Unable to Launch Rails Server using DAP

[Hawkbawk]

Description
Using a fresh Rails project, I'm unable to start debugging the Rails server using Zed's new debugger. If I instead use the just added "attach" functionality done as part of #124, things work great.

Reproduction Steps

1. Install Ruby and Rails
2. Create a new Rails project with rails new example_project
3. Create a .zed/debug.json with the following configuration

[
  {
    "request": "launch",
    "adapter": "rdbg",
    "label": "Launch Rails Server with Ruby extension (Debug)",
    "command": "bin/rails"
  }
]

4. Start debugging using that task. The console will show a cryptic

error:
error: process exited before debugger attached.

Attempted Debugging Steps
I modified the extension to print out the command and arguments that it was going to use to launch the debugging session. I then ran that same command in a terminal. It was able to start successfully and I was able to attach using rdbg -A -p <port> -h <host>. One odd thing I did notice is that the host was a integer, rather than the typical IPv4 octet style. rdbg doesn't seem to mind this though, so long as you pass the same integer to the attach request.

Known Workarounds

1. If you install the latest code from main, start the Rails server with rdbg -o -p 12345 -c -- bin/rails s and use the following debug config, all works well.

  {
    "label": "Attach to Rails server",
    "adapter": "rdbg",
    "request": "attach",
    "cwd": "$ZED_WORKTREE_ROOT",
    "env": {
      "RUBY_DEBUG_PORT": "12345"
    }
  },

2. The built-in Ruby adapter in Zed seems to handle the same JSON config in the repro steps just fine, so something seems to be different between the two, though I'm not sure what.

[andyw8]

"command": "bin/rails"

Shouldn't that be bin/rails s?

[Hawkbawk]

Oops, typo. Unfortunately, that doesn't appear to have fixed it either. Here's the full config, copy pasted so I can't make a mistake:

// Project-local debug tasks
//
// For more documentation on how to configure debug tasks,
// see: https://zed.dev/docs/debugger
[
  {
    "request": "launch",
    "adapter": "rdbg",
    "label": "Launch Rails Server with Ruby extension (Debug)",
    "command": "bin/rails server"
  },
  {
    "label": "Attach to Rails server",
    "adapter": "rdbg",
    "request": "attach",
    "cwd": "$ZED_WORKTREE_ROOT",
    "env": {
      "RUBY_DEBUG_PORT": "52203"
    }
  },
  {
    "request": "launch",
    "adapter": "Ruby",
    "label": "Launch Rails Server with Built-in Ruby DAP",
    "command": "bin/rails server"
  }
]

[Hawkbawk]

Ah, found the issue. Was much harder than it needed to be though, had to step through Zed and modify it to view the child process' stdout. Pull request incoming.