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Closure Compiler is a JavaScript optimizing compiler. It parses your JavaScript, analyzes it, removes dead code and rewrites and minimizes what's left. It also checks syntax, variable references, and types, and warns about common JavaScript pitfalls. It is used in many of Google's JavaScript apps, including Gmail, Google Web Search, Google Maps, and Google Docs. This binary checks for style issues such as incorrect or missing JSDoc usage, and missing goog.require() statements. It does not do more advanced checks such as typechecking.

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/*
 * Copyright 2016 The Closure Compiler Authors.
 *
 * 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.
 */

package com.google.javascript.jscomp.transpile;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.base.Supplier;
import com.google.common.base.Suppliers;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.util.concurrent.UncheckedExecutionException;
import com.google.javascript.jscomp.bundle.TranspilationException;
import java.net.URI;
import java.util.Objects;

/**
 * A transpiler implementation that delegates to a lower-level
 * implementation on a cache miss.  Passed a CacheBuilder to
 * allow specifying maximum size and other requirements externally.
 */
public final class CachingTranspiler implements Transpiler {

  private final LoadingCache cache;
  private final Supplier runtime;

  public CachingTranspiler(
      final Transpiler delegate, CacheBuilder builder) {
    checkNotNull(delegate);
    this.cache =
        builder.build(
            new CacheLoader() {
              @Override
              public TranspileResult load(Key key) {
                return delegate.transpile(key.path, key.code);
              }
            });
    this.runtime = Suppliers.memoize(delegate::runtime);
  }

  @Override
  public TranspileResult transpile(URI path, String code) {
    try {
      return cache.getUnchecked(new Key(path, code));
    } catch (UncheckedExecutionException e) {
      if (e.getCause() instanceof TranspilationException) {
        // If transpilation fails due to a parse error we can get an UncheckedExecutionException.
        // This is because BaseTranspiler wraps the parse error as an TranspilationException.
        // TODO(joeltine): This might better as a checked exception?
        throw new TranspilationException(e);
      } else {
        throw e;
      }
    }
  }

  @Override
  public String runtime() {
    return runtime.get();
  }

  private static final class Key {
    private final URI path;
    private final String code;

    Key(URI path, String code) {
      this.path = checkNotNull(path);
      this.code = checkNotNull(code);
    }

    @Override
    public boolean equals(Object other) {
      return other instanceof Key
          && ((Key) other).path.equals(path) && ((Key) other).code.equals(code);
    }

    @Override
    public int hashCode() {
      return Objects.hash(path, code);
    }
  }
}