Auto merge of #120136 - matthiaskrgr:rollup-3zzb0z9, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #117561 (Stabilize `slice_first_last_chunk`)
 - #117662 ([rustdoc] Allows links in headings)
 - #119815 (Format sources into the error message when loading codegen backends)
 - #119835 (Exhaustiveness: simplify empty pattern logic)
 - #119984 (Change return type of unstable `Waker::noop()` from `Waker` to `&Waker`.)
 - #120009 (never_patterns: typecheck never patterns)
 - #120122 (Don't add needs-triage to A-diagnostics)
 - #120126 (Suggest `.swap()` when encountering conflicting borrows from `mem::swap` on a slice)
 - #120134 (Restrict access to the private field of newtype indexes)

Failed merges:

 - #119968 (Remove unused/unnecessary features)

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

2 files changed, 11 insertions, 4 deletions

diff --git a/compiler/rustc_interface/src/lib.rs b/compiler/rustc_interface/src/lib.rs
index cfa46447845..764306ce6ec 100644
--- a/compiler/rustc_interface/src/lib.rs
+++ b/compiler/rustc_interface/src/lib.rs
@@ -1,9 +1,10 @@
 #![feature(box_patterns)]
 #![feature(decl_macro)]
+#![feature(error_iter)]
 #![feature(internal_output_capture)]
-#![feature(thread_spawn_unchecked)]
 #![feature(lazy_cell)]
 #![feature(let_chains)]
+#![feature(thread_spawn_unchecked)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]
 #![deny(rustc::untranslatable_diagnostic)]
diff --git a/compiler/rustc_interface/src/util.rs b/compiler/rustc_interface/src/util.rs
index 9fd44e46b31..76b9e8de75f 100644
--- a/compiler/rustc_interface/src/util.rs
+++ b/compiler/rustc_interface/src/util.rs
@@ -162,15 +162,21 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
 }
 
 fn load_backend_from_dylib(early_dcx: &EarlyDiagCtxt, path: &Path) -> MakeBackendFn {
+    fn format_err(e: &(dyn std::error::Error + 'static)) -> String {
+        e.sources().map(|e| format!(": {e}")).collect()
+    }
     let lib = unsafe { Library::new(path) }.unwrap_or_else(|err| {
-        let err = format!("couldn't load codegen backend {path:?}: {err}");
+        let err = format!("couldn't load codegen backend {path:?}{}", format_err(&err));
         early_dcx.early_fatal(err);
     });
 
     let backend_sym = unsafe { lib.get::<MakeBackendFn>(b"__rustc_codegen_backend") }
         .unwrap_or_else(|e| {
-            let err = format!("couldn't load codegen backend: {e}");
-            early_dcx.early_fatal(err);
+            let e = format!(
+                "`__rustc_codegen_backend` symbol lookup in the codegen backend failed{}",
+                format_err(&e)
+            );
+            early_dcx.early_fatal(e);
         });
 
     // Intentionally leak the dynamic library. We can't ever unload it