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.

1 files changed, 1 insertions, 1 deletions

diff --git a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
index f591afaaaf4..b0f757898e3 100644
--- a/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
+++ b/compiler/rustc_codegen_ssa/src/mir/rvalue.rs
@@ -680,7 +680,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         layout.align.abi.bytes()
                     }
                     mir::NullOp::OffsetOf(fields) => {
-                        layout.offset_of_subfield(bx.cx(), fields.iter().map(|f| f.index())).bytes()
+                        layout.offset_of_subfield(bx.cx(), fields.iter()).bytes()
                     }
                 };
                 let val = bx.cx().const_usize(val);