fix: skip service containers with an empty image (#1074)

GitHub Actions skips services whose image evaluates to an empty string, enabling conditional services via expressions like `image: ${{ matrix.image || '' }}`. Here such a service failed the job at `docker create`. Skip them before container creation, using GitHub's log message verbatim, and add a regression test.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1074
Reviewed-by: Nicolas <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

act/runner/run_context.go

@@ -379,6 +379,13 @@ func (rc *RunContext) startJobContainer() common.Executor {
 
 		// add service containers
 		for serviceID, spec := range rc.Run.Job().Services {
+			// GitHub compatibility: skip services whose image evaluates to an
+			// empty string, enabling conditional services via expressions
+			serviceImage := rc.ExprEval.Interpolate(ctx, spec.Image)
+			if serviceImage == "" {
+				logger.Infof("The service '%s' will not be started because the container definition has an empty image.", serviceID)
+				continue
+			}
 			// interpolate env
 			interpolatedEnvs := make(map[string]string, len(spec.Env))
 			for k, v := range spec.Env {
@@ -417,7 +424,7 @@ func (rc *RunContext) startJobContainer() common.Executor {
 			c := container.NewContainer(&container.NewContainerInput{
 				Name:           serviceContainerName,
 				WorkingDir:     ext.ToContainerPath(rc.Config.Workdir),
-				Image:          rc.ExprEval.Interpolate(ctx, spec.Image),
+				Image:          serviceImage,
 				Username:       username,
 				Password:       password,
 				Cmd:            interpolatedCmd,

act/runner/runner_test.go

@@ -303,6 +303,7 @@ func TestRunEvent(t *testing.T) {
 		// services
 		{workdir, "services", "push", "", platforms, secrets},
 		{workdir, "services-with-container", "push", "", platforms, secrets},
+		{workdir, "services-empty-image", "push", "", platforms, secrets},
 
 		// local remote action overrides
 		{workdir, "local-remote-action-overrides", "push", "", platforms, secrets},

act/runner/testdata/services-empty-image/push.yml

@@ -0,0 +1,10 @@
+name: services-empty-image
+on: push
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    services:
+      db:
+        image: ${{ false && 'postgres:16' || '' }}
+    steps:
+      - run: echo "empty-image service was skipped"