Implement Scene Unique Nodes

Implements https://github.com/godotengine/godot-proposals/issues/4096

* Nodes can be marked unique to the scene in the editor (or via code).
* Unique nodes can be accessed via the **%** prefix at any point in the path. From that point in the path (depending on whether the scene of the path is), the unique node will be fetched.
* Implementation is very optimal, as these nodes are cached.

3 files changed, 16 insertions, 1 deletions

diff --git a/core/string/string_name.cpp b/core/string/string_name.cpp
index 2e941b8037..9c4fc4e1b7 100644
--- a/core/string/string_name.cpp
+++ b/core/string/string_name.cpp
@@ -247,6 +247,7 @@ StringName::StringName(const char *p_name, bool p_static) {
 	_data->cname = nullptr;
 	_data->next = _table[idx];
 	_data->prev = nullptr;
+
 #ifdef DEBUG_ENABLED
 	if (unlikely(debug_stringname)) {
 		// Keep in memory, force static.
diff --git a/core/string/string_name.h b/core/string/string_name.h
index f4233854ac..ff4c41af94 100644
--- a/core/string/string_name.h
+++ b/core/string/string_name.h
@@ -35,6 +35,8 @@
 #include "core/string/ustring.h"
 #include "core/templates/safe_refcount.h"
 
+#define UNIQUE_NODE_PREFIX "%"
+
 class Main;
 
 struct StaticCString {
@@ -100,6 +102,17 @@ public:
 	bool operator==(const String &p_name) const;
 	bool operator==(const char *p_name) const;
 	bool operator!=(const String &p_name) const;
+
+	_FORCE_INLINE_ bool is_node_unique_name() const {
+		if (!_data) {
+			return false;
+		}
+		if (_data->cname != nullptr) {
+			return (char32_t)_data->cname[0] == (char32_t)UNIQUE_NODE_PREFIX[0];
+		} else {
+			return (char32_t)_data->name[0] == (char32_t)UNIQUE_NODE_PREFIX[0];
+		}
+	}
 	_FORCE_INLINE_ bool operator<(const StringName &p_name) const {
 		return _data < p_name._data;
 	}
diff --git a/core/string/ustring.cpp b/core/string/ustring.cpp
index 7cfd34b53e..7199121932 100644
--- a/core/string/ustring.cpp
+++ b/core/string/ustring.cpp
@@ -35,6 +35,7 @@
 #include "core/math/math_funcs.h"
 #include "core/os/memory.h"
 #include "core/string/print_string.h"
+#include "core/string/string_name.h"
 #include "core/string/translation.h"
 #include "core/string/ucaps.h"
 #include "core/variant/variant.h"
@@ -4357,7 +4358,7 @@ String String::property_name_encode() const {
 }
 
 // Changes made to the set of invalid characters must also be reflected in the String documentation.
-const String String::invalid_node_name_characters = ". : @ / \"";
+const String String::invalid_node_name_characters = ". : @ / \" " UNIQUE_NODE_PREFIX;
 
 String String::validate_node_name() const {
 	Vector<String> chars = String::invalid_node_name_characters.split(" ");