Add a const call mode to Object, Variant and Script.

For this to work safely (user not call queue_free or something in the expression), a const call mode was added to Object and Variant (and optionally Script).

This mode ensures only const functions can be called, making it safe to use from the editor.

Co-Authored-By: reduz <reduzio@gmail.com>

23 files changed, 179 insertions, 53 deletions

diff --git a/core/core_constants.cpp b/core/core_constants.cpp
index 67aa2bbbfb..24d8b0af6e 100644
--- a/core/core_constants.cpp
+++ b/core/core_constants.cpp
@@ -588,6 +588,7 @@ void register_global_constants() {
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_GLOBAL_DIR);
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_RESOURCE_TYPE);
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_MULTILINE_TEXT);
+	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_EXPRESSION);
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_PLACEHOLDER_TEXT);
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_COLOR_NO_ALPHA);
 	BIND_CORE_ENUM_CONSTANT(PROPERTY_HINT_IMAGE_COMPRESS_LOSSY);
diff --git a/core/extension/gdnative_interface.h b/core/extension/gdnative_interface.h
index 095c7983ee..ccd6fb0f7e 100644
--- a/core/extension/gdnative_interface.h
+++ b/core/extension/gdnative_interface.h
@@ -153,7 +153,7 @@ typedef enum {
 	GDNATIVE_CALL_ERROR_TOO_MANY_ARGUMENTS, /* expected is number of arguments */
 	GDNATIVE_CALL_ERROR_TOO_FEW_ARGUMENTS, /*  expected is number of arguments */
 	GDNATIVE_CALL_ERROR_INSTANCE_IS_NULL,
-
+	GDNATIVE_CALL_ERROR_METHOD_NOT_CONST, /* used for const call */
 } GDNativeCallErrorType;
 
 typedef struct {
diff --git a/core/math/expression.cpp b/core/math/expression.cpp
index 5a90f68b66..419056d7d6 100644
--- a/core/math/expression.cpp
+++ b/core/math/expression.cpp
@@ -1240,7 +1240,7 @@ bool Expression::_compile_expression() {
 	return false;
 }
 
-bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression::ENode *p_node, Variant &r_ret, String &r_error_str) {
+bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression::ENode *p_node, Variant &r_ret, bool p_const_calls_only, String &r_error_str) {
 	switch (p_node->type) {
 		case Expression::ENode::TYPE_INPUT: {
 			const Expression::InputNode *in = static_cast<const Expression::InputNode *>(p_node);
@@ -1266,7 +1266,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			const Expression::OperatorNode *op = static_cast<const Expression::OperatorNode *>(p_node);
 
 			Variant a;
-			bool ret = _execute(p_inputs, p_instance, op->nodes[0], a, r_error_str);
+			bool ret = _execute(p_inputs, p_instance, op->nodes[0], a, p_const_calls_only, r_error_str);
 			if (ret) {
 				return true;
 			}
@@ -1274,7 +1274,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			Variant b;
 
 			if (op->nodes[1]) {
-				ret = _execute(p_inputs, p_instance, op->nodes[1], b, r_error_str);
+				ret = _execute(p_inputs, p_instance, op->nodes[1], b, p_const_calls_only, r_error_str);
 				if (ret) {
 					return true;
 				}
@@ -1292,14 +1292,14 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			const Expression::IndexNode *index = static_cast<const Expression::IndexNode *>(p_node);
 
 			Variant base;
-			bool ret = _execute(p_inputs, p_instance, index->base, base, r_error_str);
+			bool ret = _execute(p_inputs, p_instance, index->base, base, p_const_calls_only, r_error_str);
 			if (ret) {
 				return true;
 			}
 
 			Variant idx;
 
-			ret = _execute(p_inputs, p_instance, index->index, idx, r_error_str);
+			ret = _execute(p_inputs, p_instance, index->index, idx, p_const_calls_only, r_error_str);
 			if (ret) {
 				return true;
 			}
@@ -1316,7 +1316,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			const Expression::NamedIndexNode *index = static_cast<const Expression::NamedIndexNode *>(p_node);
 
 			Variant base;
-			bool ret = _execute(p_inputs, p_instance, index->base, base, r_error_str);
+			bool ret = _execute(p_inputs, p_instance, index->base, base, p_const_calls_only, r_error_str);
 			if (ret) {
 				return true;
 			}
@@ -1336,7 +1336,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			arr.resize(array->array.size());
 			for (int i = 0; i < array->array.size(); i++) {
 				Variant value;
-				bool ret = _execute(p_inputs, p_instance, array->array[i], value, r_error_str);
+				bool ret = _execute(p_inputs, p_instance, array->array[i], value, p_const_calls_only, r_error_str);
 
 				if (ret) {
 					return true;
@@ -1353,14 +1353,14 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			Dictionary d;
 			for (int i = 0; i < dictionary->dict.size(); i += 2) {
 				Variant key;
-				bool ret = _execute(p_inputs, p_instance, dictionary->dict[i + 0], key, r_error_str);
+				bool ret = _execute(p_inputs, p_instance, dictionary->dict[i + 0], key, p_const_calls_only, r_error_str);
 
 				if (ret) {
 					return true;
 				}
 
 				Variant value;
-				ret = _execute(p_inputs, p_instance, dictionary->dict[i + 1], value, r_error_str);
+				ret = _execute(p_inputs, p_instance, dictionary->dict[i + 1], value, p_const_calls_only, r_error_str);
 				if (ret) {
 					return true;
 				}
@@ -1380,7 +1380,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 
 			for (int i = 0; i < constructor->arguments.size(); i++) {
 				Variant value;
-				bool ret = _execute(p_inputs, p_instance, constructor->arguments[i], value, r_error_str);
+				bool ret = _execute(p_inputs, p_instance, constructor->arguments[i], value, p_const_calls_only, r_error_str);
 
 				if (ret) {
 					return true;
@@ -1408,7 +1408,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 
 			for (int i = 0; i < bifunc->arguments.size(); i++) {
 				Variant value;
-				bool ret = _execute(p_inputs, p_instance, bifunc->arguments[i], value, r_error_str);
+				bool ret = _execute(p_inputs, p_instance, bifunc->arguments[i], value, p_const_calls_only, r_error_str);
 				if (ret) {
 					return true;
 				}
@@ -1429,7 +1429,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			const Expression::CallNode *call = static_cast<const Expression::CallNode *>(p_node);
 
 			Variant base;
-			bool ret = _execute(p_inputs, p_instance, call->base, base, r_error_str);
+			bool ret = _execute(p_inputs, p_instance, call->base, base, p_const_calls_only, r_error_str);
 
 			if (ret) {
 				return true;
@@ -1442,7 +1442,7 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 
 			for (int i = 0; i < call->arguments.size(); i++) {
 				Variant value;
-				ret = _execute(p_inputs, p_instance, call->arguments[i], value, r_error_str);
+				ret = _execute(p_inputs, p_instance, call->arguments[i], value, p_const_calls_only, r_error_str);
 
 				if (ret) {
 					return true;
@@ -1452,7 +1452,11 @@ bool Expression::_execute(const Array &p_inputs, Object *p_instance, Expression:
 			}
 
 			Callable::CallError ce;
-			base.callp(call->method, (const Variant **)argp.ptr(), argp.size(), r_ret, ce);
+			if (p_const_calls_only) {
+				base.call_const(call->method, (const Variant **)argp.ptr(), argp.size(), r_ret, ce);
+			} else {
+				base.callp(call->method, (const Variant **)argp.ptr(), argp.size(), r_ret, ce);
+			}
 
 			if (ce.error != Callable::CallError::CALL_OK) {
 				r_error_str = vformat(RTR("On call to '%s':"), String(call->method));
@@ -1491,13 +1495,13 @@ Error Expression::parse(const String &p_expression, const Vector<String> &p_inpu
 	return OK;
 }
 
-Variant Expression::execute(Array p_inputs, Object *p_base, bool p_show_error) {
+Variant Expression::execute(Array p_inputs, Object *p_base, bool p_show_error, bool p_const_calls_only) {
 	ERR_FAIL_COND_V_MSG(error_set, Variant(), "There was previously a parse error: " + error_str + ".");
 
 	execution_error = false;
 	Variant output;
 	String error_txt;
-	bool err = _execute(p_inputs, p_base, root, output, error_txt);
+	bool err = _execute(p_inputs, p_base, root, output, p_const_calls_only, error_txt);
 	if (err) {
 		execution_error = true;
 		error_str = error_txt;
@@ -1517,7 +1521,7 @@ String Expression::get_error_text() const {
 
 void Expression::_bind_methods() {
 	ClassDB::bind_method(D_METHOD("parse", "expression", "input_names"), &Expression::parse, DEFVAL(Vector<String>()));
-	ClassDB::bind_method(D_METHOD("execute", "inputs", "base_instance", "show_error"), &Expression::execute, DEFVAL(Array()), DEFVAL(Variant()), DEFVAL(true));
+	ClassDB::bind_method(D_METHOD("execute", "inputs", "base_instance", "show_error", "const_calls_only"), &Expression::execute, DEFVAL(Array()), DEFVAL(Variant()), DEFVAL(true), DEFVAL(false));
 	ClassDB::bind_method(D_METHOD("has_execute_failed"), &Expression::has_execute_failed);
 	ClassDB::bind_method(D_METHOD("get_error_text"), &Expression::get_error_text);
 }
diff --git a/core/math/expression.h b/core/math/expression.h
index 6ea3c1611f..2d58915996 100644
--- a/core/math/expression.h
+++ b/core/math/expression.h
@@ -257,14 +257,14 @@ private:
 	Vector<String> input_names;
 
 	bool execution_error = false;
-	bool _execute(const Array &p_inputs, Object *p_instance, Expression::ENode *p_node, Variant &r_ret, String &r_error_str);
+	bool _execute(const Array &p_inputs, Object *p_instance, Expression::ENode *p_node, Variant &r_ret, bool p_const_calls_only, String &r_error_str);
 
 protected:
 	static void _bind_methods();
 
 public:
 	Error parse(const String &p_expression, const Vector<String> &p_input_names = Vector<String>());
-	Variant execute(Array p_inputs = Array(), Object *p_base = nullptr, bool p_show_error = true);
+	Variant execute(Array p_inputs = Array(), Object *p_base = nullptr, bool p_show_error = true, bool p_const_calls_only = false);
 	bool has_execute_failed() const;
 	String get_error_text() const;
 
diff --git a/core/object/object.cpp b/core/object/object.cpp
index 6585c3fa79..440da00c17 100644
--- a/core/object/object.cpp
+++ b/core/object/object.cpp
@@ -669,6 +669,7 @@ Variant Object::callp(const StringName &p_method, const Variant **p_args, int p_
 			case Callable::CallError::CALL_ERROR_INVALID_ARGUMENT:
 			case Callable::CallError::CALL_ERROR_TOO_MANY_ARGUMENTS:
 			case Callable::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS:
+			case Callable::CallError::CALL_ERROR_METHOD_NOT_CONST:
 				return ret;
 			case Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL: {
 			}
@@ -688,6 +689,54 @@ Variant Object::callp(const StringName &p_method, const Variant **p_args, int p_
 	return ret;
 }
 
+Variant Object::call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) {
+	r_error.error = Callable::CallError::CALL_OK;
+
+	if (p_method == CoreStringNames::get_singleton()->_free) {
+		// Free is not const, so fail.
+		r_error.error = Callable::CallError::CALL_ERROR_METHOD_NOT_CONST;
+		return Variant();
+	}
+
+	Variant ret;
+	OBJ_DEBUG_LOCK
+
+	if (script_instance) {
+		ret = script_instance->call_const(p_method, p_args, p_argcount, r_error);
+		//force jumptable
+		switch (r_error.error) {
+			case Callable::CallError::CALL_OK:
+				return ret;
+			case Callable::CallError::CALL_ERROR_INVALID_METHOD:
+				break;
+			case Callable::CallError::CALL_ERROR_METHOD_NOT_CONST:
+				break;
+			case Callable::CallError::CALL_ERROR_INVALID_ARGUMENT:
+			case Callable::CallError::CALL_ERROR_TOO_MANY_ARGUMENTS:
+			case Callable::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS:
+				return ret;
+			case Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL: {
+			}
+		}
+	}
+
+	//extension does not need this, because all methods are registered in MethodBind
+
+	MethodBind *method = ClassDB::get_method(get_class_name(), p_method);
+
+	if (method) {
+		if (!method->is_const()) {
+			r_error.error = Callable::CallError::CALL_ERROR_METHOD_NOT_CONST;
+			return ret;
+		}
+		ret = method->call(this, p_args, p_argcount, r_error);
+	} else {
+		r_error.error = Callable::CallError::CALL_ERROR_INVALID_METHOD;
+	}
+
+	return ret;
+}
+
 void Object::notification(int p_notification, bool p_reversed) {
 	_notificationv(p_notification, p_reversed);
 
diff --git a/core/object/object.h b/core/object/object.h
index 7dac96bc2b..e065634000 100644
--- a/core/object/object.h
+++ b/core/object/object.h
@@ -67,6 +67,7 @@ enum PropertyHint {
 	PROPERTY_HINT_GLOBAL_DIR, ///< a directory path must be passed
 	PROPERTY_HINT_RESOURCE_TYPE, ///< a resource object type
 	PROPERTY_HINT_MULTILINE_TEXT, ///< used for string properties that can contain multiple lines
+	PROPERTY_HINT_EXPRESSION, ///< used for string properties that can contain multiple lines
 	PROPERTY_HINT_PLACEHOLDER_TEXT, ///< used to set a placeholder text for string properties
 	PROPERTY_HINT_COLOR_NO_ALPHA, ///< used for ignoring alpha component when editing a color
 	PROPERTY_HINT_IMAGE_COMPRESS_LOSSY,
@@ -759,6 +760,7 @@ public:
 	void get_method_list(List<MethodInfo> *p_list) const;
 	Variant callv(const StringName &p_method, const Array &p_args);
 	virtual Variant callp(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error);
+	virtual Variant call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error);
 
 	template <typename... VarArgs>
 	Variant call(const StringName &p_method, VarArgs... p_args) {
diff --git a/core/object/script_language.cpp b/core/object/script_language.cpp
index 66c9a80193..4623d0e525 100644
--- a/core/object/script_language.cpp
+++ b/core/object/script_language.cpp
@@ -295,6 +295,11 @@ void ScriptServer::save_global_classes() {
 }
 
 ////////////////////
+
+Variant ScriptInstance::call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error) {
+	return callp(p_method, p_args, p_argcount, r_error);
+}
+
 void ScriptInstance::get_property_state(List<Pair<StringName, Variant>> &state) {
 	List<PropertyInfo> pinfo;
 	get_property_list(&pinfo);
diff --git a/core/object/script_language.h b/core/object/script_language.h
index 0a8e79a24e..776a9bfaab 100644
--- a/core/object/script_language.h
+++ b/core/object/script_language.h
@@ -190,6 +190,7 @@ public:
 		return callp(p_method, sizeof...(p_args) == 0 ? nullptr : (const Variant **)argptrs, sizeof...(p_args), cerr);
 	}
 
+	virtual Variant call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Callable::CallError &r_error); // implement if language supports const functions
 	virtual void notification(int p_notification) = 0;
 	virtual String to_string(bool *r_valid) {
 		if (r_valid) {
diff --git a/core/variant/callable.h b/core/variant/callable.h
index 6a760958d6..bbcf5427ba 100644
--- a/core/variant/callable.h
+++ b/core/variant/callable.h
@@ -61,6 +61,7 @@ public:
 			CALL_ERROR_TOO_MANY_ARGUMENTS, // expected is number of arguments
 			CALL_ERROR_TOO_FEW_ARGUMENTS, // expected is number of arguments
 			CALL_ERROR_INSTANCE_IS_NULL,
+			CALL_ERROR_METHOD_NOT_CONST,
 		};
 		Error error = Error::CALL_OK;
 		int argument = 0;
diff --git a/core/variant/variant.cpp b/core/variant/variant.cpp
index 6007268e21..75aec9a619 100644
--- a/core/variant/variant.cpp
+++ b/core/variant/variant.cpp
@@ -3395,6 +3395,8 @@ String Variant::get_call_error_text(Object *p_base, const StringName &p_method,
 		err_text = "Method not found.";
 	} else if (ce.error == Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL) {
 		err_text = "Instance is null";
+	} else if (ce.error == Callable::CallError::CALL_ERROR_METHOD_NOT_CONST) {
+		err_text = "Method not const in const instance";
 	} else if (ce.error == Callable::CallError::CALL_OK) {
 		return "Call OK";
 	}
diff --git a/core/variant/variant.h b/core/variant/variant.h
index 992d9cad40..83d244145b 100644
--- a/core/variant/variant.h
+++ b/core/variant/variant.h
@@ -555,6 +555,7 @@ public:
 		return ret;
 	}
 
+	void call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Variant &r_ret, Callable::CallError &r_error);
 	static void call_static(Variant::Type p_type, const StringName &p_method, const Variant **p_args, int p_argcount, Variant &r_ret, Callable::CallError &r_error);
 
 	static String get_call_error_text(const StringName &p_method, const Variant **p_argptrs, int p_argcount, const Callable::CallError &ce);
diff --git a/core/variant/variant_call.cpp b/core/variant/variant_call.cpp
index 8e420ecf04..19c0e35777 100644
--- a/core/variant/variant_call.cpp
+++ b/core/variant/variant_call.cpp
@@ -1031,6 +1031,37 @@ void Variant::callp(const StringName &p_method, const Variant **p_args, int p_ar
 #endif
 		r_ret = _get_obj().obj->callp(p_method, p_args, p_argcount, r_error);
 
+	} else {
+		r_error.error = Callable::CallError::CALL_OK;
+
+		const VariantBuiltInMethodInfo *imf = builtin_method_info[type].lookup_ptr(p_method);
+
+		if (!imf) {
+			r_error.error = Callable::CallError::CALL_ERROR_INVALID_METHOD;
+			return;
+		}
+
+		imf->call(this, p_args, p_argcount, r_ret, imf->default_arguments, r_error);
+	}
+}
+
+void Variant::call_const(const StringName &p_method, const Variant **p_args, int p_argcount, Variant &r_ret, Callable::CallError &r_error) {
+	if (type == Variant::OBJECT) {
+		//call object
+		Object *obj = _get_obj().obj;
+		if (!obj) {
+			r_error.error = Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL;
+			return;
+		}
+#ifdef DEBUG_ENABLED
+		if (EngineDebugger::is_active() && !_get_obj().id.is_ref_counted() && ObjectDB::get_instance(_get_obj().id) == nullptr) {
+			r_error.error = Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL;
+			return;
+		}
+
+#endif
+		r_ret = _get_obj().obj->call_const(p_method, p_args, p_argcount, r_error);
+
 		//else if (type==Variant::METHOD) {
 	} else {
 		r_error.error = Callable::CallError::CALL_OK;
@@ -1042,6 +1073,11 @@ void Variant::callp(const StringName &p_method, const Variant **p_args, int p_ar
 			return;
 		}
 
+		if (!imf->is_const) {
+			r_error.error = Callable::CallError::CALL_ERROR_METHOD_NOT_CONST;
+			return;
+		}
+
 		imf->call(this, p_args, p_argcount, r_ret, imf->default_arguments, r_error);
 	}
 }
diff --git a/doc/classes/@GlobalScope.xml b/doc/classes/@GlobalScope.xml
index 863ea899ee..ebda0794ce 100644
--- a/doc/classes/@GlobalScope.xml
+++ b/doc/classes/@GlobalScope.xml
@@ -2521,21 +2521,24 @@
 		<constant name="PROPERTY_HINT_MULTILINE_TEXT" value="20" enum="PropertyHint">
 			Hints that a string property is text with line breaks. Editing it will show a text input field where line breaks can be typed.
 		</constant>
-		<constant name="PROPERTY_HINT_PLACEHOLDER_TEXT" value="21" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_EXPRESSION" value="21" enum="PropertyHint">
+			Hints that a string property is an [Expression].
+		</constant>
+		<constant name="PROPERTY_HINT_PLACEHOLDER_TEXT" value="22" enum="PropertyHint">
 			Hints that a string property should have a placeholder text visible on its input field, whenever the property is empty. The hint string is the placeholder text to use.
 		</constant>
-		<constant name="PROPERTY_HINT_COLOR_NO_ALPHA" value="22" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_COLOR_NO_ALPHA" value="23" enum="PropertyHint">
 			Hints that a color property should be edited without changing its alpha component, i.e. only R, G and B channels are edited.
 		</constant>
-		<constant name="PROPERTY_HINT_IMAGE_COMPRESS_LOSSY" value="23" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_IMAGE_COMPRESS_LOSSY" value="24" enum="PropertyHint">
 			Hints that an image is compressed using lossy compression.
 		</constant>
-		<constant name="PROPERTY_HINT_IMAGE_COMPRESS_LOSSLESS" value="24" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_IMAGE_COMPRESS_LOSSLESS" value="25" enum="PropertyHint">
 			Hints that an image is compressed using lossless compression.
 		</constant>
-		<constant name="PROPERTY_HINT_OBJECT_ID" value="25" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_OBJECT_ID" value="26" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_TYPE_STRING" value="26" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_TYPE_STRING" value="27" enum="PropertyHint">
 			Hint that a property represents a particular type. If a property is [constant TYPE_STRING], allows to set a type from the create dialog. If you need to create an [Array] to contain elements of a specific type, the [code]hint_string[/code] must encode nested types using [code]":"[/code] and [code]"/"[/code] for specifying [Resource] types. For instance:
 			[codeblock]
 			hint_string = "%s:" % [TYPE_INT] # Array of inteters.
@@ -2545,47 +2548,47 @@
 			[/codeblock]
 			[b]Note:[/b] The final colon is required to specify for properly detecting built-in types.
 		</constant>
-		<constant name="PROPERTY_HINT_NODE_PATH_TO_EDITED_NODE" value="27" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_NODE_PATH_TO_EDITED_NODE" value="28" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_METHOD_OF_VARIANT_TYPE" value="28" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_METHOD_OF_VARIANT_TYPE" value="29" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_METHOD_OF_BASE_TYPE" value="29" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_METHOD_OF_BASE_TYPE" value="30" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_METHOD_OF_INSTANCE" value="30" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_METHOD_OF_INSTANCE" value="31" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_METHOD_OF_SCRIPT" value="31" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_METHOD_OF_SCRIPT" value="32" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_PROPERTY_OF_VARIANT_TYPE" value="32" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_PROPERTY_OF_VARIANT_TYPE" value="33" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_PROPERTY_OF_BASE_TYPE" value="33" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_PROPERTY_OF_BASE_TYPE" value="34" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_PROPERTY_OF_INSTANCE" value="34" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_PROPERTY_OF_INSTANCE" value="35" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_PROPERTY_OF_SCRIPT" value="35" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_PROPERTY_OF_SCRIPT" value="36" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_OBJECT_TOO_BIG" value="36" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_OBJECT_TOO_BIG" value="37" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_NODE_PATH_VALID_TYPES" value="37" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_NODE_PATH_VALID_TYPES" value="38" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_SAVE_FILE" value="38" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_SAVE_FILE" value="39" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_GLOBAL_SAVE_FILE" value="39" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_GLOBAL_SAVE_FILE" value="40" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_INT_IS_OBJECTID" value="40" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_INT_IS_OBJECTID" value="41" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_INT_IS_POINTER" value="42" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_INT_IS_POINTER" value="43" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_ARRAY_TYPE" value="41" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_ARRAY_TYPE" value="42" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_LOCALE_ID" value="43" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_LOCALE_ID" value="44" enum="PropertyHint">
 			Hints that a string property is a locale code. Editing it will show a locale dialog for picking language and country.
 		</constant>
-		<constant name="PROPERTY_HINT_LOCALIZABLE_STRING" value="44" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_LOCALIZABLE_STRING" value="45" enum="PropertyHint">
 			Hints that a dictionary property is string translation map. Dictionary keys are locale codes and, values are translated strings.
 		</constant>
-		<constant name="PROPERTY_HINT_NODE_TYPE" value="45" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_NODE_TYPE" value="46" enum="PropertyHint">
 		</constant>
-		<constant name="PROPERTY_HINT_MAX" value="46" enum="PropertyHint">
+		<constant name="PROPERTY_HINT_MAX" value="47" enum="PropertyHint">
 		</constant>
 		<constant name="PROPERTY_USAGE_NONE" value="0" enum="PropertyUsageFlags">
 		</constant>
diff --git a/doc/classes/Expression.xml b/doc/classes/Expression.xml
index b37de09e04..50979c9b68 100644
--- a/doc/classes/Expression.xml
+++ b/doc/classes/Expression.xml
@@ -56,6 +56,7 @@
 			<argument index="0" name="inputs" type="Array" default="[]" />
 			<argument index="1" name="base_instance" type="Object" default="null" />
 			<argument index="2" name="show_error" type="bool" default="true" />
+			<argument index="3" name="const_calls_only" type="bool" default="false" />
 			<description>
 				Executes the expression that was previously parsed by [method parse] and returns the result. Before you use the returned object, you should check if the method failed by calling [method has_execute_failed].
 				If you defined input variables in [method parse], you can specify their values in the inputs array, in the same order.
diff --git a/editor/editor_properties.cpp b/editor/editor_properties.cpp
index 0e6c9162ce..e5105fdedc 100644
--- a/editor/editor_properties.cpp
+++ b/editor/editor_properties.cpp
@@ -165,6 +165,9 @@ void EditorPropertyMultilineText::_notification(int p_what) {
 			Ref<Font> font = get_theme_font(SNAME("font"), SNAME("Label"));
 			int font_size = get_theme_font_size(SNAME("font_size"), SNAME("Label"));
 			text->set_custom_minimum_size(Vector2(0, font->get_height(font_size) * 6));
+			text->add_theme_font_override("font", get_theme_font("expression", "EditorFonts"));
+			text->add_theme_font_size_override("font_size", get_theme_font_size("expression_size", "EditorFonts"));
+
 		} break;
 	}
 }
@@ -172,7 +175,7 @@ void EditorPropertyMultilineText::_notification(int p_what) {
 void EditorPropertyMultilineText::_bind_methods() {
 }
 
-EditorPropertyMultilineText::EditorPropertyMultilineText() {
+EditorPropertyMultilineText::EditorPropertyMultilineText(bool p_expression) {
 	HBoxContainer *hb = memnew(HBoxContainer);
 	hb->add_theme_constant_override("separation", 0);
 	add_child(hb);
@@ -189,6 +192,12 @@ EditorPropertyMultilineText::EditorPropertyMultilineText() {
 	hb->add_child(open_big_text);
 	big_text_dialog = nullptr;
 	big_text = nullptr;
+	if (p_expression) {
+		expression = true;
+		Ref<EditorStandardSyntaxHighlighter> highlighter;
+		highlighter.instantiate();
+		text->set_syntax_highlighter(highlighter);
+	}
 }
 
 ///////////////////// TEXT ENUM /////////////////////////
@@ -3771,6 +3780,9 @@ EditorProperty *EditorInspectorDefaultPlugin::get_editor_for_property(Object *p_
 			} else if (p_hint == PROPERTY_HINT_MULTILINE_TEXT) {
 				EditorPropertyMultilineText *editor = memnew(EditorPropertyMultilineText);
 				return editor;
+			} else if (p_hint == PROPERTY_HINT_EXPRESSION) {
+				EditorPropertyMultilineText *editor = memnew(EditorPropertyMultilineText(true));
+				return editor;
 			} else if (p_hint == PROPERTY_HINT_TYPE_STRING) {
 				EditorPropertyClassName *editor = memnew(EditorPropertyClassName);
 				editor->setup("Object", p_hint_text);
diff --git a/editor/editor_properties.h b/editor/editor_properties.h
index 72b2b0b283..7cd6ea4f6b 100644
--- a/editor/editor_properties.h
+++ b/editor/editor_properties.h
@@ -81,6 +81,7 @@ class EditorPropertyMultilineText : public EditorProperty {
 	void _big_text_changed();
 	void _text_changed();
 	void _open_big_text();
+	bool expression = false;
 
 protected:
 	virtual void _set_read_only(bool p_read_only) override;
@@ -89,7 +90,7 @@ protected:
 
 public:
 	virtual void update_property() override;
-	EditorPropertyMultilineText();
+	EditorPropertyMultilineText(bool p_expression = false);
 };
 
 class EditorPropertyTextEnum : public EditorProperty {
diff --git a/editor/editor_spin_slider.cpp b/editor/editor_spin_slider.cpp
index a0c818ba84..f23f0cf758 100644
--- a/editor/editor_spin_slider.cpp
+++ b/editor/editor_spin_slider.cpp
@@ -530,7 +530,7 @@ void EditorSpinSlider::_evaluate_input_text() {
 		return;
 	}
 
-	Variant v = expr->execute(Array(), nullptr, false);
+	Variant v = expr->execute(Array(), nullptr, false, true);
 	if (v.get_type() == Variant::NIL) {
 		return;
 	}
diff --git a/editor/plugins/script_text_editor.cpp b/editor/plugins/script_text_editor.cpp
index 05c707c065..7d4ffd1a25 100644
--- a/editor/plugins/script_text_editor.cpp
+++ b/editor/plugins/script_text_editor.cpp
@@ -1196,7 +1196,7 @@ void ScriptTextEditor::_edit_option(int p_op) {
 				String whitespace = line.substr(0, line.size() - line.strip_edges(true, false).size()); //extract the whitespace at the beginning
 
 				if (expression.parse(line) == OK) {
-					Variant result = expression.execute(Array(), Variant(), false);
+					Variant result = expression.execute(Array(), Variant(), false, true);
 					if (expression.get_error_text().is_empty()) {
 						results.push_back(whitespace + result.get_construct_string());
 					} else {
diff --git a/editor/property_editor.cpp b/editor/property_editor.cpp
index 771d34d841..d936e821df 100644
--- a/editor/property_editor.cpp
+++ b/editor/property_editor.cpp
@@ -1474,7 +1474,7 @@ void CustomPropertyEditor::_modified(String p_string) {
 				v = value_editor[0]->get_text().to_int();
 				return;
 			} else {
-				v = expr->execute(Array(), nullptr, false);
+				v = expr->execute(Array(), nullptr, false, false);
 			}
 
 			if (v != prev_v) {
@@ -1650,7 +1650,7 @@ real_t CustomPropertyEditor::_parse_real_expression(String text) {
 	if (err != OK) {
 		out = value_editor[0]->get_text().to_float();
 	} else {
-		out = expr->execute(Array(), nullptr, false);
+		out = expr->execute(Array(), nullptr, false, true);
 	}
 	return out;
 }
diff --git a/modules/gdscript/gdscript_analyzer.cpp b/modules/gdscript/gdscript_analyzer.cpp
index 42b02ce3b9..ea994654bf 100644
--- a/modules/gdscript/gdscript_analyzer.cpp
+++ b/modules/gdscript/gdscript_analyzer.cpp
@@ -2278,6 +2278,7 @@ void GDScriptAnalyzer::reduce_call(GDScriptParser::CallNode *p_call, bool p_is_a
 						push_error(vformat(R"(Too few arguments for %s constructor. Received %d but expected %d.)", Variant::get_type_name(builtin_type), p_call->arguments.size(), err.expected), p_call);
 						break;
 					case Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL:
+					case Callable::CallError::CALL_ERROR_METHOD_NOT_CONST:
 						break; // Can't happen in a builtin constructor.
 					case Callable::CallError::CALL_OK:
 						p_call->is_constant = true;
@@ -2380,6 +2381,7 @@ void GDScriptAnalyzer::reduce_call(GDScriptParser::CallNode *p_call, bool p_is_a
 					case Callable::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS:
 						push_error(vformat(R"*(Too few arguments for "%s()" call. Expected at least %d but received %d.)*", function_name, err.expected, p_call->arguments.size()), p_call);
 						break;
+					case Callable::CallError::CALL_ERROR_METHOD_NOT_CONST:
 					case Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL:
 						break; // Can't happen in a builtin constructor.
 					case Callable::CallError::CALL_OK:
@@ -2422,6 +2424,7 @@ void GDScriptAnalyzer::reduce_call(GDScriptParser::CallNode *p_call, bool p_is_a
 					case Callable::CallError::CALL_ERROR_TOO_FEW_ARGUMENTS:
 						push_error(vformat(R"*(Too few arguments for "%s()" call. Expected at least %d but received %d.)*", function_name, err.expected, p_call->arguments.size()), p_call);
 						break;
+					case Callable::CallError::CALL_ERROR_METHOD_NOT_CONST:
 					case Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL:
 						break; // Can't happen in a builtin constructor.
 					case Callable::CallError::CALL_OK:
diff --git a/modules/gdscript/gdscript_vm.cpp b/modules/gdscript/gdscript_vm.cpp
index 20b8d29ec3..3f25c2fa43 100644
--- a/modules/gdscript/gdscript_vm.cpp
+++ b/modules/gdscript/gdscript_vm.cpp
@@ -177,6 +177,8 @@ String GDScriptFunction::_get_call_error(const Callable::CallError &p_err, const
 		err_text = "Invalid call. Nonexistent " + p_where + ".";
 	} else if (p_err.error == Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL) {
 		err_text = "Attempt to call " + p_where + " on a null instance.";
+	} else if (p_err.error == Callable::CallError::CALL_ERROR_METHOD_NOT_CONST) {
+		err_text = "Attempt to call " + p_where + " on a const instance.";
 	} else {
 		err_text = "Bug, call error: #" + itos(p_err.error);
 	}
diff --git a/modules/visual_script/visual_script.cpp b/modules/visual_script/visual_script.cpp
index c4fafb6676..c5bcf23c8e 100644
--- a/modules/visual_script/visual_script.cpp
+++ b/modules/visual_script/visual_script.cpp
@@ -1655,6 +1655,8 @@ Variant VisualScriptInstance::_call_internal(const StringName &p_method, void *p
 				error_str += "Expected " + itos(r_error.argument) + " arguments.";
 			} else if (r_error.error == Callable::CallError::CALL_ERROR_INVALID_METHOD) {
 				error_str += "Invalid Call.";
+			} else if (r_error.error == Callable::CallError::CALL_ERROR_METHOD_NOT_CONST) {
+				error_str += "Method not const in a const instance.";
 			} else if (r_error.error == Callable::CallError::CALL_ERROR_INSTANCE_IS_NULL) {
 				error_str += "Base Instance is null";
 			}
diff --git a/scene/gui/spin_box.cpp b/scene/gui/spin_box.cpp
index e50d7e765c..890e349afb 100644
--- a/scene/gui/spin_box.cpp
+++ b/scene/gui/spin_box.cpp
@@ -62,7 +62,7 @@ void SpinBox::_text_submitted(const String &p_string) {
 		return;
 	}
 
-	Variant value = expr->execute(Array(), nullptr, false);
+	Variant value = expr->execute(Array(), nullptr, false, true);
 	if (value.get_type() != Variant::NIL) {
 		set_value(value);
 	}