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

pkg/analyzer/lib/src/services/writer.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 source_writer;
 
 
 
 class Line {
 
@@ skipping 134 matching lines @@
     var curr;
 
     tok.forEach((token){
       if (token is! SpaceToken) {
         if (curr == null) {
           curr = token;
         } else {
           curr = merge(curr, token);
         }
       } else {
-        if (curr != null) {
-          tokens.add(curr);
-          curr = null;
+        if (isNonbreaking(token)) {
+          curr = merge(curr, token);
+        } else {
+          if (curr != null) {
+            tokens.add(curr);
+            curr = null;
+          }
+          tokens.add(token);
         }
-        tokens.add(token);
       }
     });
 
     if (curr != null) {
       tokens.add(curr);
     }
 
     return tokens;
   }
 
+  static bool isNonbreaking(SpaceToken token) =>
+      token.breakWeight == UNBREAKABLE_SPACE_WEIGHT;
+
   static LineToken merge(LineToken first, LineToken second) =>
       new LineToken(first.value + second.value);
 
   bool isAllWhitespace(Chunk chunk) => isWhitespace(chunk.buffer.toString());
 
   bool isLineStart(chunk) => chunk.length == 0 && chunk.start == LINE_START;
 
   /// Test whether this token is a good start for a new working chunk
   bool goodStart(LineToken tok, Chunk workingChunk) =>
       tok is SpaceToken && tok.breakWeight >= workingChunk.start.breakWeight;
 
 }
 
 /// Test if this [string] contains only whitespace characters
 bool isWhitespace(String string) => string.codeUnits.every(
       (c) => c == 0x09 || c == 0x20 || c == 0x0A || c == 0x0D);
 
 /// Special token indicating a line start
 final LINE_START = new SpaceToken(0);
 
-const DEFAULT_SPACE_WEIGHT = -1;
+const DEFAULT_SPACE_WEIGHT = 0;
+const UNBREAKABLE_SPACE_WEIGHT = -1;
 
 /// Simple non-breaking printer
 class SimpleLinePrinter extends LinePrinter {
 
   const SimpleLinePrinter();
 
   String printLine(Line line) {
     var buffer = new StringBuffer();
     line.tokens.forEach((tok) => buffer.write(tok.toString()));
     return buffer.toString();
@@ skipping 204 matching lines @@
 
 String getTabs(int n) => n < TABS.length ? TABS[n] : repeat('\t', n);
 
 String repeat(String ch, int times) {
   var sb = new StringBuffer();
   for (var i = 0; i < times; ++i) {
     sb.write(ch);
   }
   return sb.toString();
 }