Rollup merge of rust-lang#66186 - GuillaumeGomez:long-err-explanation-E0623, r=Dylan-DPC

Add long error explanation for E0623

Part of rust-lang#61137.

r? @Dylan-DPC

Author: JohnTitor

src/librustc/error_codes.rs

@@ -1896,6 +1896,51 @@ fn foo<'a>(x: &'a i32, y: &i32) -> &'a i32 {
 ```
 "##,
 
+E0623: r##"
+A lifetime didn't match what was expected.
+
+Erroneous code example:
+
+```compile_fail,E0623
+struct Foo<'a> {
+    x: &'a isize,
+}
+
+fn bar<'short, 'long>(c: Foo<'short>, l: &'long isize) {
+    let _: Foo<'long> = c; // error!
+}
+```
+
+In this example, we tried to set a value with an incompatible lifetime to
+another one (`'long` is unrelated to `'short`). We can solve this issue in
+two different ways:
+
+Either we make `'short` live at least as long as `'long`:
+
+```
+struct Foo<'a> {
+    x: &'a isize,
+}
+
+// we set 'short to live at least as long as 'long
+fn bar<'short: 'long, 'long>(c: Foo<'short>, l: &'long isize) {
+    let _: Foo<'long> = c; // ok!
+}
+```
+
+Or we use only one lifetime:
+
+```
+struct Foo<'a> {
+    x: &'a isize,
+}
+
+fn bar<'short>(c: Foo<'short>, l: &'short isize) {
+    let _: Foo<'short> = c; // ok!
+}
+```
+"##,
+
 E0635: r##"
 The `#![feature]` attribute specified an unknown feature.
 
@@ -2329,7 +2374,6 @@ the future, [RFC 2091] prohibits their implementation without a follow-up RFC.
     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
-    E0623, // lifetime mismatch where both parameters are anonymous regions
     E0628, // generators cannot have explicit parameters
     E0631, // type mismatch in closure arguments
     E0637, // "'_" is not a valid lifetime bound

src/test/ui/associated-type-bounds/implied-region-constraints.stderr

@@ -18,3 +18,4 @@ LL |             let _failure_proves_not_implied_outlives_region_b: &'b T = &x;
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/associated-types/associated-types-project-from-hrtb-in-fn-body.stderr

@@ -11,3 +11,4 @@ LL |     let z: I::A = if cond { x } else { y };
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/associated-types/associated-types-subtyping-1.stderr

@@ -18,3 +18,4 @@ LL |     let _c: <T as Trait<'a>>::Type = b;
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0623`.

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

@@ -22,3 +22,4 @@ LL |    (a, b)
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0623`.

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

@@ -21,3 +21,4 @@ LL |    let b = bar(foo, x);
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0623`.

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

@@ -11,3 +11,4 @@ LL |    let b = bar(f, y);
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/async-await/issues/issue-63388-1.stderr

@@ -11,3 +11,4 @@ LL |         foo
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/async-await/multiple-lifetimes/ret-impl-trait-one.stderr

@@ -9,3 +9,4 @@ LL | async fn async_ret_impl_trait1<'a, 'b>(a: &'a u8, b: &'b u8) -> impl Trait<
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0623`.

src/test/ui/borrowck/borrowck-reborrow-from-shorter-lived-andmut.stderr

@@ -10,3 +10,4 @@ LL |     S { pointer: &mut *p.pointer }
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0623`.