[fiber] Add empty polyfill when not enabled

Author: salkinium

src/modm/processing/fiber.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Erik Henriksson
+ * Copyright (c) 2024, Niklas Hauser
  *
  * This file is part of the modm project.
  *
@@ -9,5 +9,22 @@
  */
 // ----------------------------------------------------------------------------
 
-#include "fiber/functions.hpp"
-#include "fiber/task.hpp"
+/*
+We use __has_include guards here to support the case when fibers are not in use
+but we still need to provide the interface to the rest of the library.
+Then only the functionality that is enabled is supported and the fiber yield()
+function returns immediately, thus blocks in-place.
+*/
+
+// includes the functions related to time
+#if __has_include(<modm/architecture/interface/clock.hpp>)
+#	include "fiber/functions.hpp"
+#endif
+// polyfill implementation of an empty yield
+#if __has_include("fiber/no_yield.hpp")
+#	include "fiber/no_yield.hpp"
+#endif
+// pulls in the fiber and scheduler implementation
+#if __has_include("fiber/task.hpp")
+#	include "fiber/task.hpp"
+#endif

src/modm/processing/fiber/no_yield.hpp

@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023, Niklas Hauser
+ *
+ * This file is part of the modm project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+// ----------------------------------------------------------------------------
+
+#pragma once
+
+/// @cond
+namespace modm::this_fiber
+{
+
+void inline
+yield()
+{
+	// do nothing and return
+}
+
+modm::fiber::id inline
+get_id()
+{
+	return 0;
+}
+
+} // namespace modm::this_fiber
+/// @endcond

src/modm/processing/module.lb

@@ -27,6 +27,12 @@ def build(env):
     env.outbasepath = "modm/src/modm/processing"
     env.copy("task.hpp")
 
+    if not env.has_module(":processing:fiber"):
+        env.outbasepath = "modm/src/modm/processing/"
+        env.copy("fiber/functions.hpp")
+        env.copy("fiber/no_yield.hpp")
+        env.copy("fiber.hpp")
+
     env.outbasepath = "modm/src/modm"
     headers = env.generated_local_files(filterfunc=lambda path: ".h" in path and not "_impl.h" in path)
     env.template("processing.hpp.in", substitutions={"headers": sorted(headers)})