Add nonnull and nullable attributes to API

This will warn if NULL is passed to any nonnull-annotated parameter, and is
also supported by sanitizers which can check for violations at runtime.

Unfortunately, it is currently only supported by clang.  GCC has a similar
feature in the nonnull attribute, but this has a different syntax (it's a
function attribute) and is more dangerous since it is used by the optimizer to
assume a null pointer is undefined behavior.  This one just warns and still
allows code to handle the situation gracefully, which I think is more
appropriate for a library API.

Note that this optimization behavior is not some unlikely edge case: switching
these attributes to the GCC one will break release builds.

1 files changed, 2 insertions, 0 deletions

diff --git a/wscript b/wscript
index f12503e9..bc21d526 100644
--- a/wscript
+++ b/wscript
@@ -60,6 +60,8 @@ def configure(conf):
                 '-Wno-double-promotion',
                 '-Wno-format-nonliteral',
                 '-Wno-implicit-fallthrough',
+                '-Wno-nullability-extension',
+                '-Wno-nullable-to-nonnull-conversion',
                 '-Wno-padded',
                 '-Wno-reserved-id-macro',
                 '-Wno-sign-conversion',