[WasmFS] Support file embedding (#16105)

This practically worked since #16050, but the JS side needs to support a
missing parent, which is how the file packager emits it.

Fixes #16014

Author: kripken

src/library_wasmfs.js

@@ -50,7 +50,8 @@ var WasmfsLibrary = {
     createDataFile: function(parent, name, data, canRead, canWrite, canOwn) {
       // Data files must be cached until the file system itself has been initialized.
       var mode = FS.getMode(canRead, canWrite);
-      wasmFS$preloadedFiles.push({pathName: parent, fileData: data, mode: mode});
+      var pathName = name ? parent + '/' + name : parent;
+      wasmFS$preloadedFiles.push({pathName: pathName, fileData: data, mode: mode});
     },
     createPath: function(parent, path, canRead, canWrite) {
       // Cache file path directory names.

tests/test_other.py

@@ -1502,7 +1502,11 @@ def test_include_file(self, args):
     result = self.run_js('a.out.js', engine=config.NODE_JS)
     self.assertContained('|hello from a file wi|', result)
 
-  def test_embed_file_dup(self):
+  @parameterized({
+    '': ([],),
+    'wasmfs': (['-sWASMFS'],),
+  })
+  def test_embed_file_dup(self, args):
     ensure_dir(self.in_dir('tst', 'test1'))
     ensure_dir(self.in_dir('tst', 'test2'))
 
@@ -1529,7 +1533,7 @@ def test_embed_file_dup(self):
       }
     ''')
 
-    self.run_process([EMXX, 'main.cpp', '--embed-file', 'tst'])
+    self.run_process([EMXX, 'main.cpp', '--embed-file', 'tst'] + args)
     self.assertContained('|frist|\n|sacond|\n|thard|\n', self.run_js('a.out.js'))
 
   def test_exclude_file(self):

tools/file_packager.py

@@ -649,7 +649,7 @@ def generate_js(data_target, data_files, metadata):
         var content = HEAPU32[start32++];
         var name = UTF8ToString(name_addr)
         // canOwn this data in the filesystem, it is a slice of wasm memory that will never change
-        Module['FS_createDataFile'](undefined, name, HEAP8.subarray(content, content + len), true, true, true);
+        Module['FS_createDataFile'](name, null, HEAP8.subarray(content, content + len), true, true, true);
       } while (HEAPU32[start32]);'''
     else:
       err('--obj-output is recommended when using --embed.  This outputs an object file for linking directly into your application is more effecient than JS encoding')