Auto merge of #89884 - Mark-Simulacrum:revert-enum-discr, r=wesleywiser

Revert enum discriminants

Reverts stabilization of arbitrary enum discriminants per https://github.com/rust-lang/rust/issues/88621#issuecomment-929482371.

Reopens #60553.

16 files changed, 151 insertions, 8 deletions

diff --git a/src/doc/unstable-book/src/language-features/arbitrary-enum-discriminant.md b/src/doc/unstable-book/src/language-features/arbitrary-enum-discriminant.md
new file mode 100644
index 00000000000..e0bb782270e
--- /dev/null
+++ b/src/doc/unstable-book/src/language-features/arbitrary-enum-discriminant.md
@@ -0,0 +1,37 @@
+# `arbitrary_enum_discriminant`
+
+The tracking issue for this feature is: [#60553]
+
+[#60553]: https://github.com/rust-lang/rust/issues/60553
+
+------------------------
+
+The `arbitrary_enum_discriminant` feature permits tuple-like and
+struct-like enum variants with `#[repr(<int-type>)]` to have explicit discriminants.
+
+## Examples
+
+```rust
+#![feature(arbitrary_enum_discriminant)]
+
+#[allow(dead_code)]
+#[repr(u8)]
+enum Enum {
+    Unit = 3,
+    Tuple(u16) = 2,
+    Struct {
+        a: u8,
+        b: u16,
+    } = 1,
+}
+
+impl Enum {
+    fn tag(&self) -> u8 {
+        unsafe { *(self as *const Self as *const u8) }
+    }
+}
+
+assert_eq!(3, Enum::Unit.tag());
+assert_eq!(2, Enum::Tuple(5).tag());
+assert_eq!(1, Enum::Struct{a: 7, b: 11}.tag());
+```
diff --git a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.rs b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.rs
index a6e5f70fdef..4da7b5ab24b 100644
--- a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.rs
+++ b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.rs
@@ -1,4 +1,5 @@
 #![crate_type="lib"]
+#![feature(arbitrary_enum_discriminant)]
 
 enum Enum {
 //~^ ERROR `#[repr(inttype)]` must be specified
diff --git a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.stderr b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.stderr
index 7af063c591d..2db5372da0c 100644
--- a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.stderr
+++ b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant-no-repr.stderr
@@ -1,5 +1,5 @@
 error[E0732]: `#[repr(inttype)]` must be specified
-  --> $DIR/arbitrary_enum_discriminant-no-repr.rs:3:1
+  --> $DIR/arbitrary_enum_discriminant-no-repr.rs:4:1
    |
 LL | / enum Enum {
 LL | |
diff --git a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
index 360bddb7bd1..f2270602d87 100644
--- a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
+++ b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
@@ -1,5 +1,5 @@
 // run-pass
-#![feature(const_raw_ptr_deref, test)]
+#![feature(arbitrary_enum_discriminant, const_raw_ptr_deref, test)]
 
 extern crate test;
 
diff --git a/src/test/ui/enum-discriminant/discriminant_value.rs b/src/test/ui/enum-discriminant/discriminant_value.rs
index 7ed1d9660a6..eb60aaf4b2d 100644
--- a/src/test/ui/enum-discriminant/discriminant_value.rs
+++ b/src/test/ui/enum-discriminant/discriminant_value.rs
@@ -1,6 +1,6 @@
 // run-pass
 #![allow(stable_features)]
-#![feature(core, core_intrinsics)]
+#![feature(arbitrary_enum_discriminant, core, core_intrinsics)]
 
 extern crate core;
 use core::intrinsics::discriminant_value;
diff --git a/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.rs b/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.rs
new file mode 100644
index 00000000000..3e90af4d36a
--- /dev/null
+++ b/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.rs
@@ -0,0 +1,10 @@
+#![crate_type="lib"]
+
+enum Enum {
+  Unit = 1,
+  //~^ ERROR custom discriminant values are not allowed in enums with tuple or struct variants
+  Tuple() = 2,
+  //~^ ERROR discriminants on non-unit variants are experimental
+  Struct{} = 3,
+  //~^ ERROR discriminants on non-unit variants are experimental
+}
diff --git a/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.stderr b/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.stderr
new file mode 100644
index 00000000000..b5f61e6e991
--- /dev/null
+++ b/src/test/ui/enum-discriminant/feature-gate-arbitrary_enum_discriminant.stderr
@@ -0,0 +1,36 @@
+error[E0658]: discriminants on non-unit variants are experimental
+  --> $DIR/feature-gate-arbitrary_enum_discriminant.rs:6:13
+   |
+LL |   Tuple() = 2,
+   |             ^
+   |
+   = note: see issue #60553 <https://github.com/rust-lang/rust/issues/60553> for more information
+   = help: add `#![feature(arbitrary_enum_discriminant)]` to the crate attributes to enable
+
+error[E0658]: discriminants on non-unit variants are experimental
+  --> $DIR/feature-gate-arbitrary_enum_discriminant.rs:8:14
+   |
+LL |   Struct{} = 3,
+   |              ^
+   |
+   = note: see issue #60553 <https://github.com/rust-lang/rust/issues/60553> for more information
+   = help: add `#![feature(arbitrary_enum_discriminant)]` to the crate attributes to enable
+
+error[E0658]: custom discriminant values are not allowed in enums with tuple or struct variants
+  --> $DIR/feature-gate-arbitrary_enum_discriminant.rs:4:10
+   |
+LL |   Unit = 1,
+   |          ^ disallowed custom discriminant
+LL |
+LL |   Tuple() = 2,
+   |   ----------- tuple variant defined here
+LL |
+LL |   Struct{} = 3,
+   |   ------------ struct variant defined here
+   |
+   = note: see issue #60553 <https://github.com/rust-lang/rust/issues/60553> for more information
+   = help: add `#![feature(arbitrary_enum_discriminant)]` to the crate attributes to enable
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/enum-discriminant/issue-70453-generics-in-discr-ice-2.rs b/src/test/ui/enum-discriminant/issue-70453-generics-in-discr-ice-2.rs
index ad9fcc25b41..f927dd18903 100644
--- a/src/test/ui/enum-discriminant/issue-70453-generics-in-discr-ice-2.rs
+++ b/src/test/ui/enum-discriminant/issue-70453-generics-in-discr-ice-2.rs
@@ -1,4 +1,4 @@
-#![feature(core_intrinsics)]
+#![feature(arbitrary_enum_discriminant, core_intrinsics)]
 
 extern crate core;
 use core::intrinsics::discriminant_value;
diff --git a/src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.rs b/src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.rs
index 42a062239d3..e62582fb516 100644
--- a/src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.rs
+++ b/src/test/ui/enum-discriminant/issue-70453-polymorphic-ctfe.rs
@@ -1,4 +1,4 @@
-#![feature(core_intrinsics)]
+#![feature(arbitrary_enum_discriminant, core_intrinsics)]
 
 extern crate core;
 use core::intrinsics::discriminant_value;
diff --git a/src/test/ui/enum-discriminant/issue-70509-partial_eq.rs b/src/test/ui/enum-discriminant/issue-70509-partial_eq.rs
index 3adac7b7262..ae389e11466 100644
--- a/src/test/ui/enum-discriminant/issue-70509-partial_eq.rs
+++ b/src/test/ui/enum-discriminant/issue-70509-partial_eq.rs
@@ -1,5 +1,5 @@
 // run-pass
-#![feature(repr128)]
+#![feature(repr128, arbitrary_enum_discriminant)]
 //~^ WARN the feature `repr128` is incomplete
 
 #[derive(PartialEq, Debug)]
diff --git a/src/test/ui/enum-discriminant/issue-70509-partial_eq.stderr b/src/test/ui/enum-discriminant/issue-70509-partial_eq.stderr
index 04fb13f37a0..5bf6ea56ebc 100644
--- a/src/test/ui/enum-discriminant/issue-70509-partial_eq.stderr
+++ b/src/test/ui/enum-discriminant/issue-70509-partial_eq.stderr
@@ -1,7 +1,7 @@
 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)]
+LL | #![feature(repr128, arbitrary_enum_discriminant)]
    |            ^^^^^^^
    |
    = note: `#[warn(incomplete_features)]` on by default
diff --git a/src/test/ui/intrinsics/panic-uninitialized-zeroed.rs b/src/test/ui/intrinsics/panic-uninitialized-zeroed.rs
index 50f1a2f25b9..324bba15e43 100644
--- a/src/test/ui/intrinsics/panic-uninitialized-zeroed.rs
+++ b/src/test/ui/intrinsics/panic-uninitialized-zeroed.rs
@@ -6,7 +6,7 @@
 
 // This test checks panic emitted from `mem::{uninitialized,zeroed}`.
 
-#![feature(never_type)]
+#![feature(never_type, arbitrary_enum_discriminant)]
 #![allow(deprecated, invalid_value)]
 
 use std::{
diff --git a/src/test/ui/parser/issue-17383.rs b/src/test/ui/parser/issue-17383.rs
new file mode 100644
index 00000000000..7bf0e64f2c0
--- /dev/null
+++ b/src/test/ui/parser/issue-17383.rs
@@ -0,0 +1,7 @@
+enum X {
+    A = 3,
+    //~^ ERROR custom discriminant values are not allowed in enums with tuple or struct variants
+    B(usize)
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/issue-17383.stderr b/src/test/ui/parser/issue-17383.stderr
new file mode 100644
index 00000000000..265d6e14866
--- /dev/null
+++ b/src/test/ui/parser/issue-17383.stderr
@@ -0,0 +1,15 @@
+error[E0658]: custom discriminant values are not allowed in enums with tuple or struct variants
+  --> $DIR/issue-17383.rs:2:9
+   |
+LL |     A = 3,
+   |         ^ disallowed custom discriminant
+LL |
+LL |     B(usize)
+   |     -------- tuple variant defined here
+   |
+   = note: see issue #60553 <https://github.com/rust-lang/rust/issues/60553> for more information
+   = help: add `#![feature(arbitrary_enum_discriminant)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.
diff --git a/src/test/ui/parser/tag-variant-disr-non-nullary.rs b/src/test/ui/parser/tag-variant-disr-non-nullary.rs
new file mode 100644
index 00000000000..a9cfdd549c7
--- /dev/null
+++ b/src/test/ui/parser/tag-variant-disr-non-nullary.rs
@@ -0,0 +1,12 @@
+enum Color {
+    Red = 0xff0000,
+    //~^ ERROR custom discriminant values are not allowed in enums with tuple or struct variants
+    Green = 0x00ff00,
+    Blue = 0x0000ff,
+    Black = 0x000000,
+    White = 0xffffff,
+    Other(usize),
+    Other2(usize, usize),
+}
+
+fn main() {}
diff --git a/src/test/ui/parser/tag-variant-disr-non-nullary.stderr b/src/test/ui/parser/tag-variant-disr-non-nullary.stderr
new file mode 100644
index 00000000000..79f044a0675
--- /dev/null
+++ b/src/test/ui/parser/tag-variant-disr-non-nullary.stderr
@@ -0,0 +1,25 @@
+error[E0658]: custom discriminant values are not allowed in enums with tuple or struct variants
+  --> $DIR/tag-variant-disr-non-nullary.rs:2:11
+   |
+LL |     Red = 0xff0000,
+   |           ^^^^^^^^ disallowed custom discriminant
+LL |
+LL |     Green = 0x00ff00,
+   |             ^^^^^^^^ disallowed custom discriminant
+LL |     Blue = 0x0000ff,
+   |            ^^^^^^^^ disallowed custom discriminant
+LL |     Black = 0x000000,
+   |             ^^^^^^^^ disallowed custom discriminant
+LL |     White = 0xffffff,
+   |             ^^^^^^^^ disallowed custom discriminant
+LL |     Other(usize),
+   |     ------------ tuple variant defined here
+LL |     Other2(usize, usize),
+   |     -------------------- tuple variant defined here
+   |
+   = note: see issue #60553 <https://github.com/rust-lang/rust/issues/60553> for more information
+   = help: add `#![feature(arbitrary_enum_discriminant)]` to the crate attributes to enable
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0658`.