attributes: Allow stripping assignment expressions

Author: CohenArthur

gcc/rust/expand/rust-attribute-visitor.cc

@@ -628,8 +628,12 @@ AttrVisitor::visit (AST::TypeCastExpr &expr)
 void
 AttrVisitor::visit (AST::AssignmentExpr &expr)
 {
-  /* outer attributes never allowed before these. while cannot strip
-   * two direct descendant expressions, can strip ones below that */
+  expander.expand_cfg_attrs (expr.get_outer_attrs ());
+  if (expander.fails_cfg_with_expand (expr.get_outer_attrs ()))
+    {
+      expr.mark_for_strip ();
+      return;
+    }
 
   /* should have no possibility for outer attrs as would be parsed
    * with outer expr */

gcc/rust/expand/rust-attribute-visitor.h

@@ -71,8 +71,12 @@ class AttrVisitor : public AST::ASTVisitor
 	    it = values.erase (it);
 	    for (auto &node : fragment.get_nodes ())
 	      {
-		it = values.insert (it, extractor (node));
-		it++;
+		auto new_node = extractor (node);
+		if (new_node != nullptr && !new_node->is_marked_for_strip ())
+		  {
+		    it = values.insert (it, std::move (new_node));
+		    it++;
+		  }
 	      }
 	  }
 	else if (value->is_marked_for_strip ())