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+From: Jani Nikula <jani@nikula.org>\r
+To: Ethan Glasser-Camp <ethan.glasser.camp@gmail.com>, notmuch@notmuchmail.org\r
+Subject: Re: [PATCH] lib: fix warnings when building with clang\r
+In-Reply-To: <87pq4c61hc.fsf@betacantrips.com>\r
+References: <1349076971-2065-1-git-send-email-jani@nikula.org>\r
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+Date: Sun, 21 Oct 2012 21:44:17 +0300\r
+Message-ID: <87vce3vf5q.fsf@nikula.org>\r
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+\r
+On Sun, 21 Oct 2012, Ethan Glasser-Camp <ethan.glasser.camp@gmail.com> wrote:\r
+> Jani Nikula <jani@nikula.org> writes:\r
+>\r
+>> Building notmuch with CC=clang and CXX=clang++ produces the warnings:\r
+>>\r
+>> CC -O2 lib/tags.o\r
+>> lib/tags.c:43:5: warning: expression result unused [-Wunused-value]\r
+>> talloc_steal (tags, list);\r
+>> ^~~~~~~~~~~~~~~~~~~~~~~~~\r
+>> /usr/include/talloc.h:345:143: note: expanded from:\r
+>> ...__location__); __talloc_steal_ret; })\r
+>> ^~~~~~~~~~~~~~~~~~\r
+>> 1 warning generated.\r
+>>\r
+>> CXX -O2 lib/message.o\r
+>> lib/message.cc:791:5: warning: expression result unused [-Wunused-value]\r
+>> talloc_reference (message, message->tag_list);\r
+>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r
+>> /usr/include/talloc.h:932:36: note: expanded from:\r
+>> ...(_TALLOC_TYPEOF(ptr))_talloc_reference_loc((ctx),(ptr), __location__)\r
+>> ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\r
+>> 1 warning generated.\r
+>>\r
+>> Check talloc_reference() return value, and explicitly ignore\r
+>> talloc_steal() return value as it has no failure modes, to silence the\r
+>> warnings.\r
+>> ---\r
+>> lib/message.cc | 4 +++-\r
+>> lib/tags.c | 2 +-\r
+>> 2 files changed, 4 insertions(+), 2 deletions(-)\r
+>>\r
+>> diff --git a/lib/message.cc b/lib/message.cc\r
+>> index 978de06..320901f 100644\r
+>> --- a/lib/message.cc\r
+>> +++ b/lib/message.cc\r
+>> @@ -788,7 +788,9 @@ notmuch_message_get_tags (notmuch_message_t *message)\r
+>> * possible to modify the message tags (which talloc_unlink's the\r
+>> * current list from the message) while still iterating because\r
+>> * the iterator will keep the current list alive. */\r
+>> - talloc_reference (message, message->tag_list);\r
+>> + if (!talloc_reference (message, message->tag_list))\r
+>> + return NULL;\r
+>> +\r
+>> return tags;\r
+>> }\r
+>\r
+> Hi! What you did with talloc_steal is obviously fine. \r
+>\r
+> I'd be happier about what you did with talloc_reference() if there were\r
+> precedent, or a clearly-articulated convention for notmuch. Instead this\r
+> is the third use in the codebase that I can see, and the other two are\r
+> each unique to themselves. In mime-node.c we print an "out-of-memory"\r
+> error and in lib/filenames.c we cast (void) talloc_reference (...), I\r
+> guess figuring that we're pretty much hosed anyhow if we run out of\r
+> memory.\r
+>\r
+> Why return NULL here? It seems like if talloc_reference fails, we're\r
+> going to crash eventually, so we should print an error to explain our\r
+> impending doom. I'd guess you're uneasy printing anything from lib/, but\r
+> still want to signal an error, and the only way you can do so is to\r
+> return NULL. I guess that silences the compiler warning, but it's not\r
+> really the correct way to handle the error IMO. On the other hand, it's\r
+> such a weird corner case that I don't even think it merits a FIXME\r
+> comment.\r
+>\r
+> How about an assert instead of a return NULL?\r
+\r
+No. I don't think a library should assert, exit, or print to stderr on\r
+this sort of thing. It's up to the calling application. Even if it\r
+probably doesn't have many choices left, given how much memory\r
+talloc_reference needs (not much).\r
+\r
+Ignoring the talloc_reference return value with (void) is just wrong,\r
+and the caller of notmuch_message_get_tags should anticipate a NULL\r
+return. So IMHO that's the pragmatic thing to do in this mostly\r
+theoretical situation, the biggest change being silencing the warning.\r
+\r
+\r
+BR,\r
+Jani.\r
projects / notmuch-archives.git / commitdiff