tests/build_system_cflags_spaces: test CFLAGS macros handling

This tests passing CFLAGS with spaces to an application and also that
even if the CFLAGS are defined after Makefile.include, they trigger
a rebuild when modified.

This includes an example how to pass macros with spaces to a docker
build.

The test as both an automated part for the CFLAGS with spaces, and a
manual part for the two other features.

tests/build_system_cflags_spaces/Makefile

@@ -0,0 +1,14 @@
+APPLICATION = cflags_with_spaces
+BOARD ?= native
+RIOTBASE ?= $(CURDIR)/../..
+
+CFLAGS += -DSUPER_STRING='"I love sentences with spaces"'
+
+include $(RIOTBASE)/Makefile.include
+
+# Changing this value should trigger a rebuild even if defined after
+# Makefile.include
+CONFIGURATION_VALUE ?= 0
+CFLAGS += -DDEFINED_AFTER_MAKEFILE_INCLUDE=$(CONFIGURATION_VALUE)
+# Exported to be available in the automated test
+test: export CONFIGURATION_VALUE ?=

tests/build_system_cflags_spaces/README.md

@@ -0,0 +1,43 @@
+Build system cflags with space test
+===================================
+
+This tests that the build system now handles CFLAGS correctly.
+
+There is an automated test for CFLAGS with spaces when defined in the Makefile.
+
+
+Other manual tests
+------------------
+
+There are also 2 other manual tests that can be run
+
+
+### Modifying CFLAGS defined after including Makefile.include
+
+CFLAGS defined after `Makefile.include` trigger a rebuild when changed.
+
+Running the test once should work and then when changing `CONFIGURATION_VALUE`
+it should pass too.
+
+    make flash test
+    CONFIGURATION_VALUE=1 make flash test
+
+
+### Setting CFLAGS with space for docker
+
+This one is a trickier as CFLAGS are modified in the Makefile, so cannot be
+detected automatically in the docker handling. The solution is to pass it with
+`DOCKER_ENVIRONMENT_CMDLINE`.
+
+When the CFLAGS is defined like this, I did not find another solution than
+escaping the space.
+
+```
+DOCKER_ENVIRONMENT_CMDLINE=$'-e CFLAGS=-DSTRING_FROM_DOCKER=\'\\\"with\ space\\\"\'' \
+  BUILD_IN_DOCKER=1 make
+grep '#define STRING_FROM_DOCKER "with space"' bin/native/riotbuild/riotbuild.h \
+  || { echo 'ERROR CFLAGS not passed correctly' >&2; false; }
+
+...
+#define STRING_FROM_DOCKER "with space"
+```

tests/build_system_cflags_spaces/main.c

@@ -0,0 +1,37 @@
+/*
+ * Copyright (C) 2019 Freie Universität Berlin
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser
+ * General Public License v2.1. See the file LICENSE in the top level
+ * directory for more details.
+ */
+
+/**
+ * @ingroup     tests
+ * @{
+ *
+ * @file
+ * @brief       Test the CFLAGS handling
+ *
+ * @author      Gaëtan Harter <gaetan.harter@fu-berlin.de>
+ *
+ * @}
+ */
+
+#include <stdio.h>
+
+/* Define a CFLAGS string with spaces from outside docker */
+/* DOCKER_ENVIRONMENT_CMDLINE=$'-e CFLAGS=-DSTRING_FROM_DOCKER=\'\\\"with\ space\\\"\''*/
+#ifndef STRING_FROM_DOCKER
+#define STRING_FROM_DOCKER ""
+#endif
+
+
+int main(void)
+{
+    puts("The output of the configuration variables:");
+    printf("SUPER_STRING: %s\n", SUPER_STRING);
+    printf("DEFINED_AFTER_MAKEFILE_INCLUDE: %u\n", DEFINED_AFTER_MAKEFILE_INCLUDE);
+    printf("CFLAGS_STRING_FROM_DOCKER: %s\n", STRING_FROM_DOCKER);
+    return 0;
+}

tests/build_system_cflags_spaces/tests/01-run.py

@@ -0,0 +1,38 @@
+#!/usr/bin/env python3
+
+# Copyright (C) 2019 Freie Universität Berlin
+#
+# This file is subject to the terms and conditions of the GNU Lesser
+# General Public License v2.1. See the file LICENSE in the top level
+# directory for more details.
+
+"""
+Test for passing `CFLAGS` with spaces to the application.
+
+It also tests that even if a `CFLAGS` is set after including Makefile.include,
+changing its value will trigger a rebuild.
+
+There is also a way to test passing additional values with spaces to docker
+documented in the `README.md`.
+"""
+
+import os
+import sys
+from testrunner import run
+
+
+# Verify the macro matches the configuration value
+CONFIGURATION_VALUE = os.environ['CONFIGURATION_VALUE']
+
+
+def testfunc(child):
+    child.expect_exact('The output of the configuration variables:')
+    child.expect_exact('SUPER_STRING: I love sentences with spaces')
+    child.expect_exact('DEFINED_AFTER_MAKEFILE_INCLUDE: %s' %
+                       CONFIGURATION_VALUE)
+    # This one is not tested here, see the output in 'riotbuild.h'
+    child.expect(r'CFLAGS_STRING_FROM_DOCKER: .*')
+
+
+if __name__ == "__main__":
+    sys.exit(run(testfunc))