Clean up:

lib/src/inline_parser.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 markdown.inline_parser;
+library markdown.src.inline_parser;
 
 import 'ast.dart';
 import 'document.dart';
 import 'util.dart';
 
 /// Maintains the internal state needed to parse inline span elements in
 /// markdown.
 class InlineParser {
   static final List<InlineSyntax> _defaultSyntaxes = <InlineSyntax>[
     // This first regexp matches plain text to accelerate parsing.  It must
     // be written so that it does not match any prefix of any following
     // syntax.  Most markdown is plain text, so it is faster to match one
     // regexp per 'word' rather than fail to match all the following regexps
     // at each non-syntax character position.  It is much more important
     // that the regexp is fast than complete (for example, adding grouping
     // is likely to slow the regexp down enough to negate its benefit).
     // Since it is purely for optimization, it can be removed for debugging.
 
     // TODO(amouravski): this regex will glom up any custom syntaxes unless
     // they're at the beginning.
     new TextSyntax(r'\s*[A-Za-z0-9]+'),
 
     // The real syntaxes.
-
     new AutolinkSyntax(),
     new LinkSyntax(),
     new ImageLinkSyntax(),
     // "*" surrounded by spaces is left alone.
     new TextSyntax(r' \* '),
     // "_" surrounded by spaces is left alone.
     new TextSyntax(r' _ '),
     // Leave already-encoded HTML entities alone. Ensures we don't turn
     // "&amp;" into "&amp;amp;"
     new TextSyntax(r'&[#a-zA-Z0-9]*;'),
@@ skipping 28 matching lines @@
 
   /// The current read position.
   int pos = 0;
 
   /// Starting position of the last unconsumed text.
   int start = 0;
 
   final List<TagState> _stack;
 
   InlineParser(this.source, this.document) : _stack = <TagState>[] {
-    /// User specified syntaxes will be the first syntaxes to be evaluated.
+    // User specified syntaxes are the first syntaxes to be evaluated.
     if (document.inlineSyntaxes != null) {
       syntaxes.addAll(document.inlineSyntaxes);
     }
+
     syntaxes.addAll(_defaultSyntaxes);
+
     // Custom link resolvers goes after the generic text syntax.
-    syntaxes.insertAll(1, <InlineSyntax>[
+    syntaxes.insertAll(1, [
       new LinkSyntax(linkResolver: document.linkResolver),
       new ImageLinkSyntax(linkResolver: document.imageLinkResolver)
     ]);
   }
 
   List<Node> parse() {
     // Make a fake top tag to hold the results.
     _stack.add(new TagState(0, 0, null));
 
     while (!isDone) {
-      bool matched = false;
+      var matched = false;
 
       // See if any of the current tags on the stack match. We don't allow tags
-      // of the same kind to nest, so this takes priority over other possible // matches.
-      for (int i = _stack.length - 1; i > 0; i--) {
+      // of the same kind to nest, so this takes priority over other possible
+      // matches.
+      for (var i = _stack.length - 1; i > 0; i--) {
         if (_stack[i].tryMatch(this)) {
           matched = true;
           break;
         }
       }
+
       if (matched) continue;
 
       // See if the current text matches any defined markdown syntax.
-      for (final syntax in syntaxes) {
+      for (var syntax in syntaxes) {
         if (syntax.tryMatch(this)) {
           matched = true;
           break;
         }
       }
+
       if (matched) continue;
 
       // If we got here, it's just text.
       advanceBy(1);
     }
 
     // Unwind any unmatched tags and get the results.
     return _stack[0].close(this, null);
   }
 
   void writeText() {
     writeTextRange(start, pos);
     start = pos;
   }
 
   void writeTextRange(int start, int end) {
-    if (end > start) {
-      final text = source.substring(start, end);
-      final nodes = _stack.last.children;
+    if (end <= start) return;
 
-      // If the previous node is text too, just append.
-      if ((nodes.length > 0) && (nodes.last is Text)) {
-        final newNode = new Text('${nodes.last.text}$text');
-        nodes[nodes.length - 1] = newNode;
-      } else {
-        nodes.add(new Text(text));
-      }
+    var text = source.substring(start, end);
+    var nodes = _stack.last.children;
+
+    // If the previous node is text too, just append.
+    if (nodes.length > 0 && nodes.last is Text) {
+      nodes[nodes.length - 1] = new Text('${nodes.last.text}$text');
+    } else {
+      nodes.add(new Text(text));
     }
   }
 
   void addNode(Node node) {
     _stack.last.children.add(node);
   }
 
   // TODO(rnystrom): Only need this because RegExp doesn't let you start
   // searching from a given offset.
+  @deprecated
   String get currentSource => source.substring(pos, source.length);
 
   bool get isDone => pos == source.length;
 
   void advanceBy(int length) {
     pos += length;
   }
 
   void consume(int length) {
     pos += length;
     start = pos;
   }
 }
 
 /// Represents one kind of markdown tag that can be parsed.
 abstract class InlineSyntax {
   final RegExp pattern;
 
   InlineSyntax(String pattern) : pattern = new RegExp(pattern, multiLine: true);
 
   bool tryMatch(InlineParser parser) {
-    final startMatch = pattern.firstMatch(parser.currentSource);
-    if ((startMatch != null) && (startMatch.start == 0)) {
+    var startMatch = pattern.matchAsPrefix(parser.source, parser.pos);
+    if (startMatch != null) {
       // Write any existing plain text up to this point.
       parser.writeText();
 
-      if (onMatch(parser, startMatch)) {
-        parser.consume(startMatch[0].length);
-      }
+      if (onMatch(parser, startMatch)) parser.consume(startMatch[0].length);
       return true;
     }
+
     return false;
   }
 
   bool onMatch(InlineParser parser, Match match);
 }
 
 /// Matches stuff that should just be passed through as straight text.
 class TextSyntax extends InlineSyntax {
   final String substitute;
+
   TextSyntax(String pattern, {String sub})
       : super(pattern),
         substitute = sub;
 
   bool onMatch(InlineParser parser, Match match) {
     if (substitute == null) {
       // Just use the original matched text.
       parser.advanceBy(match[0].length);
       return false;
     }
 
     // Insert the substitution.
     parser.addNode(new Text(substitute));
     return true;
   }
 }
 
 /// Matches autolinks like `<http://foo.com>`.
 class AutolinkSyntax extends InlineSyntax {
   AutolinkSyntax() : super(r'<((http|https|ftp)://[^>]*)>');
   // TODO(rnystrom): Make case insensitive.
 
   bool onMatch(InlineParser parser, Match match) {
-    final url = match[1];
-
-    final anchor = new Element.text('a', escapeHtml(url))
-      ..attributes['href'] = url;
+    var url = match[1];
+    var anchor = new Element.text('a', escapeHtml(url));
+    anchor.attributes['href'] = url;
     parser.addNode(anchor);
 
     return true;
   }
 }
 
 /// Matches syntax that has a pair of tags and becomes an element, like `*` for
 /// `<em>`. Allows nested tags.
 class TagSyntax extends InlineSyntax {
   final RegExp endPattern;
   final String tag;
 
-  TagSyntax(String pattern, {String tag, String end})
+  TagSyntax(String pattern, {this.tag, String end})
       : super(pattern),
-        endPattern = new RegExp((end != null) ? end : pattern, multiLine: true),
-        tag = tag;
-  // TODO(rnystrom): Doing this.field doesn't seem to work with named args.
+        endPattern = new RegExp((end != null) ? end : pattern, multiLine: true);
 
   bool onMatch(InlineParser parser, Match match) {
-    parser._stack.add(
-        new TagState(parser.pos, parser.pos + match[0].length, this));
+    parser._stack
+        .add(new TagState(parser.pos, parser.pos + match[0].length, this));
     return true;
   }
 
   bool onMatchEnd(InlineParser parser, Match match, TagState state) {
     parser.addNode(new Element(tag, state.children));
     return true;
   }
 }
 
 /// Matches inline links like `[blah] [id]` and `[blah] (url)`.
 class LinkSyntax extends TagSyntax {
   final Resolver linkResolver;
 
   /// Weather or not this link was resolved by a [Resolver]
   bool resolved = false;
 
   /// The regex for the end of a link needs to handle both reference style and
   /// inline styles as well as optional titles for inline links. To make that
   /// a bit more palatable, this breaks it into pieces.
   static get linkPattern {
-    final refLink = r'\s?\[([^\]]*)\]'; // "[id]" reflink id.
-    final title = r'(?:[ ]*"([^"]+)"|)'; // Optional title in quotes.
-    final inlineLink = '\\s?\\(([^ )]+)$title\\)'; // "(url "title")" link.
+    var refLink = r'\s?\[([^\]]*)\]'; // "[id]" reflink id.
+    var title = r'(?:[ ]*"([^"]+)"|)'; // Optional title in quotes.
+    var inlineLink = '\\s?\\(([^ )]+)$title\\)'; // "(url "title")" link.
     return '\](?:($refLink|$inlineLink)|)';
 
     // The groups matched by this are:
     // 1: Will be non-empty if it's either a ref or inline link. Will be empty
     //    if it's just a bare pair of square brackets with nothing after them.
     // 2: Contains the id inside [] for a reference-style link.
     // 3: Contains the URL for an inline link.
     // 4: Contains the title, if present, for an inline link.
   }
 
   LinkSyntax({this.linkResolver, String pattern: r'\['})
       : super(pattern, end: linkPattern);
 
   Node createNode(InlineParser parser, Match match, TagState state) {
     // If we didn't match refLink or inlineLink, then it means there was
     // nothing after the first square bracket, so it isn't a normal markdown
     // link at all. Instead, we allow users of the library to specify a special
     // resolver function ([linkResolver]) that may choose to handle
     // this. Otherwise, it's just treated as plain text.
-    if (isNullOrEmpty(match[1])) {
+    if (match[1] == null) {
       if (linkResolver == null) return null;
 
       // Treat the contents as unparsed text even if they happen to match. This
       // way, we can handle things like [LINK_WITH_UNDERSCORES] as a link and
       // not get confused by the emphasis.
       var textToResolve = parser.source.substring(state.endPos, parser.pos);
 
       // See if we have a resolver that will generate a link for us.
       resolved = true;
       return linkResolver(textToResolve);
     } else {
-      Link link = getLink(parser, match, state);
+      var link = getLink(parser, match, state);
       if (link == null) return null;
 
-      final Element node = new Element('a', state.children)
-        ..attributes["href"] = escapeHtml(link.url)
-        ..attributes['title'] = escapeHtml(link.title);
+      var node = new Element('a', state.children);
 
-      cleanMap(node.attributes);
+      node.attributes["href"] = escapeHtml(link.url);
+      if (link.title != null) node.attributes['title'] = escapeHtml(link.title);
+
       return node;
     }
   }
 
   Link getLink(InlineParser parser, Match match, TagState state) {
-    if ((match[3] != null) && (match[3] != '')) {
+    if (match[3] != null && match[3] != '') {
       // Inline link like [foo](url).
       var url = match[3];
       var title = match[4];
 
       // For whatever reason, markdown allows angle-bracketed URLs here.
       if (url.startsWith('<') && url.endsWith('>')) {
         url = url.substring(1, url.length - 1);
       }
 
       return new Link(null, url, title);
     } else {
       var id;
       // Reference link like [foo] [bar].
-      if (match[2] == '')
-          // The id is empty ("[]") so infer it from the contents.
-          id = parser.source.substring(state.startPos + 1, parser.pos);
-      else id = match[2];
+      if (match[2] == '') {
+        // The id is empty ("[]") so infer it from the contents.
+        id = parser.source.substring(state.startPos + 1, parser.pos);
+      } else {
+        id = match[2];
+      }
 
       // References are case-insensitive.
       id = id.toLowerCase();
       return parser.document.refLinks[id];
     }
   }
 
   bool onMatchEnd(InlineParser parser, Match match, TagState state) {
-    Node node = createNode(parser, match, state);
+    var node = createNode(parser, match, state);
     if (node == null) return false;
+
     parser.addNode(node);
     return true;
   }
 }
 
 /// Matches images like `![alternate text](url "optional title")` and
 /// `![alternate text][url reference]`.
 class ImageLinkSyntax extends LinkSyntax {
   final Resolver linkResolver;
+
   ImageLinkSyntax({this.linkResolver}) : super(pattern: r'!\[');
 
   Node createNode(InlineParser parser, Match match, TagState state) {
     var node = super.createNode(parser, match, state);
+
     if (resolved) return node;
     if (node == null) return null;
 
-    final Element imageElement = new Element.withTag("img")
-      ..attributes["src"] = node.attributes["href"]
-      ..attributes["title"] = node.attributes["title"]
-      ..attributes["alt"] = node.children
-      .map((e) => isNullOrEmpty(e) || e is! Text ? '' : e.text)
-      .join(' ');
+    var imageElement = new Element.withTag("img");
+    imageElement.attributes["src"] = node.attributes["href"];
 
-    cleanMap(imageElement.attributes);
+    if (node.attributes.containsKey("title")) {
+      imageElement.attributes["title"] = node.attributes["title"];
+    }
+
+    var alt = node.children.map((e) => e is! Text ? '' : e.text).join(" ");
+    if (alt != "") imageElement.attributes["alt"] = alt;
 
     node.children
       ..clear()
       ..add(imageElement);
 
     return node;
   }
 }
 
 /// Matches backtick-enclosed inline code blocks.
@@ skipping 19 matching lines @@
   final TagSyntax syntax;
 
   /// The children of this node. Will be `null` for text nodes.
   final List<Node> children;
 
   TagState(this.startPos, this.endPos, this.syntax) : children = <Node>[];
 
   /// Attempts to close this tag by matching the current text against its end
   /// pattern.
   bool tryMatch(InlineParser parser) {
-    Match endMatch = syntax.endPattern.firstMatch(parser.currentSource);
-    if ((endMatch != null) && (endMatch.start == 0)) {
+    var endMatch = syntax.endPattern.matchAsPrefix(parser.source, parser.pos);
+    if (endMatch != null) {
       // Close the tag.
       close(parser, endMatch);
       return true;
     }
 
     return false;
   }
 
   /// Pops this tag off the stack, completes it, and adds it to the output.
   /// Will discard any unmatched tags that happen to be above it on the stack.
   /// If this is the last node in the stack, returns its children.
   List<Node> close(InlineParser parser, Match endMatch) {
     // If there are unclosed tags on top of this one when it's closed, that
     // means they are mismatched. Mismatched tags are treated as plain text in
     // markdown. So for each tag above this one, we write its start tag as text
     // and then adds its children to this one's children.
-    int index = parser._stack.indexOf(this);
+    var index = parser._stack.indexOf(this);
 
     // Remove the unmatched children.
-    final unmatchedTags = parser._stack.sublist(index + 1);
+    var unmatchedTags = parser._stack.sublist(index + 1);
     parser._stack.removeRange(index + 1, parser._stack.length);
 
     // Flatten them out onto this tag.
-    for (final unmatched in unmatchedTags) {
+    for (var unmatched in unmatchedTags) {
       // Write the start tag as text.
       parser.writeTextRange(unmatched.startPos, unmatched.endPos);
 
       // Bequeath its children unto this tag.
       children.addAll(unmatched.children);
     }
 
     // Pop this off the stack.
     parser.writeText();
     parser._stack.removeLast();
 
     // If the stack is empty now, this is the special "results" node.
     if (parser._stack.length == 0) return children;
 
     // We are still parsing, so add this to its parent's children.
     if (syntax.onMatchEnd(parser, endMatch, this)) {
       parser.consume(endMatch[0].length);
     } else {
       // Didn't close correctly so revert to text.
       parser.start = startPos;
       parser.advanceBy(endMatch[0].length);
     }
 
     return null;
   }
 }