Auto merge of #114208 - GKFX:offset_of_enum, r=wesleywiser

Support enum variants in offset_of!

This MR implements support for navigating through enum variants in `offset_of!`, placing the enum variant name in the second argument to `offset_of!`. The RFC placed it in the first argument, but I think it interacts better with nested field access in the second, as you can then write things like

```rust
offset_of!(Type, field.Variant.field)
```

Alternatively, a syntactic distinction could be made between variants and fields (e.g. `field::Variant.field`) but I'm not convinced this would be helpful.

[RFC 3308 # Enum Support](https://rust-lang.github.io/rfcs/3308-offset_of.html#enum-support-offset_ofsomeenumstructvariant-field_on_variant)
Tracking Issue #106655.

2 files changed, 6 insertions, 6 deletions

diff --git a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
index fd067cb234b..81d2bba989a 100644
--- a/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
+++ b/compiler/rustc_mir_transform/src/dataflow_const_prop.rs
@@ -286,9 +286,9 @@ impl<'tcx> ValueAnalysis<'tcx> for ConstAnalysis<'_, 'tcx> {
                 let val = match null_op {
                     NullOp::SizeOf if layout.is_sized() => layout.size.bytes(),
                     NullOp::AlignOf if layout.is_sized() => layout.align.abi.bytes(),
-                    NullOp::OffsetOf(fields) => layout
-                        .offset_of_subfield(&self.ecx, fields.iter().map(|f| f.index()))
-                        .bytes(),
+                    NullOp::OffsetOf(fields) => {
+                        layout.offset_of_subfield(&self.ecx, fields.iter()).bytes()
+                    }
                     _ => return ValueOrPlace::Value(FlatSet::Top),
                 };
                 FlatSet::Elem(Scalar::from_target_usize(val, &self.tcx))
diff --git a/compiler/rustc_mir_transform/src/gvn.rs b/compiler/rustc_mir_transform/src/gvn.rs
index de0dc25808b..dce298e92e1 100644
--- a/compiler/rustc_mir_transform/src/gvn.rs
+++ b/compiler/rustc_mir_transform/src/gvn.rs
@@ -467,9 +467,9 @@ impl<'body, 'tcx> VnState<'body, 'tcx> {
                 let val = match null_op {
                     NullOp::SizeOf => layout.size.bytes(),
                     NullOp::AlignOf => layout.align.abi.bytes(),
-                    NullOp::OffsetOf(fields) => layout
-                        .offset_of_subfield(&self.ecx, fields.iter().map(|f| f.index()))
-                        .bytes(),
+                    NullOp::OffsetOf(fields) => {
+                        layout.offset_of_subfield(&self.ecx, fields.iter()).bytes()
+                    }
                 };
                 let usize_layout = self.ecx.layout_of(self.tcx.types.usize).unwrap();
                 let imm = ImmTy::try_from_uint(val, usize_layout)?;