[GDScript]: Add a strong type for the self identifier

modules/gdscript/gdscript_analyzer.cpp

@@ -898,6 +898,17 @@ GDScriptParser::DataType GDScriptAnalyzer::resolve_datatype(GDScriptParser::Type
 		}
 	}
 
+	if (!result.is_set() && first == SNAME("Self")) {
+		// Strong type for the `self` identifier. Resolves to the current class
+		// meta-type so it behaves like using the current class name directly.
+		if (parser->current_class) {
+			result = parser->current_class->datatype;
+		} else {
+			push_error(R"("Self" can only be used inside a class.)", p_type);
+			return bad_type;
+		}
+	}
+
 	if (!result.is_set()) {
 		push_error(vformat(R"(Could not find type "%s" in the current scope.)", first), p_type);
 		return bad_type;
@@ -4650,6 +4661,24 @@ void GDScriptAnalyzer::reduce_identifier(GDScriptParser::IdentifierNode *p_ident
 		return;
 	}
 
+	// Allow "Self" here, as a value it resolves to the current class meta-type.
+	// This enables expressions like `Self.new()` or `Self.my_static()` to work.
+	if (name == SNAME("Self")) {
+		if (parser->current_class == nullptr) {
+			push_error(R"("Self" can only be used inside a class.)", p_identifier);
+		} else {
+			p_identifier->datatype = parser->current_class->datatype;
+
+			Error err = OK;
+			Ref<GDScript> scr = get_depended_shallow_script(parser->current_class->datatype.script_path, err);
+			if (!err && scr.is_valid()) {
+				p_identifier->reduced_value = scr->find_class(parser->current_class->datatype.class_type->fqcn);
+				p_identifier->is_constant = true;
+			}
+		}
+		return;
+	}
+
 	// Not found.
 #ifdef SUGGEST_GODOT4_RENAMES
 	String rename_hint;

modules/gdscript/gdscript_compiler.cpp

@@ -478,6 +478,11 @@ GDScriptCodeGenerator::Address GDScriptCompiler::_parse_expression(CodeGen &code
 				} break;
 			}
 
+			// Special-case: `Self` refers to the current class meta-type.
+			if (identifier == SNAME("Self")) {
+				return GDScriptCodeGenerator::Address(GDScriptCodeGenerator::Address::CLASS);
+			}
+
 			// Not found, error.
 			_set_error("Identifier not found: " + String(identifier), p_expression);
 			r_error = ERR_COMPILATION_FAILED;

modules/gdscript/tests/scripts/analyzer/features/self_type_already_in_use.gd

@@ -0,0 +1,11 @@
+class Self:
+	var value := "OK"
+
+class TestClass:
+	static func make() -> Self:
+		return Self.new()
+
+func test():
+	var x := TestClass.make()
+	prints(x != null, x is Self)
+	prints(x.value)

modules/gdscript/tests/scripts/analyzer/features/self_type_already_in_use.out

@@ -0,0 +1,3 @@
+GDTEST_OK
+true true
+OK

modules/gdscript/tests/scripts/analyzer/features/self_type_in_typed_collections.gd

@@ -0,0 +1,11 @@
+var list: Array[Self] = []
+var dict: Dictionary[String, Self] = {}
+
+func test():
+	list.append(self)
+	print(list.size() == 1 and list.back() is Self)
+	list.clear()
+
+	dict["self"] = self
+	print(dict.has("self") and dict["self"] is Self)
+	dict.clear()

modules/gdscript/tests/scripts/analyzer/features/self_type_in_typed_collections.out

@@ -0,0 +1,3 @@
+GDTEST_OK
+true
+true

modules/gdscript/tests/scripts/analyzer/features/self_type_nested_enum.gd

@@ -0,0 +1,8 @@
+enum MyEnum { A, B }
+
+func get_enum() -> Self.MyEnum:
+	return MyEnum.A
+
+func test():
+	var e: Self.MyEnum = get_enum()
+	print(int(e) == 0)

modules/gdscript/tests/scripts/analyzer/features/self_type_nested_enum.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+true

modules/gdscript/tests/scripts/analyzer/features/self_type_nested_types.gd

@@ -0,0 +1,9 @@
+class Inner:
+	var val := "OK"
+
+func make_inner() -> Self.Inner:
+	return Self.Inner.new()
+
+func test():
+	var i: Self.Inner = make_inner()
+	print(i.val)

modules/gdscript/tests/scripts/analyzer/features/self_type_nested_types.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+OK

modules/gdscript/tests/scripts/analyzer/features/self_type_reference.gd

@@ -0,0 +1,3 @@
+func test():
+	var x: Self = self
+	print(x is Self)

modules/gdscript/tests/scripts/analyzer/features/self_type_reference.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+true

modules/gdscript/tests/scripts/parser/self_type_parsing.gd

@@ -0,0 +1,9 @@
+var a: Self
+var b: Array[Self]
+var c: Dictionary[String, Self]
+
+func f(_x: Self) -> Self:
+	return self
+
+func test():
+	pass

modules/gdscript/tests/scripts/parser/self_type_parsing.out

@@ -0,0 +1 @@
+GDTEST_OK

modules/gdscript/tests/scripts/runtime/features/self_type.gd

@@ -0,0 +1,17 @@
+class FluentInt:
+	var value:int
+
+	static func make(x:int) -> Self:
+		return Self.new(x)
+
+	func _init(x:int):
+		value = x
+	func add_one() -> Self:
+		value += 1
+		return self
+	func add_ten() -> Self:
+		value += 10
+		return self
+
+func test():
+	print(FluentInt.make(100).add_one().add_ten().value)

modules/gdscript/tests/scripts/runtime/features/self_type.out

@@ -0,0 +1,2 @@
+GDTEST_OK
+111