Support both new and old style package layouts.

utils/pub/io.dart

Index: utils/pub/io.dart
diff --git a/utils/pub/io.dart b/utils/pub/io.dart
index c622b9505ddc0b81ca2d1a5ff8d0526f0b02d519..2be46c8189aef32abc84295a46be960719546919 100644
--- a/utils/pub/io.dart
+++ b/utils/pub/io.dart
@@ -279,6 +279,44 @@ Future<File> createSymlink(from, to) {
 }
 
 /**
+ * Creates a new symlink that creates an alias from the package [from] to [to],
+ * both of which can be a [String], [File], or [Directory]. Returns a [Future]
+ * which completes to the symlink file (i.e. [to]).
+ *
+ * Unlike [createSymlink], this has heuristics to detect if [from] is using
+ * the old or new style of package layout. If it's using the new style, then
+ * it will create a symlink to the "lib" directory contained inside that
+ * package directory. Otherwise, it just symlinks to the package directory
+ * itself.
+ */
+// TODO(rnystrom): Remove this when old style packages are no longer supported.
+// See: http://code.google.com/p/dart/issues/detail?id=4964.
+Future<File> createPackageSymlink(from, to) {
+  // If from contains any Dart files at the top level (aside from build.dart)
+  // we assume that means it's an old style package.
+  return listDir(from).chain((contents) {
+    var isOldStyle = contents.some(
+        (file) => file.endsWith('.dart') && basename(file) != 'build.dart');
+
+    if (isOldStyle) {

[nweiz, 2012/09/10 19:24:47]

Shouldn't we print some sort of deprecation warning here? At some point we're
going to break the old package layout, and we want to give people plenty of
warning.

[Bob Nystrom, 2012/09/11 19:36:59]

I don't want to warn when a dependency has the old layout because that's often
outside of the user's control.

I did add a warning (and a test for it) if the entrypoint package itself uses
the old layout.

+      return createSymlink(from, to);

[nweiz, 2012/09/10 19:24:47]

Style nit: avoid the extra indentation of the else block below.

[Bob Nystrom, 2012/09/11 19:36:59]

Done.

+    } else {
+      // It's a new style package, so symlink to the 'lib' directory. But only
+      // if the package actually *has* one. Otherwise, we won't create a
+      // symlink at all.

[nweiz, 2012/09/10 19:24:47]

It seems potentially confusing to users to just silently not create a symlink. I
can imagine a user being very puzzled because they've declared a dependency and
run "pub install" but the symlink still doesn't exist. We should probably either
print a warning or add a TODO to do so.

[Bob Nystrom, 2012/09/11 19:36:59]

Done. Prints warning.

+      from = join(from, 'lib');
+      return dirExists(from).chain((exists) {
+        if (exists) {
+          return createSymlink(from, to);
+        } else {
+          return new Future.immediate(to);
+        }
+      });
+    }
+  });
+}
+
+/**
  * Given [entry] which may be a [String], [File], or [Directory] relative to
  * the current working directory, returns its full canonicalized path.
  */