Make WASMFS FS.createPath match the FS version behavior on EEXIST (#23603)

Both now continue if a path already exists (but not on other errors).

Fixes #23602.

Author: JoeOsborn

src/lib/libfs.js

@@ -1626,7 +1626,7 @@ FS.staticInit();
         try {
           FS.mkdir(current);
         } catch (e) {
-          // ignore EEXIST
+          if (e.errno != {{{ cDefs.EEXIST }}}) throw e;
         }
         parent = current;
       }

src/lib/libwasmfs.js

@@ -111,7 +111,11 @@ FS.init();
         if (!wasmFSPreloadingFlushed) {
           wasmFSPreloadedDirs.push({parentPath: parent, childName: part});
         } else {
-          FS.mkdir(current);
+          try {
+            FS.mkdir(current);
+          } catch (e) {
+            if (e.errno != {{{ cDefs.EEXIST }}}) throw e;
+          }
         }
         parent = current;
       }

test/fs/test_fs_js_api.c

@@ -38,6 +38,21 @@ EM_JS(void, test_fs_open, (), {
     assert(createFileNotHere && createFileNotHere.fd >= 0);
 });
 
+// createPath should succeed when called on existing paths ( https://github.com/emscripten-core/emscripten/issues/23602 )
+EM_JS(void, test_fs_createPath, (), {
+    FS.createPath('/', 'home', true, true);
+    FS.createPath('/home', 'nested1', true, true);
+    FS.createPath('/home', 'nested2', true, true);
+    FS.writeFile('/home/nested1/test.txt', 'a=1\nb=2\n');
+    FS.writeFile('/home/nested2/test.txt', 'a=2\nb=4\n');
+    var read1 = FS.readFile('/home/nested1/test.txt',{encoding:'utf8'});
+    var read2 = FS.readFile('/home/nested2/test.txt',{encoding:'utf8'});
+    console.log("r1",read1);
+    console.log("r2",read2);
+    assert(read1 == 'a=1\nb=2\n');
+    assert(read2 == 'a=2\nb=4\n');
+});
+
 EM_JS(void, test_fs_rename, (), {
     FS.mkdir('renamedir');
     FS.writeFile('renamedir/renametestfile', "");
@@ -456,6 +471,7 @@ void cleanup() {
 
 int main() {
     test_fs_open();
+    test_fs_createPath();
     test_fs_rename();
     test_fs_readlink();
     test_fs_read();

test/test_browser.py

@@ -1873,6 +1873,22 @@ def setup():
     shutil.copy(Path('sub/test.data'), '.')
     self.btest_exit('test_emscripten_async_load_script.c', args=['-sFORCE_FILESYSTEM'])
 
+  @also_with_wasmfs
+  def test_emscripten_overlapped_package(self):
+    # test that a program that loads multiple file_packager.py packages has a correctly initialized filesystem.
+    # this exercises https://github.com/emscripten-core/emscripten/issues/23602 whose root cause was a difference
+    # between JS FS and WASMFS behavior.
+    def setup():
+      ensure_dir('sub')
+      create_file('sub/file1.txt', 'first')
+      create_file('sub/file2.txt', 'second')
+
+    setup()
+    self.run_process([FILE_PACKAGER, 'test.data', '--preload', 'sub/file1.txt@/target/file1.txt'], stdout=open('script1.js', 'w'))
+    self.run_process([FILE_PACKAGER, 'test2.data', '--preload', 'sub/file2.txt@/target/file2.txt'], stdout=open('script2.js', 'w'))
+    self.btest_exit('test_emscripten_overlapped_package.c', args=['-sFORCE_FILESYSTEM'])
+    self.clear()
+
   def test_emscripten_api_infloop(self):
     self.btest_exit('emscripten_api_browser_infloop.cpp')
 

test/test_emscripten_overlapped_package.c

@@ -0,0 +1,46 @@
+// Copyright 2025 The Emscripten Authors.  All rights reserved.
+// Emscripten is available under two separate licenses, the MIT license and the
+// University of Illinois/NCSA Open Source License.  Both these licenses can be
+// found in the LICENSE file.
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+
+#include <emscripten.h>
+
+void error2() {
+  printf("fail2\n");
+}
+
+void load2() {
+  char buffer[10];
+  memset(buffer, 0, 10);
+  FILE *f = fopen("/target/file1.txt", "r");
+  assert(f);
+  fread(buffer, 1, 5, f);
+  fclose(f);
+  assert(strcmp(buffer, "first") == 0);
+
+  memset(buffer, 0, 10);
+  f = fopen("/target/file2.txt", "r");
+  assert(f);
+  fread(buffer, 1, 6, f);
+  fclose(f);
+  assert(strcmp(buffer, "second") == 0);
+  exit(0);
+}
+
+void load1() {
+  emscripten_async_load_script("script2.js", load2, error2);
+}
+
+void error1() {
+  printf("fail1\n");
+}
+
+int main() {
+  emscripten_async_load_script("script1.js", load1, error1);
+  return 99;
+}