Docker provider: catch container name when using podman.

When user is using podman's docker CLI emulation the containers would
fail to enter running state because the docker driver could not catch
the container name. This commit fixes that by adding a check if podman
docker emulation is used and pick the container hash correctly from the
output.

plugins/providers/docker/driver.rb

@@ -26,11 +26,21 @@ def build(dir, **opts, &block)
         result = execute('docker', 'build', *args, opts, &block)
         matches = result.match(/Successfully built (?<id>.+)$/i)
         if !matches
-          # Check for the new output format 'writing image sha256...'
-          # In this case, docker builtkit is enabled. Its format is different
-          # from standard docker
-          @logger.warn("Could not determine docker container ID. Scanning for buildkit output instead")
-          matches = result.match(/writing image .+:(?<id>[0-9a-z]+) done/i)
+          if podman?
+            # Check for podman format when it is emulating docker CLI.
+            # Podman outputs the full hash of the container on
+            # the last line after a successful build.
+            @logger.warn("Could not find docker container ID. Scanning for podman output instead")
+            match = result.split.select { |str| str.match?(/[0-9a-z]{64}/) }.last
+            return match[0..7] unless match.nil?
+          else
+            # Check for the new output format 'writing image sha256...'
+            # In this case, docker builtkit is enabled. Its format is different
+            # from standard docker
+            @logger.warn("Could not determine docker container ID. Scanning for buildkit output instead")
+            matches = result.match(/writing image .+:(?<id>[0-9a-z]+) done/i)
+          end
+
           if !matches
             # This will cause a stack trace in Vagrant, but it is a bug
             # if this happens anyways.
@@ -42,6 +52,16 @@ def build(dir, **opts, &block)
         matches[:id]
       end
 
+      # Check if podman emulating docker CLI is enabled.
+      #
+      # @return [Bool]
+      def podman?
+        execute('docker', '-v')
+          .scan(/podman/)
+          .any?
+      end
+
+
       def create(params, **opts, &block)
         image   = params.fetch(:image)
         links   = params.fetch(:links)

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

@@ -155,6 +155,7 @@
   describe '#build' do
     let(:result) { "Successfully built 1a2b3c4d" }
     let(:buildkit_result) { "writing image sha256:1a2b3c4d done" }
+    let(:podman_result) { "1a2b3c4d5e6f7g8h9i10j11k12l13m14n16o17p18q19r20s21t22u23v24w25x2" }
     let(:cid) { "1a2b3c4d" }
 
     it "builds a container with standard docker" do
@@ -172,6 +173,32 @@
 
       expect(container_id).to eq(cid)
     end
+
+    it "builds a container with podman emulating docker CLI" do
+      allow(subject).to receive(:execute).and_return(podman_result)
+      allow(subject).to receive(:podman?).and_return(true)
+
+      container_id = subject.build("/tmp/fakedir")
+
+      expect(container_id).to eq(cid)
+    end
+  end
+
+  describe '#podman?' do
+    let(:emulating_docker_output) { "podman version 1.7.1-dev" }
+    let(:real_docker_output) { "Docker version 1.8.1, build d12ea79" }
+
+    it 'returns false when docker is used' do
+      allow(subject).to receive(:execute).and_return(real_docker_output)
+
+      expect(subject.podman?).to be false
+    end
+
+    it 'returns true when podman is used' do
+      allow(subject).to receive(:execute).and_return(emulating_docker_output)
+
+      expect(subject.podman?).to be true
+    end
   end
 
   describe '#create' do