WebSharper silently fails to download resources, then fails with UseDownloadedResources

[nightroman]

Scenario:

• The project file has WebSharperDownloadResources set to true.
• The app.config has UseDownloadedResources set to true.
• Turn off the internet connection.
  • This step is artificial but the problem is real on temporary connection issues.
• Make sure the project is clean, i.e. does not have previously downloaded resources.

Build and run such a WebSharper project with the above conditions.

As a result,

• The folder WebSharper\WebSharper.JQuery.Resources.JQuery is empty (expected to have downloaded jquery-3.1.1.min.js)
• When started, the web page fails to load the missing local jquery-3.1.1.min.js

Moreover, restore the internet connection (or imagine the temporary downtime is
over), build and run again. The build is not triggered (all is up-to-date, I
presume) and the resources are not downloaded. The build has to be cleaned,
"made dirty", and started again -- then only it works.

Suggestion: if WebSharper fails to download a resource then it should fail or
at least write a warning.

[nightroman]

FWIW, my workaround or an alternative approach:

• Copy once downloaded jquery-3.1.1.min.js as my local file Content/js/jquery-3.1.1.min.js.
• Remove <WebSharperDownloadResources>true</WebSharperDownloadResources> from the project.
• In app.config set <add key="WebSharper.JQuery.Resources.JQuery" value="Content/js/jquery-3.1.1.min.js" />

[Jand42]

Currently WebSharperDownloadResources accepts true and false. I would make true throw an error on compile-time and expand the available values by adding a new option "WarnOnly" that gives only a warning.