Revert PR 81473 to resolve (on beta) issues 81626 and 81658.

Revert "Add missing brace"

This reverts commit 85ad773.

Revert "Simplify base_expr"

This reverts commit 899aae4.

Revert "Warn write-only fields"

This reverts commit d3c69a4.

Author: pnkfelix

compiler/rustc_passes/src/dead.rs

@@ -133,22 +133,6 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
         }
     }
 
-    fn handle_assign(&mut self, expr: &'tcx hir::Expr<'tcx>) {
-        if self
-            .typeck_results()
-            .expr_adjustments(expr)
-            .iter()
-            .any(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(_)))
-        {
-            self.visit_expr(expr);
-        } else if let hir::ExprKind::Field(base, ..) = expr.kind {
-            // Ignore write to field
-            self.handle_assign(base);
-        } else {
-            self.visit_expr(expr);
-        }
-    }
-
     fn handle_field_pattern_match(
         &mut self,
         lhs: &hir::Pat<'_>,
@@ -277,11 +261,6 @@ impl<'tcx> Visitor<'tcx> for MarkSymbolVisitor<'tcx> {
             hir::ExprKind::MethodCall(..) => {
                 self.lookup_and_handle_method(expr.hir_id);
             }
-            hir::ExprKind::Assign(ref left, ref right, ..) => {
-                self.handle_assign(left);
-                self.visit_expr(right);
-                return;
-            }
             hir::ExprKind::Field(ref lhs, ..) => {
                 self.handle_field_access(&lhs, expr.hir_id);
             }

src/test/ui/borrowck/borrowck-assign-to-subfield.rs

@@ -1,6 +1,5 @@
 // run-pass
 // pretty-expanded FIXME #23616
-#![allow(dead_code)]
 
 pub fn main() {
     struct A {