Fixes #10798: Enhance how docker compose driver path expands

Prior to this commit, the docker compose driver would _always_ path
expand a host volume no matter what. This is not always the correct
option, for example if that host volume is actually a reference to a key
inside a `volumes` hash instead of a path on disk. This commit changes
that by looking to see if the requested host volume is actually a
defined key inside the compose config, and if not, it will path expand
it like before. Otherwise it will leave the key "as is".

plugins/providers/docker/driver/compose.rb

@@ -102,7 +102,19 @@ module VagrantPlugins
               # will be fixed someday and the gsub below can be removed.
               host.gsub!(/^[^A-Za-z]+/, "")
             end
-            host = @machine.env.cwd.join(host).to_s
+            # if host path is a volume key, don't expand it.
+            # if both exist (a path and a key) show warning and move on
+            # otherwise assume it's a realative path and expand the host path
+            compose_config = get_composition
+            if compose_config["volumes"] && compose_config["volumes"].keys.include?(host)
+              if File.directory?(@machine.env.cwd.join(host).to_s)
+                @machine.env.ui.warn(I18n.t("docker_provider.volume_path_not_expanded",
+                                           host: host))
+              end
+            else
+              @logger.debug("Path expanding #{host} to current Vagrant working dir instead of docker-compose config file directory")
+              host = @machine.env.cwd.join(host).to_s
+            end
             "#{host}:#{guest}"
           end
           cmd     = Array(params.fetch(:cmd))

templates/locales/providers_docker.yml

@@ -104,6 +104,12 @@ en:
       destroy the container and recreate it.
     waiting_for_running: |-
       Waiting for container to enter "running" state...
+    volume_path_not_expanded: |-
+      Host path `%{host}` exists as a `volumes` key and is a folder on disk. Vagrant
+      will not expand this key like it used to and instead leave it as is defined.
+      If this folder is intended to be used, make sure its full path is defined
+      in your `volumes` config. More information can be found on volumes in the
+      docker compose documentation.
 
     messages:
       destroying: |-

test/unit/plugins/providers/docker/driver_compose_test.rb

@@ -106,6 +106,22 @@ describe VagrantPlugins::DockerProvider::Driver::Compose do
       end
     end
 
+    context 'with a volumes key in use for mounting' do
+      let(:compose_config) { {"volumes"=>{"my_volume_key"=>"data"}} }
+
+      before do
+        params[:volumes] = 'my_volume_key:my/guest/path'
+        allow(Pathname).to receive(:new).with('./path').and_call_original
+        allow(Pathname).to receive(:new).with('my_volume_key').and_call_original
+        allow(Pathname).to receive(:new).with('/compose/cwd/my_volume_key').and_call_original
+        allow(subject).to receive(:get_composition).and_return(compose_config)
+      end
+
+      it 'should not expand the relative host directory' do
+        expect(docker_yml).to receive(:write).with(%r{my_volume_key})
+      end
+    end
+
     it 'links containers' do
       params[:links].each do |link|
         expect(docker_yml).to receive(:write).with(/#{link}/)