another example that will fail:
2177 ```compile_fail,E0204
2184 This fails because `&mut T` is not `Copy`, even when `T` is `Copy` (this
2185 differs from the behavior for `&T`, which is always `Copy`).
2190 An attempt to implement the `Copy` trait for an enum failed because one of the
2191 variants does not implement `Copy`. To fix this, you must implement `Copy` for
2192 the mentioned variant. Note that this may not be possible, as in the example of
2194 ```compile_fail,E0205
2200 impl Copy for Foo { }
2203 This fails because `Vec<T>` does not implement `Copy` for any `T`.
2205 Here's another example that will fail:
2207 ```compile_fail,E0205
2215 This fails because `&mut T` is not `Copy`, even when `T` is `Copy` (this
2216 differs from the behavior for `&T`, which is always `Copy`).
2221 You can only implement `Copy` for a struct or enum. Both of the following
2222 examples will fail, because neither `i32` (primitive type) nor `&'static Bar`
2223 (reference to `Bar`) is a struct or enum:
2225 ```compile_fail,E0206
2227 impl Copy for Foo { } // error
2229 #[derive(Copy, Clone)]
2231 impl Copy for &'static Bar { } // error
2236 Any type parameter or lifetime parameter of an `impl` must meet at least one of
2237 the following criteria:
2239 - it appears in the self type of the impl
2240 - for a trait impl, it appears in the trait reference
2241 - it is bound as an associated type
2245 Suppose we have a struct `Foo` and we would like to define some methods for it.
2246 The following definition leads to a compiler error:
2248 ```compile_fail,E0207
2251 impl<T: Default> Foo {
2252 // error: the type parameter `T` is not constrained by the impl trait, self
2253 // type, or predicates [E0207]
2254 fn get(&self) -> T {
2255 <T as Default>::default()
2260 The problem is that the parameter `T` does not appear in the self type (`Foo`)
2261 of the impl. In this case, we can fix the error by moving the type parameter
2262 from the `impl` to the method `get`:
2268 // Move the type parameter from the impl to the method
2270 fn get<T: Default>(&self) -> T {
2271 <T as Default>::default()
2278 As another example, suppose we have a `Maker` trait and want to establish a
2279 type `FooMaker` that makes `Foo`s:
2281 ```compile_fail,E0207
2284 fn make(&mut self) -> Self::Item;
2293 impl<T: Default> Maker for FooMaker {
2294 // error: the type parameter `T` is not constrained by the impl trait, self
2295 // type, or predicates [E0207]
2298 fn make(&mut self) -> Foo<T> {
2299 Foo { foo: <T as Default>::default() }
2304 This fails to compile because `T` does not appear in the trait or in the
2307 One way to work around this is to introduce a phantom type parameter into
2308 `FooMaker`, like so:
2311 use std::marker::PhantomData;
2315 fn make(&mut self) -> Self::Item;
2322 // Add a type parameter to `FooMaker`
2323 struct FooMaker<T> {
2324 phantom: PhantomData<T>,
2327 impl<T: Default> Maker for FooMaker<T> {
2330 fn make(&mut self) -> Foo<T> {
2332 foo: <T as Default>::default(),
2338 Another way is to do away with the associated type in `Maker` and use an input
2339 type parameter instead:
2342 // Use a type parameter instead of an associated type here
2344 fn make(&mut self) -> Item;
2353 impl<T: Default> Maker<Foo<T>> for FooMaker {
2354 fn make(&mut self) -> Foo<T> {
2355 Foo { foo: <T as Default>::default() }
2360 ### Additional information
2362 For more information, please see [RFC 447].
2364 [RFC 447]: https://github.com/rust-lang/rfcs/blob/master/text/0447-no-unused-impl-parameters.md
2368 This error indicates a violation of one of Rust's orphan rules for trait
2369 implementations. The rule concerns the use of type parameters in an
2370 implementation of a foreign trait (a trait defined in another crate), and
2371 states that type parameters must be "covered" by a local type. To understand
2372 what this means, it is perhaps easiest to consider a few examples.
2374 If `ForeignTrait` is a trait defined in some external crate `foo`, then the
2375 following trait `impl` is an error:
2377 ```compile_fail,E0210
2378 extern crate collections;
2379 use collections::range::RangeArgument;
2381 impl<T> RangeArgument<T> for T { } // error
2386 To work around this, it can be covered with a local type, `MyType`:
2389 struct MyType<T>(T);
2390 impl<T> ForeignTrait for MyType<T> { } // Ok
2393 Please note that a type alias is not sufficient.
2395 For another example of an error, suppose there's another trait defined in `foo`
2396 named `ForeignTrait2` that takes two type parameters. Then this `impl` results
2397 in the same rule violation:
2401 impl<T> ForeignTrait2<T, MyType<T>> for MyType2 { } // error
2404 The reason for this is that there are two appearances of type parameter `T` in
2405 the `impl` header, both as parameters for `ForeignTrait2`. The first appearance
2406 is uncovered, and so runs afoul of the orphan rule.
2408 Consider one more example:
2411 impl<T> ForeignTrait2<MyType<T>, T> for MyType2 { } // Ok
2414 This only differs from the previous `impl` in that the parameters `T` and
2415 `MyType<T>` for `ForeignTrait2` have been swapped. This example does *not*
2416 violate the orphan rule; it is permitted.
2418 To see why that last example was allowed, you need to understand the general
2419 rule. Unfortunately this rule is a bit tricky to state. Consider an `impl`:
2422 impl<P1, ..., Pm> ForeignTrait<T1, ..., Tn> for T0 { ... }
2425 where `P1, ..., Pm` are the type parameters of the `impl` and `T0, ..., Tn`
2426 are types. One of the types `T0, ..., Tn` must be a local type (this is another
2427 orphan rule, see the explanation for E0117). Let `i` be the smallest integer
2428 such that `Ti` is a local type. Then no type parameter can appear in any of the
2431 For information on the design of the orphan rules, see [RFC 1023].
2433 [RFC 1023]: https://github.com/rust-lang/rfcs/pull/1023
2438 You used a function or type which doesn't fit the requirements for where it was
2439 used. Erroneous code examples:
2442 #![feature(intrinsics)]
2444 extern "rust-intrinsic" {
2445 fn size_of<T>(); // error: intrinsic has wrong type
2450 fn main() -> i32 { 0 }
2451 // error: main function expects type: `fn() {main}`: expected (), found i32
2458 // error: mismatched types in range: expected u8, found i8
2468 fn x(self: Rc<Foo>) {}
2469 // error: mismatched self type: expected `Foo`: expected struct
2470 // `Foo`, found struct `alloc::rc::Rc`
2474 For the first code example, please check the function definition. Example:
2477 #![feature(intrinsics)]
2479 extern "rust-intrinsic" {
2480 fn size_of<T>() -> usize; // ok!
2484 The second case example is a bit particular : the main function must always
2485 have this definition:
2491 They never take parameters and never return types.
2493 For the third example, when you match, all patterns must have the same type
2494 as the type you're matching on. Example:
2500 0u8...3u8 => (), // ok!
2505 And finally, for the last example, only `Box<Self>`, `&Self`, `Self`,
2506 or `&mut Self` work as explicit self parameters. Example:
2512 fn x(self: Box<Foo>) {} // ok!
2519 A generic type was described using parentheses rather than angle brackets. For
2522 ```compile_fail,E0214
2524 let v: Vec(&str) = vec!["foo"];
2528 This is not currently supported: `v` should be defined as `Vec<&str>`.
2529 Parentheses are currently only used with generic types when defining parameters
2530 for `Fn`-family traits.
2534 You used an associated type which isn't defined in the trait.
2535 Erroneous code example:
2537 ```compile_fail,E0220
2542 type Foo = T1<F=i32>; // error: associated type `F` not found for `T1`
2549 // error: Baz is used but not declared
2550 fn return_bool(&self, &Self::Bar, &Self::Baz) -> bool;
2554 Make sure that you have defined the associated type in the trait body.
2555 Also, verify that you used the right trait or you didn't misspell the
2556 associated type name. Example:
2563 type Foo = T1<Bar=i32>; // ok!
2569 type Baz; // we declare `Baz` in our trait.
2571 // and now we can use it here:
2572 fn return_bool(&self, &Self::Bar, &Self::Baz) -> bool;
2578 An attempt was made to retrieve an associated type, but the type was ambiguous.
2581 ```compile_fail,E0221
2597 In this example, `Foo` defines an associated type `A`. `Bar` inherits that type
2598 from `Foo`, and defines another associated type of the same name. As a result,
2599 when we attempt to use `Self::A`, it's ambiguous whether we mean the `A` defined
2600 by `Foo` or the one defined by `Bar`.
2602 There are two options to work around this issue. The first is simply to rename
2603 one of the types. Alternatively, one can specify the intended type using the
2617 let _: <Self as Bar>::A;
2624 An attempt was made to retrieve an associated type, but the type was ambiguous.
2627 ```compile_fail,E0223
2628 trait MyTrait {type X; }
2631 let foo: MyTrait::X;
2635 The problem here is that we're attempting to take the type of X from MyTrait.
2636 Unfortunately, the type of X is not defined, because it's only made concrete in
2637 implementations of the trait. A working version of this code might look like:
2640 trait MyTrait {type X; }
2643 impl MyTrait for MyStruct {
2648 let foo: <MyStruct as MyTrait>::X;
2652 This syntax specifies that we want the X type from MyTrait, as made concrete in
2653 MyStruct. The reason that we cannot simply use `MyStruct::X` is that MyStruct
2654 might implement two different traits with identically-named associated types.
2655 This syntax allows disambiguation between the two.
2659 You attempted to use multiple types as bounds for a closure or trait object.
2660 Rust does not currently support this. A simple example that causes this error:
2662 ```compile_fail,E0225
2664 let _: Box<std::io::Read + std::io::Write>;
2668 Send and Sync are an exception to this rule: it's possible to have bounds of
2669 one non-builtin trait, plus either or both of Send and Sync. For example, the
2670 following compiles correctly:
2674 let _: Box<std::io::Read + Send + Sync>;
2680 The trait has more type parameters specified than appear in its definition.
2682 Erroneous example code:
2684 ```compile_fail,E0230
2685 #![feature(on_unimplemented)]
2686 #[rustc_on_unimplemented = "Trait error on `{Self}` with `<{A},{B},{C}>`"]
2687 // error: there is no type parameter C on trait TraitWithThreeParams
2688 trait TraitWithThreeParams<A,B>
2692 Include the correct number of type parameters and the compilation should
2696 #![feature(on_unimplemented)]
2697 #[rustc_on_unimplemented = "Trait error on `{Self}` with `<{A},{B},{C}>`"]
2698 trait TraitWithThreeParams<A,B,C> // ok!
2704 The attribute must have a value. Erroneous code example:
2706 ```compile_fail,E0232
2707 #![feature(on_unimplemented)]
2709 #[rustc_on_unimplemented] // error: this attribute must have a value
2713 Please supply the missing value of the attribute. Example:
2716 #![feature(on_unimplemented)]
2718 #[rustc_on_unimplemented = "foo"] // ok!
2724 This error indicates that not enough type parameters were found in a type or
2727 For example, the `Foo` struct below is defined to be generic in `T`, but the
2728 type parameter is missing in the definition of `Bar`:
2730 ```compile_fail,E0243
2731 struct Foo<T> { x: T }
2733 struct Bar { x: Foo }
2738 This error indicates that too many type parameters were found in a type or
2741 For example, the `Foo` struct below has no type parameters, but is supplied
2742 with two in the definition of `Bar`:
2744 ```compile_fail,E0244
2745 struct Foo { x: bool }
2747 struct Bar<S, T> { x: Foo<S, T> }
2752 If an impl has a generic parameter with the `#[may_dangle]` attribute, then
2753 that impl must be declared as an `unsafe impl. For example:
2755 ```compile_fail,E0569
2756 #![feature(generic_param_attrs)]
2757 #![feature(dropck_eyepatch)]
2760 impl<#[may_dangle] X> Drop for Foo<X> {
2761 fn drop(&mut self) { }
2765 In this example, we are asserting that the destructor for `Foo` will not
2766 access any data of type `X`, and require this assertion to be true for
2767 overall safety in our program. The compiler does not currently attempt to
2768 verify this assertion; therefore we must tag this `impl` as unsafe.
2772 Default impls for a trait must be located in the same crate where the trait was
2773 defined. For more information see the [opt-in builtin traits RFC](https://github
2774 .com/rust-lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
2778 A cross-crate opt-out trait was implemented on something which wasn't a struct
2779 or enum type. Erroneous code example:
2781 ```compile_fail,E0321
2782 #![feature(optin_builtin_traits)]
2786 impl !Sync for Foo {}
2788 unsafe impl Send for &'static Foo {}
2789 // error: cross-crate traits with a default impl, like `core::marker::Send`,
2790 // can only be implemented for a struct/enum type, not
2794 Only structs and enums are permitted to impl Send, Sync, and other opt-out
2795 trait, and the struct or enum must be local to the current crate. So, for
2796 example, `unsafe impl Send for Rc<Foo>` is not allowed.
2800 The `Sized` trait is a special trait built-in to the compiler for types with a
2801 constant size known at compile-time. This trait is automatically implemented
2802 for types as needed by the compiler, and it is currently disallowed to
2803 explicitly implement it for a type.
2807 An associated const was implemented when another trait item was expected.
2808 Erroneous code example:
2810 ```compile_fail,E0323
2811 #![feature(associated_consts)]
2821 // error: item `N` is an associated const, which doesn't match its
2822 // trait `<Bar as Foo>`
2826 Please verify that the associated const wasn't misspelled and the correct trait
2827 was implemented. Example:
2837 type N = u32; // ok!
2844 #![feature(associated_consts)]
2853 const N : u32 = 0; // ok!
2859 A method was implemented when another trait item was expected. Erroneous
2862 ```compile_fail,E0324
2863 #![feature(associated_consts)]
2875 // error: item `N` is an associated method, which doesn't match its
2876 // trait `<Bar as Foo>`
2880 To fix this error, please verify that the method name wasn't misspelled and
2881 verify that you are indeed implementing the correct trait items. Example:
2884 #![feature(associated_consts)]
2903 An associated type was implemented when another trait item was expected.
2904 Erroneous code example:
2906 ```compile_fail,E0325
2907 #![feature(associated_consts)]
2917 // error: item `N` is an associated type, which doesn't match its
2918 // trait `<Bar as Foo>`
2922 Please verify that the associated type name wasn't misspelled and your
2923 implementation corresponds to the trait definition. Example:
2933 type N = u32; // ok!
2940 #![feature(associated_consts)]
2949 const N : u32 = 0; // ok!
2955 The types of any associated constants in a trait implementation must match the
2956 types in the trait definition. This error indicates that there was a mismatch.
2958 Here's an example of this error:
2960 ```compile_fail,E0326
2961 #![feature(associated_consts)]
2970 const BAR: u32 = 5; // error, expected bool, found u32
2976 The Unsize trait should not be implemented directly. All implementations of
2977 Unsize are provided automatically by the compiler.
2979 Erroneous code example:
2981 ```compile_fail,E0328
2984 use std::marker::Unsize;
2988 impl<T> Unsize<T> for MyType {}
2991 If you are defining your own smart pointer type and would like to enable
2992 conversion from a sized to an unsized type with the [DST coercion system]
2993 (https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md), use
2994 [`CoerceUnsized`](https://doc.rust-lang.org/std/ops/trait.CoerceUnsized.html)
2998 #![feature(coerce_unsized)]
3000 use std::ops::CoerceUnsized;
3002 pub struct MyType<T: ?Sized> {
3003 field_with_unsized_type: T,
3006 impl<T, U> CoerceUnsized<MyType<U>> for MyType<T>
3007 where T: CoerceUnsized<U> {}
3012 An attempt was made to access an associated constant through either a generic
3013 type parameter or `Self`. This is not supported yet. An example causing this
3014 error is shown below:
3017 #![feature(associated_consts)]
3025 impl Foo for MyStruct {
3026 const BAR: f64 = 0f64;
3029 fn get_bar_bad<F: Foo>(t: F) -> f64 {
3034 Currently, the value of `BAR` for a particular type can only be accessed
3035 through a concrete type, as shown below:
3038 #![feature(associated_consts)]
3046 fn get_bar_good() -> f64 {
3047 <MyStruct as Foo>::BAR
3053 An attempt was made to implement `Drop` on a concrete specialization of a
3054 generic type. An example is shown below:
3056 ```compile_fail,E0366
3061 impl Drop for Foo<u32> {
3062 fn drop(&mut self) {}
3066 This code is not legal: it is not possible to specialize `Drop` to a subset of
3067 implementations of a generic type. One workaround for this is to wrap the
3068 generic type, as shown below:
3080 fn drop(&mut self) {}
3086 An attempt was made to implement `Drop` on a specialization of a generic type.
3087 An example is shown below:
3089 ```compile_fail,E0367
3092 struct MyStruct<T> {
3096 impl<T: Foo> Drop for MyStruct<T> {
3097 fn drop(&mut self) {}
3101 This code is not legal: it is not possible to specialize `Drop` to a subset of
3102 implementations of a generic type. In order for this code to work, `MyStruct`
3103 must also require that `T` implements `Foo`. Alternatively, another option is
3104 to wrap the generic type in another that specializes appropriately:
3109 struct MyStruct<T> {
3113 struct MyStructWrapper<T: Foo> {
3117 impl <T: Foo> Drop for MyStructWrapper<T> {
3118 fn drop(&mut self) {}
3124 This error indicates that a binary assignment operator like `+=` or `^=` was
3125 applied to a type that doesn't support it. For example:
3127 ```compile_fail,E0368
3128 let mut x = 12f32; // error: binary operation `<<` cannot be applied to
3134 To fix this error, please check that this type implements this binary
3138 let mut x = 12u32; // the `u32` type does implement the `ShlAssign` trait
3143 It is also possible to overload most operators for your own type by
3144 implementing the `[OP]Assign` traits from `std::ops`.
3146 Another problem you might be facing is this: suppose you've overloaded the `+`
3147 operator for some type `Foo` by implementing the `std::ops::Add` trait for
3148 `Foo`, but you find that using `+=` does not work, as in this example:
3150 ```compile_fail,E0368
3158 fn add(self, rhs: Foo) -> Foo {
3164 let mut x: Foo = Foo(5);
3165 x += Foo(7); // error, `+= cannot be applied to the type `Foo`
3169 This is because `AddAssign` is not automatically implemented, so you need to
3170 manually implement it for your type.
3174 A binary operation was attempted on a type which doesn't support it.
3175 Erroneous code example:
3177 ```compile_fail,E0369
3178 let x = 12f32; // error: binary operation `<<` cannot be applied to
3184 To fix this error, please check that this type implements this binary
3188 let x = 12u32; // the `u32` type does implement it:
3189 // https://doc.rust-lang.org/stable/std/ops/trait.Shl.html
3194 It is also possible to overload most operators for your own type by
3195 implementing traits from `std::ops`.
3199 The maximum value of an enum was reached, so it cannot be automatically
3200 set in the next enum value. Erroneous code example:
3203 #[deny(overflowing_literals)]
3205 X = 0x7fffffffffffffff,
3206 Y, // error: enum discriminant overflowed on value after
3207 // 9223372036854775807: i64; set explicitly via
3208 // Y = -9223372036854775808 if that is desired outcome
3212 To fix this, please set manually the next enum value or put the enum variant
3213 with the maximum value at the end of the enum. Examples:
3217 X = 0x7fffffffffffffff,
3227 X = 0x7fffffffffffffff,
3233 When `Trait2` is a subtrait of `Trait1` (for example, when `Trait2` has a
3234 definition like `trait Trait2: Trait1 { ... }`), it is not allowed to implement
3235 `Trait1` for `Trait2`. This is because `Trait2` already implements `Trait1` by
3236 definition, so it is not useful to do this.
3240 ```compile_fail,E0371
3241 trait Foo { fn foo(&self) { } }
3245 impl Bar for Baz { } // error, `Baz` implements `Bar` by definition
3246 impl Foo for Baz { } // error, `Baz` implements `Bar` which implements `Foo`
3247 impl Baz for Baz { } // error, `Baz` (trivially) implements `Baz`
3248 impl Baz for Bar { } // Note: This is OK
3253 A struct without a field containing an unsized type cannot implement
3255 [unsized type](https://doc.rust-lang.org/book/unsized-types.html)
3256 is any type that the compiler doesn't know the length or alignment of at
3257 compile time. Any struct containing an unsized type is also unsized.
3259 Example of erroneous code:
3261 ```compile_fail,E0374
3262 #![feature(coerce_unsized)]
3263 use std::ops::CoerceUnsized;
3265 struct Foo<T: ?Sized> {
3269 // error: Struct `Foo` has no unsized fields that need `CoerceUnsized`.
3270 impl<T, U> CoerceUnsized<Foo<U>> for Foo<T>
3271 where T: CoerceUnsized<U> {}
3274 `CoerceUnsized` is used to coerce one struct containing an unsized type
3275 into another struct containing a different unsized type. If the struct
3276 doesn't have any fields of unsized types then you don't need explicit
3277 coercion to get the types you want. To fix this you can either
3278 not try to implement `CoerceUnsized` or you can add a field that is
3279 unsized to the struct.
3284 #![feature(coerce_unsized)]
3285 use std::ops::CoerceUnsized;
3287 // We don't need to impl `CoerceUnsized` here.
3292 // We add the unsized type field to the struct.
3293 struct Bar<T: ?Sized> {
3298 // The struct has an unsized field so we can implement
3299 // `CoerceUnsized` for it.
3300 impl<T, U> CoerceUnsized<Bar<U>> for Bar<T>
3301 where T: CoerceUnsized<U> {}
3304 Note that `CoerceUnsized` is mainly used by smart pointers like `Box`, `Rc`
3305 and `Arc` to be able to mark that they can coerce unsized types that they
3310 A struct with more than one field containing an unsized type cannot implement
3311 `CoerceUnsized`. This only occurs when you are trying to coerce one of the
3312 types in your struct to another type in the struct. In this case we try to
3313 impl `CoerceUnsized` from `T` to `U` which are both types that the struct
3314 takes. An [unsized type](https://doc.rust-lang.org/book/unsized-types.html)
3315 is any type that the compiler doesn't know the length or alignment of at
3316 compile time. Any struct containing an unsized type is also unsized.
3318 Example of erroneous code:
3320 ```compile_fail,E0375
3321 #![feature(coerce_unsized)]
3322 use std::ops::CoerceUnsized;
3324 struct Foo<T: ?Sized, U: ?Sized> {
3330 // error: Struct `Foo` has more than one unsized field.
3331 impl<T, U> CoerceUnsized<Foo<U, T>> for Foo<T, U> {}
3334 `CoerceUnsized` only allows for coercion from a structure with a single
3335 unsized type field to another struct with a single unsized type field.
3336 In fact Rust only allows for a struct to have one unsized type in a struct
3337 and that unsized type must be the last field in the struct. So having two
3338 unsized types in a single struct is not allowed by the compiler. To fix this
3339 use only one field containing an unsized type in the struct and then use
3340 multiple structs to manage each unsized type field you need.
3345 #![feature(coerce_unsized)]
3346 use std::ops::CoerceUnsized;
3348 struct Foo<T: ?Sized> {
3353 impl <T, U> CoerceUnsized<Foo<U>> for Foo<T>
3354 where T: CoerceUnsized<U> {}
3356 fn coerce_foo<T: CoerceUnsized<U>, U>(t: T) -> Foo<U> {
3357 Foo { a: 12i32, b: t } // we use coercion to get the `Foo<U>` type we need
3364 The type you are trying to impl `CoerceUnsized` for is not a struct.
3365 `CoerceUnsized` can only be implemented for a struct. Unsized types are
3366 already able to be coerced without an implementation of `CoerceUnsized`
3367 whereas a struct containing an unsized type needs to know the unsized type
3368 field it's containing is able to be coerced. An
3369 [unsized type](https://doc.rust-lang.org/book/unsized-types.html)
3370 is any type that the compiler doesn't know the length or alignment of at
3371 compile time. Any struct containing an unsized type is also unsized.
3373 Example of erroneous code:
3375 ```compile_fail,E0376
3376 #![feature(coerce_unsized)]
3377 use std::ops::CoerceUnsized;
3379 struct Foo<T: ?Sized> {
3383 // error: The type `U` is not a struct
3384 impl<T, U> CoerceUnsized<U> for Foo<T> {}
3387 The `CoerceUnsized` trait takes a struct type. Make sure the type you are
3388 providing to `CoerceUnsized` is a struct with only the last field containing an
3394 #![feature(coerce_unsized)]
3395 use std::ops::CoerceUnsized;
3401 // The `Foo<U>` is a struct so `CoerceUnsized` can be implemented
3402 impl<T, U> CoerceUnsized<Foo<U>> for Foo<T> where T: CoerceUnsized<U> {}
3405 Note that in Rust, structs can only contain an unsized type if the field
3406 containing the unsized type is the last and only unsized type field in the
3411 Default impls are only allowed for traits with no methods or associated items.
3412 For more information see the [opt-in builtin traits RFC](https://github.com/rust
3413 -lang/rfcs/blob/master/text/0019-opt-in-builtin-traits.md).
3417 You tried to implement methods for a primitive type. Erroneous code example:
3419 ```compile_fail,E0390
3425 // error: only a single inherent implementation marked with
3426 // `#[lang = "mut_ptr"]` is allowed for the `*mut T` primitive
3429 This isn't allowed, but using a trait to implement a method is a good solution.
3441 impl Bar for *mut Foo {
3448 This error indicates that some types or traits depend on each other
3449 and therefore cannot be constructed.
3451 The following example contains a circular dependency between two traits:
3453 ```compile_fail,E0391
3454 trait FirstTrait : SecondTrait {
3458 trait SecondTrait : FirstTrait {
3465 This error indicates that a type or lifetime parameter has been declared
3466 but not actually used. Here is an example that demonstrates the error:
3468 ```compile_fail,E0392
3474 If the type parameter was included by mistake, this error can be fixed
3475 by simply removing the type parameter, as shown below:
3483 Alternatively, if the type parameter was intentionally inserted, it must be
3484 used. A simple fix is shown below:
3492 This error may also commonly be found when working with unsafe code. For
3493 example, when using raw pointers one may wish to specify the lifetime for
3494 which the pointed-at data is valid. An initial attempt (below) causes this
3497 ```compile_fail,E0392
3503 We want to express the constraint that Foo should not outlive `'a`, because
3504 the data pointed to by `T` is only valid for that lifetime. The problem is
3505 that there are no actual uses of `'a`. It's possible to work around this
3506 by adding a PhantomData type to the struct, using it to tell the compiler
3507 to act as if the struct contained a borrowed reference `&'a T`:
3510 use std::marker::PhantomData;
3512 struct Foo<'a, T: 'a> {
3514 phantom: PhantomData<&'a T>
3518 PhantomData can also be used to express information about unused type
3519 parameters. You can read more about it in the API documentation:
3521 https://doc.rust-lang.org/std/marker/struct.PhantomData.html
3525 A type parameter which references `Self` in its default value was not specified.
3526 Example of erroneous code:
3528 ```compile_fail,E0393
3531 fn together_we_will_rule_the_galaxy(son: &A) {}
3532 // error: the type parameter `T` must be explicitly specified in an
3533 // object type because its default value `Self` references the
3537 A trait object is defined over a single, fully-defined trait. With a regular
3538 default parameter, this parameter can just be substituted in. However, if the
3539 default parameter is `Self`, the trait changes for each concrete type; i.e.
3540 `i32` will be expected to implement `A<i32>`, `bool` will be expected to
3541 implement `A<bool>`, etc... These types will not share an implementation of a
3542 fully-defined trait; instead they share implementations of a trait with
3543 different parameters substituted in for each implementation. This is
3544 irreconcilable with what we need to make a trait object work, and is thus
3545 disallowed. Making the trait concrete by explicitly specifying the value of the
3546 defaulted parameter will fix this issue. Fixed example:
3551 fn together_we_will_rule_the_galaxy(son: &A<i32>) {} // Ok!
3556 You implemented a trait, overriding one or more of its associated types but did
3557 not reimplement its default methods.
3559 Example of erroneous code:
3561 ```compile_fail,E0399
3562 #![feature(associated_type_defaults)]
3570 // error - the following trait items need to be reimplemented as
3571 // `Assoc` was overridden: `bar`
3576 To fix this, add an implementation for each default method from the trait:
3579 #![feature(associated_type_defaults)]
3588 fn bar(&self) {} // ok!
3594 The length of the platform-intrinsic function `simd_shuffle`
3595 wasn't specified. Erroneous code example:
3597 ```compile_fail,E0439
3598 #![feature(platform_intrinsics)]
3600 extern "platform-intrinsic" {
3601 fn simd_shuffle<A,B>(a: A, b: A, c: [u32; 8]) -> B;
3602 // error: invalid `simd_shuffle`, needs length: `simd_shuffle`
3606 The `simd_shuffle` function needs the length of the array passed as
3607 last parameter in its name. Example:
3610 #![feature(platform_intrinsics)]
3612 extern "platform-intrinsic" {
3613 fn simd_shuffle8<A,B>(a: A, b: A, c: [u32; 8]) -> B;
3619 A platform-specific intrinsic function has the wrong number of type
3620 parameters. Erroneous code example:
3622 ```compile_fail,E0440
3623 #![feature(repr_simd)]
3624 #![feature(platform_intrinsics)]
3627 struct f64x2(f64, f64);
3629 extern "platform-intrinsic" {
3630 fn x86_mm_movemask_pd<T>(x: f64x2) -> i32;
3631 // error: platform-specific intrinsic has wrong number of type
3636 Please refer to the function declaration to see if it corresponds
3637 with yours. Example:
3640 #![feature(repr_simd)]
3641 #![feature(platform_intrinsics)]
3644 struct f64x2(f64, f64);
3646 extern "platform-intrinsic" {
3647 fn x86_mm_movemask_pd(x: f64x2) -> i32;
3653 An unknown platform-specific intrinsic function was used. Erroneous
3656 ```compile_fail,E0441
3657 #![feature(repr_simd)]
3658 #![feature(platform_intrinsics)]
3661 struct i16x8(i16, i16, i16, i16, i16, i16, i16, i16);
3663 extern "platform-intrinsic" {
3664 fn x86_mm_adds_ep16(x: i16x8, y: i16x8) -> i16x8;
3665 // error: unrecognized platform-specific intrinsic function
3669 Please verify that the function name wasn't misspelled, and ensure
3670 that it is declared in the rust source code (in the file
3671 src/librustc_platform_intrinsics/x86.rs). Example:
3674 #![feature(repr_simd)]
3675 #![feature(platform_intrinsics)]
3678 struct i16x8(i16, i16, i16, i16, i16, i16, i16, i16);
3680 extern "platform-intrinsic" {
3681 fn x86_mm_adds_epi16(x: i16x8, y: i16x8) -> i16x8; // ok!
3687 Intrinsic argument(s) and/or return value have the wrong type.
3688 Erroneous code example:
3690 ```compile_fail,E0442
3691 #![feature(repr_simd)]
3692 #![feature(platform_intrinsics)]
3695 struct i8x16(i8, i8, i8, i8, i8, i8, i8, i8,
3696 i8, i8, i8, i8, i8, i8, i8, i8);
3698 struct i32x4(i32, i32, i32, i32);
3700 struct i64x2(i64, i64);
3702 extern "platform-intrinsic" {
3703 fn x86_mm_adds_epi16(x: i8x16, y: i32x4) -> i64x2;
3704 // error: intrinsic arguments/return value have wrong type
3708 To fix this error, please refer to the function declaration to give
3709 it the awaited types. Example:
3712 #![feature(repr_simd)]
3713 #![feature(platform_intrinsics)]
3716 struct i16x8(i16, i16, i16, i16, i16, i16, i16, i16);
3718 extern "platform-intrinsic" {
3719 fn x86_mm_adds_epi16(x: i16x8, y: i16x8) -> i16x8; // ok!
3725 Intrinsic argument(s) and/or return value have the wrong type.
3726 Erroneous code example:
3728 ```compile_fail,E0443
3729 #![feature(repr_simd)]
3730 #![feature(platform_intrinsics)]
3733 struct i16x8(i16, i16, i16, i16, i16, i16, i16, i16);
3735 struct i64x8(i64, i64, i64, i64, i64, i64, i64, i64);
3737 extern "platform-intrinsic" {
3738 fn x86_mm_adds_epi16(x: i16x8, y: i16x8) -> i64x8;
3739 // error: intrinsic argument/return value has wrong type
3743 To fix this error, please refer to the function declaration to give
3744 it the awaited types. Example:
3747 #![feature(repr_simd)]
3748 #![feature(platform_intrinsics)]
3751 struct i16x8(i16, i16, i16, i16, i16, i16, i16, i16);
3753 extern "platform-intrinsic" {
3754 fn x86_mm_adds_epi16(x: i16x8, y: i16x8) -> i16x8; // ok!
3760 A platform-specific intrinsic function has wrong number of arguments.
3761 Erroneous code example:
3763 ```compile_fail,E0444
3764 #![feature(repr_simd)]
3765 #![feature(platform_intrinsics)]
3768 struct f64x2(f64, f64);
3770 extern "platform-intrinsic" {
3771 fn x86_mm_movemask_pd(x: f64x2, y: f64x2, z: f64x2) -> i32;
3772 // error: platform-specific intrinsic has invalid number of arguments
3776 Please refer to the function declaration to see if it corresponds
3777 with yours. Example:
3780 #![feature(repr_simd)]
3781 #![feature(platform_intrinsics)]
3784 struct f64x2(f64, f64);
3786 extern "platform-intrinsic" {
3787 fn x86_mm_movemask_pd(x: f64x2) -> i32; // ok!
3793 The `typeof` keyword is currently reserved but unimplemented.
3794 Erroneous code example:
3796 ```compile_fail,E0516
3798 let x: typeof(92) = 92;
3802 Try using type inference instead. Example:
3812 A non-default implementation was already made on this type so it cannot be
3813 specialized further. Erroneous code example:
3815 ```compile_fail,E0520
3816 #![feature(specialization)]
3823 impl<T> SpaceLlama for T {
3824 default fn fly(&self) {}
3828 // applies to all `Clone` T and overrides the previous impl
3829 impl<T: Clone> SpaceLlama for T {
3833 // since `i32` is clone, this conflicts with the previous implementation
3834 impl SpaceLlama for i32 {
3835 default fn fly(&self) {}
3836 // error: item `fly` is provided by an `impl` that specializes
3837 // another, but the item in the parent `impl` is not marked
3838 // `default` and so it cannot be specialized.
3842 Specialization only allows you to override `default` functions in
3845 To fix this error, you need to mark all the parent implementations as default.
3849 #![feature(specialization)]
3856 impl<T> SpaceLlama for T {
3857 default fn fly(&self) {} // This is a parent implementation.
3860 // applies to all `Clone` T; overrides the previous impl
3861 impl<T: Clone> SpaceLlama for T {
3862 default fn fly(&self) {} // This is a parent implementation but was
3863 // previously not a default one, causing the error
3866 // applies to i32, overrides the previous two impls
3867 impl SpaceLlama for i32 {
3868 fn fly(&self) {} // And now that's ok!
3874 The number of elements in an array or slice pattern differed from the number of
3875 elements in the array being matched.
3877 Example of erroneous code:
3879 ```compile_fail,E0527
3880 #![feature(slice_patterns)]
3882 let r = &[1, 2, 3, 4];
3884 &[a, b] => { // error: pattern requires 2 elements but array
3886 println!("a={}, b={}", a, b);
3891 Ensure that the pattern is consistent with the size of the matched
3892 array. Additional elements can be matched with `..`:
3895 #![feature(slice_patterns)]
3897 let r = &[1, 2, 3, 4];
3899 &[a, b, ..] => { // ok!
3900 println!("a={}, b={}", a, b);
3907 An array or slice pattern required more elements than were present in the
3910 Example of erroneous code:
3912 ```compile_fail,E0528
3913 #![feature(slice_patterns)]
3917 &[a, b, c, rest..] => { // error: pattern requires at least 3
3918 // elements but array has 2
3919 println!("a={}, b={}, c={} rest={:?}", a, b, c, rest);
3924 Ensure that the matched array has at least as many elements as the pattern
3925 requires. You can match an arbitrary number of remaining elements with `..`:
3928 #![feature(slice_patterns)]
3930 let r = &[1, 2, 3, 4, 5];
3932 &[a, b, c, rest..] => { // ok!
3933 // prints `a=1, b=2, c=3 rest=[4, 5]`
3934 println!("a={}, b={}, c={} rest={:?}", a, b, c, rest);
3941 An array or slice pattern was matched against some other type.
3943 Example of erroneous code:
3945 ```compile_fail,E0529
3946 #![feature(slice_patterns)]
3950 [a, b] => { // error: expected an array or slice, found `f32`
3951 println!("a={}, b={}", a, b);
3956 Ensure that the pattern and the expression being matched on are of consistent
3960 #![feature(slice_patterns)]
3965 println!("a={}, b={}", a, b);
3972 An unknown field was specified into an enum's structure variant.
3974 Erroneous code example:
3976 ```compile_fail,E0559
3981 let s = Field::Fool { joke: 0 };
3982 // error: struct variant `Field::Fool` has no field named `joke`
3985 Verify you didn't misspell the field's name or that the field exists. Example:
3992 let s = Field::Fool { joke: 0 }; // ok!
3997 An unknown field was specified into a structure.
3999 Erroneous code example:
4001 ```compile_fail,E0560
4006 let s = Simba { mother: 1, father: 0 };
4007 // error: structure `Simba` has no field named `father`
4010 Verify you didn't misspell the field's name or that the field exists. Example:
4018 let s = Simba { mother: 1, father: 0 }; // ok!
4023 The requested ABI is unsupported by the current target.
4025 The rust compiler maintains for each target a blacklist of ABIs unsupported on
4026 that target. If an ABI is present in such a list this usually means that the
4027 target / ABI combination is currently unsupported by llvm.
4029 If necessary, you can circumvent this check using custom target specifications.
4033 A return statement was found outside of a function body.
4035 Erroneous code example:
4037 ```compile_fail,E0572
4038 const FOO: u32 = return 0; // error: return statement outside of function body
4043 To fix this issue, just remove the return keyword or move the expression into a
4049 fn some_fn() -> u32 {
4061 register_diagnostics! {
4066 E0103, // @GuillaumeGomez: I was unable to get this error, try your best!
4072 // E0159, // use of trait `{}` as struct constructor
4073 // E0163, // merged into E0071
4076 // E0172, // non-trait found in a type sum, moved to resolve
4077 // E0173, // manual implementations of unboxed closure traits are experimental
4080 // E0187, // can't infer the kind of the closure
4081 // E0188, // can not cast an immutable reference to a mutable pointer
4082 // E0189, // deprecated: can only cast a boxed pointer to a boxed object
4083 // E0190, // deprecated: can only cast a &-pointer to an &-object
4084 E0196, // cannot determine a type for this closure
4085 E0203, // type parameter has more than one relaxed default bound,
4086 // and only one is supported
4088 // E0209, // builtin traits can only be implemented on structs or enums
4089 E0212, // cannot extract an associated type from a higher-ranked trait bound
4090 // E0213, // associated types are not accepted in this context
4091 // E0215, // angle-bracket notation is not stable with `Fn`
4092 // E0216, // parenthetical notation is only stable with `Fn`
4093 // E0217, // ambiguous associated type, defined in multiple supertraits
4094 // E0218, // no associated type defined
4095 // E0219, // associated type defined in higher-ranked supertrait
4096 // E0222, // Error code E0045 (variadic function must have C calling
4097 // convention) duplicate
4098 E0224, // at least one non-builtin train is required for an object type
4099 E0227, // ambiguous lifetime bound, explicit lifetime bound required
4100 E0228, // explicit lifetime bound required
4101 E0231, // only named substitution parameters are allowed
4104 // E0235, // structure constructor specifies a structure of type but
4105 // E0236, // no lang item for range syntax
4106 // E0237, // no lang item for range syntax
4107 // E0238, // parenthesized parameters may only be used with a trait
4108 // E0239, // `next` method of `Iterator` trait has unexpected type
4112 E0245, // not a trait
4113 // E0246, // invalid recursive type
4115 // E0248, // value used as a type, now reported earlier during resolution as E0412
4117 // E0319, // trait impls for defaulted traits allowed just for structs/enums
4118 E0320, // recursive overflow during dropck
4119 // E0372, // coherence not object safe
4120 E0377, // the trait `CoerceUnsized` may only be implemented for a coercion
4121 // between structures with the same definition
4122 E0436, // functional record update requires a struct
4123 E0521, // redundant default implementations of trait
4124 E0533, // `{}` does not name a unit variant, unit struct or a constant
4125 E0562, // `impl Trait` not allowed outside of function
4126 // and inherent method return types
4127 E0563, // cannot determine a type for this `impl Trait`: {}
4128 E0564, // only named lifetimes are allowed in `impl Trait`,
4129 // but `{}` was found in the type `{}`
4130 E0567, // auto traits can not have type parameters
4131 E0568, // auto-traits can not have predicates,