building image with docker compose build: invalid reference format: repository name must be lowercase

Description

I can build an image normally with docker-compose build but trying to build the same image with docker compose build throws an invalid reference format: repository name must be lowercase error

Steps to reproduce the issue:

In the root of my project I run: docker compose build usersrv
The details of the docker-compose and Docker file are below

Docker compose file (partial):

 usersrv:
    build:
      context: .
      dockerfile: ./user/Dockerfile
      target: Dev
    depends_on:
      - pgdb
      - nats
    container_name: usersrvcont
    entrypoint: CompileDaemon --build="go build -o userServer ./user/server/" --command=./userServer
    env_file: ./user/docker-compose.env

Sample Docker file can be found here

Describe the results you received:
I received the following error message:

The new 'docker compose' command is currently experimental. To provide feedback or request new features please open issues at https://github.com/docker/compose-cli
[+] Building 0.1s (3/3) FINISHED                                                
 => [internal] load build definition from Dockerfile                       0.0s
 => => transferring dockerfile: 32B                                        0.0s
 => [internal] load .dockerignore                                          0.0s
 => => transferring context: 35B                                           0.0s
 => [internal] load metadata for docker.io/library/alpine:latest           0.0s
failed to solve: rpc error: code = Unknown desc = failed to solve with frontend dockerfile.v0: failed to create LLB definition: failed to parse stage name "Dev": invalid reference format: repository name must be lowercase

Describe the results you expected:
Image builds successfully

Additional information you deem important (e.g. issue happens only occasionally):

Output of docker version:

Client: Docker Engine - Community
 Cloud integration: 1.0.7
 Version:           20.10.2
 API version:       1.41
 Go version:        go1.13.15
 Git commit:        2291f61
 Built:             Mon Dec 28 16:12:42 2020
 OS/Arch:           darwin/amd64
 Context:           default
 Experimental:      true

Server: Docker Engine - Community
 Engine:
  Version:          20.10.2
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.13.15
  Git commit:       8891c58
  Built:            Mon Dec 28 16:15:28 2020
  OS/Arch:          linux/amd64
  Experimental:     true
 containerd:
  Version:          1.4.3
  GitCommit:        269548fa27e0089a8b8278fc4fc781d7f65a939b
 runc:
  Version:          1.0.0-rc92
  GitCommit:        ff819c7e9184c13b7c2607fe6c30ae19403a7aff
 docker-init:
  Version:          0.19.0
  GitCommit:        de40ad0

Output of docker context show:

default

Output of docker info:

Client:
 Context:    default
 Debug Mode: false
 Plugins:
  app: Docker App (Docker Inc., v0.9.1-beta3)
  buildx: Build with BuildKit (Docker Inc., v0.5.1-docker)
  scan: Docker Scan (Docker Inc., v0.5.0)

Server:
 Containers: 7
  Running: 0
  Paused: 0
  Stopped: 7
 Images: 558
 Server Version: 20.10.2
 Storage Driver: overlay2
  Backing Filesystem: extfs
  Supports d_type: true
  Native Overlay Diff: true
 Logging Driver: json-file
 Cgroup Driver: cgroupfs
 Cgroup Version: 1
 Plugins:
  Volume: local
  Network: bridge host ipvlan macvlan null overlay
  Log: awslogs fluentd gcplogs gelf journald json-file local logentries splunk syslog
 Swarm: inactive
 Runtimes: io.containerd.runtime.v1.linux runc io.containerd.runc.v2
 Default Runtime: runc
 Init Binary: docker-init
 containerd version: 269548fa27e0089a8b8278fc4fc781d7f65a939b
 runc version: ff819c7e9184c13b7c2607fe6c30ae19403a7aff
 init version: de40ad0
 Security Options:
  seccomp
   Profile: default
 Kernel Version: 4.19.121-linuxkit
 Operating System: Docker Desktop
 OSType: linux
 Architecture: x86_64
 CPUs: 2
 Total Memory: 3.847GiB
 Name: docker-desktop
 ID: DVTV:5YQI:46VQ:HL5K:66CP:4SDY:HWI4:EER4:ONW5:DOOD:3C2B:AVZD
 Docker Root Dir: /var/lib/docker
 Debug Mode: true
  File Descriptors: 41
  Goroutines: 46
  System Time: 2021-03-10T20:04:26.0178707Z
  EventsListeners: 3
 HTTP Proxy: gateway.docker.internal:3128
 HTTPS Proxy: gateway.docker.internal:3129
 Registry: https://index.docker.io/v1/
 Labels:
 Experimental: true
 Insecure Registries:
  127.0.0.0/8
 Live Restore Enabled: false

Additional environment details (AWS ECS, Azure ACI, local, etc.):

Local environment

$ docker-compose version
docker-compose version 1.27.4, build 40524192
docker-py version: 4.3.1
CPython version: 3.7.7
OpenSSL version: OpenSSL 1.1.1g  21 Apr 2020

Reproduce docker compose build usersrv from the reported project root and compare it with docker-compose build usersrv. Inspect the linked user/Dockerfile, especially the Dev build target, and trace how the two commands parse that file. Done means the reported image builds successfully with the new docker compose command or the incompatibility is documented with a confirmed scope.