fix: preserve symlinked Node action entrypoints (#1202)

Node resolves an ESM main to its realpath but leaves `process.argv[1]` as passed. `/var/run/act` reaches the action through the `/var/run` -> `/run` symlink most images ship, so the two disagree and actions comparing them skip their own `run()`. Passing `--preserve-symlinks-main` makes them match.

Trade-off: an action whose `runs.main` is a symlink now resolves dependencies from the link's directory rather than the target's.

Fixes https://gitea.com/gitea/runner/issues/1201
Co-authored-by: silverwind <me@silverwind.io>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1202
Reviewed-by: silverwind <2021+silverwind@noreply.gitea.com>
Co-authored-by: bircni <bircni@noreply.gitea.com>

act/runner/action.go

@@ -185,7 +185,7 @@ func runActionImpl(step actionStep, actionDir string, remoteAction *remoteAction
 			if err := maybeCopyToActionDir(ctx, step, actionDir, actionPath, containerActionDir); err != nil {
 				return err
 			}
-			containerArgs := []string{"node", path.Join(containerActionDir, action.Runs.Main)}
+			containerArgs := nodeActionCommand(path.Join(containerActionDir, action.Runs.Main))
 			logger.Debugf("executing remote job container: %s", containerArgs)
 
 			rc.ApplyExtraPath(ctx, step.getEnv())
@@ -232,6 +232,11 @@ func runActionImpl(step actionStep, actionDir string, remoteAction *remoteAction
 	}
 }
 
+// /var/run is a symlink, so without the flag node's import.meta.url differs from argv[1], which ESM actions compare.
+func nodeActionCommand(script string) []string {
+	return []string{"node", "--preserve-symlinks-main", script}
+}
+
 // https://github.com/nektos/act/issues/228#issuecomment-629709055
 // files in .gitignore are not copied in a Docker container
 // this causes issues with actions that ignore other important resources
@@ -592,7 +597,7 @@ func runPreStep(step actionStep) common.Executor {
 				return err
 			}
 
-			containerArgs := []string{"node", path.Join(containerActionDir, action.Runs.Pre)}
+			containerArgs := nodeActionCommand(path.Join(containerActionDir, action.Runs.Pre))
 			logger.Debugf("executing remote job container: %s", containerArgs)
 
 			rc.ApplyExtraPath(ctx, step.getEnv())
@@ -693,7 +698,7 @@ func runPostStep(step actionStep) common.Executor {
 
 			populateEnvsFromSavedState(step.getEnv(), step, rc)
 
-			containerArgs := []string{"node", path.Join(containerActionDir, action.Runs.Post)}
+			containerArgs := nodeActionCommand(path.Join(containerActionDir, action.Runs.Post))
 			logger.Debugf("executing remote job container: %s", containerArgs)
 
 			rc.ApplyExtraPath(ctx, step.getEnv())

act/runner/action_test.go

@@ -8,6 +8,10 @@ import (
 	"context"
 	"io"
 	"io/fs"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
 	"strings"
 	"sync"
 	"testing"
@@ -234,7 +238,7 @@ func TestActionRunner(t *testing.T) {
 				return true
 			})
 
-			cm.On("Exec", []string{"node", "/var/run/act/actions/dir/path"}, envMatcher, "", "").Return(func(ctx context.Context) error { return nil })
+			cm.On("Exec", []string{"node", "--preserve-symlinks-main", "/var/run/act/actions/dir/path"}, envMatcher, "", "").Return(func(ctx context.Context) error { return nil })
 
 			tt.step.getRunContext().JobContainer = cm
 
@@ -246,6 +250,32 @@ func TestActionRunner(t *testing.T) {
 	}
 }
 
+func TestNodeActionCommandPreservesSymlinkedEntrypoint(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("symlink creation requires privileges on Windows")
+	}
+	requireHostTools(t, "node")
+
+	actionDir := t.TempDir()
+	entrypoint := filepath.Join(actionDir, "index.mjs")
+	require.NoError(t, os.WriteFile(entrypoint, []byte(`
+import {fileURLToPath} from "node:url";
+const self = fileURLToPath(import.meta.url);
+if (process.argv[1] !== self) {
+	console.log("argv[1]:", process.argv[1], "import.meta.url:", self);
+	process.exitCode = 1;
+}
+`), 0o600))
+
+	symlinkedActionDir := filepath.Join(t.TempDir(), "action")
+	require.NoError(t, os.Symlink(actionDir, symlinkedActionDir))
+	symlinkedEntrypoint := filepath.Join(symlinkedActionDir, "index.mjs")
+
+	args := nodeActionCommand(symlinkedEntrypoint)
+	output, err := exec.CommandContext(t.Context(), args[0], args[1:]...).CombinedOutput()
+	require.NoError(t, err, "%s", output)
+}
+
 func TestNewStepContainerDoesNotUseDockerSecrets(t *testing.T) {
 	cm := &containerMock{}
 

act/runner/step_action_local_test.go

@@ -254,7 +254,8 @@ func TestStepActionLocalPost(t *testing.T) {
 			if tt.mocks.exec {
 				suffixMatcher := func(suffix string) any {
 					return mock.MatchedBy(func(array []string) bool {
-						return strings.HasSuffix(array[1], suffix)
+						return len(array) == 3 && array[0] == "node" && array[1] == "--preserve-symlinks-main" &&
+							strings.HasSuffix(array[2], suffix)
 					})
 				}
 				cm.On("Exec", suffixMatcher("runner/local/action/post.js"), sal.env, "", "").Return(func(ctx context.Context) error { return tt.err })

act/runner/step_action_remote_test.go

@@ -470,10 +470,10 @@ func TestStepActionRemotePost(t *testing.T) {
 			if tt.mocks.exec {
 				// Use mock.MatchedBy to match the exec command with hash-based path
 				execMatcher := mock.MatchedBy(func(args []string) bool {
-					if len(args) != 2 {
+					if len(args) != 3 {
 						return false
 					}
-					return args[0] == "node" && strings.Contains(args[1], "post.js")
+					return args[0] == "node" && args[1] == "--preserve-symlinks-main" && strings.Contains(args[2], "post.js")
 				})
 
 				cm.On("Exec", execMatcher, sar.env, "", "").Return(func(ctx context.Context) error { return tt.err })