common: add STATIC_IF and STATIC_IF_NOT macros

A common pattern to use with IS_ENABLED is like this:

/*
 * This var should only be used if CONFIG_FOO. The linker errors if
 * CONFIG_FOO is not defined is intentional.
 */
 #ifdef CONFIG_FOO
 static
 #else
 extern
 #endif
 int some_var;

The issue with this is that it leads to an over-verbose and
potentially hard to read pattern, and does not have the check that
CONFIG_FOO was only defined to blank.

Suppose a macro like this existed:

STATIC_IF(CONFIG_FOO) int some_var;

... which expands to "static" when CONFIG_FOO is defined to empty,
"extern" when CONFIG_FOO is not defined, and errors when CONFIG_FOO is
defined to non-empty.

This CL implements that, as well as the inverse (STATIC_IF_NOT).

BUG=chromium:989786
BRANCH=none
TEST=provided unit tests, buildall

Change-Id: Ib57aaba62bc184fda9aa782a780d5f13ba44ae88
Signed-off-by: Jack Rosenthal <jrosenth@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/1731859
Reviewed-by: Daisuke Nojiri <dnojiri@chromium.org>

1 files changed, 50 insertions, 0 deletions

diff --git a/test/static_if.c b/test/static_if.c
new file mode 100644
index 0000000000..46e8057d7f
--- /dev/null
+++ b/test/static_if.c
@@ -0,0 +1,50 @@
+/* Copyright 2019 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+/* Test the STATIC_IF and STATIC_IF_NOT macros. */
+
+#include "common.h"
+#include "test_util.h"
+
+#undef CONFIG_UNDEFINED
+#define CONFIG_BLANK
+
+STATIC_IF(CONFIG_UNDEFINED) int this_var_is_extern;
+STATIC_IF_NOT(CONFIG_BLANK) int this_var_is_extern_too;
+STATIC_IF(CONFIG_BLANK) int this_var_is_static;
+STATIC_IF_NOT(CONFIG_UNDEFINED) int this_var_is_static_too;
+
+static int test_static_if_blank(void)
+{
+	TEST_ASSERT(this_var_is_static == 0);
+	TEST_ASSERT(this_var_is_static_too == 0);
+
+	return EC_SUCCESS;
+}
+
+static int test_static_if_unused_no_fail(void)
+{
+	/*
+	 * This should not cause linker errors because the variables
+	 * go unused (usage is optimized away).
+	 */
+	if (IS_ENABLED(CONFIG_UNDEFINED))
+		this_var_is_extern = 1;
+
+	if (!IS_ENABLED(CONFIG_BLANK))
+		this_var_is_extern_too = 1;
+
+	return EC_SUCCESS;
+}
+
+void run_test(void)
+{
+	test_reset();
+
+	RUN_TEST(test_static_if_blank);
+	RUN_TEST(test_static_if_unused_no_fail);
+
+	test_print_result();
+}