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docs/test: add UI test and docs for E0476 #108444

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Feb 26, 2023
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2 changes: 1 addition & 1 deletion compiler/rustc_error_codes/src/error_codes.rs
Original file line number Diff line number Diff line change
Expand Up @@ -253,6 +253,7 @@ E0466: include_str!("./error_codes/E0466.md"),
E0468: include_str!("./error_codes/E0468.md"),
E0469: include_str!("./error_codes/E0469.md"),
E0472: include_str!("./error_codes/E0472.md"),
E0476: include_str!("./error_codes/E0476.md"),
E0477: include_str!("./error_codes/E0477.md"),
E0478: include_str!("./error_codes/E0478.md"),
E0482: include_str!("./error_codes/E0482.md"),
Expand Down Expand Up @@ -611,7 +612,6 @@ E0793: include_str!("./error_codes/E0793.md"),
// E0473, // dereference of reference outside its lifetime
// E0474, // captured variable `..` does not outlive the enclosing closure
// E0475, // index of slice outside its lifetime
E0476, // lifetime of the source pointer does not outlive lifetime bound...
// E0479, // the type `..` (provided as the value of a type parameter) is...
// E0480, // lifetime of method receiver does not outlive the method call
// E0481, // lifetime of function argument does not outlive the function call
Expand Down
21 changes: 21 additions & 0 deletions compiler/rustc_error_codes/src/error_codes/E0476.md
Original file line number Diff line number Diff line change
@@ -0,0 +1,21 @@
The coerced type does not outlive the value being coerced to.

Example of erroneous code:

```compile_fail,E0476
#![feature(coerce_unsized)]
#![feature(unsize)]

use std::marker::Unsize;
use std::ops::CoerceUnsized;

// error: lifetime of the source pointer does not outlive lifetime bound of the
// object type
impl<'a, 'b, T, S> CoerceUnsized<&'a T> for &'b S where S: Unsize<T> {}
```

During a coercion, the "source pointer" (the coerced type) did not outlive the
"object type" (value being coerced to). In the above example, `'b` is not a
subtype of `'a`. This error can currently only be encountered with the unstable
`CoerceUnsized` trait which allows custom coercions of unsized types behind a
smart pointer to be implemented.
2 changes: 1 addition & 1 deletion src/tools/error_index_generator/main.rs
Original file line number Diff line number Diff line change
Expand Up @@ -22,7 +22,7 @@ macro_rules! register_diagnostics {
pub fn error_codes() -> Vec<(&'static str, Option<&'static str>)> {
let mut errors: Vec<(&str, Option<&str>)> = vec![
$((stringify!($error_code), Some($message)),)+
$((stringify!($undocumented), None),)+
$((stringify!($undocumented), None),)*
];
errors.sort();
errors
Expand Down
2 changes: 1 addition & 1 deletion src/tools/tidy/src/error_codes.rs
Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ const IGNORE_DOCTEST_CHECK: &[&str] = &["E0464", "E0570", "E0601", "E0602", "E06

// Error codes that don't yet have a UI test. This list will eventually be removed.
const IGNORE_UI_TEST_CHECK: &[&str] =
&["E0461", "E0465", "E0476", "E0514", "E0554", "E0640", "E0717", "E0729"];
&["E0461", "E0465", "E0514", "E0554", "E0640", "E0717", "E0729"];

macro_rules! verbose_print {
($verbose:expr, $($fmt:tt)*) => {
Expand Down
13 changes: 13 additions & 0 deletions tests/ui/error-codes/E0476.rs
Original file line number Diff line number Diff line change
@@ -0,0 +1,13 @@
#![feature(coerce_unsized)]
#![feature(unsize)]

use std::marker::Unsize;
use std::ops::CoerceUnsized;

struct Wrapper<T>(T);

impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
//~^ ERROR lifetime of the source pointer does not outlive lifetime bound of the object type [E0476]
//~^^ ERROR E0119

fn main() {}
31 changes: 31 additions & 0 deletions tests/ui/error-codes/E0476.stderr
Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
error[E0119]: conflicting implementations of trait `CoerceUnsized<&Wrapper<_>>` for type `&Wrapper<_>`
--> $DIR/E0476.rs:9:1
|
LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
= note: conflicting implementation in crate `core`:
- impl<'a, 'b, T, U> CoerceUnsized<&'a U> for &'b T
where 'b: 'a, T: Unsize<U>, T: ?Sized, U: ?Sized;

error[E0476]: lifetime of the source pointer does not outlive lifetime bound of the object type
--> $DIR/E0476.rs:9:1
|
LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
|
note: object type is valid for the lifetime `'a` as defined here
--> $DIR/E0476.rs:9:6
|
LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
| ^^
note: source pointer is only valid for the lifetime `'b` as defined here
--> $DIR/E0476.rs:9:10
|
LL | impl<'a, 'b, T, S> CoerceUnsized<&'a Wrapper<T>> for &'b Wrapper<S> where S: Unsize<T> {}
| ^^

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0119, E0476.
For more information about an error, try `rustc --explain E0119`.