Roslyn Source Generator skipped because of trailing space in .cs file name [closed]

Question

I had an issue where a Roslyn source generator was not being called at all in a .NET project, the breakpoint of the Initialize method did not hit, while the launchSettings.json was correct and it did in fact work for some other projects.

Answer 1

The cause was a filename with a space at the end before the .cs extension, in my example it was: ValueTypeMapping .cs

Because of this trailing space, Roslyn silently skipped analyzers and source generators during the build for the project — without any indication or error messages. I did do /bl build and had the MS build structured log viewer where it didn't look like it had anything, I also did a /pp build and that proved the analyzer was not passed <Analyzer Include= should show {SourceGeneratorName}.dll, which it didn't.

To prevent this in the future, I added a build validation step to fail fast if any file has a trailing space:

<Target Name="ValidateNoTrailingSpacesInFileNames" BeforeTargets="CoreCompile">
    <ItemGroup>
        <!-- Check if the Filename part (without extension) ends with a space using Regex -->
        <FilesWithTrailingSpaces
            Include="@(Compile)"
            Condition="'%(Filename)' != '' AND $([System.Text.RegularExpressions.Regex]::IsMatch('%(Filename)', '\s$'))"
             />
        <!-- Explanation:
             '$([System.Text.RegularExpressions.Regex]::IsMatch('%(Filename)', '\s$'))'
             Calls the static Regex.IsMatch method.
             Input: '%(Filename)'
             Pattern: '\s$' (whitespace \s at the end $)
             MSBuild evaluates the boolean result ('True'/'False') directly in the condition.
        -->
    </ItemGroup>

    <Error
        Text="File '%(FilesWithTrailingSpaces.Identity)' has trailing spaces before its extension (Filename: '%(FilesWithTrailingSpaces.Filename)'). Please rename it."
        Condition="@(FilesWithTrailingSpaces) != ''" />
</Target>

To my Directory.Build.props file (on the repository level).