1068175 - ActorsParent.cpp misuses NS_WARN_IF, triggering warnings for "warning: expression result unused [-Wunused-value]"

Status: RESOLVED WORKSFORME

(Core :: Storage: IndexedDB, defect)

Description

[Daniel Holbert [:dholbert]]

As shown in this Try log (with FAIL_ON_WARNINGS added back to dom/indexedDB)...
https://tbpl.mozilla.org/php/getParsedLog.php?id=48212707&tree=Try#error0

...ActorsParent.cpp misuses NS_WARN_IF (not checking its result), which triggers these build warnings:
{
/builds/slave/try-osx64_g-000000000000000000/build/dom/indexedDB/ActorsParent.cpp:11887:16: error: expression result unused [-Werror,-Wunused-value]
    NS_WARN_IF(!PBackgroundIDBFactoryRequestParent::Send__delete__(this,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../dist/include/nsDebug.h:48:38: note: expanded from macro 'NS_WARN_IF'
#define NS_WARN_IF(condition) (bool)(condition)
                                     ^
/builds/slave/try-osx64_g-000000000000000000/build/dom/indexedDB/ActorsParent.cpp:12600:16: error: expression result unused [-Werror,-Wunused-value]
    NS_WARN_IF(!PBackgroundIDBFactoryRequestParent::Send__delete__(this,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../../dist/include/nsDebug.h:48:38: note: expanded from macro 'NS_WARN_IF'
#define NS_WARN_IF(condition) (bool)(condition)
                                     ^
/builds/slave/try-osx64_g-000000000000000000/build/dom/indexedDB/ActorsParent.cpp:13650:16: error: ignoring return value of function declared with const attribute [-Werror,-Wunused-value]
    NS_WARN_IF(NS_FAILED(mTransaction->RollbackSavepoint()));
}


Note that NS_WARN_IF is supposed to be used *inside* of an "if" statement -- not as a standalone statement on its own.

I believe these statements really want to be capturing their result in a DebugOnly<> variable, and checking that variable with NS_WARN_IF_FALSE()  (which is completely different from NS_WARN_IF. Yes, the naming is confusing.)

Comment 1

[Ben Turner (not reading bugmail, use the needinfo flag!)]

Bug 994190 was backed out so this is WFM. I'll fix before relanding.