resource.h error C28182: Dereferencing NULL pointer

[mtfriesen]

We started hitting a build error when dependabot updated our WIL submodule in microsoft/xdp-for-windows#947.

    14>Lib:
         xdptests.vcxproj -> D:\a\xdp-for-windows\xdp-for-windows\artifacts\bin\x64_Debug\test\xdptests.lib
    14>D:\a\xdp-for-windows\xdp-for-windows\submodules\wil\include\wil\resource.h(4000): error C28182: Dereferencing NULL pointer. 'Temp_value_#32186' contains the same NULL value as 'new(1*144, nothrow)' did.  [D:\a\xdp-for-windows\xdp-for-windows\test\functional\lib\xdptests.vcxproj]
    14>D:\a\xdp-for-windows\xdp-for-windows\submodules\wil\include\wil\resource.h(4000): error C28182: Dereferencing NULL pointer. 'Temp_value_#32553' contains the same NULL value as 'new(1*144, nothrow)' did.  [D:\a\xdp-for-windows\xdp-for-windows\test\functional\lib\xdptests.vcxproj]
    14>D:\a\xdp-for-windows\xdp-for-windows\submodules\wil\include\wil\resource.h(4000): error C28182: Dereferencing NULL pointer. 'Temp_value_#32650' contains the same NULL value as 'new(1*144, nothrow)' did.  [D:\a\xdp-for-windows\xdp-for-windows\test\functional\lib\xdptests.vcxproj]
    14>Done Building Project "D:\a\xdp-for-windows\xdp-for-windows\test\functional\lib\xdptests.vcxproj" (default targets) -- FAILED.

I don't have a deep enough understanding of C++ to understand why the WIL changes suddenly raise a compiler error - the diff seems benign to me - could you please take a look?

wil_build_error.txt

[dunhor]

I don't have a deep enough understanding of C++ to understand why the WIL changes suddenly raise a compiler error

Because it's not a compiler error, it's a static analysis warning.

My guess is that it's warning because it changed from a constructor call to an initializer list and it believes that even when new(std::nothrow) returns null, the object will be initialized. I did a little test and it seems as though this is a false positive. Even when using initializer list syntax, the object should not be initialized unless new(std::nothrow) returns a non-null pointer, so this warning is bogus. This false positive should be reported to the MSVC folks.

My 2 cents - don't use the MSVC analyzer. It's wrong far too often to be useful and definitely don't treat its warnings as errors.

[mtfriesen]

Thanks @dunhor for the detailed response. Agree the cost/benefit of the analyzer is questionable. XDP treats warnings as errors by policy, but we can easily suppress this class of error when including WIL.