[BUG] Mix of mapping and list causes error, which is not caught

[ArcticFall]

Description

Using a list of mappings (dashes and colon) in docker compose causes an error, when using docker compose config, that is hard to read and therefore fix.

e.g. the following code mixes a list with mappings:

environment:
  - MYSQL_DATABASE: nextcloud
  - MYSQL_INITDB_SKIP_TZINFO: 1

running docker compose config returns the following error message:
panic: interface conversion: interface {} is string, not map[string]interface {}

It would be better, if this was caught and a meaningful error message would be displayed, the help users fix the error. e.g. a line number and more descriptive text.

see previous discussion in #11267

Steps To Reproduce

Have this in a docker-compose file:

environment:
  - MYSQL_DATABASE: nextcloud
  - MYSQL_INITDB_SKIP_TZINFO: 1

Run: docker compose config
Get error: panic: interface conversion: interface {} is string, not map[string]interface {}

Compose Version

2.24.6

Docker Environment

Client: Docker Engine - Community
Version: 25.0.3
Context: default
Debug Mode: false
Plugins:
buildx: Docker Buildx (Docker Inc.)
Version: v0.12.1
Path: /usr/libexec/docker/cli-plugins/docker-buildx
compose: Docker Compose (Docker Inc.)
Version: v2.24.6
Path: /usr/libexec/docker/cli-plugins/docker-compose

Anything else?

No response

[ndeloof]

the following code mixes a list with mappings:

no, you example uses a list of nested mappings, while environment can be set either as list a string or a mapping:

environment:
  - MYSQL_DATABASE=nextcloud
  - MYSQL_INITDB_SKIP_TZINFO=1

or

environment:
  MYSQL_DATABASE: nextcloud
  MYSQL_INITDB_SKIP_TZINFO: 1

still, the error isn't very helpful and compose should not panic, this we have to fix

[ndeloof]

Latest release avoids a panic an reports:
failed to load project: services.toto.environment.[0]: unexpected type map[string]interface {}