Fixing 'Version conflict detected for Microsoft.CodeAnalysis.Common'

I’ve been upgrading projects from .NET 7 to .NET 8, and mostly it’s been remarkably smooth: edit the .csproj files, replace net7.0 with net8.0, then upgrade any 7.x NuGet packages to their 8.x counterparts, and so far, it’s just worked.

Today I got a weird error message:

error: NU1107: Version conflict detected for Microsoft.CodeAnalysis.Common. Install/reference Microsoft.CodeAnalysis.Common 4.5.0 directly to project Rockaway.WebApp to resolve this issue.

error:  Rockaway.WebApp -> Microsoft.EntityFrameworkCore.Tools 8.0.0 -> Microsoft.EntityFrameworkCore.Design 8.0.0 -> Microsoft.CodeAnalysis.CSharp.Workspaces 4.5.0 -> Microsoft.CodeAnalysis.Common (= 4.5.0)
error:  Rockaway.WebApp -> Microsoft.VisualStudio.Web.CodeGeneration.Design 7.0.10 -> Microsoft.DotNet.Scaffolding.Shared 7.0.10 -> Microsoft.CodeAnalysis.CSharp.Features 4.4.0 -> Microsoft.CodeAnalysis.Common (= 4.4.0).

I’m a big fan of error messages that tell you how to fix the error which caused them, like “Install/reference Microsoft.CodeAnalysis.Common 4.5.0 directly to project Rockaway.WebApp to resolve this issue.” in this one… except, if you look at the notes for Microsoft.CodeAnalysis.Common, it quite clearly says:

“Do not install this package manually, it will be added as a prerequisite by other packages that require it.”

Here’s what’s actually going on.

Before upgrading, my project uses two NuGet packages, both version 7.x because they shipped with .NET 7:

• Microsoft.EntityFrameworkCore.Tools 7.0.12
• Microsoft.VisualStudio.Web.CodeGeneration.Design 7.0.10

Both of these packages have an indirect dependency on Microsoft.CodeAnalysis.Common 4.4.0 – this doesn’t appear anywhere in the .csproj file, so I’m guessing it’s controlled by this line:

<IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>

So you try to upgrade Microsoft.EntityFrameworkCore.Tools to 8.x and it fails, because that package requires Microsoft.CodeAnalysis.Common 4.5.0, but your project includes Microsoft.VisualStudio.Web.CodeGeneration.Design 7.x, which requires Microsoft.CodeAnalysis.Common v4.4.0

The solution that worked for me was to remove the other package (v7.x), upgrade EF Core Tools, then install the other package (which installs the latest version, 8.x):

dotnet remove package Microsoft.VisualStudio.Web.CodeGeneration.Design
dotnet add package Microsoft.EntityFrameworkCore.Tools --version 8
dotnet add package Microsoft.VisualStudio.Web.CodeGeneration.Design