Stabilize #[repr(transparent)] on enums in Rust 1.42.0

src/librustc_feature/accepted.rs

@@ -257,6 +257,8 @@ declare_features! (
     /// Allows relaxing the coherence rules such that
     /// `impl<T> ForeignTrait<LocalType> for ForeignType<T>` is permitted.
     (accepted, re_rebalance_coherence, "1.41.0", Some(55437), None),
+    /// Allows #[repr(transparent)] on univariant enums (RFC 2645).
+    (accepted, transparent_enums, "1.42.0", Some(60405), None),
     /// Allows using subslice patterns, `[a, .., b]` and `[a, xs @ .., b]`.
     (accepted, slice_patterns, "1.42.0", Some(62254), None),
 

src/librustc_feature/active.rs

@@ -468,9 +468,6 @@ declare_features! (
     /// Allows `if/while p && let q = r && ...` chains.
     (active, let_chains, "1.37.0", Some(53667), None),
 
-    /// Allows #[repr(transparent)] on enums (RFC 2645).
-    (active, transparent_enums, "1.37.0", Some(60405), None),
-
     /// Allows #[repr(transparent)] on unions (RFC 2645).
     (active, transparent_unions, "1.37.0", Some(60405), None),
 

src/librustc_typeck/check/mod.rs

@@ -2433,16 +2433,6 @@ fn check_transparent(tcx: TyCtxt<'_>, sp: Span, def_id: DefId) {
     }
     let sp = tcx.sess.source_map().def_span(sp);
 
-    if adt.is_enum() && !tcx.features().transparent_enums {
-        feature_err(
-            &tcx.sess.parse_sess,
-            sym::transparent_enums,
-            sp,
-            "transparent enums are unstable",
-        )
-        .emit();
-    }
-
     if adt.is_union() && !tcx.features().transparent_unions {
         feature_err(
             &tcx.sess.parse_sess,

src/test/codegen/repr-transparent-aggregates-1.rs

@@ -10,7 +10,7 @@
 // ignore-windows
 // See repr-transparent.rs
 
-#![feature(transparent_enums, transparent_unions)]
+#![feature(transparent_unions)]
 
 #![crate_type="lib"]
 

src/test/codegen/repr-transparent-aggregates-2.rs

@@ -13,7 +13,7 @@
 // ignore-x86_64
 // See repr-transparent.rs
 
-#![feature(transparent_enums, transparent_unions)]
+#![feature(transparent_unions)]
 
 #![crate_type="lib"]
 

src/test/codegen/repr-transparent-aggregates-3.rs

@@ -3,7 +3,7 @@
 // only-mips64
 // See repr-transparent.rs
 
-#![feature(transparent_enums, transparent_unions)]
+#![feature(transparent_unions)]
 
 #![crate_type="lib"]
 

src/test/codegen/repr-transparent.rs

@@ -1,7 +1,7 @@
 // compile-flags: -C no-prepopulate-passes
 
 #![crate_type="lib"]
-#![feature(repr_simd, transparent_enums, transparent_unions)]
+#![feature(repr_simd, transparent_unions)]
 
 use std::marker::PhantomData;
 

src/test/ui/lint/lint-ctypes-enum.rs

@@ -1,4 +1,4 @@
-#![feature(transparent_enums, transparent_unions)]
+#![feature(transparent_unions)]
 #![feature(ptr_internals)]
 #![deny(improper_ctypes)]
 #![allow(dead_code)]

src/test/ui/repr/repr-transparent.rs

@@ -3,7 +3,7 @@
 // - repr-transparent-other-reprs.rs
 // - repr-transparent-other-items.rs
 
-#![feature(repr_align, transparent_enums, transparent_unions)]
+#![feature(transparent_unions)]
 
 use std::marker::PhantomData;
 
@@ -60,6 +60,16 @@ enum TooManyVariants { //~ ERROR transparent enum needs exactly one variant, but
     Bar,
 }
 
+#[repr(transparent)]
+enum NontrivialAlignZstEnum {
+    Foo(u32, [u16; 0]), //~ ERROR alignment larger than 1
+}
+
+#[repr(transparent)]
+enum GenericAlignEnum<T> {
+    Foo { bar: ZstAlign32<T>, baz: u32 } //~ ERROR alignment larger than 1
+}
+
 #[repr(transparent)]
 union UnitUnion { //~ ERROR transparent union needs exactly one non-zero-sized field, but has 0
     u: (),

src/test/ui/repr/repr-transparent.stderr

@@ -94,14 +94,26 @@ LL |     Foo(String),
 LL |     Bar,
    |     --- too many variants in `TooManyVariants`
 
+error[E0691]: zero-sized field in transparent enum has alignment larger than 1
+  --> $DIR/repr-transparent.rs:65:14
+   |
+LL |     Foo(u32, [u16; 0]),
+   |              ^^^^^^^^ has alignment larger than 1
+
+error[E0691]: zero-sized field in transparent enum has alignment larger than 1
+  --> $DIR/repr-transparent.rs:70:11
+   |
+LL |     Foo { bar: ZstAlign32<T>, baz: u32 }
+   |           ^^^^^^^^^^^^^^^^^^ has alignment larger than 1
+
 error[E0690]: transparent union needs exactly one non-zero-sized field, but has 0
-  --> $DIR/repr-transparent.rs:64:1
+  --> $DIR/repr-transparent.rs:74:1
    |
 LL | union UnitUnion {
    | ^^^^^^^^^^^^^^^ needs exactly one non-zero-sized field, but has 0
 
 error[E0690]: transparent union needs exactly one non-zero-sized field, but has 2
-  --> $DIR/repr-transparent.rs:69:1
+  --> $DIR/repr-transparent.rs:79:1
    |
 LL | union TooManyFields {
    | ^^^^^^^^^^^^^^^^^^^ needs exactly one non-zero-sized field, but has 2
@@ -110,7 +122,7 @@ LL |     u: u32,
 LL |     s: i32
    |     ------ this field is non-zero-sized
 
-error: aborting due to 15 previous errors
+error: aborting due to 17 previous errors
 
 Some errors have detailed explanations: E0084, E0690, E0691, E0731.
 For more information about an error, try `rustc --explain E0084`.