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, 34 insertions, 0 deletions

diff --git a/test/static_if_error.c b/test/static_if_error.c
new file mode 100644
index 0000000000..bbe4839981
--- /dev/null
+++ b/test/static_if_error.c
@@ -0,0 +1,34 @@
+/* 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 fail on unexpected
+ * input.
+ */
+
+#include "common.h"
+#include "test_util.h"
+
+#define CONFIG_FOO TEST_VALUE
+
+/*
+ * At compiler invocation, define TEST_MACRO to STATIC_IF or
+ * STATIC_IF_NOT.
+ */
+#ifndef TEST_MACRO
+#error "This error should not be seen in the compiler output!"
+#endif
+
+/* This is intended to cause a compilation error. */
+TEST_MACRO(CONFIG_FOO) __maybe_unused int foo;
+
+void run_test(void)
+{
+	test_reset();
+
+	/* Nothing to do, observe compilation error */
+
+	test_print_result();
+}