Files generated before build (e.g. by NPM or Gulp) into the wwwroot folder might not be accessible

I have a BeforeTargets=“BeforeBuild” script defined in my csproj file that executes a Gulp task which generates a bunch of js files taking more than 4 seconds to finish. These files are not accessible by the web application only after rebuilding the solution. However, if the script finishes quickly (couple milliseconds) then it will be fine after the first build.

<Target Name="NpmInstall" BeforeTargets="BeforeBuild">
  <Exec Command="npm install" />
  <Exec Command="gulp" />
</Target>

This might be a duplicate by one of the following issues, however, none of the workarounds fixed this scenario where the goal is to access these files locally on my development environment and not after publishing the website.

https://github.com/aspnet/websdk/issues/114 https://github.com/dotnet/sdk/issues/1044

[rainersigwald]

Is the problem that the NpmInstall generates javascript files that you expect to be picked up by the build and deployed with your application?

I suspect that the problem is that you don’t add the files to the appropriate item after generating them in NpmInstall. The default glob (wildcard) includes apply only to files that exist on disk before the build starts. If files are created during the build, they will be discovered for the next build (so it’ll work on rebuild) but not the current build. The solution is to explicitly create the items after creating the files on disk, perhaps something like

  <Target Name="NpmInstall" BeforeTargets="BeforeBuild">
    <Exec Command="npm install" />
    <Exec Command="gulp" />

    <ItemGroup>
      <None Include="path\to\generated\files\*.js" />
    </ItemGroup>
  </Target>

what is the best target to use here? Is BeforeBuild target the ideal one? I remember there is some complication here.

BeforeTargets="BeforeBuild" is a very good place for this. @livarcocc I think you’re thinking of AfterTargets="Build" which has some nasty edge cases.

@barthamark can you elaborate on

However, if the script finishes quickly (couple milliseconds) then it will be fine after the first build.

? That surprises me.

[barthamark]

In the meantime I found that this is caused by the modular framework I am using. It gathers all the resources found in the module’s wwwroot folder (which is a .NET Standard project) and registers them as static resources. I couldn’t reproduce it in a simple ASP.NET Core project. The BeforeBuild task will block the project build until the NPM task is not finished which is the expected way so all the resources are accessible after the build meaning it can’t be a .NET bug (or at least I can’t reproduce it for now). Thank you for your help. I’ll close this issue.