AK+LibRegex: Only set node metadata on Trie::ensure_child if missing

a290034 passed an empty vector to this,
which caused nodes that appeared multiple times to reset the trie
metadata...which broke the optimisation.

This patchset makes the function take a 'provide missing metadata'
function instead, and only invokes it when the node is missing rather
than unconditionally setting the metadata on all nodes.

Author: alimpfard

AK/Trie.h

@@ -95,23 +95,29 @@ class Trie {
     ValueType const& value() const { return m_value; }
     ValueType& value() { return m_value; }
 
-    ErrorOr<Trie*> ensure_child(ValueType value, Optional<MetadataType> metadata = {})
+    template<typename F = Function<Optional<MetadataType>()>>
+    ErrorOr<Trie*> ensure_child(ValueType value, F metadata_if_missing = [] { return OptionalNone {}; })
     {
         auto it = m_children.find(value);
         if (it == m_children.end()) {
             OwnPtr<Trie> node;
+            Optional<MetadataType> missing_metadata;
+
+            if constexpr (requires { { metadata_if_missing() } -> SpecializationOf<ErrorOr>; })
+                missing_metadata = TRY(metadata_if_missing());
+            else
+                missing_metadata = metadata_if_missing();
+
             if constexpr (requires { { value->try_clone() } -> SpecializationOf<ErrorOr>; })
-                node = TRY(adopt_nonnull_own_or_enomem(new (nothrow) Trie(TRY(value->try_clone()), move(metadata))));
+                node = TRY(adopt_nonnull_own_or_enomem(new (nothrow) Trie(TRY(value->try_clone()), move(missing_metadata))));
             else
-                node = TRY(adopt_nonnull_own_or_enomem(new (nothrow) Trie(value, move(metadata))));
+                node = TRY(adopt_nonnull_own_or_enomem(new (nothrow) Trie(value, move(missing_metadata))));
             auto& node_ref = *node;
             TRY(m_children.try_set(move(value), node.release_nonnull()));
             return &static_cast<BaseType&>(node_ref);
         }
 
         auto& node_ref = *it->value;
-        if (metadata.has_value())
-            node_ref.m_metadata = move(metadata);
         return &static_cast<BaseType&>(node_ref);
     }
 
@@ -129,9 +135,9 @@ class Trie {
         };
         for (; it != end; ++it) {
             if constexpr (requires { { ValueType::ElementType::try_create(*it) } -> SpecializationOf<ErrorOr>; })
-                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(TRY(ValueType::ElementType::try_create(*it)), TRY(invoke_provide_missing_metadata(static_cast<BaseType&>(*last_root_node), it)))));
+                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(TRY(ValueType::ElementType::try_create(*it)), [&] { return invoke_provide_missing_metadata(static_cast<BaseType&>(*last_root_node), it); })));
             else
-                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(*it, TRY(invoke_provide_missing_metadata(static_cast<BaseType&>(*last_root_node), it)))));
+                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(*it, [&] { return invoke_provide_missing_metadata(static_cast<BaseType&>(*last_root_node), it); })));
         }
         last_root_node->set_metadata(move(metadata));
         return static_cast<BaseType*>(last_root_node);
@@ -144,9 +150,9 @@ class Trie {
         Trie* last_root_node = &traverse_until_last_accessible_node(it, end);
         for (; it != end; ++it) {
             if constexpr (requires { { ValueType::ElementType::try_create(*it) } -> SpecializationOf<ErrorOr>; })
-                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(TRY(ValueType::ElementType::try_create(*it)), {})));
+                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(TRY(ValueType::ElementType::try_create(*it)))));
             else
-                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(*it, {})));
+                last_root_node = static_cast<Trie*>(TRY(last_root_node->ensure_child(*it)));
         }
         return static_cast<BaseType*>(last_root_node);
     }

Libraries/LibRegex/RegexOptimizer.cpp

@@ -1467,7 +1467,7 @@ void Optimizer::append_alternation(ByteCode& target, Span<ByteCode> alternatives
                     node_key_bytes.append(edge.jump_insn);
             }
 
-            active_node = static_cast<decltype(active_node)>(MUST(active_node->ensure_child(DisjointSpans<ByteCodeValueType const> { move(node_key_bytes) }, Vector<NodeMetadataEntry> {})));
+            active_node = static_cast<decltype(active_node)>(MUST(active_node->ensure_child(DisjointSpans<ByteCodeValueType const> { move(node_key_bytes) }, [] -> Vector<NodeMetadataEntry> { return {}; })));
 
             auto next_compare = [&alternative, &state](StaticallyInterpretedCompares& compares) {
                 TemporaryChange state_change { state.instruction_position, state.instruction_position };