Mvc: Layout not rendered via ViewStart.cshtml: Question on Razor View discovery in .Net Core preview 1

[Ponant]

Hi,
I was using a simple but otherwise great library in .Net Core 1.1 by Scott Allen https://github.com/OdeToCode/AddFeatureFolders/ that allows one to put controllers and views in a Feature-folder architecture. The View discovery of this NuGet was working perfectly fine in 1.1, but implementing this architecture in .Net Core 2.0 Preview 1 makes the Layout View via ViewStart.cshtml not discoverable. I tested this with an empty template from preview 1 with the minimum required (one controller one view, one shared folder hosting a layout, and one viewstart and viewimport). The workaround is to call Layout="_Layout" from the view to be rendered in RenderBody() (e.g. Index view of a Home controller) https://github.com/OdeToCode/AddFeatureFolders/issues/16.
Thus my question: is there any change that occurred to the view engine since 1.1 you can point me to and that could be at the origin of this malfunctioning? I have seen some comments but they seem to concern Razor pages only
https://github.com/aspnet/Mvc/issues/6308
https://github.com/aspnet/Mvc/issues/6428

[pranavkm]

Could you share a repro app (preferably as a GitHub repo)? There haven't been too many changes to the _ViewStart discovery in regular cshtml views since 1.0, so it'd hard you to point to a specific changeset.

[Ponant]

@pranavkm https://github.com/Ponant/LayoutFeature .
Navigate to http://localhost:56964/myroute and you should see only Index. If instead you uncomment Layout="_Layout" in the Index.cshtml, then you should see Layout and Index.

[rynowak]

@pranavkm is there a bug here? If we're not compatible with 1.1 then this is bad.

[Ponant]

It seems that Scott's NuGet is searching in the correct locations

Mvc\Home\_Layout.cshtml
Mvc\Shared\_Layout.cshtml

But somehow the program fails to load them unless I explicitly call them from the Home/Index View

[pranavkm]

@rynowak - we missed a path normalization (\\ -> /') when switching from ViewHierarchyUtility to RazorTemplateEngine to look for imports. I'm verifying the fix now.

[rynowak]

So it sounds like no tooling impact right? This is just in the pieces that resolve the layout?

[pranavkm]

Yup. It's isolated to the view engine + view location expanders.

[Ponant]

@pranavkm @rynowak , do you think that will be fixed for the second round, i.e. Preview 2?

[pranavkm]

@Ponant - we're close to signing off on our preview2 work, and its unlikely we would reset for a bug fix at this point. This should be available for 2.0.0 release though.
That said for preview2 you should be able to workaround this by inserting a view location expander, that runs after the FeatureViewLocationExpander, that replaces back slashes with forward slashes:

```C#
public class FixBackSlashViewLocationExpander : IViewLocationExpander
{
public IEnumerable ExpandViewLocations(ViewLocationExpanderContext context, IEnumerable viewLocations)
{
foreach (var path in viewLocations)
{
yield return path.Replace('\', '/');
}
}

public void PopulateValues(ViewLocationExpanderContext context){}
}
```

[Ponant]

@pranavkm , your workaround should work for preview 1 also, or only preview 2? Thanks

[pranavkm]

Both of those releases.

[Ponant]

OK I will try this in the meanwhile.

[Ponant]

To complete @pranavkm workaround, one needs to configure services as such

            services.Configure<RazorViewEngineOptions>(options =>
            {
                options.ViewLocationExpanders.Add(new FixBackSlashViewLocationExpander());
            });