Don't you just hate errors that will tell you something is wrong, but not tell you what? I ran into that case recently while refactoring an Azure Functions project.

Worker failed to index functions
Result: Failure
Exception: System.InvalidOperationException: Functions must declare at least one binding. No bindings were found in the function $func.
at Microsoft.Azure.Functions.Worker.GrpcWorker.GetFunctionMetadataAsync(String functionAppDirectory) 

Notice how this error message doesn't tell you which function is missing bindings? I mean, it really wants too. See that $func? It's trying to tell you which function is missing bindings, but it's not going to just come out and say it.

What's causing the error? It's because I have a [Function()] but no triggers.

So how do you figure out which function is messed up or missing the bindings? The trick I used was to search GitHub for the error message I was getting. That led me to this line of code. Generally speaking, the Azure Function host is looking for the bindings sections in the function metadata.

The function metadata is generated at compile time, and it's stored in a file named functions.metadata. I found the file in my bin folder for the project. Within moments, I saw the problem.

Hey there! If this article was helpful or you have any constructive tidbits to add, please let me know on X, BlueSky, or LinkedIn.

First, here is an example of a well-defined function:

  {
    "name": "AliveCheck",
    "scriptFile": "{... removed for brevity ...}",
    "entryPoint": "{... removed for brevity ...}",
    "language": "dotnet-isolated",
    "properties": {
      "IsCodeless": false
    },
    "bindings": [
      {
        "name": "req",
        "direction": "In",
        "type": "httpTrigger",
        "authLevel": "Function",
        "methods": [
          "GET"
        ],
        "properties": {}
      },
      {
        "name": "$return",
        "type": "http",
        "direction": "Out"
      }
    ]
  }

You'll notice that the bindings section is present, and multiple entries.

My function was missing a bindings section.

  {
    "name": "GetWorkItems",
    "scriptFile": "{... removed for brevity ...}",
    "entryPoint": "{... removed for brevity ...}",
    "language": "dotnet-isolated",
    "properties": {
      "IsCodeless": false
    },
    "bindings": []
  }

Why was this happening? It's because I forgot to add a Trigger to my function. Here's what I had:

[Function(nameof(GetWorkItems))]
public async Task<List<WorkItem>> GetWorkItems(string workItemType)
{
    // ...    
}

Notice there is no Trigger! That's why the function was missing the bindings section in the metadata.

This problem was quickly resolved by adding a trigger to the function.

[Function(nameof(GetWorkItems))]
public async Task<List<WorkItem>> GetWorkItems([QueueTrigger("work-items")] string workItemType)
{
    // ...
}

I hope this helps you resolve the same or similar problem. If this was helpful, let me know on X, BlueSky, or LinkedIn.