GDScript: Implement lambdas compilation and runtime

modules/gdscript/gdscript.h

@@ -270,6 +270,7 @@ public:
 class GDScriptInstance : public ScriptInstance {
 	friend class GDScript;
 	friend class GDScriptFunction;
+	friend class GDScriptLambdaCallable;
 	friend class GDScriptCompiler;
 	friend struct GDScriptUtilityFunctionsDefinitions;
 

modules/gdscript/gdscript_analyzer.cpp

@@ -2101,6 +2101,8 @@ void GDScriptAnalyzer::reduce_call(GDScriptParser::CallNode *p_call, bool is_awa
 
 		if (is_self && parser->current_function != nullptr && parser->current_function->is_static && !is_static) {
 			push_error(vformat(R"*(Cannot call non-static function "%s()" from static function "%s()".)*", p_call->function_name, parser->current_function->identifier->name), p_call->callee);
+		} else if (is_self && !is_static && !lambda_stack.is_empty()) {
+			push_error(vformat(R"*(Cannot call non-static function "%s()" from a lambda function.)*", p_call->function_name), p_call->callee);
 		}
 
 		call_type = return_type;
@@ -2223,6 +2225,8 @@ void GDScriptAnalyzer::reduce_get_node(GDScriptParser::GetNodeNode *p_get_node)
 
 	if (!ClassDB::is_parent_class(GDScriptParser::get_real_class_name(parser->current_class->base_type.native_type), result.native_type)) {
 		push_error(R"*(Cannot use shorthand "get_node()" notation ("$") on a class that isn't a node.)*", p_get_node);
+	} else if (!lambda_stack.is_empty()) {
+		push_error(R"*(Cannot use shorthand "get_node()" notation ("$") inside a lambda. Use a captured variable instead.)*", p_get_node);
 	}
 
 	p_get_node->set_datatype(result);
@@ -2614,6 +2618,30 @@ void GDScriptAnalyzer::reduce_lambda(GDScriptParser::LambdaNode *p_lambda) {
 
 	resolve_suite(p_lambda->function->body);
 
+	int captures_amount = p_lambda->captures.size();
+	if (captures_amount > 0) {
+		// Create space for lambda parameters.
+		// At the beginning to not mess with optional parameters.
+		int param_count = p_lambda->function->parameters.size();
+		p_lambda->function->parameters.resize(param_count + captures_amount);
+		for (int i = param_count - 1; i >= 0; i--) {
+			p_lambda->function->parameters.write[i + captures_amount] = p_lambda->function->parameters[i];
+			p_lambda->function->parameters_indices[p_lambda->function->parameters[i]->identifier->name] = i + captures_amount;
+		}
+
+		// Add captures as extra parameters at the beginning.
+		for (int i = 0; i < p_lambda->captures.size(); i++) {
+			GDScriptParser::IdentifierNode *capture = p_lambda->captures[i];
+			GDScriptParser::ParameterNode *capture_param = parser->alloc_node<GDScriptParser::ParameterNode>();
+			capture_param->identifier = capture;
+			capture_param->usages = capture->usages;
+			capture_param->set_datatype(capture->get_datatype());
+
+			p_lambda->function->parameters.write[i] = capture_param;
+			p_lambda->function->parameters_indices[capture->name] = i;
+		}
+	}
+
 	lambda_stack.pop_back();
 	parser->current_function = previous_function;
 }
@@ -3577,13 +3605,6 @@ Ref<GDScriptParserRef> GDScriptAnalyzer::get_parser_for(const String &p_path) {
 	return ref;
 }
 
-const GDScriptParser::LambdaNode *GDScriptAnalyzer::get_current_lambda() const {
-	if (lambda_stack.size()) {
-		return lambda_stack.back()->get();
-	}
-	return nullptr;
-}
-
 Error GDScriptAnalyzer::resolve_inheritance() {
 	return resolve_inheritance(parser->head);
 }

modules/gdscript/gdscript_analyzer.h

@@ -111,7 +111,6 @@ class GDScriptAnalyzer {
 	void mark_node_unsafe(const GDScriptParser::Node *p_node);
 	bool class_exists(const StringName &p_class) const;
 	Ref<GDScriptParserRef> get_parser_for(const String &p_path);
-	const GDScriptParser::LambdaNode *get_current_lambda() const;
 #ifdef DEBUG_ENABLED
 	bool is_shadowing(GDScriptParser::IdentifierNode *p_local, const String &p_context);
 #endif

modules/gdscript/gdscript_byte_codegen.cpp

@@ -383,6 +383,18 @@ GDScriptFunction *GDScriptByteCodeGenerator::write_end() {
 		function->_methods_count = 0;
 	}
 
+	if (lambdas_map.size()) {
+		function->lambdas.resize(lambdas_map.size());
+		function->_lambdas_ptr = function->lambdas.ptrw();
+		function->_lambdas_count = lambdas_map.size();
+		for (const Map<GDScriptFunction *, int>::Element *E = lambdas_map.front(); E; E = E->next()) {
+			function->lambdas.write[E->get()] = E->key();
+		}
+	} else {
+		function->_lambdas_ptr = nullptr;
+		function->_lambdas_count = 0;
+	}
+
 	if (debug_stack) {
 		function->stack_debug = stack_debug;
 	}
@@ -1118,6 +1130,17 @@ void GDScriptByteCodeGenerator::write_call_script_function(const Address &p_targ
 	append(p_function_name);
 }
 
+void GDScriptByteCodeGenerator::write_lambda(const Address &p_target, GDScriptFunction *p_function, const Vector<Address> &p_captures) {
+	append(GDScriptFunction::OPCODE_CREATE_LAMBDA, 1 + p_captures.size());
+	for (int i = 0; i < p_captures.size(); i++) {
+		append(p_captures[i]);
+	}
+
+	append(p_target);
+	append(p_captures.size());
+	append(p_function);
+}
+
 void GDScriptByteCodeGenerator::write_construct(const Address &p_target, Variant::Type p_type, const Vector<Address> &p_arguments) {
 	// Try to find an appropriate constructor.
 	bool all_have_type = true;

modules/gdscript/gdscript_byte_codegen.h

@@ -93,6 +93,7 @@ class GDScriptByteCodeGenerator : public GDScriptCodeGenerator {
 	Map<Variant::ValidatedUtilityFunction, int> utilities_map;
 	Map<GDScriptUtilityFunctions::FunctionPtr, int> gds_utilities_map;
 	Map<MethodBind *, int> method_bind_map;
+	Map<GDScriptFunction *, int> lambdas_map;
 
 	// Lists since these can be nested.
 	List<int> if_jmp_addrs;
@@ -293,6 +294,15 @@ class GDScriptByteCodeGenerator : public GDScriptCodeGenerator {
 		return pos;
 	}
 
+	int get_lambda_function_pos(GDScriptFunction *p_lambda_function) {
+		if (lambdas_map.has(p_lambda_function)) {
+			return lambdas_map[p_lambda_function];
+		}
+		int pos = lambdas_map.size();
+		lambdas_map[p_lambda_function] = pos;
+		return pos;
+	}
+
 	void alloc_ptrcall(int p_params) {
 		if (p_params >= ptrcall_max) {
 			ptrcall_max = p_params;
@@ -386,6 +396,10 @@ class GDScriptByteCodeGenerator : public GDScriptCodeGenerator {
 		opcodes.push_back(get_method_bind_pos(p_method));
 	}
 
+	void append(GDScriptFunction *p_lambda_function) {
+		opcodes.push_back(get_lambda_function_pos(p_lambda_function));
+	}
+
 	void patch_jump(int p_address) {
 		opcodes.write[p_address] = opcodes.size();
 	}
@@ -452,6 +466,7 @@ public:
 	virtual void write_call_self(const Address &p_target, const StringName &p_function_name, const Vector<Address> &p_arguments) override;
 	virtual void write_call_self_async(const Address &p_target, const StringName &p_function_name, const Vector<Address> &p_arguments) override;
 	virtual void write_call_script_function(const Address &p_target, const Address &p_base, const StringName &p_function_name, const Vector<Address> &p_arguments) override;
+	virtual void write_lambda(const Address &p_target, GDScriptFunction *p_function, const Vector<Address> &p_captures) override;
 	virtual void write_construct(const Address &p_target, Variant::Type p_type, const Vector<Address> &p_arguments) override;
 	virtual void write_construct_array(const Address &p_target, const Vector<Address> &p_arguments) override;
 	virtual void write_construct_typed_array(const Address &p_target, const GDScriptDataType &p_element_type, const Vector<Address> &p_arguments) override;

modules/gdscript/gdscript_codegen.h

@@ -127,6 +127,7 @@ public:
 	virtual void write_call_self(const Address &p_target, const StringName &p_function_name, const Vector<Address> &p_arguments) = 0;
 	virtual void write_call_self_async(const Address &p_target, const StringName &p_function_name, const Vector<Address> &p_arguments) = 0;
 	virtual void write_call_script_function(const Address &p_target, const Address &p_base, const StringName &p_function_name, const Vector<Address> &p_arguments) = 0;
+	virtual void write_lambda(const Address &p_target, GDScriptFunction *p_function, const Vector<Address> &p_captures) = 0;
 	virtual void write_construct(const Address &p_target, Variant::Type p_type, const Vector<Address> &p_arguments) = 0;
 	virtual void write_construct_array(const Address &p_target, const Vector<Address> &p_arguments) = 0;
 	virtual void write_construct_typed_array(const Address &p_target, const GDScriptDataType &p_element_type, const Vector<Address> &p_arguments) = 0;

modules/gdscript/gdscript_compiler.cpp

@@ -1091,6 +1091,34 @@ GDScriptCodeGenerator::Address GDScriptCompiler::_parse_expression(CodeGen &code
 			}
 			return GDScriptCodeGenerator::Address(); // Assignment does not return a value.
 		} break;
+		case GDScriptParser::Node::LAMBDA: {
+			const GDScriptParser::LambdaNode *lambda = static_cast<const GDScriptParser::LambdaNode *>(p_expression);
+			GDScriptCodeGenerator::Address result = codegen.add_temporary(_gdtype_from_datatype(lambda->get_datatype()));
+
+			Vector<GDScriptCodeGenerator::Address> captures;
+			captures.resize(lambda->captures.size());
+			for (int i = 0; i < lambda->captures.size(); i++) {
+				captures.write[i] = _parse_expression(codegen, r_error, lambda->captures[i]);
+				if (r_error) {
+					return GDScriptCodeGenerator::Address();
+				}
+			}
+
+			GDScriptFunction *function = _parse_function(r_error, codegen.script, codegen.class_node, lambda->function, false, true);
+			if (r_error) {
+				return GDScriptCodeGenerator::Address();
+			}
+
+			gen->write_lambda(result, function, captures);
+
+			for (int i = 0; i < captures.size(); i++) {
+				if (captures[i].mode == GDScriptCodeGenerator::Address::TEMPORARY) {
+					gen->pop_temporary();
+				}
+			}
+
+			return result;
+		} break;
 		default: {
 			ERR_FAIL_V_MSG(GDScriptCodeGenerator::Address(), "Bug in bytecode compiler, unexpected node in parse tree while parsing expression."); // Unreachable code.
 		} break;
@@ -1804,8 +1832,8 @@ Error GDScriptCompiler::_parse_block(CodeGen &codegen, const GDScriptParser::Sui
 	return OK;
 }
 
-Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready) {
-	Error error = OK;
+GDScriptFunction *GDScriptCompiler::_parse_function(Error &r_error, GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready, bool p_for_lambda) {
+	r_error = OK;
 	CodeGen codegen;
 	codegen.generator = memnew(GDScriptByteCodeGenerator);
 
@@ -1822,7 +1850,11 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 	return_type.builtin_type = Variant::NIL;
 
 	if (p_func) {
-		func_name = p_func->identifier->name;
+		if (p_func->identifier) {
+			func_name = p_func->identifier->name;
+		} else {
+			func_name = "<anonymous lambda>";
+		}
 		is_static = p_func->is_static;
 		rpc_mode = p_func->rpc_mode;
 		return_type = _gdtype_from_datatype(p_func->get_datatype(), p_script);
@@ -1853,11 +1885,11 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 	}
 
 	// Parse initializer if applies.
-	bool is_implicit_initializer = !p_for_ready && !p_func;
-	bool is_initializer = p_func && String(p_func->identifier->name) == GDScriptLanguage::get_singleton()->strings._init;
-	bool is_for_ready = p_for_ready || (p_func && String(p_func->identifier->name) == "_ready");
+	bool is_implicit_initializer = !p_for_ready && !p_func && !p_for_lambda;
+	bool is_initializer = p_func && !p_for_lambda && String(p_func->identifier->name) == GDScriptLanguage::get_singleton()->strings._init;
+	bool is_for_ready = p_for_ready || (p_func && !p_for_lambda && String(p_func->identifier->name) == "_ready");
 
-	if (is_implicit_initializer || is_for_ready) {
+	if (!p_for_lambda && (is_implicit_initializer || is_for_ready)) {
 		// Initialize class fields.
 		for (int i = 0; i < p_class->members.size(); i++) {
 			if (p_class->members[i].type != GDScriptParser::ClassNode::Member::VARIABLE) {
@@ -1884,10 +1916,10 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 						codegen.generator->write_construct_array(dst_address, Vector<GDScriptCodeGenerator::Address>());
 					}
 				}
-				GDScriptCodeGenerator::Address src_address = _parse_expression(codegen, error, field->initializer, false, true);
-				if (error) {
+				GDScriptCodeGenerator::Address src_address = _parse_expression(codegen, r_error, field->initializer, false, true);
+				if (r_error) {
 					memdelete(codegen.generator);
-					return error;
+					return nullptr;
 				}
 
 				codegen.generator->write_assign(dst_address, src_address);
@@ -1914,10 +1946,10 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 			codegen.generator->start_parameters();
 			for (int i = p_func->parameters.size() - optional_parameters; i < p_func->parameters.size(); i++) {
 				const GDScriptParser::ParameterNode *parameter = p_func->parameters[i];
-				GDScriptCodeGenerator::Address src_addr = _parse_expression(codegen, error, parameter->default_value, true);
-				if (error) {
+				GDScriptCodeGenerator::Address src_addr = _parse_expression(codegen, r_error, parameter->default_value, true);
+				if (r_error) {
 					memdelete(codegen.generator);
-					return error;
+					return nullptr;
 				}
 				GDScriptCodeGenerator::Address dst_addr = codegen.parameters[parameter->identifier->name];
 				codegen.generator->write_assign_default_parameter(dst_addr, src_addr);
@@ -1928,10 +1960,10 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 			codegen.generator->end_parameters();
 		}
 
-		Error err = _parse_block(codegen, p_func->body);
-		if (err) {
+		r_error = _parse_block(codegen, p_func->body);
+		if (r_error) {
 			memdelete(codegen.generator);
-			return err;
+			return nullptr;
 		}
 	}
 
@@ -1957,6 +1989,10 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 			signature += "::" + String(func_name);
 		}
 
+		if (p_for_lambda) {
+			signature += "(lambda)";
+		}
+
 		codegen.generator->set_signature(signature);
 	}
 #endif
@@ -1964,8 +2000,10 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 	if (p_func) {
 		codegen.generator->set_initial_line(p_func->start_line);
 #ifdef TOOLS_ENABLED
-		p_script->member_lines[func_name] = p_func->start_line;
-		p_script->doc_functions[func_name] = p_func->doc_description;
+		if (!p_for_lambda) {
+			p_script->member_lines[func_name] = p_func->start_line;
+			p_script->doc_functions[func_name] = p_func->doc_description;
+		}
 #endif
 	} else {
 		codegen.generator->set_initial_line(0);
@@ -1994,11 +2032,13 @@ Error GDScriptCompiler::_parse_function(GDScript *p_script, const GDScriptParser
 #endif
 	}
 
-	p_script->member_functions[func_name] = gd_function;
+	if (!p_for_lambda) {
+		p_script->member_functions[func_name] = gd_function;
+	}
 
 	memdelete(codegen.generator);
 
-	return OK;
+	return gd_function;
 }
 
 Error GDScriptCompiler::_parse_setter_getter(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::VariableNode *p_variable, bool p_is_setter) {
@@ -2391,7 +2431,8 @@ Error GDScriptCompiler::_parse_class_blocks(GDScript *p_script, const GDScriptPa
 			if (!has_ready && function->identifier->name == "_ready") {
 				has_ready = true;
 			}
-			Error err = _parse_function(p_script, p_class, function);
+			Error err = OK;
+			_parse_function(err, p_script, p_class, function);
 			if (err) {
 				return err;
 			}
@@ -2416,7 +2457,8 @@ Error GDScriptCompiler::_parse_class_blocks(GDScript *p_script, const GDScriptPa
 
 	{
 		// Create an implicit constructor in any case.
-		Error err = _parse_function(p_script, p_class, nullptr);
+		Error err = OK;
+		_parse_function(err, p_script, p_class, nullptr);
 		if (err) {
 			return err;
 		}
@@ -2424,7 +2466,8 @@ Error GDScriptCompiler::_parse_class_blocks(GDScript *p_script, const GDScriptPa
 
 	if (!has_ready && p_class->onready_used) {
 		//create a _ready constructor
-		Error err = _parse_function(p_script, p_class, nullptr, true);
+		Error err = OK;
+		_parse_function(err, p_script, p_class, nullptr, true);
 		if (err) {
 			return err;
 		}

modules/gdscript/gdscript_compiler.h

@@ -128,7 +128,7 @@ class GDScriptCompiler {
 	GDScriptCodeGenerator::Address _parse_match_pattern(CodeGen &codegen, Error &r_error, const GDScriptParser::PatternNode *p_pattern, const GDScriptCodeGenerator::Address &p_value_addr, const GDScriptCodeGenerator::Address &p_type_addr, const GDScriptCodeGenerator::Address &p_previous_test, bool p_is_first, bool p_is_nested);
 	void _add_locals_in_block(CodeGen &codegen, const GDScriptParser::SuiteNode *p_block);
 	Error _parse_block(CodeGen &codegen, const GDScriptParser::SuiteNode *p_block, bool p_add_locals = true);
-	Error _parse_function(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready = false);
+	GDScriptFunction *_parse_function(Error &r_error, GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::FunctionNode *p_func, bool p_for_ready = false, bool p_for_lambda = false);
 	Error _parse_setter_getter(GDScript *p_script, const GDScriptParser::ClassNode *p_class, const GDScriptParser::VariableNode *p_variable, bool p_is_setter);
 	Error _parse_class_level(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);
 	Error _parse_class_blocks(GDScript *p_script, const GDScriptParser::ClassNode *p_class, bool p_keep_state);

modules/gdscript/gdscript_disassembler.cpp

@@ -721,7 +721,7 @@ void GDScriptFunction::disassemble(const Vector<String> &p_code_lines) const {
 				text += "await ";
 				text += DADDR(1);
 
-				incr += 2;
+				incr = 2;
 			} break;
 			case OPCODE_AWAIT_RESUME: {
 				text += "await resume ";
@@ -729,6 +729,25 @@ void GDScriptFunction::disassemble(const Vector<String> &p_code_lines) const {
 
 				incr = 2;
 			} break;
+			case OPCODE_CREATE_LAMBDA: {
+				int captures_count = _code_ptr[ip + 1 + instr_var_args];
+				GDScriptFunction *lambda = _lambdas_ptr[_code_ptr[ip + 2 + instr_var_args]];
+
+				text += DADDR(1 + captures_count);
+				text += "create lambda from ";
+				text += lambda->name.operator String();
+				text += "function, captures (";
+
+				for (int i = 0; i < captures_count; i++) {
+					if (i > 0) {
+						text += ", ";
+					}
+					text += DADDR(1 + i);
+				}
+				text += ")";
+
+				incr = 3 + captures_count;
+			} break;
 			case OPCODE_JUMP: {
 				text += "jump ";
 				text += itos(_code_ptr[ip + 1]);

modules/gdscript/gdscript_function.cpp

@@ -150,6 +150,10 @@ GDScriptFunction::GDScriptFunction() {
 }
 
 GDScriptFunction::~GDScriptFunction() {
+	for (int i = 0; i < lambdas.size(); i++) {
+		memdelete(lambdas[i]);
+	}
+
 #ifdef DEBUG_ENABLED
 
 	MutexLock lock(GDScriptLanguage::get_singleton()->lock);

modules/gdscript/gdscript_function.h

@@ -301,6 +301,7 @@ public:
 		OPCODE_CALL_PTRCALL_PACKED_COLOR_ARRAY,
 		OPCODE_AWAIT,
 		OPCODE_AWAIT_RESUME,
+		OPCODE_CREATE_LAMBDA,
 		OPCODE_JUMP,
 		OPCODE_JUMP_IF,
 		OPCODE_JUMP_IF_NOT,
@@ -459,6 +460,8 @@ private:
 	const GDScriptUtilityFunctions::FunctionPtr *_gds_utilities_ptr = nullptr;
 	int _methods_count = 0;
 	MethodBind **_methods_ptr = nullptr;
+	int _lambdas_count = 0;
+	GDScriptFunction **_lambdas_ptr = nullptr;
 	const int *_code_ptr = nullptr;
 	int _code_size = 0;
 	int _argument_count = 0;
@@ -488,6 +491,7 @@ private:
 	Vector<Variant::ValidatedUtilityFunction> utilities;
 	Vector<GDScriptUtilityFunctions::FunctionPtr> gds_utilities;
 	Vector<MethodBind *> methods;
+	Vector<GDScriptFunction *> lambdas;
 	Vector<int> code;
 	Vector<GDScriptDataType> argument_types;
 	GDScriptDataType return_type;

modules/gdscript/gdscript_lambda_callable.cpp

@@ -0,0 +1,95 @@
+/*************************************************************************/
+/*  gdscript_lambda_callable.cpp                                         */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#include "gdscript_lambda_callable.h"
+
+#include "core/templates/hashfuncs.h"
+#include "gdscript.h"
+
+bool GDScriptLambdaCallable::compare_equal(const CallableCustom *p_a, const CallableCustom *p_b) {
+	// Lambda callables are only compared by reference.
+	return p_a == p_b;
+}
+
+bool GDScriptLambdaCallable::compare_less(const CallableCustom *p_a, const CallableCustom *p_b) {
+	// Lambda callables are only compared by reference.
+	return p_a < p_b;
+}
+
+uint32_t GDScriptLambdaCallable::hash() const {
+	return h;
+}
+
+String GDScriptLambdaCallable::get_as_text() const {
+	if (function->get_name() != StringName()) {
+		return function->get_name().operator String() + "(lambda)";
+	}
+	return "(anonymous lambda)";
+}
+
+CallableCustom::CompareEqualFunc GDScriptLambdaCallable::get_compare_equal_func() const {
+	return compare_equal;
+}
+
+CallableCustom::CompareLessFunc GDScriptLambdaCallable::get_compare_less_func() const {
+	return compare_less;
+}
+
+ObjectID GDScriptLambdaCallable::get_object() const {
+	return script->get_instance_id();
+}
+
+void GDScriptLambdaCallable::call(const Variant **p_arguments, int p_argcount, Variant &r_return_value, Callable::CallError &r_call_error) const {
+	int captures_amount = captures.size();
+
+	if (captures_amount > 0) {
+		Vector<const Variant *> args;
+		args.resize(p_argcount + captures_amount);
+		for (int i = 0; i < captures_amount; i++) {
+			args.write[i] = &captures[i];
+		}
+		for (int i = 0; i < p_argcount; i++) {
+			args.write[i + captures_amount] = p_arguments[i];
+		}
+
+		r_return_value = function->call(nullptr, args.ptrw(), args.size(), r_call_error);
+		r_call_error.argument -= captures_amount;
+	} else {
+		r_return_value = function->call(nullptr, p_arguments, p_argcount, r_call_error);
+	}
+}
+
+GDScriptLambdaCallable::GDScriptLambdaCallable(Ref<GDScript> p_script, GDScriptFunction *p_function, const Vector<Variant> &p_captures) {
+	script = p_script;
+	function = p_function;
+	captures = p_captures;
+
+	h = (uint32_t)hash_djb2_one_64((uint64_t)this);
+}

modules/gdscript/gdscript_lambda_callable.h

@@ -0,0 +1,65 @@
+/*************************************************************************/
+/*  gdscript_lambda_callable.h                                           */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                      https://godotengine.org                          */
+/*************************************************************************/
+/* Copyright (c) 2007-2021 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2021 Godot Engine contributors (cf. AUTHORS.md).   */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef GDSCRIPT_LAMBDA_CALLABLE
+#define GDSCRIPT_LAMBDA_CALLABLE
+
+#include "core/object/reference.h"
+#include "core/templates/vector.h"
+#include "core/variant/callable.h"
+#include "core/variant/variant.h"
+
+class GDScript;
+class GDScriptFunction;
+class GDScriptInstance;
+
+class GDScriptLambdaCallable : public CallableCustom {
+	GDScriptFunction *function = nullptr;
+	Ref<GDScript> script;
+	uint32_t h;
+
+	Vector<Variant> captures;
+
+	static bool compare_equal(const CallableCustom *p_a, const CallableCustom *p_b);
+	static bool compare_less(const CallableCustom *p_a, const CallableCustom *p_b);
+
+public:
+	uint32_t hash() const override;
+	String get_as_text() const override;
+	CompareEqualFunc get_compare_equal_func() const override;
+	CompareLessFunc get_compare_less_func() const override;
+	ObjectID get_object() const override;
+	void call(const Variant **p_arguments, int p_argcount, Variant &r_return_value, Callable::CallError &r_call_error) const override;
+
+	GDScriptLambdaCallable(Ref<GDScript> p_script, GDScriptFunction *p_function, const Vector<Variant> &p_captures);
+	virtual ~GDScriptLambdaCallable() = default;
+};
+
+#endif // GDSCRIPT_LAMBDA_CALLABLE

modules/gdscript/gdscript_parser.cpp

@@ -4032,11 +4032,11 @@ void GDScriptParser::TreePrinter::print_if(IfNode *p_if, bool p_is_elif) {
 void GDScriptParser::TreePrinter::print_lambda(LambdaNode *p_lambda) {
 	print_function(p_lambda->function, "Lambda");
 	push_text("| captures [ ");
-	for (const Map<StringName, IdentifierNode *>::Element *E = p_lambda->captures.front(); E; E = E->next()) {
-		push_text(E->key().operator String());
-		if (E->next()) {
+	for (int i = 0; i < p_lambda->captures.size(); i++) {
+		if (i > 0) {
 			push_text(" , ");
 		}
+		push_text(p_lambda->captures[i]->name.operator String());
 	}
 	push_line(" ]");
 }

modules/gdscript/gdscript_parser.h

@@ -796,7 +796,8 @@ public:
 	struct LambdaNode : public ExpressionNode {
 		FunctionNode *function = nullptr;
 		FunctionNode *parent_function = nullptr;
-		Map<StringName, IdentifierNode *> captures;
+		Vector<IdentifierNode *> captures;
+		Map<StringName, int> captures_indices;
 
 		bool has_name() const {
 			return function && function->identifier;

modules/gdscript/gdscript_vm.cpp

@@ -33,6 +33,7 @@
 #include "core/core_string_names.h"
 #include "core/os/os.h"
 #include "gdscript.h"
+#include "gdscript_lambda_callable.h"
 
 Variant *GDScriptFunction::_get_variant(int p_address, GDScriptInstance *p_instance, Variant *p_stack, String &r_error) const {
 	int address = p_address & ADDR_MASK;
@@ -232,6 +233,7 @@ String GDScriptFunction::_get_call_error(const Callable::CallError &p_err, const
 		&&OPCODE_CALL_PTRCALL_PACKED_COLOR_ARRAY,    \
 		&&OPCODE_AWAIT,                              \
 		&&OPCODE_AWAIT_RESUME,                       \
+		&&OPCODE_CREATE_LAMBDA,                      \
 		&&OPCODE_JUMP,                               \
 		&&OPCODE_JUMP_IF,                            \
 		&&OPCODE_JUMP_IF_NOT,                        \
@@ -1452,13 +1454,17 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 				if (err.error != Callable::CallError::CALL_OK) {
 					String methodstr = *methodname;
 					String basestr = _get_var_type(base);
+					bool is_callable = false;
 
 					if (methodstr == "call") {
-						if (argc >= 1) {
+						if (argc >= 1 && base->get_type() != Variant::CALLABLE) {
 							methodstr = String(*argptrs[0]) + " (via call)";
 							if (err.error == Callable::CallError::CALL_ERROR_INVALID_ARGUMENT) {
 								err.argument += 1;
 							}
+						} else {
+							methodstr = base->operator String() + " (Callable)";
+							is_callable = true;
 						}
 					} else if (methodstr == "free") {
 						if (err.error == Callable::CallError::CALL_ERROR_INVALID_METHOD) {
@@ -1478,7 +1484,7 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 							}
 						}
 					}
-					err_text = _get_call_error(err, "function '" + methodstr + "' in base '" + basestr + "'", (const Variant **)argptrs);
+					err_text = _get_call_error(err, "function '" + methodstr + (is_callable ? "" : "' in base '" + basestr) + "'", (const Variant **)argptrs);
 					OPCODE_BREAK;
 				}
 #endif
@@ -2057,6 +2063,34 @@ Variant GDScriptFunction::call(GDScriptInstance *p_instance, const Variant **p_a
 			}
 			DISPATCH_OPCODE;
 
+			OPCODE(OPCODE_CREATE_LAMBDA) {
+				CHECK_SPACE(2 + instr_arg_count);
+
+				ip += instr_arg_count;
+
+				int captures_count = _code_ptr[ip + 1];
+				GD_ERR_BREAK(captures_count < 0);
+
+				int lambda_index = _code_ptr[ip + 2];
+				GD_ERR_BREAK(lambda_index < 0 || lambda_index >= _lambdas_count);
+				GDScriptFunction *lambda = _lambdas_ptr[lambda_index];
+
+				Vector<Variant> captures;
+				captures.resize(captures_count);
+				for (int i = 0; i < captures_count; i++) {
+					GET_INSTRUCTION_ARG(arg, i);
+					captures.write[i] = *arg;
+				}
+
+				GDScriptLambdaCallable *callable = memnew(GDScriptLambdaCallable(Ref<GDScript>(script), lambda, captures));
+
+				GET_INSTRUCTION_ARG(result, captures_count);
+				*result = Callable(callable);
+
+				ip += 3;
+			}
+			DISPATCH_OPCODE;
+
 			OPCODE(OPCODE_JUMP) {
 				CHECK_SPACE(2);
 				int to = _code_ptr[ip + 1];