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

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

Index: pkg/analyzer/lib/src/services/formatter_impl.dart
===================================================================
--- pkg/analyzer/lib/src/services/formatter_impl.dart	(revision 32082)
+++ pkg/analyzer/lib/src/services/formatter_impl.dart	(working copy)
@@ -367,7 +367,7 @@
   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;
@@ -923,7 +923,7 @@
   visitImportDirective(ImportDirective node) {
     visitNodes(node.metadata, followedBy: newlines);
     token(node.keyword);
-    space();
+    nonBreakingSpace();
     visit(node.uri);
     token(node.asToken, precededBy: space, followedBy: space);
     allowContinuedLines((){
@@ -1481,11 +1481,11 @@
   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;
     }
   }
 
@@ -1503,22 +1503,21 @@
     }
   }
 
-  /// 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;
+    currentBreakWeight = breakWeight;
   }
 
-  /// Mark a breakable space
-  breakableSpace() {
-    space();
-    breakWeight =
-        countNewlinesBetween(previousToken, previousToken.next) > 0 ? 1 : 0;
-  }
-
   /// Append the given [string] to the source writer if it's non-null.
   append(String string) {
     if (string != null && !string.isEmpty) {