error: unused attribute const_fn_union with incr-comp

Every time I try to recompile the compiler using incremental compilation with ./x.py build -i --stage 1 --keep-stage 1 src/libstd I get the following error ...

error: unused attribute                                                                                                
  --> src/libcore/slice/mod.rs:66:5                                                                                    
   |                                                                                                                   
66 |     #[allow_internal_unstable(const_fn_union)]                                                                    
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |                                                 
   = note: `-D unused-attributes` implied by `-D warnings`
                                                                                                                       
error: unused attribute                                                                                                
    --> src/libcore/str/mod.rs:2170:5                      
     |                                                                                                                 
2170 |     #[allow_internal_unstable(const_fn_union)]                                                                  
     |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^                                                                  
                                                                                                                       
error: aborting due to 2 previous errors                                                                               
                                                                                                                                                                                                                                              
error: could not compile `core`.

@oli-obk

@oli-obk, J'Accuse…! :)

The following change could be used as a workaround ...

diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index b5462d98837..e55baded913 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -64,6 +64,7 @@ impl<T> [T] {
     #[inline]
     // SAFETY: const sound because we transmute out the length field as a usize (which it must be)
     #[allow_internal_unstable(const_fn_union)]
+    #[allow(unused_attributes)]
     pub const fn len(&self) -> usize {
         unsafe {
             crate::ptr::Repr { rust: self }.raw.len
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index ece61dde490..d02d232a20e 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -2168,6 +2168,7 @@ impl str {
     #[inline(always)]
     // SAFETY: const sound because we transmute two types with the same layout
     #[allow_internal_unstable(const_fn_union)]
+    #[allow(unused_attributes)]
     pub const fn as_bytes(&self) -> &[u8] {
         #[repr(C)]
         union Slices<'a> {

Rollup merge of rust-lang#65106 - Mark-Simulacrum:unused-attr-allow, …

Rollup merge of rust-lang#67884 - anp:allow-unused-const-attr, r=oli-obk

cc #58633

Whitelist #[allow_internal_unstable]

Rollup merge of rust-lang#72713 - rust-lang:jonas-schievink-patch-2, …

closing as "worked-around", (we think this really only affects people working on rustc development itself).

((there are some notes about fixme's mentioned in linked prs but I'm not going to try to address those right now.))

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error: unused attribute const_fn_union with incr-comp #65023

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error: unused attribute const_fn_union with incr-comp #65023

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Centril commented on Oct 3, 2019

spastorino commented on Oct 3, 2019

pnkfelix commented on Mar 25, 2020

pnkfelix commented on Oct 6, 2020

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