Auto merge of #115367 - frank-king:feature/unnamed-fields-hir, r=davidtwco

Lowering unnamed fields and anonymous adt

This implements #49804.

Goals:
- [x] lowering anonymous ADTs from AST to HIR
- [x] generating definitions of anonymous ADTs
- [x] uniqueness check of the unnamed fields
- [x] field projection of anonymous ADTs
- [x] `#[repr(C)]` check of the anonymous ADTs

Non-Goals (will be in the next PRs)
- capturing generic params for the anonymous ADTs from the parent ADT
- pattern matching of anonymous ADTs
- structural expressions of anonymous ADTs
- rustdoc support of anonymous ADTs

1 files changed, 15 insertions, 5 deletions

diff --git a/compiler/rustc_mir_build/src/thir/cx/expr.rs b/compiler/rustc_mir_build/src/thir/cx/expr.rs
index 35adcc33480..79719f6f4cc 100644
--- a/compiler/rustc_mir_build/src/thir/cx/expr.rs
+++ b/compiler/rustc_mir_build/src/thir/cx/expr.rs
@@ -734,11 +734,21 @@ impl<'tcx> Cx<'tcx> {
                 });
                 ExprKind::Loop { body }
             }
-            hir::ExprKind::Field(source, ..) => ExprKind::Field {
-                lhs: self.mirror_expr(source),
-                variant_index: FIRST_VARIANT,
-                name: self.typeck_results.field_index(expr.hir_id),
-            },
+            hir::ExprKind::Field(source, ..) => {
+                let mut kind = ExprKind::Field {
+                    lhs: self.mirror_expr(source),
+                    variant_index: FIRST_VARIANT,
+                    name: self.typeck_results.field_index(expr.hir_id),
+                };
+                let nested_field_tys_and_indices =
+                    self.typeck_results.nested_field_tys_and_indices(expr.hir_id);
+                for &(ty, idx) in nested_field_tys_and_indices {
+                    let expr = Expr { temp_lifetime, ty, span: source.span, kind };
+                    let lhs = self.thir.exprs.push(expr);
+                    kind = ExprKind::Field { lhs, variant_index: FIRST_VARIANT, name: idx };
+                }
+                kind
+            }
             hir::ExprKind::Cast(source, cast_ty) => {
                 // Check for a user-given type annotation on this `cast`
                 let user_provided_types = self.typeck_results.user_provided_types();