No-error-message: Setting extension bundle in dotnet-isolated results in 0 Functions started

[paulyuk]

If I use one of the common host.json files that asserts extension bundles, the deployed app will silently fail to load with 0 functions started.

I expected to get an error message saying extension bundle config in host.json is invalid, and read to learn how to set properly for dotnet-isolated.

Repros in cloud and using Core Tools 4.0.5198.

Repro steps

1. func init -> dotnet-isolated
2. func new -> HTTP
3. Change host.json to this:

{
    "version": "2.0",
    "logging": { "fileLoggingMode": "debugOnly", "logLevel": { "default": "Information", "Host.Results": "Error", "Function": "Error", "Host.Aggregator": "Trace" } },
    "extensionBundle": {
        "id": "Microsoft.Azure.Functions.ExtensionBundle",
        "version": "[4.0.0, 5.0.0)"
    }
}

4. func start, or deploy

Expected behavior

In Application insights logs I would see a specific message after 0 Functions start:

"ExtensionsBundle config in host.json is invalid for dotnet-isolated. See for details."

[mattchenderson]

This is the line of code that needs to be updated:

azure-functions-host/src/WebJobs.Script/DependencyInjection/ScriptStartupTypeLocator.cs

Line 102 in 6ae92c8

isPrecompiledFunctionApp = isPrecompiledFunctionApp || functionMetadata.Language == DotNetScriptTypes.DotNetAssembly;

An additional OR statement is needed to catch isolated as well. The value being looked for right now is just "DotNetAssembly", but I believe functionMetadata.Language will be "dotnet-isolated" in this case.