Support multiple levels of relative symlinks

dart/sdk/bin/dart2js

Index: dart/sdk/bin/dart2js
diff --git a/dart/sdk/bin/dart2js b/dart/sdk/bin/dart2js
index 79a857be83efe500109c4f7c760fa2a9c008f2f9..63d55f933e1acc65741d4ea2a89a250a12094cb6 100755
--- a/dart/sdk/bin/dart2js
+++ b/dart/sdk/bin/dart2js
@@ -3,12 +3,25 @@
 # 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.
 
+# The GNU version of readlink which has a -f option isn't available by default
+# on Mac OS X.  So we provide our own version.  We try to avoid calling external
+# programs such as dirname and readlink in the common case (not a symlink).  The
+# reason for this is that we notice an overhead in calling external programs and
+# this affects script startup time which becomes notiable when running many
+# compilations in parallel (as it happens, for example, during testing).
 function follow_links() {
   file="$1"
   while [ -h "$file" ]; do

[kustermann, 2013/12/06 13:50:41]

I think, this doesn't work in all cases, e.g.

/home/foobar/applications/dart2js/bin -> /home/foobar/dart-sdk/bin
$ /home/foobar/applications/dart2js/bin/dart2js --version

Since dart2js itself is not a symlink, the "[ -h $file ]" will result in false.

What you need to do is to split the path into all of it's components and resolve
all of them by calling readlink until you reach the fixed point.

-    # On Mac OS, readlink -f doesn't work.
-    file="$(readlink "$file")"
+    target="$(readlink "$file")"
+    if [[ "$target" != /* ]]; then

[kustermann, 2013/12/06 13:50:41]

What does this do?

+      target="$(dirname "$file")/$target"
+    fi
+    file="$target"
   done
+  # Make sure that ${foo%/*} can be used instead of dirname.
+  if [ "${file%/*}" = "$file" ]; then
+    file="./$file"
+  fi

[kustermann, 2013/12/06 13:50:41]

Why is that necessary?

(IMHO, a function follow_links should take a path and follow all links and
return a path without links in the components. That's it).

Additionally, the argument we pass to follow_links on line 29 is supposed to be
an absolute path, right?

   echo "$file"
 }