module: add --preserve-symlinks-main

Add `--preserve-symlinks-main` option which behaves like
`--preserve-symlinks` but for `require.main`.

PR-URL: https://github.com/nodejs/node/pull/19911
Reviewed-By: James M Snell <jasnell@gmail.com>

1 files changed, 57 insertions, 0 deletions

diff --git a/test/es-module/test-esm-preserve-symlinks-main.js b/test/es-module/test-esm-preserve-symlinks-main.js
new file mode 100644
index 0000000000..fbca5dce74
--- /dev/null
+++ b/test/es-module/test-esm-preserve-symlinks-main.js
@@ -0,0 +1,57 @@
+'use strict';
+
+const common = require('../common');
+const { spawn } = require('child_process');
+const assert = require('assert');
+const path = require('path');
+const fs = require('fs');
+
+const tmpdir = require('../common/tmpdir');
+tmpdir.refresh();
+const tmpDir = tmpdir.path;
+
+fs.mkdirSync(path.join(tmpDir, 'nested'));
+fs.mkdirSync(path.join(tmpDir, 'nested2'));
+
+const entry = path.join(tmpDir, 'nested', 'entry.js');
+const entry_link_absolute_path = path.join(tmpDir, 'link.js');
+const submodule = path.join(tmpDir, 'nested2', 'submodule.js');
+const submodule_link_absolute_path = path.join(tmpDir, 'submodule_link.js');
+
+fs.writeFileSync(entry, `
+const assert = require('assert');
+
+// this import only resolves with --preserve-symlinks-main set
+require('./submodule_link.js');
+`);
+fs.writeFileSync(submodule, '');
+
+try {
+  fs.symlinkSync(entry, entry_link_absolute_path);
+  fs.symlinkSync(submodule, submodule_link_absolute_path);
+} catch (err) {
+  if (err.code !== 'EPERM') throw err;
+  common.skip('insufficient privileges for symlinks');
+}
+
+function doTest(flags, done) {
+  // invoke the main file via a symlink.  In this case --preserve-symlinks-main
+  // dictates that it'll resolve relative imports in the main file relative to
+  // the symlink, and not relative to the symlink target; the file structure set
+  // up above requires this to not crash when loading ./submodule_link.js
+  spawn(process.execPath,
+        flags.concat([
+          '--preserve-symlinks',
+          '--preserve-symlinks-main', entry_link_absolute_path
+        ]),
+        { stdio: 'inherit' }).on('exit', (code) => {
+    assert.strictEqual(code, 0);
+    done();
+  });
+}
+
+// first test the commonjs module loader
+doTest([], () => {
+  // now test the new loader
+  doTest(['--experimental-modules'], () => {});
+});