Auto merge of #88556 - m-ou-se:rollup-q636wyd, r=m-ou-se

Rollup of 9 pull requests

Successful merges:

 - #86376 (Emit specific warning to clarify that `#[no_mangle]` should not be applied on foreign statics or functions)
 - #88040 (BTree: remove Ord bound from new)
 - #88053 (Fix the flock fallback implementation)
 - #88350 (add support for clobbering xer, cr, and cr[0-7] for asm! on OpenPower/PowerPC)
 - #88410 (Remove bolding on associated constants)
 - #88525 (fix(rustc_typeck): produce better errors for dyn auto trait)
 - #88542 (Use the return value of readdir_r() instead of errno)
 - #88548 (Stabilize `Iterator::intersperse()`)
 - #88551 (Stabilize `UnsafeCell::raw_get()`)

Failed merges:

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

2 files changed, 31 insertions, 0 deletions

diff --git a/compiler/rustc_error_codes/src/error_codes.rs b/compiler/rustc_error_codes/src/error_codes.rs
index c2e62328cb1..45d91c2047d 100644
--- a/compiler/rustc_error_codes/src/error_codes.rs
+++ b/compiler/rustc_error_codes/src/error_codes.rs
@@ -480,6 +480,7 @@ E0781: include_str!("./error_codes/E0781.md"),
 E0782: include_str!("./error_codes/E0782.md"),
 E0783: include_str!("./error_codes/E0783.md"),
 E0784: include_str!("./error_codes/E0784.md"),
+E0785: include_str!("./error_codes/E0785.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard
diff --git a/compiler/rustc_error_codes/src/error_codes/E0785.md b/compiler/rustc_error_codes/src/error_codes/E0785.md
new file mode 100644
index 00000000000..373320539ef
--- /dev/null
+++ b/compiler/rustc_error_codes/src/error_codes/E0785.md
@@ -0,0 +1,30 @@
+An inherent `impl` was written on a dyn auto trait.
+
+Erroneous code example:
+
+```compile_fail,E0785
+#![feature(auto_traits)]
+
+auto trait AutoTrait {}
+
+impl dyn AutoTrait {}
+```
+
+Dyn objects allow any number of auto traits, plus at most one non-auto trait.
+The non-auto trait becomes the "principal trait".
+
+When checking if an impl on a dyn trait is coherent, the principal trait is
+normally the only one considered. Since the erroneous code has no principal
+trait, it cannot be implemented at all.
+
+Working example:
+
+```
+#![feature(auto_traits)]
+
+trait PrincipalTrait {}
+
+auto trait AutoTrait {}
+
+impl dyn PrincipalTrait + AutoTrait + Send {}
+```