Change lookup_ast_item's return type

Wrap the function's return type within an optional.

gcc/rust/ChangeLog:

	* metadata/rust-export-metadata.cc (ExportContext::emit_trait):
	Adapt call site to the new return type.
	(ExportContext::emit_function): Likewise.
	(ExportContext::emit_macro): Likewise.
	* util/rust-hir-map.cc (Mappings::lookup_ast_item): Change the
	function's return type.
	* util/rust-hir-map.h: Update the function's prototype.

Signed-off-by: Pierre-Emmanuel Patry <pierre-emmanuel.patry@embecosm.com>

gcc/rust/metadata/rust-export-metadata.cc

@@ -56,10 +56,8 @@ void
 ExportContext::emit_trait (const HIR::Trait &trait)
 {
   // lookup the AST node for this
-  AST::Item *item = nullptr;
-  bool ok
-    = mappings.lookup_ast_item (trait.get_mappings ().get_nodeid (), &item);
-  rust_assert (ok);
+  AST::Item *item
+    = mappings.lookup_ast_item (trait.get_mappings ().get_nodeid ()).value ();
 
   std::stringstream oss;
   AST::Dump dumper (oss);
@@ -72,9 +70,8 @@ void
 ExportContext::emit_function (const HIR::Function &fn)
 {
   // lookup the AST node for this
-  AST::Item *item = nullptr;
-  bool ok = mappings.lookup_ast_item (fn.get_mappings ().get_nodeid (), &item);
-  rust_assert (ok);
+  AST::Item *item
+    = mappings.lookup_ast_item (fn.get_mappings ().get_nodeid ()).value ();
 
   // is this a CFG macro or not
   if (item->is_marked_for_strip ())
@@ -119,9 +116,7 @@ ExportContext::emit_macro (NodeId macro)
   std::stringstream oss;
   AST::Dump dumper (oss);
 
-  AST::Item *item;
-  auto ok = mappings.lookup_ast_item (macro, &item);
-  rust_assert (ok);
+  AST::Item *item = mappings.lookup_ast_item (macro).value ();
 
   dumper.go (*item);
 

gcc/rust/util/rust-hir-map.cc

@@ -1225,15 +1225,14 @@ Mappings::insert_ast_item (AST::Item *item)
   ast_item_mappings[item->get_node_id ()] = item;
 }
 
-bool
-Mappings::lookup_ast_item (NodeId id, AST::Item **result)
+tl::optional<AST::Item *>
+Mappings::lookup_ast_item (NodeId id)
 {
   auto it = ast_item_mappings.find (id);
   if (it == ast_item_mappings.end ())
-    return false;
+    return tl::nullopt;
 
-  *result = it->second;
-  return true;
+  return it->second;
 }
 
 HIR::ImplBlock *

gcc/rust/util/rust-hir-map.h

@@ -345,7 +345,7 @@ class Mappings
   bool node_is_module (NodeId query);
 
   void insert_ast_item (AST::Item *item);
-  bool lookup_ast_item (NodeId id, AST::Item **result);
+  tl::optional<AST::Item *> lookup_ast_item (NodeId id);
 
   HIR::ImplBlock *lookup_builtin_marker ();