VS Project References Broken On Case Sensitivity of GUID

Question

Since upgrading to VS 2015, my team has experienced random quirky things which I'm sure are being worked out at Microsoft right now. One pretty annoying one is that we seem to lose project references, especially after branching. I began to work on a new branch of our solution yesterday only to find out that types were unrecognized and namespace usings were being cited as unnecessary (because they were for the types that had suddenly become unrecognized).

The references in the project did not show any icons indicating a problem with the reference, but just to see if it would work, I removed and re-added a project reference, which caused its types to be recognized once more.

This, of course, updated the project file, so I looked to see what changes had been made. The only difference between the project that could not detect the reference and the one that now can is that the alpha characters in the GUID had been changed from lower case to upper case. For example:

Old, broken reference:


    {95d34b2e-2ceb-499e-ab9e-b644b0af710d}
    Project.Name.Redacted

New, fixed reference:


    {95D34B2E-2CEB-499E-AB9E-B644B0AF710D}
    Project.Name.Redacted

I'm looking for the reason this is happening and how I might fix it without having to manually remove and re-add references all over the place (and without having to convert all the project file GUIDs to upper case).

I should note that these "broken" references are not breaking the build, and that they only show up in the Error List as IntelliSense error, not build errors. So, the references aren't really broken, they've just broken IntelliSense (which is arguably worse?!).

user_4218542 · Answer

I suffered a similar issue when updating VS2017 v15.7 to v15.9.

The answer for me was to close down VS, clear out the hidden .vs folder in my solution's root directory and restart VS.

user_4455524 · Answer

Today in visual studio 2019 (16.2.2) I was encountering build system issues where projects were being unnecessarily (and repeatedly) rebuilt whenever I initiated the building of my solution.

(None of the usual steps resolved the build issues, eg deleting the ".vs" folder, or deleting "bin" and "obj" directories, etc).

At first it appeared to be related to the character-casing of guids, because I was able to get the problem to go away by editing the guids and saving the project. However that was a red-herring ... I was unwittingly fixing the problem by changing the timestamps of all my csproj files. The build system seemed a lot happier after those timestamps were updated, and it stopped the annoying behavior (continuously attempting to rebuild projects that had already been built.)

The character casing of the guids didn't end up being the problem at all. As far as I can tell, VS 2019 is ok with both upper- and lower-case guids. They can even mismatch the source project, based on my experimentation (eg. the original source project can use uppercase and referencing projects can use lowercase).

If it is helpful to anyone, below is a powershell that will let you adjust the write-time of all csproj files under a path. This will be another trick I use whenever the msbuild system is misbehaving in visual studio.

$datenow = get-date

$files = Get-ChildItem -path "C:\Data\Workspaces\LumberTrack\" -recurse | where { $_.PSIsContainer -eq $false} 

foreach ($file in $files)
{
if ($file.Extension -eq ".csproj") 
{
   Set-ItemProperty $file.FullName LastWriteTime $datenow
   Write-Output $file.FullName
}    
}    
}

VS Project References Broken On Case Sensitivity of GUID

5 Answers