src/ir/names.cpp

/*
 * Copyright 2021 WebAssembly Community Group participants
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include "ir/names.h"
#include <sstream>

namespace wasm::Names {

// Reserved words in JS that we will not emit up to size 4 - size 5 and above
// would mean we use an astronomical number of symbols, which is not realistic
// anyhow.
static std::unordered_set<std::string> reserved = {"do",
                                                   "if",
                                                   "in",
                                                   "for",
                                                   "new",
                                                   "try",
                                                   "var",
                                                   "env",
                                                   "let",
                                                   "case",
                                                   "else",
                                                   "enum",
                                                   "void",
                                                   "this",
                                                   "with"};

// Possible initial letters.
static std::string validInitialChars =
  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$";

// Possible later letters.
static std::string validLaterChars =
  "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_$0123456789";

std::string MinifiedNameGenerator::getName() {
  std::string name;
  do {
    size_t n = state++;
    std::stringstream ss;
    ss << validInitialChars[n % validInitialChars.size()];
    n /= validInitialChars.size();
    // `m` is the number of `state` counts each of the `n` represents.
    size_t m = validInitialChars.size();
    while (n) {
      if (n % (validLaterChars.size() + 1) == 0) {
        // Skip states that contain zeros in later positions.
        state += m;
        ++n;
      }
      ss << validLaterChars[(n % (validLaterChars.size() + 1)) - 1];
      n /= (validLaterChars.size() + 1);
      m *= (validLaterChars.size() + 1);
    }
    name = ss.str();
  } while (reserved.count(name));
  return name;
}

} // namespace wasm::Names