Remove redundancy in source map entries.

sdk/lib/_internal/compiler/implementation/source_map_builder.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library source_map_builder;
 
 import 'util/util.dart';
 import 'scanner/scannerlib.dart' show Token;
 import 'source_file.dart';
 import 'util/uri_extras.dart' show relativize;
 
 class SourceMapBuilder {
   static const int VLQ_BASE_SHIFT = 5;
   static const int VLQ_BASE_MASK = (1 << 5) - 1;
   static const int VLQ_CONTINUATION_BIT = 1 << 5;
   static const int VLQ_CONTINUATION_MASK = 1 << 5;
   static const String BASE64_DIGITS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmn'
                                       'opqrstuvwxyz0123456789+/';
 
   final Uri uri;
   final Uri fileUri;
 
+  SourceFile targetFile;
   List<SourceMapEntry> entries;
 
   Map<String, int> sourceUrlMap;
   List<String> sourceUrlList;
   Map<String, int> sourceNameMap;
   List<String> sourceNameList;
 
   int previousTargetLine;
   int previousTargetColumn;
   int previousSourceUrlIndex;
   int previousSourceLine;
   int previousSourceColumn;
   int previousSourceNameIndex;
   bool firstEntryInLine;
 
-  SourceMapBuilder(this.uri, this.fileUri) {
+  SourceMapBuilder(this.uri, this.fileUri, this.targetFile) {
     entries = new List<SourceMapEntry>();
 
     sourceUrlMap = new Map<String, int>();
     sourceUrlList = new List<String>();
     sourceNameMap = new Map<String, int>();
     sourceNameList = new List<String>();
 
     previousTargetLine = 0;
     previousTargetColumn = 0;
     previousSourceUrlIndex = 0;
     previousSourceLine = 0;
     previousSourceColumn = 0;
     previousSourceNameIndex = 0;
     firstEntryInLine = true;
   }
 
+  resetPreviousSourceLocation() {
+    previousSourceUrlIndex = 0;
+    previousSourceLine = 0;
+    previousSourceColumn = 0;
+    previousSourceNameIndex = 0;
+  }
+
+  updatePreviousSourceLocation(SourceFileLocation sourceLocation) {
+    previousSourceLine = sourceLocation.getLine();
+    previousSourceColumn = sourceLocation.getColumn();
+    String sourceUrl = sourceLocation.getSourceUrl();
+    previousSourceUrlIndex = indexOf(sourceUrlList, sourceUrl, sourceUrlMap);
+    String sourceName = sourceLocation.getSourceName();
+    if (sourceName != null) {
+      previousSourceNameIndex =
+          indexOf(sourceNameList, sourceName, sourceNameMap);
+    }
+  }
+
+  bool sameAsPreviousLocation(SourceFileLocation sourceLocation) {
+    if (sourceLocation == null) {
+      return true;
+    }
+    int sourceUrlIndex =
+        indexOf(sourceUrlList, sourceLocation.getSourceUrl(), sourceUrlMap);
+    return
+       sourceUrlIndex == previousSourceUrlIndex &&
+       sourceLocation.getLine() == previousSourceLine &&
+       sourceLocation.getColumn() == previousSourceColumn;
+  }
+
   void addMapping(int targetOffset, SourceFileLocation sourceLocation) {
+
+    bool sameLine(int position, otherPosition) {
+      return targetFile.getLine(position) == targetFile.getLine(otherPosition);
+    }
+
+    if (!entries.isEmpty && sameLine(targetOffset, entries.last.targetOffset)) {
+      if (sameAsPreviousLocation(sourceLocation)) {
+        // The entry points to the same source location as the previous entry in
+        // the same line, hence it is not needed for the source map.
+        //
+        // TODO(zarah): Remove this check and make sure that [addMapping] is not
+        // called for this position. Instead, when consecutive lines in the
+        // generated code point to the same source location, record this and use
+        // it to generate the entries of the source map.
+        return;
+      }
+    }
+
+    if (sourceLocation != null) {
+      updatePreviousSourceLocation(sourceLocation);
+    }
     entries.add(new SourceMapEntry(sourceLocation, targetOffset));
   }
 
   void printStringListOn(List<String> strings, StringBuffer buffer) {
     bool first = true;
     buffer.write('[');
     for (String string in strings) {
       if (!first) buffer.write(',');
       buffer.write('"');
       writeJsonEscapedCharsOn(string, buffer);
       buffer.write('"');
       first = false;
     }
     buffer.write(']');
   }
 
-  String build(SourceFile targetFile) {
+  String build() {
+    resetPreviousSourceLocation();
     StringBuffer mappingsBuffer = new StringBuffer();
     entries.forEach((SourceMapEntry entry) => writeEntry(entry, targetFile,
                                                          mappingsBuffer));
     StringBuffer buffer = new StringBuffer();
     buffer.write('{\n');
     buffer.write('  "version": 3,\n');
     if (uri != null && fileUri != null) {
       buffer.write('  "file": "${relativize(uri, fileUri, false)}",\n');
     }
     buffer.write('  "sourceRoot": "",\n');
@@ skipping 37 matching lines @@
 
     if (entry.sourceLocation == null) return;
 
     String sourceUrl = entry.sourceLocation.getSourceUrl();
     int sourceLine = entry.sourceLocation.getLine();
     int sourceColumn = entry.sourceLocation.getColumn();
     String sourceName = entry.sourceLocation.getSourceName();
 
     int sourceUrlIndex = indexOf(sourceUrlList, sourceUrl, sourceUrlMap);
     encodeVLQ(output, sourceUrlIndex - previousSourceUrlIndex);
-    previousSourceUrlIndex = sourceUrlIndex;
-
     encodeVLQ(output, sourceLine - previousSourceLine);
-    previousSourceLine = sourceLine;
     encodeVLQ(output, sourceColumn - previousSourceColumn);
-    previousSourceColumn = sourceColumn;
+    updatePreviousSourceLocation(entry.sourceLocation);
 
     if (sourceName == null) {
       return;
     }
 
     int sourceNameIndex = indexOf(sourceNameList, sourceName, sourceNameMap);
     encodeVLQ(output, sourceNameIndex - previousSourceNameIndex);
-    previousSourceNameIndex = sourceNameIndex;
+
   }
 
   int indexOf(List<String> list, String value, Map<String, int> map) {
     return map.putIfAbsent(value, () {
       int index = list.length;
       list.add(value);
       return index;
     });
   }
 
@@ skipping 53 matching lines @@
   TokenSourceFileLocation(SourceFile sourceFile, this.token)
     : super(sourceFile);
 
   int get offset => token.charOffset;
 
   String getSourceName() {
     if (token.isIdentifier()) return token.value;
     return null;
   }
 }