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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 2007 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;

import com.google.debugging.sourcemap.proto.Mapping.OriginalMapping;
import org.jspecify.nullness.Nullable;

/**
 * A source excerpt provider is responsible for building source code excerpt
 * of specific locations, such as a specific line or a region around a
 * given line number.
 */
public interface SourceExcerptProvider {
  /**
   * Source excerpt variety.
   */
  enum SourceExcerpt {
    /**
     * Line excerpt.
     */
    LINE {
      @Override
      public String get(
          SourceExcerptProvider source,
          String sourceName,
          int lineNumber,
          int unused,
          ExcerptFormatter formatter) {
        return formatter.formatLine(
            source.getSourceLine(sourceName, lineNumber), lineNumber);
      }
    },
    /** Multiple lines excerpt. */
    FULL {
      @Override
      public String get(
          SourceExcerptProvider source,
          String sourceName,
          int startLineNumber,
          int length,
          ExcerptFormatter formatter) {
        return formatter.formatRegion(source.getSourceLines(sourceName, startLineNumber, length));
      }
    },
    /**
     * Region excerpt.
     */
    REGION {
      @Override
      public String get(
          SourceExcerptProvider source,
          String sourceName,
          int lineNumber,
          int length,
          ExcerptFormatter formatter) {
        return formatter.formatRegion(
            source.getSourceRegion(sourceName, lineNumber));
      }
    };

    /** Get a source excerpt string based on the type of the source excerpt. */
    public String get(
        SourceExcerptProvider source,
        String sourceName,
        int lineNumber,
        ExcerptFormatter formatter) {
      return this.get(source, sourceName, lineNumber, -1, formatter);
    }

    /** Get a source excerpt string based on the type of the source excerpt. */
    public abstract String get(
        SourceExcerptProvider source,
        String sourceName,
        int lineNumber,
        int length,
        ExcerptFormatter formatter);
  }

  /**
   * Get the line indicated by the line number. This call will return only the
   * specific line.
   *
   * @param lineNumber the line number, 1 being the first line of the file
   * @return the line indicated, or {@code null} if it does not exist
   */
  String getSourceLine(String sourceName, int lineNumber);

  /**
   * Gets the specific lines returned by the beginning and excerpt length. Must not start or end
   * with a carriage return. Implementations may decide to truncate lines but will always include
   * the first line and never be longer than the specified length.
   *
   * @param lineNumber the line number, 1 being the first line of the file
   * @param length the desired length of the excerpt (in chars). If -1, returns just a single line.
   *     Otherwise, returns as many lines as needed. (including the remainder of the last line)
   * @return the region around the line number indicated, or {@code null} if it does not exist
   */
  @Nullable
  Region getSourceLines(String sourceName, int lineNumber, int length);

  /**
   * Get a region around the indicated line number. The exact definition of a region is
   * implementation specific, but it must contain the line indicated by the line number. A region
   * must not start or end by a carriage return.
   *
   * @param lineNumber the line number, 1 being the first line of the file
   * @return the region around the line number indicated, or {@code null} if it does not exist
   */
  @Nullable
  Region getSourceRegion(String sourceName, int lineNumber);

  /**
   * If the source file is associated with an inputSourceMap, does a lookup
   * for the original file position based on this source map.
   */
  OriginalMapping getSourceMapping(String sourceName, int lineNumber, int columnNumber);

  /**
   * A excerpt formatter is responsible of formatting source excerpts.
   */
  interface ExcerptFormatter {
    /**
     * Format a line excerpt.
     */
    String formatLine(String line, int lineNumber);

    /** Format a region excerpt. */
    String formatRegion(@Nullable Region region);
  }
}