How do I find the culprit code that is making C++ list give me 'attempting to reference a deleted function' error with MSVC 14.20.27508?

Question

I have been porting my code from Visual Studio 2017 to Visual Studio 2019. It was building properly before. But now I am getting these errors:

C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.20.27508\include\list(1010): error C2280: 'std::pair<_Kty,_Ty> &std::pair<_Kty,_Ty>::operator =(volatile const std::pair<_Kty,_Ty> &)': attempting to reference a deleted function        178 114
C:\Program Files (x86)\Microsoft Visual Studio\2019\Professional\VC\Tools\MSVC\14.20.27508\include\list(1010): error C2280: 'std::pair<_Kty,_Ty> &std::pair<_Kty,_Ty>::operator =(volatile const std::pair<_Kty,_Ty> &)': attempting to reference a deleted function        54  114

These errors do not refer to lines in my code, so I can't see what I have written that might cause them. And this code built without error in earlier versions of the tools.

Here are the project properties of the failing build:

Note: most of the projects are building fine.

With Windows SDK Version set to 7.0 and Platform Toolset set to Visual Studio 2017 - Windows XP (v141_xp) the same project builds successfully.

I understand there is a problem in my code, somewhere, but it is not showing any error in any code that belongs to the project I am building, it is only showing the error in the list header.

I want to find the culprit code that is causing this build failure. What scenarios would make list give me these errors?

Why does it build fine with Windows SDK 7 and v141_xp toolset and, not with upgraded SDK and toolset?

Answer 1

Your project properties are possibly a red herring.

The error is that the type std::pair<_Kty,_Ty> has a deleted copy assignment operator, which can happen if various of its other constructors or assignment operators are explicitly defined or if the copy assignment operator is explicitly deleted. While std::list does not require T to be copy-assignable since c++11, you should perhaps double-check the std::lists that you are using in your program and see if you can make sure it's none of those that is leading up to this error.

To get better help you'll need to post an MCVE.

(long comment converted into Answer)