Adding support for `sourceRoot` to the SingleMapping class.

pkg/source_maps/lib/parser.dart

Index: pkg/source_maps/lib/parser.dart
diff --git a/pkg/source_maps/lib/parser.dart b/pkg/source_maps/lib/parser.dart
index 23835a60f3499546ca9e3dd2cd5eb4431128db8f..050408b2f1e96f4d9ea45a4c455d31e42138857a 100644
--- a/pkg/source_maps/lib/parser.dart
+++ b/pkg/source_maps/lib/parser.dart
@@ -16,6 +16,8 @@ import 'src/vlq.dart';
 /// Parses a source map directly from a json string.
 // TODO(sigmund): evaluate whether other maps should have the json parsed, or
 // the string represenation.
+// TODO(tjblasi): Ignore the first line of [jsonMap] if the JSON safety string
+// `)]}'` begins the string representation of the map.
 Mapping parse(String jsonMap, {Map<String, Map> otherMaps}) =>
   parseJson(JSON.decode(jsonMap), otherMaps: otherMaps);
 
@@ -146,6 +148,9 @@ class SingleMapping extends Mapping {
   /// Entries indicating the beginning of each span.
   final List<TargetLineEntry> lines;
 
+  /// Source root appended to the start of all entries in [urls].
+  String sourceRoot = null;
+
   SingleMapping._internal(this.targetUrl, this.urls, this.names, this.lines);
 
   factory SingleMapping.fromEntries(
@@ -192,9 +197,9 @@ class SingleMapping extends Mapping {
 
   SingleMapping.fromJson(Map map)
       : targetUrl = map['file'],
-        // TODO(sigmund): add support for 'sourceRoot'
         urls = map['sources'],
         names = map['names'],
+        sourceRoot = map['sourceRoot'],
         lines = <TargetLineEntry>[] {
     int line = 0;
     int column = 0;
@@ -303,7 +308,7 @@ class SingleMapping extends Mapping {
 
     var result = {
       'version': 3,
-      'sourceRoot': '',
+      'sourceRoot': sourceRoot == null ? '' : sourceRoot,
       'sources': urls,
       'names' : names,
       'mappings' : buff.toString()
@@ -350,6 +355,9 @@ class SingleMapping extends Mapping {
     var entry = _findColumn(line, column, _findLine(line));
     if (entry == null || entry.sourceUrlId == null) return null;
     var url = urls[entry.sourceUrlId];
+    if (sourceRoot != null) {
+      url = sourceRoot + url;

[Siggi Cherem (dart-lang), 2014/07/14 22:46:53]

is source root guaranteed to be have the trailing slash or should we use
something like path.url.join(sourceRoot, url)?

[tjblasi, 2014/07/15 00:13:58]

I wasn't sure how aware `sourceRoot` processing is supposed to be. The spec just
says "This value is prepended to the individual entries in the “source” field.",
so I wasn't sure if given two files:

/packages/aFile.dart
/packages/anotherFile.dart

It would be legal (if ill-advised) to do:

sourceRoot = "/packages/a"
sources = ["File.dart", "notherFile.dart"]


If you know one way or another, great! Otherwise, I could ping John Lenz.

[Siggi Cherem (dart-lang), 2014/07/15 00:29:38]

minor nit: rewrite to use string interolation instead:

  url = '$sourceRoot$url';

[Siggi Cherem (dart-lang), 2014/07/15 00:29:38]

I honestly don't know :). Let's check with John about it. It might also be a
good idea to clarify this in the spec document.

I'm OK submitting either one or the other for the time being and follow up once
we get more details from John.

[tjblasi, 2014/07/15 16:45:10]

From John:
"No, it isn't specifically a directory although I would expect that is the
common use case.  It is simply a string prepended."

[tjblasi, 2014/07/15 16:45:10]

Done.

+    }
     if (files != null && files[url] != null) {
       var file = files[url];
       var start = file.getOffset(entry.sourceLine, entry.sourceColumn);
@@ -374,6 +382,8 @@ class SingleMapping extends Mapping {
     return (new StringBuffer("$runtimeType : [")
         ..write('targetUrl: ')
         ..write(targetUrl)
+        ..write(', sourceRoot: ')
+        ..write(sourceRoot)
         ..write(', urls: ')
         ..write(urls)
         ..write(', names: ')
@@ -392,13 +402,16 @@ class SingleMapping extends Mapping {
             ..write(': ')
             ..write(line)
             ..write(':')
-            ..write(entry.column)
-            ..write('   -->   ')
-            ..write(urls[entry.sourceUrlId])
-            ..write(': ')
-            ..write(entry.sourceLine)
-            ..write(':')
-            ..write(entry.sourceColumn);
+            ..write(entry.column);
+        if (entry.sourceUrlId != null) {
+          buff..write('   -->   ')
+              ..write(sourceRoot)
+              ..write(urls[entry.sourceUrlId])
+              ..write(': ')
+              ..write(entry.sourceLine)
+              ..write(':')
+              ..write(entry.sourceColumn);
+        }
         if (entry.sourceNameId != null) {
           buff..write(' (')
               ..write(names[entry.sourceNameId])