Improved linebreaking for imports (darbug.com/16366) and non-breaking line support.

pkg/analyzer/lib/src/services/formatter_impl.dart

 // Copyright (c) 2013, 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 formatter_impl;
 
 import 'dart:math';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/java_core.dart' show CharSequence;
@@ skipping 349 matching lines @@
   int leadingSpaces = 0;
 
   /// A flag to specify whether line-leading spaces should be preserved (and
   /// addded to the indent level).
   bool allowLineLeadingSpaces;
 
   /// Used for matching EOL comments
   final twoSlashes = new RegExp(r'//[^/]');
 
   /// A weight for potential breakpoints.
-  int breakWeight = DEFAULT_SPACE_WEIGHT;
+  int currentBreakWeight = DEFAULT_SPACE_WEIGHT;
 
   /// Original pre-format selection information (may be null).
   final Selection preSelection;
 
   final bool codeTransforms;
 
 
   /// The source being formatted (used in interpolation handling)
   final String source;
 
@@ skipping 535 matching lines @@
 
   visitImplementsClause(ImplementsClause node) {
     token(node.keyword);
     space();
     visitCommaSeparatedNodes(node.interfaces);
   }
 
   visitImportDirective(ImportDirective node) {
     visitNodes(node.metadata, followedBy: newlines);
     token(node.keyword);
-    space();
+    nonBreakingSpace();
     visit(node.uri);
     token(node.asToken, precededBy: space, followedBy: space);
     allowContinuedLines((){
       visit(node.prefix);
       visitNodes(node.combinators, precededBy: space, separatedBy: space);
     });
     token(node.semicolon);
   }
 
   visitIndexExpression(IndexExpression node) {
@@ skipping 537 matching lines @@
       if (followedBy != null) {
         followedBy();
       }
       previousToken = token;
     }
   }
 
   emitSpaces() {
     if (leadingSpaces > 0) {
       if (allowLineLeadingSpaces || !writer.currentLine.isWhitespace()) {
-        writer.spaces(leadingSpaces, breakWeight: breakWeight);
+        writer.spaces(leadingSpaces, breakWeight: currentBreakWeight);
       }
       leadingSpaces = 0;
       allowLineLeadingSpaces = false;
-      breakWeight = DEFAULT_SPACE_WEIGHT;
+      currentBreakWeight = DEFAULT_SPACE_WEIGHT;
     }
   }
 
   checkForSelectionUpdate(Token token) {
     // Cache the first token on or AFTER the selection offset
     if (preSelection != null && selection == null) {
       // Check for overshots
       var overshot = token.offset - preSelection.offset;
       if (overshot >= 0) {
         //TODO(pquitslund): update length (may need truncating)
         selection = new Selection(
             writer.toString().length + leadingSpaces - overshot,
             preSelection.length);
       }
     }
   }
 
-  /// Emit a non-breakable space. If [allowLineLeading] is specified, spaces
+  /// Emit a non-breakable space.
+  nonBreakingSpace() {
+    space(breakWeight: UNBREAKABLE_SPACE_WEIGHT);
+  }
+
+  /// Emit a space. If [allowLineLeading] is specified, spaces
   /// will be preserved at the start of a line (in addition to the
   /// indent-level), otherwise line-leading spaces will be ignored.
-  space({n: 1, allowLineLeading: false}) {
+  space({n: 1, allowLineLeading: false, breakWeight: DEFAULT_SPACE_WEIGHT}) {
     //TODO(pquitslund): replace with a proper space token
     leadingSpaces+=n;
     allowLineLeadingSpaces = allowLineLeading;
-  }
-
-  /// Mark a breakable space
-  breakableSpace() {
-    space();
-    breakWeight =
-        countNewlinesBetween(previousToken, previousToken.next) > 0 ? 1 : 0;
+    currentBreakWeight = breakWeight;
   }
 
   /// Append the given [string] to the source writer if it's non-null.
   append(String string) {
     if (string != null && !string.isEmpty) {
       emitSpaces();
       writer.print(string);
     }
   }
 
@@ skipping 169 matching lines @@
     var lastLine =
         lineInfo.getLocation(lastOffset).lineNumber;
     var currentLine =
         lineInfo.getLocation(currentOffset).lineNumber;
     return currentLine - lastLine;
   }
 
   String toString() => writer.toString();
 
 }