Rollup merge of rust-lang#81634 - jesusprubio:jesusprubio/add-long-explanation-e0521, r=GuillaumeGomez

Add long explanation e0521

Helps with rust-lang#61137

Author: JohnTitor

compiler/rustc_error_codes/src/error_codes.rs

@@ -267,6 +267,7 @@ E0516: include_str!("./error_codes/E0516.md"),
 E0517: include_str!("./error_codes/E0517.md"),
 E0518: include_str!("./error_codes/E0518.md"),
 E0520: include_str!("./error_codes/E0520.md"),
+E0521: include_str!("./error_codes/E0521.md"),
 E0522: include_str!("./error_codes/E0522.md"),
 E0524: include_str!("./error_codes/E0524.md"),
 E0525: include_str!("./error_codes/E0525.md"),
@@ -597,7 +598,6 @@ E0780: include_str!("./error_codes/E0780.md"),
     E0514, // metadata version mismatch
     E0519, // local crate and dependency have same (crate-name, disambiguator)
     // two dependencies have same (crate-name, disambiguator) but different SVH
-    E0521, // borrowed data escapes outside of closure
     E0523,
 //  E0526, // shuffle indices are not constant
 //  E0540, // multiple rustc_deprecated attributes

compiler/rustc_error_codes/src/error_codes/E0521.md

@@ -0,0 +1,28 @@
+Borrowed data escapes outside of closure.
+
+Erroneous code example:
+
+```compile_fail,E0521
+let mut list: Vec<&str> = Vec::new();
+
+let _add = |el: &str| {
+    list.push(el); // error: `el` escapes the closure body here
+};
+```
+
+A type anotation of a closure parameter implies a new lifetime declaration.
+Consider to drop it, the compiler is reliably able to infer them.
+
+```
+let mut list: Vec<&str> = Vec::new();
+
+let _add = |el| {
+    list.push(el);
+};
+```
+
+See the [Closure type inference and annotation][closure-infere-annotation] and
+[Lifetime elision][lifetime-elision] sections of the Book for more details.
+
+[closure-infere-annotation]: https://doc.rust-lang.org/book/ch13-01-closures.html#closure-type-inference-and-annotation
+[lifetime-elision]: https://doc.rust-lang.org/reference/lifetime-elision.html

src/test/ui/borrowck/issue-45983.stderr

@@ -10,3 +10,4 @@ LL |     give_any(|y| x = Some(y));
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/borrowck/issue-7573.stderr

@@ -12,3 +12,4 @@ LL |         lines_to_use.push(installed_id);
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/borrowck/regions-escape-bound-fn-2.stderr

@@ -10,3 +10,4 @@ LL |     with_int(|y| x = Some(y));
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/borrowck/regions-escape-bound-fn.stderr

@@ -10,3 +10,4 @@ LL |     with_int(|y| x = Some(y));
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/borrowck/regions-escape-unboxed-closure.stderr

@@ -10,3 +10,4 @@ LL |     with_int(&mut |y| x = Some(y));
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/closures/closure-expected-type/expect-region-supply-region.stderr

@@ -20,3 +20,4 @@ LL |         f = Some(x);
 
 error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/generator/ref-escapes-but-not-over-yield.stderr

@@ -12,3 +12,4 @@ LL |         a = &b;
 
 error: aborting due to previous error
 
+For more information about this error, try `rustc --explain E0521`.

src/test/ui/nll/closure-requirements/propagate-approximated-shorter-to-static-comparing-against-free.stderr

@@ -83,4 +83,5 @@ LL | }
 
 error: aborting due to 2 previous errors
 
-For more information about this error, try `rustc --explain E0597`.
+Some errors have detailed explanations: E0521, E0597.
+For more information about an error, try `rustc --explain E0521`.