Fix: c99: static assert: clang build fails due to multiple typedef

Unlike c11, c99 does not allow redefinition of the same typedef, and
clang is strict about it. Building code with tracepoints with -std=c99
with clang fails with:

warning: redefinition of typedef 'lttng_ust_static_assert_Tracepoint_name_length_is_too_long' is a C11 feature [-Wtypedef-redefinition]

Fix this by placing the (potentially negative size) array as argument to
a function prototype instead.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I06b6edbcd93f43f349451c23b0520df59f4fb346

diff --git a/include/lttng/ust-compiler.h b/include/lttng/ust-compiler.h
index 38c89b0892adaca4be0ce4142470d3be4bc80d34..c0aae11e6c3fb1fe377685f4ea1f3c6cf99131e3 100644 (file)
--- a/include/lttng/ust-compiler.h
+++ b/include/lttng/ust-compiler.h
@@ -85,15 +85,17 @@
 /*
  * Evaluates the predicate and emit a compilation error on failure.
  *
- * If the predicate evaluates to true, this macro emits a typedef of an array
- * of size 0.
+ * If the predicate evaluates to true, this macro emits a function
+ * prototype with an argument type which is an array of size 0.
  *
- * If the predicate evaluates to false, this macro emits a typedef of an array
- * of negative size which is invalid in C and forces a compiler error. The msg
- * parameter is used in the tentative typedef so it is printed to the user.
+ * If the predicate evaluates to false, this macro emits a function
+ * prototype with an argument type which is an array of negative size
+ * which is invalid in C and forces a compiler error. The
+ * c_identifier_msg parameter is used as the argument identifier so it
+ * is printed to the user when the error is reported.
  */
 #define lttng_ust_static_assert(predicate, msg, c_identifier_msg)  \
-    typedef char lttng_ust_static_assert_##c_identifier_msg[2*!!(predicate)-1]
+       void lttng_ust_static_assert_proto(char c_identifier_msg[2*!!(predicate)-1])
 #endif
 
 /* Combine two tokens. */