Rollup merge of rust-lang#64404 - GuillaumeGomez:err-E0495, r=cramertj

Add long error explanation for E0495

Part of rust-lang#61137.

Author: Centril

src/librustc/error_codes.rs

@@ -1580,6 +1580,47 @@ where
 ```
 "##,
 
+E0495: r##"
+A lifetime cannot be determined in the given situation.
+
+Erroneous code example:
+
+```compile_fail,E0495
+fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T {
+    match (&t,) { // error!
+        ((u,),) => u,
+    }
+}
+
+let y = Box::new((42,));
+let x = transmute_lifetime(&y);
+```
+
+In this code, you have two ways to solve this issue:
+ 1. Enforce that `'a` lives at least as long as `'b`.
+ 2. Use the same lifetime requirement for both input and output values.
+
+So for the first solution, you can do it by replacing `'a` with `'a: 'b`:
+
+```
+fn transmute_lifetime<'a: 'b, 'b, T>(t: &'a (T,)) -> &'b T {
+    match (&t,) { // ok!
+        ((u,),) => u,
+    }
+}
+```
+
+In the second you can do it by simply removing `'b` so they both use `'a`:
+
+```
+fn transmute_lifetime<'a, T>(t: &'a (T,)) -> &'a T {
+    match (&t,) { // ok!
+        ((u,),) => u,
+    }
+}
+```
+"##,
+
 E0496: r##"
 A lifetime name is shadowing another lifetime name. Erroneous code example:
 
@@ -2275,8 +2316,6 @@ rejected in your own crates.
     E0488, // lifetime of variable does not enclose its declaration
     E0489, // type/lifetime parameter not in scope here
     E0490, // a value of type `..` is borrowed for too long
-    E0495, // cannot infer an appropriate lifetime due to conflicting
-           // requirements
     E0566, // conflicting representation hints
     E0623, // lifetime mismatch where both parameters are anonymous regions
     E0628, // generators cannot have explicit parameters

src/test/ui/associated-types/cache/project-fn-ret-contravariant.transmute.stderr

@@ -23,3 +23,4 @@ LL |    bar(foo, x)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/associated-types/cache/project-fn-ret-invariant.transmute.stderr

@@ -19,3 +19,4 @@ LL | fn baz<'a,'b>(x: Type<'a>) -> Type<'static> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/c-variadic/variadic-ffi-4.stderr

@@ -209,4 +209,5 @@ LL | | }
 
 error: aborting due to 8 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0308, E0495.
+For more information about an error, try `rustc --explain E0308`.

src/test/ui/error-codes/E0621-does-not-trigger-for-closures.stderr

@@ -27,3 +27,4 @@ LL |     invoke(&x, |a, b| if a > b { a } else { b });
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/impl-header-lifetime-elision/dyn-trait.stderr

@@ -19,3 +19,4 @@ LL | fn with_dyn_debug_static<'a>(x: Box<dyn Debug + 'a>) {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/in-band-lifetimes/mismatched_trait_impl-2.stderr

@@ -18,3 +18,4 @@ LL | |     }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/in-band-lifetimes/mismatched_trait_impl.stderr

@@ -32,3 +32,4 @@ LL |         x
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/issues/issue-16683.stderr

@@ -27,3 +27,4 @@ LL | trait T<'a> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/issues/issue-17758.stderr

@@ -28,3 +28,4 @@ LL | trait Foo<'a> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/issues/issue-20831-debruijn.stderr

@@ -94,4 +94,5 @@ LL | impl<'a> Publisher<'a> for MyStruct<'a> {
 
 error: aborting due to 3 previous errors
 
-For more information about this error, try `rustc --explain E0308`.
+Some errors have detailed explanations: E0308, E0495.
+For more information about an error, try `rustc --explain E0308`.

src/test/ui/issues/issue-52213.stderr

@@ -25,3 +25,4 @@ LL |         ((u,),) => u,
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/issues/issue-55796.stderr

@@ -42,3 +42,4 @@ LL |         Box::new(self.in_edges(u).map(|e| e.target()))
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/issue-55394.stderr

@@ -27,3 +27,4 @@ LL | impl Foo<'_> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/normalization-bounds-error.stderr

@@ -20,3 +20,4 @@ LL | fn visit_seq<'d, 'a: 'd>() -> <&'a () as Visitor<'d>>::Value {}
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/type-alias-free-regions.stderr

@@ -50,3 +50,4 @@ LL | impl<'a> FromTuple<'a> for C<'a> {
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/user-annotations/constant-in-expr-inherent-1.stderr

@@ -21,3 +21,4 @@ LL |     <Foo<'a>>::C
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/nll/user-annotations/constant-in-expr-trait-item-3.stderr

@@ -21,3 +21,4 @@ LL |     T::C
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/object-lifetime/object-lifetime-default-elision.stderr

@@ -50,3 +50,4 @@ LL | fn load3<'a,'b>(ss: &'a dyn SomeTrait) -> &'b dyn SomeTrait {
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/region-object-lifetime-2.stderr

@@ -27,3 +27,4 @@ LL |     x.borrowed()
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/region-object-lifetime-4.stderr

@@ -27,3 +27,4 @@ LL |     x.borrowed()
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/region-object-lifetime-in-coercion.stderr

@@ -48,4 +48,5 @@ LL | fn d<'a,'b>(v: &'a [u8]) -> Box<dyn Foo+'b> {
 
 error: aborting due to 4 previous errors
 
-For more information about this error, try `rustc --explain E0621`.
+Some errors have detailed explanations: E0495, E0621.
+For more information about an error, try `rustc --explain E0495`.

src/test/ui/regions/regions-addr-of-self.stderr

@@ -26,3 +26,4 @@ LL |         let p: &'static mut usize = &mut self.cats_chased;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-addr-of-upvar-self.stderr

@@ -23,3 +23,4 @@ LL |             let p: &'static mut usize = &mut self.food;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-assoc-type-region-bound-in-trait-not-met.stderr

@@ -46,3 +46,4 @@ LL | impl<'a,'b> Foo<'b> for &'a i64 {
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-assoc-type-static-bound-in-trait-not-met.stderr

@@ -21,3 +21,4 @@ LL | impl<'a> Foo for &'a i32 {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-close-object-into-object-2.stderr

@@ -21,3 +21,4 @@ LL |     box B(&*v) as Box<dyn X>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-close-object-into-object-4.stderr

@@ -21,3 +21,4 @@ LL |     box B(&*v) as Box<dyn X>
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-close-over-type-parameter-multiple.stderr

@@ -25,3 +25,4 @@ LL | fn make_object_bad<'a,'b,'c,A:SomeTrait+'a+'b>(v: A) -> Box<dyn SomeTrait +
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-creating-enums4.stderr

@@ -23,3 +23,4 @@ LL | fn mk_add_bad2<'a,'b>(x: &'a Ast<'a>, y: &'a Ast<'a>, z: &Ast) -> Ast<'b> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-escape-method.stderr

@@ -25,3 +25,4 @@ LL |     s.f(|p| p)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-escape-via-trait-or-not.stderr

@@ -25,3 +25,4 @@ LL |     with(|o| o)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-free-region-ordering-incorrect.stderr

@@ -30,3 +30,4 @@ LL | |         }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-infer-call-3.stderr

@@ -27,3 +27,4 @@ LL |     let z = with(|y| { select(x, y) });
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-nested-fns.stderr

@@ -57,4 +57,5 @@ LL | fn nested<'x>(x: &'x isize) {
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0312`.
+Some errors have detailed explanations: E0312, E0495.
+For more information about an error, try `rustc --explain E0312`.

src/test/ui/regions/regions-normalize-in-where-clause-list.stderr

@@ -23,3 +23,4 @@ LL | fn bar<'a, 'b>()
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-ret-borrowed-1.stderr

@@ -25,3 +25,4 @@ LL |     with(|o| o)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-ret-borrowed.stderr

@@ -25,3 +25,4 @@ LL |     with(|o| o)
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-return-ref-to-upvar-issue-17403.stderr

@@ -27,3 +27,4 @@ LL |         let y = f();
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/regions/regions-trait-object-subtyping.stderr

@@ -61,5 +61,5 @@ LL | fn foo4<'a:'b,'b>(x: Wrapper<&'a mut dyn Dummy>) -> Wrapper<&'b mut dyn Dum
 
 error: aborting due to 3 previous errors
 
-Some errors have detailed explanations: E0308, E0478.
+Some errors have detailed explanations: E0308, E0478, E0495.
 For more information about an error, try `rustc --explain E0308`.

src/test/ui/reject-specialized-drops-8142.stderr

@@ -111,5 +111,5 @@ LL | struct W<'l1, 'l2> { x: &'l1 i8, y: &'l2 u8 }
 
 error: aborting due to 8 previous errors
 
-Some errors have detailed explanations: E0308, E0366, E0367.
+Some errors have detailed explanations: E0308, E0366, E0367, E0495.
 For more information about an error, try `rustc --explain E0308`.

src/test/ui/traits/trait-impl-of-supertrait-has-wrong-lifetime-parameters.stderr

@@ -20,3 +20,4 @@ LL | impl<'a,'b> T2<'a, 'b> for S<'a, 'b> {
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/underscore-lifetime/dyn-trait-underscore.stderr

@@ -24,3 +24,4 @@ LL |     Box::new(items.iter())
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0495`.

src/test/ui/wf/wf-static-method.stderr

@@ -105,5 +105,5 @@ LL |     <IndirectEvil>::static_evil(b)
 
 error: aborting due to 5 previous errors
 
-Some errors have detailed explanations: E0312, E0478.
+Some errors have detailed explanations: E0312, E0478, E0495.
 For more information about an error, try `rustc --explain E0312`.