Design: Allow IDesignTimeDbContextFactory to short-circuit service provider creation

[ajcvickers]

Implement some way to specify/find a DbContext and IDesignTimeDbContextFactory such that BuildWebHost is never called even if it is present. This should allow a clean escape hatch to be used when building the service provider has side effects that the app needs to prevent.

See discussion in #9033

[bricelam]

Workaround

To prevent EF Core from calling Program.BuildWebHost(), rename it.

[aghe]

Just comment what is in Configure() from Startup when you use the tools for migrations.

[bricelam]

Is there an issue in Hosting that we should report here? If we only ever access the service provider from the IWebHost, why is it calling Startup.Configure()?

[aghe]

From what I see at a quick look on the code BuildWebHost will always call that.

There is a method there seems that is called in BuildWebHost

private static ConfigureBuilder FindConfigureDelegate(Type startupType, string environmentName)
    {
      return new ConfigureBuilder(StartupLoader.FindMethod(startupType, "Configure{0}", environmentName, typeof (void), true));
    }

Maybe I'm wrong

[divega]

@bricelam AFAIR there was a conversation about this around the preview 1 timeframe when there was an exception thrown because there was no certificate to run the web host in production mode. Our general feedback was that the call to .Build() was doing way too much work eagerly which intuitively seemed to belong in .Run().

If this doesn't change .Build() will still really be a poor choice of an entry point for design time.

@glennc said he would follow up on that. Not sure if issues have been filed.

[ajcvickers]

@divega to follow up with @glennc and/or hosting.