Auto merge of #140324 - matthiaskrgr:rollup-jlzvdre, r=matthiaskrgr

Rollup of 8 pull requests

Successful merges:

 - #139865 (Stabilize proc_macro::Span::{start,end,line,column}.)
 - #140086 (If creating a temporary directory fails with permission denied then retry with backoff)
 - #140216 (Document that "extern blocks must be unsafe" in Rust 2024)
 - #140253 (Add XtensaAsmPrinter)
 - #140272 (Improve error message for `||` (or) in let chains)
 - #140305 (Track per-obligation recursion depth only if there is inference in the new solver)
 - #140306 (handle specialization in the new trait solver)
 - #140308 (stall generator witness obligations: add regression test)

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 6 insertions, 2 deletions

diff --git a/library/std/src/keyword_docs.rs b/library/std/src/keyword_docs.rs
index 91701576130..c9595b051e2 100644
--- a/library/std/src/keyword_docs.rs
+++ b/library/std/src/keyword_docs.rs
@@ -388,11 +388,15 @@ mod enum_keyword {}
 /// lazy_static;`. The other use is in foreign function interfaces (FFI).
 ///
 /// `extern` is used in two different contexts within FFI. The first is in the form of external
-/// blocks, for declaring function interfaces that Rust code can call foreign code by.
+/// blocks, for declaring function interfaces that Rust code can call foreign code by. This use
+/// of `extern` is unsafe, since we are asserting to the compiler that all function declarations
+/// are correct. If they are not, using these items may lead to undefined behavior.
 ///
 /// ```rust ignore
+/// // SAFETY: The function declarations given below are in
+/// // line with the header files of `my_c_library`.
 /// #[link(name = "my_c_library")]
-/// extern "C" {
+/// unsafe extern "C" {
 ///     fn my_c_function(x: i32) -> bool;
 /// }
 /// ```