Fix case insensitive upload (#15245)

AUTHORS

@@ -602,3 +602,4 @@ a license to everyone to use it as detailed in LICENSE.)
 * Christian Lloyd <clloyd@teladochealth.com> (copyright owned by Teladoc Health, Inc.)
 * Sean Morris <sean@seanmorr.is>
 * Mitchell Wills <mwills@google.com> (copyright owned by Google, Inc.)
+* Alex Walsh (alexwalsh6x7@gmail.com>

test/other/test_collision_icase.js

@@ -0,0 +1,14 @@
+FS.createDataFile('/', "file.txt", "foo");
+var errCode = 0;
+try {
+  FS.createDataFile('/', "fILe.txt", "foo2");
+}
+catch (e)
+{
+  errCode = e.errno;
+}
+var fileContents = FS.readFile("/file.txt");
+out('file.txt: ' + fileContents);
+var ret = FS.analyzePath('/file.txt');
+out('file.txt collison: ' + ret.object.name_next);
+out('errorCode: ' + errCode);

test/other/test_crash_icase.c

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2026 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 <assert.h>
+#include <stdio.h>
+
+#include <emscripten.h>
+
+void loadScript() {
+  printf("load2");
+  FILE* file = fopen("file1.txt", "r");
+
+  if (!file) {
+    assert(false);
+  }
+
+  while (!feof(file)) {
+    char c = fgetc(file);
+    if (c != EOF) {
+      putchar(c);
+    }
+  }
+  fclose(file);
+  exit(0);
+}
+
+void scriptLoadFail() {
+  printf("failed to load data_files.js\n");
+  assert(false);
+}
+
+int main() {
+  emscripten_async_load_script("data_files.js", loadScript, scriptLoadFail);
+  return 99;
+}

test/test_other.py

@@ -13794,9 +13794,24 @@ def test_recursive_cache_lock(self):
     self.assertContained('AssertionError: attempt to lock the cache while a parent process is holding the lock', err)
 
   @also_with_wasmfs
+  @crossplatform
   def test_fs_icase(self):
     # c++20 for ends_with().
     self.do_other_test('test_fs_icase.cpp', cflags=['-sCASE_INSENSITIVE_FS', '-std=c++20'])
+    create_file('file1.txt', 'one')
+    create_file('fILe1.txt', 'two')
+    # `--from-emcc` needed here otherwise the output defines `var Module =` which will shadow the
+    # global `Module`.
+    self.run_process([FILE_PACKAGER, 'test.data', '--preload', 'file1.txt', 'fILe1.txt', '--from-emcc', '--js-output=data_files.js'])
+    self.do_runf('other/test_crash_icase.c', cflags=['-sFORCE_FILESYSTEM', '-sCASE_INSENSITIVE_FS'])
+
+  @crossplatform
+  def test_collision_icase(self):
+    self.set_setting('DEFAULT_LIBRARY_FUNCS_TO_INCLUDE', ['$FS'])
+    self.set_setting('INCLUDE_FULL_LIBRARY', 1)
+    self.set_setting('CASE_INSENSITIVE_FS', 1)
+    self.add_pre_run(read_file(test_file('other/test_collision_icase.js')))
+    self.do_runf('hello_world.c', 'file.txt: 102,111,111\nfile.txt collison: undefined\nerrorCode: 20')
 
   @crossplatform
   @with_all_fs

tools/file_packager.py

@@ -683,8 +683,12 @@ def generate_preload_js(data_target, data_files, metadata):
         } catch (e) {
           err(`Preloading file ${name} failed`, e);
         }\n'''
-  create_data = '''// canOwn this data in the filesystem, it is a slice into the heap that will never change
-        Module['FS_createDataFile'](name, null, data, true, true, true);
+  create_data = '''try {
+          // canOwn this data in the filesystem, it is a slice into the heap that will never change
+          Module['FS_createDataFile'](name, null, data, true, true, true);
+        } catch(e) {
+          err(`Preloading file ${name} failed`, e);
+        }
         Module['removeRunDependency'](`fp ${name}`);'''
 
   finish_handler = create_preloaded if options.use_preload_plugins else create_data