[PATCH] D65704: DirectoryWatcher::create: Adding better error handling.

[Puyan Lotfi via Phabricator via cfe-commits]

plotfi marked 2 inline comments as done.
plotfi added inline comments.


================
Comment at: cfe/trunk/unittests/DirectoryWatcher/DirectoryWatcherTest.cpp:287
       /*waitForInitialSync=*/true);
+  if (!DW) return;
 
----------------
gribozavr wrote:
> plotfi wrote:
> > gribozavr wrote:
> > > plotfi wrote:
> > > > gribozavr wrote:
> > > > > Why? This is a test -- ignoring errors would only hide them from developers.
> > > > Please see how llvm::Expected works. This does not ignore or hide anything. 
> > > I think I know how llvm::Expected works.
> > > 
> > > The problem that this check and return hides is that if DirectoryWatcher::create returns an error, the rest of the test is silently slipped. The test should be using something like `cantFail` instead.
> > If DirectoryWatcher returns an error and you hit the early return, without taking the error the Expected destructor will print a callstack and halt the program. I can check this again, but I am quite sure that without invoking something like takeError you will hit the crash in the case of an early return. 
> That's good -- but I think a `cantFail` call would be more readable.
Ah, you should have said so then. Except this is arguably worse. I want this test to tell me that the cause of the crash (in this case, exceeding the inotify limit). What I want to happen is:

```
Note: Google Test filter = DirectoryWatcherTest.AddFiles
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from DirectoryWatcherTest
[ RUN      ] DirectoryWatcherTest.AddFiles
Expected<T> must be checked before access or destruction.
Unchecked Expected<T> contained error:
inotify_init1() error: out of inotify entries #0 0x0000000000246b8f llvm::sys::PrintStackTrace(llvm::raw_ostream&) /mnt/nvme0/llvm-project/llvm/lib/Support/Unix/Signals.inc:533:13
 #1 0x00000000002450d2 llvm::sys::RunSignalHandlers() /mnt/nvme0/llvm-project/llvm/lib/Support/Signals.cpp:69:18
 #2 0x0000000000247268 SignalHandler(int) /mnt/nvme0/llvm-project/llvm/lib/Support/Unix/Signals.inc:385:1
 #3 0x00007f17924eb890 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x12890)
 #4 0x00007f1790f94e97 gsignal /build/glibc-OTsEL5/glibc-
...

```

Wrapping the llvm::Expected in a cantFail hides this message, and instead you get the much less useful:

```
Note: Google Test filter = DirectoryWatcherTest.AddFiles
[==========] Running 1 test from 1 test case.                                                                                                                                                                                                
[----------] Global test environment set-up.
[----------] 1 test from DirectoryWatcherTest
[ RUN      ] DirectoryWatcherTest.AddFiles
Failure value returned from cantFail wrapped call
UNREACHABLE executed at /mnt/nvme0/llvm-project/llvm/include/llvm/Support/Error.h:707!
 #0 0x0000000000246e0f llvm::sys::PrintStackTrace(llvm::raw_ostream&) /mnt/nvme0/llvm-project/llvm/lib/Support/Unix/Signals.inc:533:13
 #1 0x0000000000245352 llvm::sys::RunSignalHandlers() /mnt/nvme0/llvm-project/llvm/lib/Support/Signals.cpp:69:18
 #2 0x00000000002474e8 SignalHandler(int) /mnt/nvme0/llvm-project/llvm/lib/Support/Unix/Signals.inc:385:1
 #3 0x00007f20c64a8890 __restore_rt (/lib/x86_64-linux-gnu/libpthread.so.0+0x12890)
 #4 0x00007f20c4f51e97 gsignal /build/glibc-OTsEL5/glibc-2.27/signal/../sysdeps/unix/sysv/linux/raise.c:51:0
 #5 0x00007f20c4f53801 abort /build/glibc-OTsEL5/glibc-2.27/stdlib/abort.c:81:0
 #6 0x0000000000232b31 (build/tools/clang/unittests/DirectoryWatcher/./DirectoryWatcherTests+0x232b31)

```

I can add comments assuring that llvm::Expected will dump an error prior to halting, but I specifically _want_ llvm::Expected to propagate up what perror would print to the console otherwise. 



Repository:
  rL LLVM

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D65704/new/

https://reviews.llvm.org/D65704