Errors in Windows Forms

In early December 2018, Microsoft announced the release of the .NET Core 3 Preview 1. A little earlier (about mid-October), GitHub started to actively disclose the sources of Windows Forms - the .NET Core UI platform for creating Windows desktop applications. You can see the commit statistics here. Now anyone can download the WinForms source code for review.

We also downloaded the sources to search for errors there with PVS-Studio. The check did not cause any difficulties. We needed: Visual Studio 2019, .NET Core 3.0 SDK Preview, PVS-Studio. What did we find? 833 High and Medium warnings (249 and 584, respectively) were issued for 540,000 lines of code (not including empty ones) in 1670 cs files.

Example:

PVS-Studio: V3003 The use of 'if (A) {...} else if (A) {...}' pattern was detected. There is a probability of logical error presence. Check lines: 213, 224. ButtonStandardAdapter.cs 213
]
Attachment 35663

If and else if blocks check the same condition. It looks like copy-paste. Is it an error? If you look at the declaration of the IsHighContrastHighlighted method, you may doubt it:

Attachment 35661

The method can probably return different values for sequential calls. And what is happening in the caller method, of course, looks strange, but has the right to exist. However, I would advise the authors to take a look at this code fragment. Just in case. It is also a good example of how difficult it is to draw conclusions when analyzing unfamiliar code.

You can find more examples in this article.