func pack errors in custom handler project because 'functions.metadata' not found

[lilyjma]

Version

4.3.0

Description

Running func pack in a custom handler errors because 'functions.metadata' not found in deployment structure. The custom handler is an mcp server, and has FWR set to dotnet-isolated. Running dotnet publish as suggested doesn't help -

local.settings.json found in root directory (/Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet).
Resolving worker runtime to 'dotnet-isolated'.
local.settings.json found in root directory (/Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet).
Resolving worker runtime to 'dotnet-isolated'.
 
Validating project...
 
  Validate host.json: PASSED
 
Building .NET project...
  Determining projects to restore...
  All projects are up-to-date for restore.
  QuickstartWeatherServer -> /Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet/bin/Release/net8.0/QuickstartWeatherServer.dll
  QuickstartWeatherServer -> /Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet/output/
 
 
Validating published output...
  Validate Published Structure: FAILED
    Required file 'functions.metadata' not found in deployment structure. Ensure 'dotnet publish' has been run.
Published output validation failed: Required file 'functions.metadata' not found in deployment structure. Ensure 'dotnet publish' has been run.

Running command inside output directory

I tried running func pack inside the output directory instead of the root. Ran into a different error -

lily@MacBookPro output % func pack 
local.settings.json found in root directory (/Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet/output).
Resolving worker runtime to 'dotnet-isolated'.
local.settings.json found in root directory (/Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet/output).
Resolving worker runtime to 'dotnet-isolated'.

Validating project...

  Validate host.json: PASSED

Building .NET project...
MSBUILD : error MSB1003: Specify a project or solution file. The current working directory does not contain a project or solution file.


Error publishing .NET project

Here's what's inside that directory

/Users/lily/Desktop/Functions/mcp/functions-hosting/test/mcp-sdk-functions-hosting-dotnet/output
lily@MacBookPro output % ls -la
total 3304
drwxr-xr-x  22 lily  staff     704 Oct 23 19:22 .
drwxr-xr-x@ 24 lily  staff     768 Oct 27 10:50 ..
-rw-r--r--   1 lily  staff     361 Oct 23 19:09 host.json
drwxr-xr-x   5 lily  staff     160 Oct 23 19:22 infra
-rw-r--r--   1 lily  staff     175 Oct 14 12:42 local.settings.json
-rwxr--r--   1 lily  staff  332856 Jun 10 13:55 Microsoft.Extensions.AI.Abstractions.dll
-rwxr--r--   1 lily  staff   63768 Sep 16  2024 Microsoft.Extensions.DependencyInjection.Abstractions.dll
-rwxr--r--   1 lily  staff   30480 Sep 16  2024 Microsoft.Extensions.Diagnostics.Abstractions.dll
-rwxr--r--   1 lily  staff   51472 Sep 16  2024 Microsoft.Extensions.Hosting.Abstractions.dll
-rwxr--r--   1 lily  staff   65288 Jan 16  2025 Microsoft.Extensions.Logging.Abstractions.dll
-rwxr--r--   1 lily  staff   64776 Jan 17  2024 Microsoft.Extensions.Options.dll
-rwxr--r--   1 lily  staff   60416 Jun 20 12:25 ModelContextProtocol.AspNetCore.dll
-rwxr--r--   1 lily  staff  729600 Jun 20 12:25 ModelContextProtocol.Core.dll
-rwxr--r--   1 lily  staff   32256 Jun 20 12:25 ModelContextProtocol.dll
-rwxr-xr-x   1 lily  staff  124448 Oct 23 19:18 QuickstartWeatherServer
-rw-r--r--   1 lily  staff   10072 Oct 23 19:18 QuickstartWeatherServer.deps.json
-rw-r--r--   1 lily  staff   16384 Oct 23 19:18 QuickstartWeatherServer.dll
-rw-r--r--   1 lily  staff   23452 Oct 23 19:18 QuickstartWeatherServer.pdb
-rw-r--r--   1 lily  staff     469 Oct 23 19:18 QuickstartWeatherServer.runtimeconfig.json
-rw-r--r--   1 lily  staff      53 Oct 15 17:30 QuickstartWeatherServer.staticwebassets.endpoints.json
-rwxr--r--   1 lily  staff   41752 May  8 19:55 System.Net.ServerSentEvents.dll
-rw-r--r--   1 lily  staff     499 Oct 23 19:22 web.config

FYI @im-samz

Steps to reproduce

1. Clone this repo: https://github.com/Azure-Samples/mcp-sdk-functions-hosting-dotnet
2. Run func pack in the root

[im-samz]

Just repro'd. Similar to #4676, we need to generalize this scenario so that "Validate Published Structure" is branching based on a real scenario. That is, I want our validate...structure validations to branch based on known scenarios.

From Fabio:

[this issue] is being caused by the FUNCTIONS_WORKER_RUNTIME set to dotnet-isolated and you [are] trying to do the build from the project root. This is interpreting the payload as a .NET Isolated payload because of that configuration.

Is this a side effect of our approach for leveraging custom handlers for MCP and our simplification with configurationWorkload?

@fabiocav - who can help us get to the bottom of why this is happening?