GDScript: Properly validate return type

When the type cannot be validated at compile time, the runtime must do a
check to ensure type safety is kept, as the code might be assuming the
return type is correct in another place, leading to crashes if the
contract is broken.

1 files changed, 79 insertions, 2 deletions

diff --git a/modules/gdscript/gdscript_byte_codegen.cpp b/modules/gdscript/gdscript_byte_codegen.cpp
index e27329d18b..a31d46bbba 100644
--- a/modules/gdscript/gdscript_byte_codegen.cpp
+++ b/modules/gdscript/gdscript_byte_codegen.cpp
@@ -1286,8 +1286,85 @@ void GDScriptByteCodeGenerator::write_newline(int p_line) {
 }
 
 void GDScriptByteCodeGenerator::write_return(const Address &p_return_value) {
-	append(GDScriptFunction::OPCODE_RETURN, 1);
-	append(p_return_value);
+	if (!function->return_type.has_type || p_return_value.type.has_type) {
+		// Either the function is untyped or the return value is also typed.
+
+		// If this is a typed function, then we need to check for potential conversions.
+		if (function->return_type.has_type) {
+			if (function->return_type.kind == GDScriptDataType::BUILTIN && function->return_type.builtin_type == Variant::ARRAY && function->return_type.has_container_element_type()) {
+				// Typed array.
+				const GDScriptDataType &element_type = function->return_type.get_container_element_type();
+
+				Variant script = function->return_type.script_type;
+				int script_idx = get_constant_pos(script);
+				script_idx |= (GDScriptFunction::ADDR_TYPE_LOCAL_CONSTANT << GDScriptFunction::ADDR_BITS);
+
+				append(GDScriptFunction::OPCODE_RETURN_TYPED_ARRAY, 2);
+				append(p_return_value);
+				append(script_idx);
+				append(element_type.kind == GDScriptDataType::BUILTIN ? element_type.builtin_type : Variant::OBJECT);
+				append(element_type.native_type);
+			} else if (function->return_type.kind == GDScriptDataType::BUILTIN && p_return_value.type.kind == GDScriptDataType::BUILTIN && function->return_type.builtin_type != p_return_value.type.builtin_type) {
+				// Add conversion.
+				append(GDScriptFunction::OPCODE_RETURN_TYPED_BUILTIN, 1);
+				append(p_return_value);
+				append(function->return_type.builtin_type);
+			} else {
+				// Just assign.
+				append(GDScriptFunction::OPCODE_RETURN, 1);
+				append(p_return_value);
+			}
+		} else {
+			append(GDScriptFunction::OPCODE_RETURN, 1);
+			append(p_return_value);
+		}
+	} else {
+		switch (function->return_type.kind) {
+			case GDScriptDataType::BUILTIN: {
+				if (function->return_type.builtin_type == Variant::ARRAY && function->return_type.has_container_element_type()) {
+					const GDScriptDataType &element_type = function->return_type.get_container_element_type();
+
+					Variant script = function->return_type.script_type;
+					int script_idx = get_constant_pos(script);
+					script_idx |= (GDScriptFunction::ADDR_TYPE_LOCAL_CONSTANT << GDScriptFunction::ADDR_BITS);
+
+					append(GDScriptFunction::OPCODE_RETURN_TYPED_ARRAY, 2);
+					append(p_return_value);
+					append(script_idx);
+					append(element_type.kind == GDScriptDataType::BUILTIN ? element_type.builtin_type : Variant::OBJECT);
+					append(element_type.native_type);
+				} else {
+					append(GDScriptFunction::OPCODE_RETURN_TYPED_BUILTIN, 1);
+					append(p_return_value);
+					append(function->return_type.builtin_type);
+				}
+			} break;
+			case GDScriptDataType::NATIVE: {
+				append(GDScriptFunction::OPCODE_RETURN_TYPED_NATIVE, 2);
+				append(p_return_value);
+				int class_idx = GDScriptLanguage::get_singleton()->get_global_map()[function->return_type.native_type];
+				class_idx |= (GDScriptFunction::ADDR_TYPE_GLOBAL << GDScriptFunction::ADDR_BITS);
+				append(class_idx);
+			} break;
+			case GDScriptDataType::GDSCRIPT:
+			case GDScriptDataType::SCRIPT: {
+				Variant script = function->return_type.script_type;
+				int script_idx = get_constant_pos(script);
+				script_idx |= (GDScriptFunction::ADDR_TYPE_LOCAL_CONSTANT << GDScriptFunction::ADDR_BITS);
+
+				append(GDScriptFunction::OPCODE_RETURN_TYPED_SCRIPT, 2);
+				append(p_return_value);
+				append(script_idx);
+			} break;
+			default: {
+				ERR_PRINT("Compiler bug: unresolved return.");
+
+				// Shouldn't get here, but fail-safe to a regular return;
+				append(GDScriptFunction::OPCODE_RETURN, 1);
+				append(p_return_value);
+			} break;
+		}
+	}
 }
 
 void GDScriptByteCodeGenerator::write_assert(const Address &p_test, const Address &p_message) {