Fix ldbcmd cant use custom comparator (#12159)

Summary:
According to this [Q&A](https://github.com/facebook/rocksdb/wiki/RocksDB-FAQ#:~:text=Q%3A%20If%20I%20use%20non%2Ddefault%20comparators%20or%20merge%20operators%2C%20can%20I%20still%20use%20ldb%20tool%3F), user should be able to use LDB with passing a customized comparator into the option.

In the process of opening DB in order to perform ldb commands, there is a exception saying comparator not match even if a option with customized comparator is provided. After initializing the column family to open DB, the `LDBCommand::OverrideBaseCFOptions` method does not update the comparator inside column family descriptor using the passed in options. This can cause a mismatch while doing version edit, and in function `ToggleUDT CompareComparator` it will failed and return a exception saying comparator not match.

Propose fix by updating the column family descriptor's option using the user passed in option. Also a test case is provided to illustrate the steps.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/12159

Reviewed By: hx235

Differential Revision: D52267367

Pulled By: ajkr

fbshipit-source-id: c240f93f440e02cb485893de058a46c6dbf9654b

tools/ldb_cmd.cc

@@ -762,6 +762,10 @@ void LDBCommand::OverrideBaseCFOptions(ColumnFamilyOptions* cf_opts) {
     }
   }
 
+  if (options_.comparator != nullptr) {
+    cf_opts->comparator = options_.comparator;
+  }
+
   cf_opts->force_consistency_checks = force_consistency_checks_;
   if (use_table_options) {
     cf_opts->table_factory.reset(NewBlockBasedTableFactory(table_options));

tools/ldb_cmd_test.cc

@@ -14,6 +14,7 @@
 #include "file/filename.h"
 #include "port/stack_trace.h"
 #include "rocksdb/advanced_options.h"
+#include "rocksdb/comparator.h"
 #include "rocksdb/convenience.h"
 #include "rocksdb/db.h"
 #include "rocksdb/file_checksum.h"
@@ -1207,6 +1208,50 @@ TEST_F(LdbCmdTest, RenameDbAndLoadOptions) {
   ASSERT_OK(DestroyDB(new_dbname, opts));
 }
 
+class MyComparator : public Comparator {
+ public:
+  int Compare(const rocksdb::Slice& a, const rocksdb::Slice& b) const override {
+    return a.compare(b);
+  }
+  void FindShortSuccessor(std::string* /*key*/) const override {}
+  void FindShortestSeparator(std::string* /*start*/,
+                             const Slice& /*limit*/) const override {}
+  const char* Name() const override { return "my_comparator"; }
+};
+
+TEST_F(LdbCmdTest, CustomComparator) {
+  Env* env = TryLoadCustomOrDefaultEnv();
+  MyComparator my_comparator;
+  Options opts;
+  opts.env = env;
+  opts.create_if_missing = true;
+  opts.create_missing_column_families = true;
+  opts.comparator = &my_comparator;
+
+  std::string dbname = test::PerThreadDBPath(env, "ldb_cmd_test");
+  DB* db = nullptr;
+
+  std::vector<ColumnFamilyDescriptor> cfds = {{kDefaultColumnFamilyName, opts}};
+  std::vector<ColumnFamilyHandle*> handles;
+  ASSERT_OK(DestroyDB(dbname, opts));
+  ASSERT_OK(DB::Open(opts, dbname, cfds, &handles, &db));
+  ASSERT_OK(db->Put(WriteOptions(), "k1", "v1"));
+
+  for (auto& h : handles) {
+    ASSERT_OK(db->DestroyColumnFamilyHandle(h));
+  }
+  delete db;
+
+  char arg1[] = "./ldb";
+  std::string arg2 = "--db=" + dbname;
+  char arg3[] = "get";
+  char arg4[] = "k1";
+  char* argv[] = {arg1, const_cast<char*>(arg2.c_str()), arg3, arg4};
+
+  ASSERT_EQ(0,
+            LDBCommandRunner::RunCommand(4, argv, opts, LDBOptions(), nullptr));
+}
+
 }  // namespace ROCKSDB_NAMESPACE
 
 int main(int argc, char** argv) {