config: support overriding the guest directory with HOST_DIR set

internal/commands/config/config.go

@@ -98,10 +98,6 @@ func runConfig(_ *cobra.Command, _ []string) error {
 		return fmt.Errorf("%w: --builds-dir and TART_EXECUTOR_HOST_DIR are mutually exclusive",
 			ErrConfigFailed)
 	}
-	if tartConfig.HostDir && guestBuildsDir != "" {
-		return fmt.Errorf("%w: --guest-builds-dir and TART_EXECUTOR_HOST_DIR are mutually exclusive",
-			ErrConfigFailed)
-	}
 
 	if buildsDir != "" && guestBuildsDir != "" {
 		return fmt.Errorf("%w: --builds-dir and --guest-builds-dir are mutually exclusive",
@@ -128,7 +124,9 @@ func runConfig(_ *cobra.Command, _ []string) error {
 		if err := os.MkdirAll(buildsDir, 0700); err != nil {
 			return err
 		}
-	case guestBuildsDir != "":
+	}
+
+	if guestBuildsDir != "" {
 		gitlabRunnerConfig.BuildsDir = guestBuildsDir
 	}
 

internal/commands/config/config_test.go

@@ -0,0 +1,63 @@
+package config
+
+import (
+	"encoding/json"
+	"io"
+	"os"
+	"testing"
+
+	"github.com/cirruslabs/gitlab-tart-executor/internal/tart"
+	"github.com/stretchr/testify/require"
+)
+
+func TestConfigHostDirWithGuestBuildsDir(t *testing.T) {
+	envHostDir := "CUSTOM_ENV_TART_EXECUTOR_HOST_DIR"
+	envJobID := "CUSTOM_ENV_CI_JOB_ID"
+	guestBuildsDirValue := "/custom/guest/builds"
+
+	savedHostDir, hadHostDir := os.LookupEnv(envHostDir)
+	savedJobID, hadJobID := os.LookupEnv(envJobID)
+	savedGuestBuildsDir := guestBuildsDir
+
+	os.Setenv(envHostDir, "true")
+	os.Setenv(envJobID, "test-123")
+	guestBuildsDir = guestBuildsDirValue
+
+	defer func() {
+		os.Unsetenv(envHostDir)
+		os.Unsetenv(envJobID)
+		if hadHostDir {
+			os.Setenv(envHostDir, savedHostDir)
+		}
+		if hadJobID {
+			os.Setenv(envJobID, savedJobID)
+		}
+		guestBuildsDir = savedGuestBuildsDir
+	}()
+
+	r, w, err := os.Pipe()
+	require.NoError(t, err)
+	tmp := os.Stdout
+	os.Stdout = w
+	defer func() {
+		os.Stdout = tmp
+	}()
+
+	err = runConfig(nil, nil)
+	w.Close()
+	require.NoError(t, err)
+
+	out, err := io.ReadAll(r)
+	require.NoError(t, err)
+
+	var result struct {
+		BuildsDir string            `json:"builds_dir"`
+		JobEnv    map[string]string `json:"job_env"`
+	}
+	require.NoError(t, json.Unmarshal(out, &result))
+	require.Equal(t, guestBuildsDirValue, result.BuildsDir)
+
+	require.Contains(t, result.JobEnv, tart.EnvTartExecutorInternalBuildsDirOnHost)
+	require.Contains(t, result.JobEnv, tart.EnvTartExecutorInternalBuildsDir)
+	require.Equal(t, guestBuildsDirValue, result.JobEnv[tart.EnvTartExecutorInternalBuildsDir])
+}