helpers: Move static_assert definition to shared
Collect the fallback definitions of static_assert() from desktop-shell
and the test shell, and move them to helpers.h. This allows code
throughout the tree to use static_assert() for build-time assertions,
where it is supported by the compiler.
As GCC goes out of its way to only add static_assert() when C11 has been
explicitly requested - which we don't do - make sure to use the more
widely available _Static_assert() if that is provided.
This will be used in future patches to ensure two array lengths don't go
out of sync.
Signed-off-by: Daniel Stone <daniels@collabora.com>
Reviewed-by: Pekka Paalanen <pekka.paalanen@collabora.co.uk>
diff --git a/desktop-shell/shell.c b/desktop-shell/shell.c
index 8b7a23a..ea3c453 100644
--- a/desktop-shell/shell.c
+++ b/desktop-shell/shell.c
@@ -47,10 +47,6 @@
#define DEFAULT_NUM_WORKSPACES 1
#define DEFAULT_WORKSPACE_CHANGE_ANIMATION_LENGTH 200
-#ifndef static_assert
-#define static_assert(cond, msg)
-#endif
-
struct focus_state {
struct desktop_shell *shell;
struct weston_seat *seat;
diff --git a/shared/helpers.h b/shared/helpers.h
index 46f745d..0ebcc4a 100644
--- a/shared/helpers.h
+++ b/shared/helpers.h
@@ -100,6 +100,40 @@
(type *)( (char *)__mptr - offsetof(type,member) );})
#endif
+/**
+ * Build-time static assertion support
+ *
+ * A build-time equivalent to assert(), will generate a compilation error
+ * if the supplied condition does not evaluate true.
+ *
+ * The following example demonstrates use of static_assert to ensure that
+ * arrays which are supposed to mirror each other have a consistent
+ * size.
+ *
+ * This is only a fallback definition; support must be provided by the
+ * compiler itself.
+ *
+ * @code
+ * int small[4];
+ * long expanded[4];
+ *
+ * static_assert(ARRAY_LENGTH(small) == ARRAY_LENGTH(expanded),
+ * "size mismatch between small and expanded arrays");
+ * for (i = 0; i < ARRAY_LENGTH(small); i++)
+ * expanded[i] = small[4];
+ * @endcode
+ *
+ * @param condition Expression to check for truth
+ * @param msg Message to print on failure
+ */
+#ifndef static_assert
+# ifdef _Static_assert
+# define static_assert(cond, msg) _Static_assert(cond, msg)
+# else
+# define static_assert(cond, msg)
+# endif
+#endif
+
#ifdef __cplusplus
}
#endif
diff --git a/tests/weston-test-desktop-shell.c b/tests/weston-test-desktop-shell.c
index de84425..c780316 100644
--- a/tests/weston-test-desktop-shell.c
+++ b/tests/weston-test-desktop-shell.c
@@ -41,10 +41,6 @@
#include "shared/helpers.h"
#include "libweston-desktop/libweston-desktop.h"
-#ifndef static_assert
-#define static_assert(cond, msg)
-#endif
-
struct desktest_shell {
struct wl_listener compositor_destroy_listener;
struct weston_desktop *desktop;
