Add self-hosted macOS runner support?

Behaviour

Docker Desktop works on macOS (Docker runs in a Linux VM managed by Docker Desktop).

GitHub Actions docs say only Linux runners are supported for Docker builds.

Multi-arch builds on GitHub hosted runners via setup-qemu-action are INSANELY slow (from 10 minutes to 1.5 hours). The same multi-arch builds on my Intel MacBook Pro with Docker Desktop is very fast.

It would be great if I could utilise my own hardware to build multi-arch images quickly with GitHub Actions.

Steps to reproduce this issue

Send a job using setup-qemu-action to a self hosted macOS runner.

Expected behaviour

setup-qemu-action should work on self hosted macOS runners.

Actual behaviour

When I attempt a build on a self-hosted macOS runner I get this error:

Error: Only supported on linux platform

Configuration

name: ci

on:
  push:
    branches:
      - '*multiarch'

jobs:
  ci:
    runs-on:
      - macOS
      - self-hosted
    steps:
      - name: Checkout
        uses: actions/checkout@v2

      - name: Docker meta
        id: docker_meta
        uses: crazy-max/ghaction-docker-meta@v1
        with:
          images: FOO/BAR
          tag-sha: true

      - name: Set up QEMU
        uses: docker/setup-qemu-action@v1

... snipped since error occurs in `setup-qemu-action`

Logs

Run docker/setup-qemu-action@v1
  with:
    image: tonistiigi/binfmt:latest
    platforms: all
Error: Only supported on linux platform

[tonistiigi]

I run a GitHub self hosted runner in a container with docker desktop for Mac.

Why would it detect it as macos then if it is already in Linux container.

@crazy-max Anyway, I think we can allow this if docker is available.

[crazy-max]

@mrmachine I’ve removed os limitation (#30). Can you try with crazy-max/docker-setup-qemu-action@remove-limitation?