Rollup merge of rust-lang#77488 - varkor:repr128-incomplete_features, r=jonas-schievink

Mark `repr128` as `incomplete_features`

As mentioned in rust-lang#56071 and noticed in rust-lang#77457, `repr(u128)` and `repr(i128)` do not work properly due to lack of LLVM support. We should thus warn users trying to use the feature that they may encounter ICEs when using it.

Closes rust-lang#77457.

Author: JohnTitor

compiler/rustc_feature/src/active.rs

@@ -622,6 +622,7 @@ pub const INCOMPLETE_FEATURES: &[Symbol] = &[
     sym::const_trait_bound_opt_out,
     sym::lazy_normalization_consts,
     sym::specialization,
+    sym::repr128,
 ];
 
 /// Some features are not allowed to be used together at the same time, if

src/test/ui/enum-discriminant/discriminant_size.rs

@@ -1,5 +1,6 @@
 // run-pass
 #![feature(core_intrinsics, repr128)]
+//~^ WARN the feature `repr128` is incomplete
 
 use std::intrinsics::discriminant_value;
 

src/test/ui/enum-discriminant/discriminant_size.stderr

@@ -0,0 +1,11 @@
+warning: the feature `repr128` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/discriminant_size.rs:2:29
+   |
+LL | #![feature(core_intrinsics, repr128)]
+   |                             ^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #56071 <https://github.com/rust-lang/rust/issues/56071> for more information
+
+warning: 1 warning emitted
+

src/test/ui/enum-discriminant/issue-70509-partial_eq.rs

@@ -1,5 +1,6 @@
 // run-pass
 #![feature(repr128, arbitrary_enum_discriminant)]
+//~^ WARN the feature `repr128` is incomplete
 
 #[derive(PartialEq, Debug)]
 #[repr(i128)]

src/test/ui/enum-discriminant/issue-70509-partial_eq.stderr

@@ -0,0 +1,11 @@
+warning: the feature `repr128` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-70509-partial_eq.rs:2:12
+   |
+LL | #![feature(repr128, arbitrary_enum_discriminant)]
+   |            ^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #56071 <https://github.com/rust-lang/rust/issues/56071> for more information
+
+warning: 1 warning emitted
+

src/test/ui/enum-discriminant/repr128.rs

@@ -1,5 +1,6 @@
 // run-pass
 #![feature(repr128, core_intrinsics, discriminant_kind)]
+//~^ WARN the feature `repr128` is incomplete
 
 use std::intrinsics::discriminant_value;
 use std::marker::DiscriminantKind;

src/test/ui/enum-discriminant/repr128.stderr

@@ -0,0 +1,11 @@
+warning: the feature `repr128` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/repr128.rs:2:12
+   |
+LL | #![feature(repr128, core_intrinsics, discriminant_kind)]
+   |            ^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #56071 <https://github.com/rust-lang/rust/issues/56071> for more information
+
+warning: 1 warning emitted
+

src/test/ui/issues/issue-43398.rs

@@ -2,6 +2,7 @@
 
 #![feature(core_intrinsics)]
 #![feature(repr128)]
+//~^ WARN the feature `repr128` is incomplete
 
 #[repr(i128)]
 enum Big { A, B }

src/test/ui/issues/issue-43398.stderr

@@ -0,0 +1,11 @@
+warning: the feature `repr128` is incomplete and may not be safe to use and/or cause compiler crashes
+  --> $DIR/issue-43398.rs:4:12
+   |
+LL | #![feature(repr128)]
+   |            ^^^^^^^
+   |
+   = note: `#[warn(incomplete_features)]` on by default
+   = note: see issue #56071 <https://github.com/rust-lang/rust/issues/56071> for more information
+
+warning: 1 warning emitted
+