support multi-level symlinks to SDK exes

sdk/bin/dart

Index: sdk/bin/dart
diff --git a/sdk/bin/dart b/sdk/bin/dart
index 675963f746cab46906ff24938d59bf6f07a8023a..0ae05b5d509d594e0d39689b05f1c4d39436a348 100755
--- a/sdk/bin/dart
+++ b/sdk/bin/dart
@@ -3,17 +3,15 @@
 # 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.
 
-function follow_links() {
-  file="$1"
-  while [ -h "$file" ]; do
-    # On Mac OS, readlink -f doesn't work.
-    file="$(readlink "$file")"
-  done
-  echo "$file"
-}
+PROG_NAME=$(cd -P -- "$(dirname -- "$0")" && pwd -P) && \
+  PROG_NAME=$PROG_NAME/$(basename -- "$0")
 
-# Unlike $0, $BASH_SOURCE points to the absolute path of this file.
-PROG_NAME="$(follow_links "$BASH_SOURCE")"
+# resolve symlinks
+while [ -h $PROG_NAME ]; do
+    DIR=$(dirname -- "$PROG_NAME")
+    SYM=$(readlink $PROG_NAME)
+    PROG_NAME=$(cd $DIR && cd $(dirname -- "$SYM") && pwd)/$(basename -- "$SYM")
+done
 
 # Handle the case where dart-sdk/bin has been symlinked to.
 CUR_DIR="$(cd "${PROG_NAME%/*}" ; pwd -P)"