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com.google.debugging.sourcemap.SourceMapGeneratorV3 Maven / Gradle / Ivy

/*
 * Copyright 2011 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.debugging.sourcemap;

import static com.google.common.base.Preconditions.checkState;
import static com.google.common.base.Strings.nullToEmpty;

import com.google.common.base.Preconditions;
import com.google.debugging.sourcemap.SourceMapConsumerV3.EntryVisitor;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Deque;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Objects;
import javax.annotation.Nullable;

/**
 * Collects information mapping the generated (compiled) source back to
 * its original source for debugging purposes.
 *
 * Source Map Revision 3 Proposal:
 * https://docs.google.com/document/d/1U1RGAehQwRypUTovF1KRlpiOFze0b-_2gc6fAH0KY0k/edit?usp=sharing
 */
public final class SourceMapGeneratorV3 implements SourceMapGenerator {

  /**
   * This interface provides the merging strategy when an extension conflict
   * appears because of merging two source maps on method
   * {@link #mergeMapSection}.
   */
  public interface ExtensionMergeAction {

    /**
     * Returns the merged value between two extensions with the same name when
     * merging two source maps
     *
     * @param extensionKey The extension name in conflict
     * @param currentValue The extension value in the current source map
     * @param newValue The extension value in the input source map
     * @return The merged value
     */
    Object merge(String extensionKey, Object currentValue,
        Object newValue);
  }

  private static final int UNMAPPED = -1;


  /**
   * A pre-order traversal ordered list of mappings stored in this map.
   */
  private final List mappings = new ArrayList<>();

  /**
   * A map of source names to source name index
   */
  private final LinkedHashMap sourceFileMap =
       new LinkedHashMap<>();

  /**
   * A map of source names to source file contents
   */
  private final LinkedHashMap sourceFileContentMap =
       new LinkedHashMap<>();

  /**
   * A map of source names to source name index
   */
  private final LinkedHashMap originalNameMap =
       new LinkedHashMap<>();

  /**
   * Cache of the last mappings source name.
   */
  private String lastSourceFile = null;

  /**
   * Cache of the last mappings source name index.
   */
  private int lastSourceFileIndex = -1;

  /**
   * For validation store the last mapping added.
   */
  private Mapping lastMapping;

  /**
   * The position that the current source map is offset in the
   * buffer being used to generated the compiled source file.
   */
  private FilePosition offsetPosition = new FilePosition(0, 0);

  /**
   * The position that the current source map is offset in the
   * generated the compiled source file by the addition of a
   * an output wrapper prefix.
   */
  private FilePosition prefixPosition = new FilePosition(0, 0);

  /**
   * A list of extensions to be added to sourcemap. The value is a object
   * to permit single values, like strings or numbers, and JsonObject or
   * JsonArray objects.
   */
  private final LinkedHashMap extensions = new LinkedHashMap<>();

  /**
   * The source root path for relocating source fails or avoid duplicate values
   * on the source entry.
   */
  private String sourceRootPath;

  /**
   * {@inheritDoc}
   */
  @Override
  public void reset() {
    mappings.clear();
    lastMapping = null;
    sourceFileMap.clear();
    sourceFileContentMap.clear();
    originalNameMap.clear();
    lastSourceFile = null;
    lastSourceFileIndex = -1;
    offsetPosition = new FilePosition(0, 0);
    prefixPosition = new FilePosition(0, 0);
  }

  /**
   * @param validate Whether to perform (potentially costly) validation on the
   * generated source map.
   */
  @Override
  public void validate(boolean validate) {
    // Nothing currently.
  }

  /**
   * Sets the prefix used for wrapping the generated source file before
   * it is written. This ensures that the source map is adjusted for the
   * change in character offsets.
   *
   * @param prefix The prefix that is added before the generated source code.
   */
  @Override
  public void setWrapperPrefix(String prefix) {
    // Determine the current line and character position.
    int prefixLine = 0;
    int prefixIndex = 0;

    for (int i = 0; i < prefix.length(); ++i) {
      if (prefix.charAt(i) == '\n') {
        prefixLine++;
        prefixIndex = 0;
      } else {
        prefixIndex++;
      }
    }

    prefixPosition = new FilePosition(prefixLine, prefixIndex);
  }

  /**
   * Sets the source code that exists in the buffer for which the
   * generated code is being generated. This ensures that the source map
   * accurately reflects the fact that the source is being appended to
   * an existing buffer and as such, does not start at line 0, position 0
   * but rather some other line and position.
   *
   * @param offsetLine The index of the current line being printed.
   * @param offsetIndex The column index of the current character being printed.
   */
  @Override
  public void setStartingPosition(int offsetLine, int offsetIndex) {
    checkState(offsetLine >= 0);
    checkState(offsetIndex >= 0);
    offsetPosition = new FilePosition(offsetLine, offsetIndex);
  }

  /**
   * Adds a mapping for the given node.  Mappings must be added in order.
   * @param startPosition The position on the starting line
   * @param endPosition The position on the ending line.
   */
  @Override
  public void addMapping(
      String sourceName, @Nullable String symbolName,
      FilePosition sourceStartPosition,
      FilePosition startPosition, FilePosition endPosition) {

    // Don't bother if there is not sufficient information to be useful.
    if (sourceName == null || sourceStartPosition.getLine() < 0) {
      return;
    }

    FilePosition adjustedStart = startPosition;
    FilePosition adjustedEnd = endPosition;

    if (offsetPosition.getLine() != 0
        || offsetPosition.getColumn() != 0) {
      // If the mapping is found on the first line, we need to offset
      // its character position by the number of characters found on
      // the *last* line of the source file to which the code is
      // being generated.
      int offsetLine = offsetPosition.getLine();
      int startOffsetPosition = offsetPosition.getColumn();
      int endOffsetPosition = offsetPosition.getColumn();

      if (startPosition.getLine() > 0) {
        startOffsetPosition = 0;
      }

      if (endPosition.getLine() > 0) {
        endOffsetPosition = 0;
      }

      adjustedStart = new FilePosition(
          startPosition.getLine() + offsetLine,
          startPosition.getColumn() + startOffsetPosition);

      adjustedEnd = new FilePosition(
          endPosition.getLine() + offsetLine,
          endPosition.getColumn() + endOffsetPosition);
    }

    // Create the new mapping.
    Mapping mapping = new Mapping();
    mapping.sourceFile = sourceName;
    mapping.originalPosition = sourceStartPosition;
    mapping.originalName = symbolName;
    mapping.startPosition = adjustedStart;
    mapping.endPosition = adjustedEnd;

    // Validate the mappings are in a proper order.
    if (lastMapping != null) {
      int lastLine = lastMapping.startPosition.getLine();
      int lastColumn = lastMapping.startPosition.getColumn();
      int nextLine = mapping.startPosition.getLine();
      int nextColumn = mapping.startPosition.getColumn();
      Preconditions.checkState(nextLine > lastLine
          || (nextLine == lastLine && nextColumn >= lastColumn),
          "Incorrect source mappings order, previous : (%s,%s)\n"
          + "new : (%s,%s)",
          lastLine, lastColumn, nextLine, nextColumn);
    }

    lastMapping = mapping;
    mappings.add(mapping);
  }

  @Override public void addSourcesContent(String source, String content) {
    sourceFileContentMap.put(source, content);
  }

  class ConsumerEntryVisitor implements EntryVisitor {

    @Override
    public void visit(
        String sourceName, String symbolName,
        FilePosition sourceStartPosition,
        FilePosition startPosition, FilePosition endPosition) {
      addMapping(sourceName, symbolName,
          sourceStartPosition, startPosition, endPosition);
    }
  }

  /**
   * Merges current mapping with {@code mapSectionContents} considering the
   * offset {@code (line, column)}. Any extension in the map section will be
   * ignored.
   *
   * @param line The line offset
   * @param column The column offset
   * @param mapSectionContents The map section to be appended
   * @throws SourceMapParseException
   */
  public void mergeMapSection(int line, int column, String mapSectionContents)
      throws SourceMapParseException {
    setStartingPosition(line, column);
    SourceMapConsumerV3 section = new SourceMapConsumerV3();
    section.parse(mapSectionContents);
    section.visitMappings(new ConsumerEntryVisitor());
  }

  /**
   * Works like {@link #mergeMapSection(int, int, String)}, except that
   * extensions from the @{code mapSectionContents} are merged to the top level
   * source map. For conflicts a {@code mergeAction} is performed.
   *
   * @param line The line offset
   * @param column The column offset
   * @param mapSectionContents The map section to be appended
   * @param mergeAction The merge action for conflicting extensions
   * @throws SourceMapParseException
   */
  public void mergeMapSection(int line, int column, String mapSectionContents,
      ExtensionMergeAction mergeAction)
      throws SourceMapParseException {
    setStartingPosition(line, column);
    SourceMapConsumerV3 section = new SourceMapConsumerV3();
    section.parse(mapSectionContents);
    section.visitMappings(new ConsumerEntryVisitor());
    for (Entry entry : section.getExtensions().entrySet()) {
       String extensionKey = entry.getKey();
       if (extensions.containsKey(extensionKey)) {
         extensions.put(extensionKey,
             mergeAction.merge(extensionKey,
                               extensions.get(extensionKey),
                               entry.getValue()));
       } else {
         extensions.put(extensionKey, entry.getValue());
       }
     }
  }

  /**
   * Writes out the source map in the following format (line numbers are for reference only and are
   * not part of the format):
   *
   * 
   * 1.  {
   * 2.    version: 3,
   * 3.    file: "out.js",
   * 4.    lineCount: 2,
   * 5.    sourceRoot: "",
   * 6.    sources: ["foo.js", "bar.js"],
   * 7.    sourcesContent: ["var foo", "var bar"],
   * 8.    names: ["src", "maps", "are", "fun"],
   * 9.    mappings: "a;;abcde,abcd,a;"
   * 10.   x_org_extension: value
   * 11. }
   * 
   *
   * 

   *   
Line 1 : The entire file is a single JSON object
   *   
Line 2 : File version (always the first entry in the object)
   *   
Line 3 : [Optional] The name of the file that this source map is associated with.
   *   
Line 4 : [Optional] The number of lines represented in the source map.
   *   
Line 5 : [Optional] An optional source root, useful for relocating source files on a
   *       server or removing repeated prefix values in the "sources" entry.
   *   
Line 6 : A list of sources used by the "mappings" entry relative to the sourceRoot.
   *   
Line 7 : An optional list of the full content of the source files.
   *   
Line 8 : A list of symbol names used by the "mapping" entry. This list may be incomplete.
   *       Line 9 : The mappings field.
   *   
Line 10: Any custom field (extension).
   * 
   */
  @Override
  public void appendTo(Appendable out, @Nullable String name) throws IOException {
    int maxLine = prepMappings() + 1;

    // Add the header fields.
    out.append("{\n");
    appendFirstField(out, "version", "3");
    if (name != null) {
      appendField(out, "file", escapeString(name));
    }
    appendField(out, "lineCount", String.valueOf(maxLine));

    //optional source root
    if (this.sourceRootPath != null && !this.sourceRootPath.isEmpty()) {
      appendField(out, "sourceRoot", escapeString(this.sourceRootPath));
    }

    // Add the mappings themselves.
    appendFieldStart(out, "mappings");
    // out.append("[");
    (new LineMapper(out, maxLine)).appendLineMappings();

    // out.append("]");
    appendFieldEnd(out);

    // Files names
    appendFieldStart(out, "sources");
    out.append("[");
    addSourceNameMap(out);
    out.append("]");
    appendFieldEnd(out);

    // Sources contents
    addSourcesContentMap(out);

    // Identifier names
    appendFieldStart(out, "names");
    out.append("[");
    addSymbolNameMap(out);
    out.append("]");
    appendFieldEnd(out);

    // Extensions, only if there is any
    for (String key : this.extensions.keySet()) {
      Object objValue = this.extensions.get(key);
      String value;
      if (objValue instanceof String) {
        value = escapeString((String) objValue);  // escapes native String
      } else {
        value = objValue.toString();
      }
      appendField(out, key, value);
    }

    out.append("\n}\n");
  }

  /**
   * A prefix to be added to the beginning of each sourceName passed to
   * {@link #addMapping}. Debuggers expect (prefix + sourceName) to be a URL
   * for loading the source code.
   *
   * @param path The URL prefix to save in the sourcemap file. (Not validated.)
   */
  public void setSourceRoot(String path){
    this.sourceRootPath = path;
  }

  /**
   * Adds field extensions to the json source map. The value is allowed to be
   * any value accepted by json, eg. string, JsonObject, JsonArray, etc.
   *
   * Extensions must follow the format x_orgranization_field (based on V3
   * proposal), otherwise a {@code SourceMapParseExtension} will be thrown.
   *
   * @param name The name of the extension with format organization_field
   * @param object The value of the extension as a valid json value
   * @throws SourceMapParseException  if extension name is malformed
   */
  public void addExtension(String name, Object object)
      throws SourceMapParseException{
    if (!name.startsWith("x_")){
      throw new SourceMapParseException("Extension '" + name +
                                        "' must start with 'x_'");
    }
    this.extensions.put(name, object);
  }

  /**
   * Removes an extension by name if present.
   *
   * @param name The name of the extension with format organization_field
   */
  public void removeExtension(String name) {
    if (this.extensions.containsKey(name)) {
      this.extensions.remove(name);
    }
  }

  /**
   * Check whether or not the sourcemap has an extension.
   *
   * @param name The name of the extension with format organization_field
   * @return If the extension exist
   */
  public boolean hasExtension(String name) {
    return this.extensions.containsKey(name);
  }

  /**
   * Returns the value mapped by the specified extension
   * or {@code null} if this extension does not exist.
   *
   * @param name
   * @return the extension value or {@code null}
   */
  public Object getExtension(String name) {
    return this.extensions.get(name);
  }

  /**
   * Writes the source name map to 'out'.
   */
  private void addSourceNameMap(Appendable out) throws IOException {
    addNameMap(out, sourceFileMap);
  }

  private void addSourcesContentMap(Appendable out) throws IOException {
    boolean found = false;
    int size = sourceFileMap.size();
    List contents = new ArrayList<>(size);
    contents.addAll(Collections.nCopies(size, ""));
    for (Map.Entry entry : sourceFileContentMap.entrySet()) {
      Integer index = sourceFileMap.get(entry.getKey());
      if (index != null && index < size) {
        contents.set(index, entry.getValue());
        found = true;
      }
    }
    if (!found) {
      return;
    }
    appendFieldStart(out, "sourcesContent");
    out.append("[");
    for (int i = 0; i < size; i++) {
      if (i != 0) {
        out.append(",");
      }
      String sourceContent = contents.get(i);
      out.append(escapeString(nullToEmpty(sourceContent)));
    }
    out.append("]");
    appendFieldEnd(out);
  }

  /**
   * Writes the source name map to 'out'.
   */
  private void addSymbolNameMap(Appendable out) throws IOException {
    addNameMap(out, originalNameMap);
  }

  private static void addNameMap(Appendable out, Map map)
      throws IOException {
    int i = 0;
    for (Entry entry : map.entrySet()) {
      String key = entry.getKey();
      if (i != 0) {
        out.append(",");
      }
      out.append(escapeString(key));
      i++;
    }
  }

  /**
   * Escapes the given string for JSON.
   */
  private static String escapeString(String value) {
    return Util.escapeString(value);
  }

  // Source map field helpers.

  private static void appendFirstField(
      Appendable out, String name, CharSequence value)
      throws IOException {
    appendFieldStart(out, name, true);
    out.append(value);
  }

  private static void appendField(
      Appendable out, String name, CharSequence value)
      throws IOException {
    appendFieldStart(out, name, false);
    out.append(value);
  }

  private static void appendFieldStart(Appendable out, String name)
      throws IOException {
    appendFieldStart(out, name, false);
  }

  private static void appendFieldStart(Appendable out, String name, boolean first)
      throws IOException {
    if (!first) {
      out.append(",\n");
    }
    out.append("\"");
    out.append(name);
    out.append("\"");
    out.append(":");
  }

  @SuppressWarnings("unused")
  private static void appendFieldEnd(Appendable out)
     throws IOException {
  }

  /**
   * Assigns sequential ids to used mappings, and returns the last line mapped.
   */
  private int prepMappings() throws IOException {
    // Mark any unused mappings.
    (new MappingTraversal()).traverse(new UsedMappingCheck());

    // Renumber used mappings and keep track of the last line.
    int id = 0;
    int maxLine = 0;
    for (Mapping m : mappings) {
      if (m.used) {
        m.id = id++;
        int endPositionLine = m.endPosition.getLine();
        maxLine = Math.max(maxLine, endPositionLine);
      }
    }

    // Adjust for the prefix.
    return maxLine + prefixPosition.getLine();
  }

  /**
   * A mapping from a given position in an input source file to a given position
   * in the generated code.
   */
  static class Mapping {
    /**
     * A unique ID for this mapping for record keeping purposes.
     */
    int id = UNMAPPED;

    /**
     * The source file index.
     */
    String sourceFile;

    /**
     * The position of the code in the input source file. Both
     * the line number and the character index are indexed by
     * 1 for legacy reasons via the Rhino Node class.
     */
    FilePosition originalPosition;

    /**
     * The starting position of the code in the generated source
     * file which this mapping represents. Indexed by 0.
     */
    FilePosition startPosition;

    /**
     * The ending position of the code in the generated source
     * file which this mapping represents. Indexed by 0.
     */
    FilePosition endPosition;

    /**
     * The original name of the token found at the position
     * represented by this mapping (if any).
     */
    String originalName;

    /**
     * Whether the mapping is actually used by the source map.
     */
    boolean used = false;
  }

  /**
   * Mark any visited mapping as "used".
   */
  private static class UsedMappingCheck implements MappingVisitor {
    /**
     * @throws IOException
     */
    @Override
    public void visit(Mapping m, int line, int col, int nextLine, int nextCol)
        throws IOException {
      if (m != null) {
        m.used = true;
      }
    }
  }

  private interface MappingVisitor {
    /**
     * @param m The mapping for the current code segment. null if the segment
     *     is unmapped.
     * @param line The starting line for this code segment.
     * @param col The starting column for this code segment.
     * @param endLine The ending line
     * @param endCol The ending column
     * @throws IOException
     */
    void visit(Mapping m, int line, int col, int endLine, int endCol)
        throws IOException;
  }

  /**
   * Walk the mappings and visit each segment of the mappings, unmapped
   * segments are visited with a null mapping, unused mapping are not visited.
   */
  private class MappingTraversal {
    // The last line and column written
    private int line;
    private int col;

    MappingTraversal() {
    }

    // Append the line mapping entries.
    void traverse(MappingVisitor v) throws IOException {
      // The mapping list is ordered as a pre-order traversal.  The mapping
      // positions give us enough information to rebuild the stack and this
      // allows the building of the source map in O(n) time.
      Deque stack = new ArrayDeque<>();
      for (Mapping m : mappings) {
        // Find the closest ancestor of the current mapping:
        // An overlapping mapping is an ancestor of the current mapping, any
        // non-overlapping mappings are siblings (or cousins) and must be
        // closed in the reverse order of when they encountered.
        while (!stack.isEmpty() && !isOverlapped(stack.peek(), m)) {
          Mapping previous = stack.pop();
          maybeVisit(v, previous);
        }

        // Any gaps between the current line position and the start of the
        // current mapping belong to the parent.
        Mapping parent = stack.peek();
        maybeVisitParent(v, parent, m);

        stack.push(m);
      }

      // There are no more children to be had, simply close the remaining
      // mappings in the reverse order of when they encountered.
      while (!stack.isEmpty()) {
        Mapping m = stack.pop();
        maybeVisit(v, m);
      }
    }

    /**
     * @return The line adjusted for the prefix position.
     */
    private int getAdjustedLine(FilePosition p) {
      return p.getLine() + prefixPosition.getLine();
    }

    /**
     * @return The column adjusted for the prefix position.
     */
    private int getAdjustedCol(FilePosition p) {
      int rawLine = p.getLine();
      int rawCol = p.getColumn();
      // Only the first line needs the character position adjusted.
      return (rawLine != 0)
          ? rawCol : rawCol + prefixPosition.getColumn();
    }

    /**
     * @return Whether m1 ends before m2 starts.
     */
    private boolean isOverlapped(Mapping m1, Mapping m2) {
      // No need to use adjusted values here, relative positions are sufficient.
      int l1 = m1.endPosition.getLine();
      int l2 = m2.startPosition.getLine();
      int c1 = m1.endPosition.getColumn();
      int c2 = m2.startPosition.getColumn();

      return (l1 == l2 && c1 >= c2) || l1 > l2;
    }

    /**
     * Write any needed entries from the current position to the end of the
     * provided mapping.
     */
    private void maybeVisit(MappingVisitor v, Mapping m) throws IOException {
      int nextLine = getAdjustedLine(m.endPosition);
      int nextCol = getAdjustedCol(m.endPosition);
      // If this anything remaining in this mapping beyond the
      // current line and column position, write it out now.
      if (line < nextLine || (line == nextLine && col < nextCol)) {
        visit(v, m, nextLine, nextCol);
      }
    }

    /**
     * Write any needed entries to complete the provided mapping.
     */
    private void maybeVisitParent(MappingVisitor v, Mapping parent, Mapping m)
        throws IOException {
      int nextLine = getAdjustedLine(m.startPosition);
      int nextCol = getAdjustedCol(m.startPosition);
      // If the previous value is null, no mapping exists.
      checkState(line < nextLine || col <= nextCol);
      if (line < nextLine || (line == nextLine && col < nextCol)) {
        visit(v, parent, nextLine, nextCol);
      }
    }

    /**
     * Write any entries needed between the current position the next position
     * and update the current position.
     */
    private void visit(MappingVisitor v, Mapping m,
        int nextLine, int nextCol)
        throws IOException {
      checkState(line <= nextLine);
      checkState(line < nextLine || col < nextCol);

      if (line == nextLine && col == nextCol) {
        // Nothing to do.
        throw new IllegalStateException();
      }

      v.visit(m, line, col, nextLine, nextCol);

      line = nextLine;
      col = nextCol;
    }
  }

  /**
   * Appends the index source map to the given buffer.
   *
   * @param out The stream to which the map will be appended.
   * @param name The name of the generated source file that this source map
   *   represents.
   * @param sections An ordered list of map sections to include in the index.
   * @throws IOException
   */
  @Override
  public void appendIndexMapTo(
      Appendable out, String name, List sections)
      throws IOException {
    // Add the header fields.
    out.append("{\n");
    appendFirstField(out, "version", "3");
    appendField(out, "file", escapeString(name));

    // Add the line character maps.
    appendFieldStart(out, "sections");
    out.append("[\n");
    boolean first = true;
    for (SourceMapSection section : sections) {
      if (first) {
        first = false;
      } else {
        out.append(",\n");
      }
      out.append("{\n");
      appendFieldStart(out, "offset", true);
      appendOffsetValue(out, section.getLine(), section.getColumn());
      if (section.getSectionType() == SourceMapSection.SectionType.URL) {
        appendField(out, "url", escapeString(section.getSectionValue()));
      } else if (section.getSectionType() == SourceMapSection.SectionType.MAP) {
        appendField(out, "map", section.getSectionValue());
      } else {
        throw new IOException("Unexpected section type");
      }
      out.append("\n}");
    }

    out.append("\n]");
    appendFieldEnd(out);

    out.append("\n}\n");
  }

  private static void appendOffsetValue(Appendable out, int line, int column) throws IOException {
    out.append("{\n");
    appendFirstField(out, "line", String.valueOf(line));
    appendField(out, "column", String.valueOf(column));
    out.append("\n}");
  }

  private int getSourceId(String sourceName) {
    if (!Objects.equals(sourceName, lastSourceFile)) {
      lastSourceFile = sourceName;
      Integer index = sourceFileMap.get(sourceName);
      if (index != null) {
        lastSourceFileIndex = index;
      } else {
        lastSourceFileIndex = sourceFileMap.size();
        sourceFileMap.put(sourceName, lastSourceFileIndex);
      }
    }
    return lastSourceFileIndex;
  }

  private int getNameId(String symbolName) {
    int originalNameIndex;
    Integer index = originalNameMap.get(symbolName);
    if (index != null) {
      originalNameIndex = index;
    } else {
      originalNameIndex = originalNameMap.size();
      originalNameMap.put(symbolName, originalNameIndex);
    }
    return originalNameIndex;
  }

  private class LineMapper implements MappingVisitor {
    // The destination.
    private final Appendable out;
    private final int maxLine; // TODO(johnlenz): This shouldn't be necessary to track.

    private int previousLine = -1;
    private int previousColumn = 0;

    // Previous values used for storing relative ids.
    private int previousSourceFileId;
    private int previousSourceLine;
    private int previousSourceColumn;
    private int previousNameId;

    LineMapper(Appendable out, int maxLine) {
      this.out = out;
      this.maxLine = maxLine;
    }

    /**
     * As each segment is visited write out the appropriate line mapping.
     */
    @Override
    public void visit(Mapping m, int line, int col, int nextLine, int nextCol)
      throws IOException {
      if (previousLine != line) {
        previousColumn = 0;
      }

      if (line != nextLine || col != nextCol) {
        // TODO(johnlenz): For some reason, we have mappings beyond the max line.
        // So far they're just null mappings and we can ignore them.
        // (If they're non-null, we assert-fail.)
        if (line < maxLine) {
          if (previousLine == line) { // not the first entry for the line
            out.append(',');
          }
          writeEntry(m, col);
          previousLine = line;
          previousColumn = col;
        } else {
          checkState(m == null);
        }
      }

      for (int i = line; i <= nextLine && i < maxLine; i++) {
        if (i == nextLine) {
          break;
        }

        closeLine(false);
        openLine(false);
      }
    }

    /**
     * Writes an entry for the given column (of the generated text) and
     * associated mapping.
     * The values are stored as relative to the last seen values for each
     * field and encoded as Base64VLQs.
     */
    void writeEntry(Mapping m, int column) throws IOException {
      // The relative generated column number
      Base64VLQ.encode(out, column - previousColumn);
      previousColumn = column;
      if (m != null) {
        // The relative source file id
        int sourceId = getSourceId(m.sourceFile);
        Base64VLQ.encode(out, sourceId - previousSourceFileId);
        previousSourceFileId = sourceId;

        // The relative source file line and column
        int srcline = m.originalPosition.getLine();
        int srcColumn = m.originalPosition.getColumn();
        Base64VLQ.encode(out, srcline - previousSourceLine);
        previousSourceLine = srcline;

        Base64VLQ.encode(out, srcColumn - previousSourceColumn);
        previousSourceColumn = srcColumn;

        if (m.originalName != null) {
          // The relative id for the associated symbol name
          int nameId = getNameId(m.originalName);
          Base64VLQ.encode(out, (nameId - previousNameId));
          previousNameId = nameId;
        }
      }
    }

    // Append the line mapping entries.
    void appendLineMappings() throws IOException {
      // Start the first line.
      openLine(true);

      (new MappingTraversal()).traverse(this);

      // And close the final line.
      closeLine(true);
    }

    /**
     * Begin the entry for a new line.
     */
    private void openLine(boolean firstEntry) throws IOException {
      if (firstEntry) {
        out.append('\"');
      }
    }

    /**
     * End the entry for a line.
     */
    private void closeLine(boolean finalEntry) throws IOException {
      out.append(';');
      if (finalEntry) {
        out.append('\"');
      }
    }
  }

}