Precompute `IgnoreInfo` in Scanner.

pkg/analyzer/lib/src/task/dart.dart

Index: pkg/analyzer/lib/src/task/dart.dart
diff --git a/pkg/analyzer/lib/src/task/dart.dart b/pkg/analyzer/lib/src/task/dart.dart
index 3d9d552329932b3980bcfe8b95d5800764b49440..a9ad9633c3110dd2575a519e6d5be61f26501f75 100644
--- a/pkg/analyzer/lib/src/task/dart.dart
+++ b/pkg/analyzer/lib/src/task/dart.dart
@@ -2520,8 +2520,6 @@ class DartDelta extends Delta {
  * of errors.
  */
 class DartErrorsTask extends SourceBasedAnalysisTask {
-  static final RegExp spacesRegExp = new RegExp(r'\s+');
-
   /**
    * The task descriptor describing this kind of task.
    */
@@ -2529,17 +2527,14 @@ class DartErrorsTask extends SourceBasedAnalysisTask {
       createTask, buildInputs, <ResultDescriptor>[DART_ERRORS]);
 
   /**
-   * The name of the [LINE_INFO_INPUT] input.
+   * The name of the [IGNORE_INFO_INPUT] input.
    */
-  static const String LINE_INFO_INPUT = 'LINE_INFO_INPUT';
+  static const String IGNORE_INFO_INPUT = 'IGNORE_INFO_INPUT';
 
   /**
-   * The name of the [PARSED_UNIT_INPUT] input.
+   * The name of the [LINE_INFO_INPUT] input.
    */
-  static const String PARSED_UNIT_INPUT = 'PARSED_UNIT_INPUT';
-
-  // Prefix for comments ignoring error codes.
-  static const String _normalizedIgnorePrefix = '//ignore:';
+  static const String LINE_INFO_INPUT = 'LINE_INFO_INPUT';
 
   DartErrorsTask(InternalAnalysisContext context, AnalysisTarget target)
       : super(context, target);
@@ -2584,71 +2579,29 @@ class DartErrorsTask extends SourceBasedAnalysisTask {
     outputs[DART_ERRORS] = errors;
   }
 
-  Token _advanceToLine(Token token, LineInfo lineInfo, int line) {
-    int offset = lineInfo.getOffsetOfLine(line - 1); // 0-based
-    while (token.offset < offset) {
-      token = token.next;
-    }
-    return token;
-  }
-
   List<AnalysisError> _filterIgnores(List<AnalysisError> errors) {
     if (errors.isEmpty) {
       return errors;
     }
 
-    // Sort errors.
-    errors.sort((AnalysisError e1, AnalysisError e2) => e1.offset - e2.offset);
+    IgnoreInfo ignoreInfo = getRequiredInput(IGNORE_INFO_INPUT);
+    if (!ignoreInfo.hasIgnores) {
+      return errors;
+    }
 
-    CompilationUnit cu = getRequiredInput(PARSED_UNIT_INPUT);
-    Token token = cu.beginToken;
     LineInfo lineInfo = getRequiredInput(LINE_INFO_INPUT);
 
     bool isIgnored(AnalysisError error) {
       int errorLine = lineInfo.getLocation(error.offset).lineNumber;
-      token = _advanceToLine(token, lineInfo, errorLine);
-
-      //Check for leading comment.
-      Token comments = token.precedingComments;
-      while (comments?.next != null) {
-        comments = comments.next;
-      }
-      if (_isIgnoredBy(error, comments)) {
-        return true;
-      }
-
-      //Check for trailing comment.
-      int lineNumber = errorLine + 1;
-      if (lineNumber <= lineInfo.lineCount) {
-        Token nextLine = _advanceToLine(token, lineInfo, lineNumber);
-        comments = nextLine.precedingComments;
-        if (comments != null && nextLine.previous.type != TokenType.EOF) {
-          int commentLine = lineInfo.getLocation(comments.offset).lineNumber;
-          if (commentLine == errorLine) {
-            return _isIgnoredBy(error, comments);
-          }
-        }
-      }
-
-      return false;
+      String errorCode = error.errorCode.name.toLowerCase();
+      // Ignores can be on the line or just preceding the error.
+      return ignoreInfo.ignoredAt(errorCode, errorLine) ||
+          ignoreInfo.ignoredAt(errorCode, errorLine - 1);
     }
 
     return errors.where((AnalysisError e) => !isIgnored(e)).toList();
   }
 
-  bool _isIgnoredBy(AnalysisError error, Token comment) {
-    //Normalize first.
-    String contents =
-        comment?.lexeme?.toLowerCase()?.replaceAll(spacesRegExp, '');
-    if (contents == null || !contents.startsWith(_normalizedIgnorePrefix)) {
-      return false;
-    }
-    return contents
-        .substring(_normalizedIgnorePrefix.length)
-        .split(',')
-        .contains(error.errorCode.name.toLowerCase());
-  }
-
   /**
    * Return a map from the names of the inputs of this kind of task to the task
    * input descriptors describing those inputs for a task with the
@@ -2658,7 +2611,7 @@ class DartErrorsTask extends SourceBasedAnalysisTask {
     Source source = target;
     Map<String, TaskInput> inputs = <String, TaskInput>{};
     inputs[LINE_INFO_INPUT] = LINE_INFO.of(source);
-    inputs[PARSED_UNIT_INPUT] = PARSED_UNIT.of(source);
+    inputs[IGNORE_INFO_INPUT] = IGNORE_INFO.of(source);
     EnginePlugin enginePlugin = AnalysisEngine.instance.enginePlugin;
     // for Source
     List<ResultDescriptor> errorsForSource = enginePlugin.dartErrorsForSource;
@@ -5429,10 +5382,21 @@ class ScanDartTask extends SourceBasedAnalysisTask {
       'ScanDartTask',
       createTask,
       buildInputs,
-      <ResultDescriptor>[LINE_INFO, SCAN_ERRORS, TOKEN_STREAM],
+      <ResultDescriptor>[LINE_INFO, IGNORE_INFO, SCAN_ERRORS, TOKEN_STREAM],

[scheglov, 2016/05/27 18:05:47]

We try to keep these sorted.
IGNORE_INFO would be the first item in the list.

[pquitslund, 2016/05/27 21:50:53]

Done.

       suitabilityFor: suitabilityFor);
 
   /**
+   * A regular expression for matching 'ignore' comments.  Produces matches
+   * containing 3 groups.  For example:
+   *
+   *     * ['//ignore: error_code', '//ignore:',  'error_code']
+   *
+   * Resulting codes may be in a list ('error_code_1,error_code2').
+   */
+  static final RegExp _IGNORE_MATCHER =
+      new RegExp(r'(//[ ]*ignore:)(.*)$', multiLine: true);

[scheglov, 2016/05/27 18:05:47]

Do we use the (//ignore:) group?
I don't know whether this might have a performance cost.

[pquitslund, 2016/05/27 21:50:53]

Ah!  Yea.  Great catch.  No need for that first group.

+
+  /**
    * Initialize a newly created task to access the content of the source
    * associated with the given [target] in the given [context].
    */
@@ -5482,8 +5446,11 @@ class ScanDartTask extends SourceBasedAnalysisTask {
       scanner.preserveComments = context.analysisOptions.preserveComments;
       scanner.scanGenericMethodComments = context.analysisOptions.strongMode;
 
+      LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+
       outputs[TOKEN_STREAM] = scanner.tokenize();
-      outputs[LINE_INFO] = new LineInfo(scanner.lineStarts);
+      outputs[LINE_INFO] = lineInfo;
+      outputs[IGNORE_INFO] = calculateIgnores(fragment.content, lineInfo);
       outputs[SCAN_ERRORS] = getUniqueErrors(errorListener.errors);
     } else if (target is Source) {
       String content = getRequiredInput(CONTENT_INPUT_NAME);
@@ -5493,8 +5460,11 @@ class ScanDartTask extends SourceBasedAnalysisTask {
       scanner.preserveComments = context.analysisOptions.preserveComments;
       scanner.scanGenericMethodComments = context.analysisOptions.strongMode;
 
+      LineInfo lineInfo = new LineInfo(scanner.lineStarts);
+
       outputs[TOKEN_STREAM] = scanner.tokenize();
-      outputs[LINE_INFO] = new LineInfo(scanner.lineStarts);
+      outputs[LINE_INFO] = lineInfo;
+      outputs[IGNORE_INFO] = calculateIgnores(content, lineInfo);
       outputs[SCAN_ERRORS] = getUniqueErrors(errorListener.errors);
     } else {
       throw new AnalysisException(
@@ -5528,6 +5498,23 @@ class ScanDartTask extends SourceBasedAnalysisTask {
   }
 
   /**
+   * Calculate ignores for the given [content] with line [info].
+   */
+  static IgnoreInfo calculateIgnores(String content, LineInfo info) {

[Brian Wilkerson, 2016/05/27 18:21:18]

This could be a static method on IgnoreInfo.

[pquitslund, 2016/05/27 21:50:53]

Done.

+    IgnoreInfo ignoreInfo = new IgnoreInfo();
+    for (Match match in _IGNORE_MATCHER.allMatches(content)) {
+      // Matches contain 3 groups:
+      //   ['//ignore: error_code', '//ignore:',  'error_code']
+      // And resulting codes may be in a list.
+      List<String> codes = match.group(2).split(',');
+      for (String code in codes) {
+        ignoreInfo.add(info.getLocation(match.start).lineNumber, code.trim());

[Brian Wilkerson, 2016/05/27 18:21:18]

It would be more efficient to define LineInfo.addAll and use it.

[pquitslund, 2016/05/27 21:50:53]

Done.

+      }
+    }
+    return ignoreInfo;

[Brian Wilkerson, 2016/05/27 18:21:18]

For memory efficiency, it would be good to use a single empty instance of
IgnoreInfo when there are no matches.

[pquitslund, 2016/05/27 21:50:53]

Good idea.  Done

+  }
+
+  /**
    * Create a [ScanDartTask] based on the given [target] in the given [context].
    */
   static ScanDartTask createTask(