From f7ef1c9f4163df30ae67ab177d5c306cb90b3d47 Mon Sep 17 00:00:00 2001
From: Gary Guo <gary@garyguo.net>
Date: Fri, 24 Sep 2021 21:58:25 +0100
Subject: [PATCH] Disallow non-c-like but "fieldless" ADTs from being casted to
integer...
... if they use arbitrary enum discriminant. Code like
```rust
enum Enum {
Foo = 1,
Bar(),
Baz{}
}
```
seems to be unintentionally allowed so we couldn't disallow them now,
but we could disallow them if arbitrary enum discriminant is used before
1.56 hits stable.
---
compiler/rustc_middle/src/ty/adt.rs | 18 +++++++++++++++++-
src/test/ui/cast/issue-88621.rs | 13 +++++++++++++
src/test/ui/cast/issue-88621.stderr | 9 +++++++++
.../arbitrary_enum_discriminant.rs | 13 -------------
4 files changed, 39 insertions(+), 14 deletions(-)
create mode 100644 src/test/ui/cast/issue-88621.rs
create mode 100644 src/test/ui/cast/issue-88621.stderr
diff --git a/compiler/rustc_middle/src/ty/adt.rs b/compiler/rustc_middle/src/ty/adt.rs
index 44f741c5df1a2..69eb73b42552c 100644
--- a/compiler/rustc_middle/src/ty/adt.rs
+++ b/compiler/rustc_middle/src/ty/adt.rs
@@ -7,7 +7,7 @@ use rustc_data_structures::fx::FxHashMap;
use rustc_data_structures::stable_hasher::{HashStable, StableHasher};
use rustc_errors::ErrorReported;
use rustc_hir as hir;
-use rustc_hir::def::{DefKind, Res};
+use rustc_hir::def::{CtorKind, DefKind, Res};
use rustc_hir::def_id::DefId;
use rustc_index::vec::{Idx, IndexVec};
use rustc_query_system::ich::StableHashingContext;
@@ -314,6 +314,22 @@ impl<'tcx> AdtDef {
/// Whether the ADT lacks fields. Note that this includes uninhabited enums,
/// e.g., `enum Void {}` is considered payload free as well.
pub fn is_payloadfree(&self) -> bool {
+ // Treat the ADT as not payload-free if arbitrary_enum_discriminant is used (#88621).
+ // This would disallow the following kind of enum from being casted into integer.
+ // ```
+ // enum Enum {
+ // Foo() = 1,
+ // Bar{} = 2,
+ // Baz = 3,
+ // }
+ // ```
+ if self
+ .variants
+ .iter()
+ .any(|v| matches!(v.discr, VariantDiscr::Explicit(_)) && v.ctor_kind != CtorKind::Const)
+ {
+ return false;
+ }
self.variants.iter().all(|v| v.fields.is_empty())
}
diff --git a/src/test/ui/cast/issue-88621.rs b/src/test/ui/cast/issue-88621.rs
new file mode 100644
index 0000000000000..9242b80e22939
--- /dev/null
+++ b/src/test/ui/cast/issue-88621.rs
@@ -0,0 +1,13 @@
+#![feature(arbitrary_enum_discriminant)]
+
+#[repr(u8)]
+enum Kind2 {
+ Foo() = 1,
+ Bar{} = 2,
+ Baz = 3,
+}
+
+fn main() {
+ let _ = Kind2::Foo() as u8;
+ //~^ ERROR non-primitive cast
+}
diff --git a/src/test/ui/cast/issue-88621.stderr b/src/test/ui/cast/issue-88621.stderr
new file mode 100644
index 0000000000000..e96d866515238
--- /dev/null
+++ b/src/test/ui/cast/issue-88621.stderr
@@ -0,0 +1,9 @@
+error[E0605]: non-primitive cast: `Kind2` as `u8`
+ --> $DIR/issue-88621.rs:11:13
+ |
+LL | let _ = Kind2::Foo() as u8;
+ | ^^^^^^^^^^^^^^^^^^ an `as` expression can only be used to convert between primitive types or to coerce to a specific trait object
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0605`.
diff --git a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
index 22c5332c9259f..ccc423e4a194c 100644
--- a/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
+++ b/src/test/ui/enum-discriminant/arbitrary_enum_discriminant.rs
@@ -22,14 +22,6 @@ impl Enum {
}
}
-#[allow(dead_code)]
-#[repr(u8)]
-enum FieldlessEnum {
- Unit = 3,
- Tuple() = 2,
- Struct {} = 1,
-}
-
fn main() {
const UNIT: Enum = Enum::Unit;
const TUPLE: Enum = Enum::Tuple(5);
@@ -48,9 +40,4 @@ fn main() {
assert_eq!(3, UNIT_TAG);
assert_eq!(2, TUPLE_TAG);
assert_eq!(1, STRUCT_TAG);
-
- // Ensure `as` conversions are correct
- assert_eq!(3, FieldlessEnum::Unit as u8);
- assert_eq!(2, FieldlessEnum::Tuple() as u8);
- assert_eq!(1, FieldlessEnum::Struct{} as u8);
}