report better error message instead of : Could not resolve configuration for package demo

[mw66]

System information

• dub version: DUB version 1.36.0, built on Mar 1 2024
• OS Platform and distribution: Linux Ubuntu 20.04.6
• compiler version dmd.2.107.1.linux.tar.xz

Bug Description

https://forum.dlang.org/thread/ucsmoyjsvpbwljnqjoaj@forum.dlang.org

Very simple thing from https://dub.pm/getting-started/first-steps/

After I add dependencies, it cannot build:

$ cat dub.json
{
        "authors": [
                "mw"
        ],
        "copyright": "Copyright © 2024, mw",
        "description": "msgpack-rpc-d demo.",
        "license": "MIT",
        "name": "demo",
        "dependencies": {
                "msgpack-rpc": "~>0.1.3"
        },
        "subConfigurations": {
                "msgpack-rpc": "default"
        }
}

$ dub build
Could not resolve configuration for package demo

How to reproduce?

See above.

Expected Behavior

better error message, so the user can know where to look at, i.e

Trying to build your dependency msgpack-rpc, it spits out

     Warning The sub configuration directive "vibe-d" -> [libevent] references a configuration that does not exist.
Error Could not resolve configuration for package msgpack-rpc