From 067704f1cd6e169d8c9382b755a26c4880a2f941 Mon Sep 17 00:00:00 2001
From: Aaron Franke <arnfranke@yahoo.com>
Date: Sun, 8 Oct 2023 16:22:25 -0500
Subject: [PATCH] Add a keyword for abstract classes in GDScript

Co-authored-by: Danil Alexeev <danil@alexeev.xyz>
---
 doc/classes/ScriptExtension.xml               |  2 +-
 editor/create_dialog.cpp                      |  4 +
 modules/gdscript/gdscript.cpp                 |  1 +
 modules/gdscript/gdscript.h                   |  3 +-
 modules/gdscript/gdscript_analyzer.cpp        | 13 ++-
 modules/gdscript/gdscript_compiler.cpp        |  1 +
 modules/gdscript/gdscript_editor.cpp          |  2 +-
 modules/gdscript/gdscript_parser.cpp          | 97 ++++++++++++++-----
 modules/gdscript/gdscript_parser.h            | 19 ++--
 modules/gdscript/gdscript_tokenizer.cpp       |  4 +
 modules/gdscript/gdscript_tokenizer.h         |  1 +
 .../errors/construct_abstract_class.gd        | 10 ++
 .../errors/construct_abstract_class.out       |  3 +
 .../construct_abstract_script.notest.gd       |  1 +
 .../features/extend_abstract_class.gd         |  9 +-
 .../parser/errors/duplicate_abstract.gd       |  7 ++
 .../parser/errors/duplicate_abstract.out      |  2 +
 17 files changed, 137 insertions(+), 42 deletions(-)
 create mode 100644 modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.gd
 create mode 100644 modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.out
 create mode 100644 modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_script.notest.gd
 create mode 100644 modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.gd
 create mode 100644 modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.out

diff --git a/doc/classes/ScriptExtension.xml b/doc/classes/ScriptExtension.xml
index 0a4b81d442..17742534b1 100644
--- a/doc/classes/ScriptExtension.xml
+++ b/doc/classes/ScriptExtension.xml
@@ -162,7 +162,7 @@
 		<method name="_is_abstract" qualifiers="virtual const">
 			<return type="bool" />
 			<description>
-				Returns [code]true[/code] if the script is an abstract script. An abstract script does not have a constructor and cannot be instantiated.
+				Returns [code]true[/code] if the script is an abstract script. Abstract scripts cannot be instantiated directly, instead other scripts should inherit them. Abstract scripts will be either unselectable or hidden in the Create New Node dialog (unselectable if there are non-abstract classes inheriting it, otherwise hidden).
 			</description>
 		</method>
 		<method name="_is_placeholder_fallback_enabled" qualifiers="virtual const">
diff --git a/editor/create_dialog.cpp b/editor/create_dialog.cpp
index 1301960ad1..906f1a2a4a 100644
--- a/editor/create_dialog.cpp
+++ b/editor/create_dialog.cpp
@@ -219,6 +219,10 @@ bool CreateDialog::_should_hide_type(const StringName &p_type) const {
 				i = script_path.find_char('/', i + 1);
 			}
 		}
+		// Abstract scripts cannot be instantiated.
+		String path = ScriptServer::get_global_class_path(p_type);
+		Ref<Script> scr = ResourceLoader::load(path, "Script");
+		return scr.is_null() || scr->is_abstract();
 	}
 
 	return false;
diff --git a/modules/gdscript/gdscript.cpp b/modules/gdscript/gdscript.cpp
index 0d229c04d6..aaea09c52d 100644
--- a/modules/gdscript/gdscript.cpp
+++ b/modules/gdscript/gdscript.cpp
@@ -2747,6 +2747,7 @@ void GDScriptLanguage::get_reserved_words(List<String> *p_words) const {
 		"when",
 		"while",
 		// Declarations.
+		"abstract",
 		"class",
 		"class_name",
 		"const",
diff --git a/modules/gdscript/gdscript.h b/modules/gdscript/gdscript.h
index 3267db83dc..dbdac757f1 100644
--- a/modules/gdscript/gdscript.h
+++ b/modules/gdscript/gdscript.h
@@ -62,6 +62,7 @@ class GDScript : public Script {
 	bool tool = false;
 	bool valid = false;
 	bool reloading = false;
+	bool _is_abstract = false;
 
 	struct MemberInfo {
 		int index = 0;
@@ -247,7 +248,6 @@ public:
 	void cancel_pending_functions(bool warn);
 
 	virtual bool is_valid() const override { return valid; }
-	virtual bool is_abstract() const override { return false; } // GDScript does not support abstract classes.
 
 	bool inherits_script(const Ref<Script> &p_script) const override;
 
@@ -280,6 +280,7 @@ public:
 	virtual void get_script_signal_list(List<MethodInfo> *r_signals) const override;
 
 	bool is_tool() const override { return tool; }
+	bool is_abstract() const override { return _is_abstract; }
 	Ref<GDScript> get_base() const;
 
 	const HashMap<StringName, MemberInfo> &debug_get_member_indices() const { return member_indices; }
diff --git a/modules/gdscript/gdscript_analyzer.cpp b/modules/gdscript/gdscript_analyzer.cpp
index ce223a8836..b2de61cf1b 100644
--- a/modules/gdscript/gdscript_analyzer.cpp
+++ b/modules/gdscript/gdscript_analyzer.cpp
@@ -3573,10 +3573,15 @@ void GDScriptAnalyzer::reduce_call(GDScriptParser::CallNode *p_call, bool p_is_a
 
 	bool is_constructor = (base_type.is_meta_type || (p_call->callee && p_call->callee->type == GDScriptParser::Node::IDENTIFIER)) && p_call->function_name == SNAME("new");
 
-	if (is_constructor && Engine::get_singleton()->has_singleton(base_type.native_type)) {
-		push_error(vformat(R"(Cannot construct native class "%s" because it is an engine singleton.)", base_type.native_type), p_call);
-		p_call->set_datatype(call_type);
-		return;
+	if (is_constructor) {
+		if (Engine::get_singleton()->has_singleton(base_type.native_type)) {
+			push_error(vformat(R"(Cannot construct native class "%s" because it is an engine singleton.)", base_type.native_type), p_call);
+			p_call->set_datatype(call_type);
+			return;
+		}
+		if ((base_type.kind == GDScriptParser::DataType::CLASS && base_type.class_type->is_abstract) || (base_type.kind == GDScriptParser::DataType::SCRIPT && base_type.script_type.is_valid() && base_type.script_type->is_abstract())) {
+			push_error(vformat(R"(Cannot construct abstract class "%s".)", base_type.to_string()), p_call);
+		}
 	}
 
 	if (get_function_signature(p_call, is_constructor, base_type, p_call->function_name, return_type, par_types, default_arg_count, method_flags)) {
diff --git a/modules/gdscript/gdscript_compiler.cpp b/modules/gdscript/gdscript_compiler.cpp
index 4e7c5ce360..2e6fe46f8e 100644
--- a/modules/gdscript/gdscript_compiler.cpp
+++ b/modules/gdscript/gdscript_compiler.cpp
@@ -2710,6 +2710,7 @@ Error GDScriptCompiler::_prepare_compilation(GDScript *p_script, const GDScriptP
 	p_script->clearing = false;
 
 	p_script->tool = parser->is_tool();
+	p_script->_is_abstract = p_class->is_abstract;
 
 	if (p_script->local_name != StringName()) {
 		if (ClassDB::class_exists(p_script->local_name) && ClassDB::is_class_exposed(p_script->local_name)) {
diff --git a/modules/gdscript/gdscript_editor.cpp b/modules/gdscript/gdscript_editor.cpp
index c8f51b25f5..4cd011ab50 100644
--- a/modules/gdscript/gdscript_editor.cpp
+++ b/modules/gdscript/gdscript_editor.cpp
@@ -1491,7 +1491,7 @@ static void _find_identifiers(const GDScriptParser::CompletionContext &p_context
 
 	static const char *_keywords_with_space[] = {
 		"and", "not", "or", "in", "as", "class", "class_name", "extends", "is", "func", "signal", "await",
-		"const", "enum", "static", "var", "if", "elif", "else", "for", "match", "when", "while",
+		"const", "enum", "abstract", "static", "var", "if", "elif", "else", "for", "match", "when", "while",
 		nullptr
 	};
 
diff --git a/modules/gdscript/gdscript_parser.cpp b/modules/gdscript/gdscript_parser.cpp
index fd3a17a04a..a225d2fa6f 100644
--- a/modules/gdscript/gdscript_parser.cpp
+++ b/modules/gdscript/gdscript_parser.cpp
@@ -633,7 +633,8 @@ void GDScriptParser::parse_program() {
 					PUSH_PENDING_ANNOTATIONS_TO_HEAD;
 					if (annotation->name == SNAME("@tool") || annotation->name == SNAME("@icon")) {
 						// Some annotations need to be resolved and applied in the parser.
-						annotation->apply(this, head, nullptr); // `head->outer == nullptr`.
+						// The root class is not in any class, so `head->outer == nullptr`.
+						annotation->apply(this, head, nullptr);
 					} else {
 						head->annotations.push_back(annotation);
 					}
@@ -677,9 +678,25 @@ void GDScriptParser::parse_program() {
 		reset_extents(head, current);
 	}
 
+	bool has_early_abstract = false;
 	while (can_have_class_or_extends) {
 		// Order here doesn't matter, but there should be only one of each at most.
 		switch (current.type) {
+			case GDScriptTokenizer::Token::ABSTRACT: {
+				PUSH_PENDING_ANNOTATIONS_TO_HEAD;
+				if (head->start_line == 1) {
+					reset_extents(head, current);
+				}
+				advance();
+				if (has_early_abstract) {
+					push_error(R"(Expected "class_name", "extends", or "class" after "abstract".)");
+				} else {
+					has_early_abstract = true;
+				}
+				if (current.type == GDScriptTokenizer::Token::NEWLINE) {
+					end_statement("class_name abstract");
+				}
+			} break;
 			case GDScriptTokenizer::Token::CLASS_NAME:
 				PUSH_PENDING_ANNOTATIONS_TO_HEAD;
 				advance();
@@ -688,6 +705,10 @@ void GDScriptParser::parse_program() {
 				} else {
 					parse_class_name();
 				}
+				if (has_early_abstract) {
+					head->is_abstract = true;
+					has_early_abstract = false;
+				}
 				break;
 			case GDScriptTokenizer::Token::EXTENDS:
 				PUSH_PENDING_ANNOTATIONS_TO_HEAD;
@@ -698,6 +719,10 @@ void GDScriptParser::parse_program() {
 					parse_extends();
 					end_statement("superclass");
 				}
+				if (has_early_abstract) {
+					head->is_abstract = true;
+					has_early_abstract = false;
+				}
 				break;
 			case GDScriptTokenizer::Token::TK_EOF:
 				PUSH_PENDING_ANNOTATIONS_TO_HEAD;
@@ -732,7 +757,7 @@ void GDScriptParser::parse_program() {
 
 #undef PUSH_PENDING_ANNOTATIONS_TO_HEAD
 
-	parse_class_body(true);
+	parse_class_body(has_early_abstract, true);
 
 	head->end_line = current.end_line;
 	head->end_column = current.end_column;
@@ -837,12 +862,13 @@ bool GDScriptParser::has_class(const GDScriptParser::ClassNode *p_class) const {
 	return false;
 }
 
-GDScriptParser::ClassNode *GDScriptParser::parse_class(bool p_is_static) {
+GDScriptParser::ClassNode *GDScriptParser::parse_class(bool p_is_abstract, bool p_is_static) {
 	ClassNode *n_class = alloc_node<ClassNode>();
 
 	ClassNode *previous_class = current_class;
 	current_class = n_class;
 	n_class->outer = previous_class;
+	n_class->is_abstract = p_is_abstract;
 
 	if (consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected identifier for the class name after "class".)")) {
 		n_class->identifier = parse_identifier();
@@ -879,7 +905,7 @@ GDScriptParser::ClassNode *GDScriptParser::parse_class(bool p_is_static) {
 		end_statement("superclass");
 	}
 
-	parse_class_body(multiline);
+	parse_class_body(false, multiline);
 	complete_extents(n_class);
 
 	if (multiline) {
@@ -938,7 +964,7 @@ void GDScriptParser::parse_extends() {
 }
 
 template <typename T>
-void GDScriptParser::parse_class_member(T *(GDScriptParser::*p_parse_function)(bool), AnnotationInfo::TargetKind p_target, const String &p_member_kind, bool p_is_static) {
+void GDScriptParser::parse_class_member(T *(GDScriptParser::*p_parse_function)(bool, bool), AnnotationInfo::TargetKind p_target, const String &p_member_kind, bool p_is_abstract, bool p_is_static) {
 	advance();
 
 	// Consume annotations.
@@ -954,7 +980,7 @@ void GDScriptParser::parse_class_member(T *(GDScriptParser::*p_parse_function)(b
 		}
 	}
 
-	T *member = (this->*p_parse_function)(p_is_static);
+	T *member = (this->*p_parse_function)(p_is_abstract, p_is_static);
 	if (member == nullptr) {
 		return;
 	}
@@ -1008,14 +1034,29 @@ void GDScriptParser::parse_class_member(T *(GDScriptParser::*p_parse_function)(b
 	}
 }
 
-void GDScriptParser::parse_class_body(bool p_is_multiline) {
+void GDScriptParser::parse_class_body(bool p_is_abstract, bool p_is_multiline) {
 	bool class_end = false;
+	// The header parsing code might have skipped over abstract, so we start by checking the previous token.
+	bool next_is_abstract = p_is_abstract;
+	if (next_is_abstract && (current.type != GDScriptTokenizer::Token::CLASS_NAME && current.type != GDScriptTokenizer::Token::CLASS)) {
+		push_error(R"(Expected "class_name" or "class" after "abstract".)");
+	}
 	bool next_is_static = false;
 	while (!class_end && !is_at_end()) {
 		GDScriptTokenizer::Token token = current;
 		switch (token.type) {
+			case GDScriptTokenizer::Token::ABSTRACT: {
+				advance();
+				next_is_abstract = true;
+				if (check(GDScriptTokenizer::Token::NEWLINE)) {
+					advance();
+				}
+				if (!check(GDScriptTokenizer::Token::CLASS_NAME) && !check(GDScriptTokenizer::Token::CLASS)) {
+					push_error(R"(Expected "class_name" or "class" after "abstract".)");
+				}
+			} break;
 			case GDScriptTokenizer::Token::VAR:
-				parse_class_member(&GDScriptParser::parse_variable, AnnotationInfo::VARIABLE, "variable", next_is_static);
+				parse_class_member(&GDScriptParser::parse_variable, AnnotationInfo::VARIABLE, "variable", false, next_is_static);
 				if (next_is_static) {
 					current_class->has_static_data = true;
 				}
@@ -1027,11 +1068,12 @@ void GDScriptParser::parse_class_body(bool p_is_multiline) {
 				parse_class_member(&GDScriptParser::parse_signal, AnnotationInfo::SIGNAL, "signal");
 				break;
 			case GDScriptTokenizer::Token::FUNC:
-				parse_class_member(&GDScriptParser::parse_function, AnnotationInfo::FUNCTION, "function", next_is_static);
-				break;
-			case GDScriptTokenizer::Token::CLASS:
-				parse_class_member(&GDScriptParser::parse_class, AnnotationInfo::CLASS, "class");
+				parse_class_member(&GDScriptParser::parse_function, AnnotationInfo::FUNCTION, "function", false, next_is_static);
 				break;
+			case GDScriptTokenizer::Token::CLASS: {
+				parse_class_member(&GDScriptParser::parse_class, AnnotationInfo::CLASS, "class", next_is_abstract);
+				next_is_abstract = false;
+			} break;
 			case GDScriptTokenizer::Token::ENUM:
 				parse_class_member(&GDScriptParser::parse_enum, AnnotationInfo::NONE, "enum");
 				break;
@@ -1122,11 +1164,11 @@ void GDScriptParser::parse_class_body(bool p_is_multiline) {
 	}
 }
 
-GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_static) {
-	return parse_variable(p_is_static, true);
+GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_abstract, bool p_is_static) {
+	return parse_variable(p_is_abstract, p_is_static, true);
 }
 
-GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_static, bool p_allow_property) {
+GDScriptParser::VariableNode *GDScriptParser::parse_variable(bool p_is_abstract, bool p_is_static, bool p_allow_property) {
 	VariableNode *variable = alloc_node<VariableNode>();
 
 	if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected variable name after "var".)")) {
@@ -1362,7 +1404,7 @@ void GDScriptParser::parse_property_getter(VariableNode *p_variable) {
 	}
 }
 
-GDScriptParser::ConstantNode *GDScriptParser::parse_constant(bool p_is_static) {
+GDScriptParser::ConstantNode *GDScriptParser::parse_constant(bool p_is_abstract, bool p_is_static) {
 	ConstantNode *constant = alloc_node<ConstantNode>();
 
 	if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected constant name after "const".)")) {
@@ -1430,7 +1472,7 @@ GDScriptParser::ParameterNode *GDScriptParser::parse_parameter() {
 	return parameter;
 }
 
-GDScriptParser::SignalNode *GDScriptParser::parse_signal(bool p_is_static) {
+GDScriptParser::SignalNode *GDScriptParser::parse_signal(bool p_is_abstract, bool p_is_static) {
 	SignalNode *signal = alloc_node<SignalNode>();
 
 	if (!consume(GDScriptTokenizer::Token::IDENTIFIER, R"(Expected signal name after "signal".)")) {
@@ -1475,7 +1517,7 @@ GDScriptParser::SignalNode *GDScriptParser::parse_signal(bool p_is_static) {
 	return signal;
 }
 
-GDScriptParser::EnumNode *GDScriptParser::parse_enum(bool p_is_static) {
+GDScriptParser::EnumNode *GDScriptParser::parse_enum(bool p_is_abstract, bool p_is_static) {
 	EnumNode *enum_node = alloc_node<EnumNode>();
 	bool named = false;
 
@@ -1628,7 +1670,7 @@ void GDScriptParser::parse_function_signature(FunctionNode *p_function, SuiteNod
 	consume(GDScriptTokenizer::Token::COLON, vformat(R"(Expected ":" after %s declaration.)", p_type));
 }
 
-GDScriptParser::FunctionNode *GDScriptParser::parse_function(bool p_is_static) {
+GDScriptParser::FunctionNode *GDScriptParser::parse_function(bool p_is_abstract, bool p_is_static) {
 	FunctionNode *function = alloc_node<FunctionNode>();
 
 	make_completion_context(COMPLETION_OVERRIDE_METHOD, function);
@@ -1893,11 +1935,11 @@ GDScriptParser::Node *GDScriptParser::parse_statement() {
 			break;
 		case GDScriptTokenizer::Token::VAR:
 			advance();
-			result = parse_variable(false, false);
+			result = parse_variable(false, false, false);
 			break;
 		case GDScriptTokenizer::Token::TK_CONST:
 			advance();
-			result = parse_constant(false);
+			result = parse_constant(false, false);
 			break;
 		case GDScriptTokenizer::Token::IF:
 			advance();
@@ -4110,6 +4152,7 @@ GDScriptParser::ParseRule *GDScriptParser::get_rule(GDScriptTokenizer::Token::Ty
 		{ nullptr,                                          nullptr,                                        PREC_NONE }, // MATCH,
 		{ nullptr,                                          nullptr,                                        PREC_NONE }, // WHEN,
 		// Keywords
+		{ nullptr,                                          nullptr,                                        PREC_NONE }, // ABSTRACT
 		{ nullptr,                                          &GDScriptParser::parse_cast,                 	PREC_CAST }, // AS,
 		{ nullptr,                                          nullptr,                                        PREC_NONE }, // ASSERT,
 		{ &GDScriptParser::parse_await,                  	nullptr,                                        PREC_NONE }, // AWAIT,
@@ -5676,6 +5719,9 @@ void GDScriptParser::TreePrinter::print_cast(CastNode *p_cast) {
 }
 
 void GDScriptParser::TreePrinter::print_class(ClassNode *p_class) {
+	if (p_class->is_abstract) {
+		push_text("Abstract ");
+	}
 	push_text("Class ");
 	if (p_class->identifier == nullptr) {
 		push_text("<unnamed>");
@@ -6301,17 +6347,18 @@ void GDScriptParser::TreePrinter::print_while(WhileNode *p_while) {
 }
 
 void GDScriptParser::TreePrinter::print_tree(const GDScriptParser &p_parser) {
-	ERR_FAIL_NULL_MSG(p_parser.get_tree(), "Parse the code before printing the parse tree.");
+	ClassNode *class_tree = p_parser.get_tree();
+	ERR_FAIL_NULL_MSG(class_tree, "Parse the code before printing the parse tree.");
 
 	if (p_parser.is_tool()) {
 		push_line("@tool");
 	}
-	if (!p_parser.get_tree()->icon_path.is_empty()) {
+	if (!class_tree->icon_path.is_empty()) {
 		push_text(R"(@icon (")");
-		push_text(p_parser.get_tree()->icon_path);
+		push_text(class_tree->icon_path);
 		push_line("\")");
 	}
-	print_class(p_parser.get_tree());
+	print_class(class_tree);
 
 	print_line(String(printed));
 }
diff --git a/modules/gdscript/gdscript_parser.h b/modules/gdscript/gdscript_parser.h
index 47eab0c342..ee246c762a 100644
--- a/modules/gdscript/gdscript_parser.h
+++ b/modules/gdscript/gdscript_parser.h
@@ -748,6 +748,7 @@ public:
 		ClassNode *outer = nullptr;
 		bool extends_used = false;
 		bool onready_used = false;
+		bool is_abstract = false;
 		bool has_static_data = false;
 		bool annotated_static_unload = false;
 		String extends_path;
@@ -1499,16 +1500,16 @@ private:
 
 	// Main blocks.
 	void parse_program();
-	ClassNode *parse_class(bool p_is_static);
+	ClassNode *parse_class(bool p_is_abstract, bool p_is_static);
 	void parse_class_name();
 	void parse_extends();
-	void parse_class_body(bool p_is_multiline);
+	void parse_class_body(bool p_is_abstract, bool p_is_multiline);
 	template <typename T>
-	void parse_class_member(T *(GDScriptParser::*p_parse_function)(bool), AnnotationInfo::TargetKind p_target, const String &p_member_kind, bool p_is_static = false);
-	SignalNode *parse_signal(bool p_is_static);
-	EnumNode *parse_enum(bool p_is_static);
+	void parse_class_member(T *(GDScriptParser::*p_parse_function)(bool, bool), AnnotationInfo::TargetKind p_target, const String &p_member_kind, bool p_is_abstract = false, bool p_is_static = false);
+	SignalNode *parse_signal(bool p_is_abstract, bool p_is_static);
+	EnumNode *parse_enum(bool p_is_abstract, bool p_is_static);
 	ParameterNode *parse_parameter();
-	FunctionNode *parse_function(bool p_is_static);
+	FunctionNode *parse_function(bool p_is_abstract, bool p_is_static);
 	void parse_function_signature(FunctionNode *p_function, SuiteNode *p_body, const String &p_type);
 	SuiteNode *parse_suite(const String &p_context, SuiteNode *p_suite = nullptr, bool p_for_lambda = false);
 	// Annotations
@@ -1532,12 +1533,12 @@ private:
 	bool rpc_annotation(AnnotationNode *p_annotation, Node *p_target, ClassNode *p_class);
 	// Statements.
 	Node *parse_statement();
-	VariableNode *parse_variable(bool p_is_static);
-	VariableNode *parse_variable(bool p_is_static, bool p_allow_property);
+	VariableNode *parse_variable(bool p_is_abstract, bool p_is_static);
+	VariableNode *parse_variable(bool p_is_abstract, bool p_is_static, bool p_allow_property);
 	VariableNode *parse_property(VariableNode *p_variable, bool p_need_indent);
 	void parse_property_getter(VariableNode *p_variable);
 	void parse_property_setter(VariableNode *p_variable);
-	ConstantNode *parse_constant(bool p_is_static);
+	ConstantNode *parse_constant(bool p_is_abstract, bool p_is_static);
 	AssertNode *parse_assert();
 	BreakNode *parse_break();
 	ContinueNode *parse_continue();
diff --git a/modules/gdscript/gdscript_tokenizer.cpp b/modules/gdscript/gdscript_tokenizer.cpp
index c1cdb11814..93a06b2b76 100644
--- a/modules/gdscript/gdscript_tokenizer.cpp
+++ b/modules/gdscript/gdscript_tokenizer.cpp
@@ -101,6 +101,7 @@ static const char *token_names[] = {
 	"match", // MATCH,
 	"when", // WHEN,
 	// Keywords
+	"abstract", // ABSTRACT,
 	"as", // AS,
 	"assert", // ASSERT,
 	"await", // AWAIT,
@@ -198,6 +199,7 @@ bool GDScriptTokenizer::Token::is_identifier() const {
 		case IDENTIFIER:
 		case MATCH: // Used in String.match().
 		case WHEN: // New keyword, avoid breaking existing code.
+		case ABSTRACT:
 		// Allow constants to be treated as regular identifiers.
 		case CONST_PI:
 		case CONST_INF:
@@ -213,6 +215,7 @@ bool GDScriptTokenizer::Token::is_node_name() const {
 	// This is meant to allow keywords with the $ notation, but not as general identifiers.
 	switch (type) {
 		case IDENTIFIER:
+		case ABSTRACT:
 		case AND:
 		case AS:
 		case ASSERT:
@@ -495,6 +498,7 @@ GDScriptTokenizer::Token GDScriptTokenizerText::annotation() {
 
 #define KEYWORDS(KEYWORD_GROUP, KEYWORD)     \
 	KEYWORD_GROUP('a')                       \
+	KEYWORD("abstract", Token::ABSTRACT)     \
 	KEYWORD("as", Token::AS)                 \
 	KEYWORD("and", Token::AND)               \
 	KEYWORD("assert", Token::ASSERT)         \
diff --git a/modules/gdscript/gdscript_tokenizer.h b/modules/gdscript/gdscript_tokenizer.h
index e8c02efa1f..cfaa2aae05 100644
--- a/modules/gdscript/gdscript_tokenizer.h
+++ b/modules/gdscript/gdscript_tokenizer.h
@@ -105,6 +105,7 @@ public:
 			MATCH,
 			WHEN,
 			// Keywords
+			ABSTRACT,
 			AS,
 			ASSERT,
 			AWAIT,
diff --git a/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.gd b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.gd
new file mode 100644
index 0000000000..394e728510
--- /dev/null
+++ b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.gd
@@ -0,0 +1,10 @@
+extends RefCounted
+
+const AbstractScript = preload("./construct_abstract_script.notest.gd")
+
+abstract class AbstractClass:
+	pass
+
+func test():
+	var _a := AbstractScript.new()
+	var _b := AbstractClass.new()
diff --git a/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.out b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.out
new file mode 100644
index 0000000000..51b73e6f2d
--- /dev/null
+++ b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_class.out
@@ -0,0 +1,3 @@
+GDTEST_ANALYZER_ERROR
+>> ERROR at line 9: Cannot construct abstract class "AbstractScript".
+>> ERROR at line 10: Cannot construct abstract class "AbstractClass".
diff --git a/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_script.notest.gd b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_script.notest.gd
new file mode 100644
index 0000000000..feac3d8251
--- /dev/null
+++ b/modules/gdscript/tests/scripts/analyzer/errors/construct_abstract_script.notest.gd
@@ -0,0 +1 @@
+abstract class_name AbstractScript
diff --git a/modules/gdscript/tests/scripts/analyzer/features/extend_abstract_class.gd b/modules/gdscript/tests/scripts/analyzer/features/extend_abstract_class.gd
index 95c3268130..0a6e0378a1 100644
--- a/modules/gdscript/tests/scripts/analyzer/features/extend_abstract_class.gd
+++ b/modules/gdscript/tests/scripts/analyzer/features/extend_abstract_class.gd
@@ -8,5 +8,12 @@ class B extends A:
 class C extends CanvasItem:
 	pass
 
+abstract class X:
+	pass
+
+class Y extends X:
+	func test() -> String:
+		return "ok"
+
 func test():
-	print('ok')
+	print(Y.new().test())
diff --git a/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.gd b/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.gd
new file mode 100644
index 0000000000..3bca7d4a0d
--- /dev/null
+++ b/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.gd
@@ -0,0 +1,7 @@
+extends RefCounted
+
+abstract abstract class A:
+	pass
+
+func test():
+	pass
diff --git a/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.out b/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.out
new file mode 100644
index 0000000000..5ebfac7c74
--- /dev/null
+++ b/modules/gdscript/tests/scripts/parser/errors/duplicate_abstract.out
@@ -0,0 +1,2 @@
+GDTEST_PARSER_ERROR
+Expected "class_name", "extends", or "class" after "abstract".