Jani Nikula <jani@nikula.org> writes: > Building notmuch with CC=clang and CXX=clang++ produces the warnings: > > CC -O2 lib/tags.o > lib/tags.c:43:5: warning: expression result unused [-Wunused-value] > talloc_steal (tags, list); > ^~~~~~~~~~~~~~~~~~~~~~~~~ > /usr/include/talloc.h:345:143: note: expanded from: > ...__location__); __talloc_steal_ret; }) > ^~~~~~~~~~~~~~~~~~ > 1 warning generated. > > CXX -O2 lib/message.o > lib/message.cc:791:5: warning: expression result unused [-Wunused-value] > talloc_reference (message, message->tag_list); > ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > /usr/include/talloc.h:932:36: note: expanded from: > ...(_TALLOC_TYPEOF(ptr))_talloc_reference_loc((ctx),(ptr), __location__) > ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > 1 warning generated. > > Check talloc_reference() return value, and explicitly ignore > talloc_steal() return value as it has no failure modes, to silence the > warnings. > --- > lib/message.cc | 4 +++- > lib/tags.c | 2 +- > 2 files changed, 4 insertions(+), 2 deletions(-) > > diff --git a/lib/message.cc b/lib/message.cc > index 978de06..320901f 100644 > --- a/lib/message.cc > +++ b/lib/message.cc > @@ -788,7 +788,9 @@ notmuch_message_get_tags (notmuch_message_t *message) > * possible to modify the message tags (which talloc_unlink's the > * current list from the message) while still iterating because > * the iterator will keep the current list alive. */ > - talloc_reference (message, message->tag_list); > + if (!talloc_reference (message, message->tag_list)) > + return NULL; > + > return tags; > } Hi! What you did with talloc_steal is obviously fine. I'd be happier about what you did with talloc_reference() if there were precedent, or a clearly-articulated convention for notmuch. Instead this is the third use in the codebase that I can see, and the other two are each unique to themselves. In mime-node.c we print an "out-of-memory" error and in lib/filenames.c we cast (void) talloc_reference (...), I guess figuring that we're pretty much hosed anyhow if we run out of memory. Why return NULL here? It seems like if talloc_reference fails, we're going to crash eventually, so we should print an error to explain our impending doom. I'd guess you're uneasy printing anything from lib/, but still want to signal an error, and the only way you can do so is to return NULL. I guess that silences the compiler warning, but it's not really the correct way to handle the error IMO. On the other hand, it's such a weird corner case that I don't even think it merits a FIXME comment. How about an assert instead of a return NULL? Ethan