Suggest to run Docker for Mac if it isn't running

Instead of suggesting docker-machine.

Signed-off-by: Ben Firshman <ben@firshman.co.uk>

compose/cli/errors.py

@@ -14,6 +14,7 @@ from requests.packages.urllib3.exceptions import ReadTimeoutError
 
 from ..const import API_VERSION_TO_ENGINE_VERSION
 from .utils import call_silently
+from .utils import is_docker_for_mac_installed
 from .utils import is_mac
 from .utils import is_ubuntu
 
@@ -47,16 +48,7 @@ def handle_connection_errors(client):
         if e.args and isinstance(e.args[0], ReadTimeoutError):
             log_timeout_error(client.timeout)
             raise ConnectionError()
-
-        if call_silently(['which', 'docker']) != 0:
-            if is_mac():
-                exit_with_error(docker_not_found_mac)
-            if is_ubuntu():
-                exit_with_error(docker_not_found_ubuntu)
-            exit_with_error(docker_not_found_generic)
-        if call_silently(['which', 'docker-machine']) == 0:
-            exit_with_error(conn_error_docker_machine)
-        exit_with_error(conn_error_generic.format(url=client.base_url))
+        exit_with_error(get_conn_error_message(client.base_url))
     except APIError as e:
         log_api_error(e, client.api_version)
         raise ConnectionError()
@@ -96,6 +88,20 @@ def exit_with_error(msg):
     raise ConnectionError()
 
 
+def get_conn_error_message(url):
+    if call_silently(['which', 'docker']) != 0:
+        if is_mac():
+            return docker_not_found_mac
+        if is_ubuntu():
+            return docker_not_found_ubuntu
+        return docker_not_found_generic
+    if is_docker_for_mac_installed():
+        return conn_error_docker_for_mac
+    if call_silently(['which', 'docker-machine']) == 0:
+        return conn_error_docker_machine
+    return conn_error_generic.format(url=url)
+
+
 docker_not_found_mac = """
     Couldn't connect to Docker daemon. You might need to install Docker:
 
@@ -121,6 +127,10 @@ conn_error_docker_machine = """
     Couldn't connect to Docker daemon - you might need to run `docker-machine start default`.
 """
 
+conn_error_docker_for_mac = """
+    Couldn't connect to Docker daemon. You might need to start Docker for Mac.
+"""
+
 
 conn_error_generic = """
     Couldn't connect to Docker daemon at {url} - is it running?

compose/cli/utils.py

@@ -103,3 +103,7 @@ def get_build_version():
 
     with open(filename) as fh:
         return fh.read().strip()
+
+
+def is_docker_for_mac_installed():
+    return is_mac() and os.path.isdir('/Applications/Docker.app')