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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.

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/*
 * Copyright 2017 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.newtypes;

import com.google.common.collect.HashMultimap;
import com.google.common.collect.SetMultimap;
import java.util.Collection;
import java.util.HashMap;
import java.util.Map;

/**
 * Configuration options for {@link JSType#toString}.  This object is
 * passed around to all internal types.
 */
public class ToStringContext {

  /**
   * Returns a context that keeps track of printed type variables.
   * The first variable printed with each non-uniquified (simple)
   * name is left as-is. Any later variables are printed in full
   * disambiguated form. For example, if the same context is passed
   * to the "expected" and "found" types in a mismatch message where
   * the types only differ by similarly-named type variables, the
   * result might be {@code
   *   Expected: Foo,
   *   Found: Foo.
   * }
   */
  public static ToStringContext disambiguateTypeVars(JSType... types) {
    DisambiguateTypeVars ctx = new DisambiguateTypeVars();
    StringBuilder sb = new StringBuilder();
    for (JSType type : types) {
      type.appendTo(sb, ctx);
    }
    ctx.freeze();
    return ctx;
  }

  /** The default context for toString(). */
  static final ToStringContext TO_STRING = new ToStringContext();

  /** The default context for toAnnotationString(). */
  static final ToStringContext FOR_ANNOTATION =
      new ToStringContext() {
        @Override
        boolean forAnnotation() {
          return true;
        }
      };

  // Nobody else should be making instances.
  private ToStringContext() {}

  String formatTypeVar(String typeVar) {
    return UniqueNameGenerator.getOriginalName(typeVar);
  }

  boolean forAnnotation() {
    return false;
  }

  private static class DisambiguateTypeVars extends ToStringContext {
    // Map from typevar name prefix (a string without #) to all seen typevars that share the prefix
    final SetMultimap simpleToUnique = HashMultimap.create();
    // Maps the actual internal name of a typevar to the display name chosen for this context
    final Map renamings = new HashMap<>();

    @Override
    String formatTypeVar(String typeVar) {
      String result = renamings.get(typeVar);
      if (result != null) {
        return result;
      }
      String simple = super.formatTypeVar(typeVar);
      simpleToUnique.put(simple, typeVar);
      result = simple + "#" + simpleToUnique.get(simple).size();
      renamings.put(typeVar, result);
      return result;
    }

    /**
     * Removes unnecessary #-suffixes from the renamings map for all cases where the non-suffixed
     * name is not ambiguous.  This is called after the context has seen all the types that will
     * be printed, but before actually generating any messages.  Any new typevars seen after
     * freezing will always be suffixed, even if not necessary for disambiguation.
     */
    void freeze() {
      for (Map.Entry> entry : simpleToUnique.asMap().entrySet()) {
        if (entry.getValue().size() == 1) {
          renamings.put(entry.getValue().iterator().next(), entry.getKey());
        }
      }
    }
  }
}