one-off container are not indexed, and must be ignored by exec --index command

pkg/compose/create.go

@@ -506,7 +506,10 @@ func (s *composeService) prepareLabels(labels types.Labels, service types.Servic
 	}
 	labels[api.ConfigHashLabel] = hash
 
-	labels[api.ContainerNumberLabel] = strconv.Itoa(number)
+	if number > 0 {
+		// One-off containers are not indexed
+		labels[api.ContainerNumberLabel] = strconv.Itoa(number)
+	}
 
 	var dependencies []string
 	for s, d := range service.DependsOn {

pkg/compose/run.go

@@ -109,7 +109,7 @@ func (s *composeService) prepareRun(ctx context.Context, project *types.Project,
 		return "", err
 	}
 
-	created, err := s.createContainer(ctx, project, service, service.ContainerName, 1, createOpts)
+	created, err := s.createContainer(ctx, project, service, service.ContainerName, -1, createOpts)
 	if err != nil {
 		return "", err
 	}

pkg/e2e/compose_exec_test.go

@@ -65,3 +65,32 @@ func TestLocalComposeExec(t *testing.T) {
 		assert.Check(t, !strings.Contains(res.Stdout(), "FOO="), res.Combined())
 	})
 }
+
+func TestLocalComposeExecOneOff(t *testing.T) {
+	c := NewParallelCLI(t)
+
+	const projectName = "compose-e2e-exec-one-off"
+	cmdArgs := func(cmd string, args ...string) []string {
+		ret := []string{"--project-directory", "fixtures/simple-composefile", "--project-name", projectName, cmd}
+		ret = append(ret, args...)
+		return ret
+	}
+
+	cleanup := func() {
+		c.RunDockerComposeCmd(t, cmdArgs("down", "--timeout=0")...)
+	}
+	cleanup()
+	t.Cleanup(cleanup)
+
+	c.RunDockerComposeCmd(t, cmdArgs("run", "-d", "simple")...)
+
+	t.Run("exec in one-off container", func(t *testing.T) {
+		res := c.RunDockerComposeCmd(t, cmdArgs("exec", "-e", "FOO", "simple", "/usr/bin/env")...)
+		assert.Check(t, !strings.Contains(res.Stdout(), "FOO="), res.Combined())
+	})
+
+	t.Run("exec with index", func(t *testing.T) {
+		res := c.RunDockerComposeCmdNoCheck(t, cmdArgs("exec", "--index", "1", "-e", "FOO", "simple", "/usr/bin/env")...)
+		res.Assert(t, icmd.Expected{ExitCode: 1, Err: "service \"simple\" is not running container #1"})
+	})
+}

pkg/e2e/compose_run_test.go

@@ -62,7 +62,6 @@ func TestLocalComposeRun(t *testing.T) {
 		assert.Assert(t, runContainerID != "")
 		res = c.RunDockerCmd(t, "inspect", runContainerID)
 		res.Assert(t, icmd.Expected{Out: ` "Status": "exited"`})
-		res.Assert(t, icmd.Expected{Out: `"com.docker.compose.container-number": "1"`})
 		res.Assert(t, icmd.Expected{Out: `"com.docker.compose.project": "run-test"`})
 		res.Assert(t, icmd.Expected{Out: `"com.docker.compose.oneoff": "True",`})
 		res.Assert(t, icmd.Expected{Out: `"com.docker.compose.slug": "` + truncatedSlug})