Return EISDIR when trying to create a path ending in / with open

If we open a path that in a / and we're about to create a file, instead return EISDIR.

Author: hoodmane

src/library_fs.js

@@ -1053,6 +1053,7 @@ FS.staticInit();
         mode = 0;
       }
       var node;
+      var isDirPath = path.endsWith("/");
       if (typeof path == 'object') {
         node = path;
       } else {
@@ -1074,6 +1075,8 @@ FS.staticInit();
           if ((flags & {{{ cDefs.O_EXCL }}})) {
             throw new FS.ErrnoError({{{ cDefs.EEXIST }}});
           }
+        } else if(isDirPath) {
+          throw new FS.ErrnoError({{{ cDefs.EISDIR }}});
         } else {
           // node doesn't exist, try to create it
           node = FS.mknod(path, mode, 0);

test/fs/test_fs_eisdir.c

@@ -0,0 +1,36 @@
+#include <unistd.h>
+#include <sys/stat.h>
+#include <stdio.h>
+#include <fcntl.h>
+#include <errno.h>
+#include <string.h>
+#include <assert.h>
+
+#if defined(__EMSCRIPTEN__)
+#include <emscripten.h>
+#endif
+
+void makedir(const char *dir) {
+  int rtn = mkdir(dir, 0777);
+  assert(rtn == 0);
+}
+
+void changedir(const char *dir) {
+  int rtn = chdir(dir);
+  assert(rtn == 0);
+}
+
+void setup() {
+#if defined(__EMSCRIPTEN__) && defined(NODEFS)
+  makedir("working");
+  EM_ASM(FS.mount(NODEFS, { root: '.' }, 'working'));
+  changedir("working");
+#endif
+}
+
+int main() {
+    setup();
+    open("./does-not-exist/", O_CREAT);
+    assert(errno == EISDIR);
+    printf("success\n");
+}

test/test_core.py

@@ -5900,6 +5900,16 @@ def test_fs_rename_on_existing(self, args):
       self.set_setting('FORCE_FILESYSTEM')
     self.do_runf('fs/test_fs_rename_on_existing.c', 'success', emcc_args=args)
 
+  @parameterized({
+    '': ([],),
+    'nodefs': (['-DNODEFS', '-lnodefs.js'],),
+    'noderawfs': (['-sNODERAWFS'],)
+  })
+  def test_fs_eisdir(self, args):
+    if self.get_setting('WASMFS'):
+      self.set_setting('FORCE_FILESYSTEM')
+    self.do_runf('fs/test_fs_eisdir.c', 'success', emcc_args=args)
+
   def test_sigalrm(self):
     self.do_runf('test_sigalrm.c', 'Received alarm!')
     self.set_setting('EXIT_RUNTIME')