1217308 - Static analysis incorrectly reports "Unused value of must-use type"

Status: NEW

(Developer Infrastructure :: Source Code Analysis, defect)

Description

[Xidorn Quan [:xidorn] UTC+10]

See this error: https://treeherder.mozilla.org/logviewer.html#?job_id=12848952&repo=try

It reports:
>  netwerk/base/TLSServerSocket.cpp:337:5: error: Unused value of must-use type 'already_AddRefed<nsITLSServerSecurityObserver>'
>      observer = mSecurityObserver.forget();
>      ^

The corresponding code is:
> 328: TLSServerConnectionInfo::~TLSServerConnectionInfo()
> 329: {
> 330:   if (!mSecurityObserver) {
> 331:     return;
> 332:   }
> 333: 
> 334:   already_AddRefed<nsITLSServerSecurityObserver> observer;
> 335:   {
> 336:     MutexAutoLock lock(mLock);
> 337:     observer = mSecurityObserver.forget();
> 338:   }
> 339: 
> 340:   NS_ReleaseOnMainThread(Move(observer));
> 341: }

Obviously, `observer` is used in line 340, but it is incorrectly reported to be unused.